@misc{SchmeisserHaeberleBarquinhaetal., author = {Schmeißer, Dieter and Haeberle, J{\"o}rg and Barquinha, Pedro and Gaspar, Diana and Pereira, Lu{\´i}s and Martins, Rodrigo and Fortunato, Elvira}, title = {Electronic structure of amorphous ZnO films}, series = {Physica Status Solidi C}, volume = {11}, journal = {Physica Status Solidi C}, number = {9-10}, issn = {1610-1642}, doi = {10.1002/pssc.201400010}, pages = {1476 -- 1480}, abstract = {We use resonant photoemission spectroscopy (resPES) to study the electronic properties of amorphous ZnO (a-ZnO) layers. We report on the core levels, the valence band (VB) PES data, and the X-ray absorption (XAS) data which we use for the conduction band (CB) density of states. From these results we are able to derive the partial density of states (pDOS) of O2p and Zn4s4p states in the VB and CB, respectively as well as a band scheme. At the O1s resonance we observe a band of localized defect states which is located between the Fermi energy and the CBM. At the Zn2p edge the XAS data indicate that localized Zn4s4p states are involved in the DOS starting already at the Fermi energy.}, language = {en} } @misc{TallaridaDasCibrevetal., author = {Tallarida, Massimo and Das, Chittaranjan and Cibrev, Dejan and Kukli, Kaupo and Tamm, Aile and Ritala, Mikko and Lana-Villarreal, Teresa and Gómez, Roberto and Leskel{\"a}, Markku and Schmeißer, Dieter}, title = {Modification of Hematite Electronic Properties with Trimethyl Aluminum to Enhance the Efficiency of Photoelectrodes}, series = {The Journal of Physical Chemistry Letters}, volume = {5}, journal = {The Journal of Physical Chemistry Letters}, number = {20}, doi = {10.1021/jz501751w}, pages = {3582 -- 3587}, abstract = {The electronic properties of hematite were investigated by means of synchrotron radiation photoemission (SR-PES) and X-ray absorption spectroscopy (XAS). Hematite samples were exposed to trimethyl aluminum (TMA) pulses, a widely used Al-precursor for the atomic layer deposition (ALD) of Al2O3. SR-PES and XAS showed that the electronic properties of hematite were modified by the interaction with TMA. In particular, the hybridization of O 2p states with Fe 3d and Fe 4s4p changed upon TMA pulses due to electron inclusion as polarons. The change of hybridization correlates with an enhancement of the photocurrent density due to water oxidation for the hematite electrodes. Such an enhancement has been associated with an improvement in charge carrier transport. Our findings open new perspectives for the understanding and utilization of electrode modifications by very thin ALD films and show that the interactions between metal precursors and substrates seem to be important factors in defining their electronic and photoelectrocatalytic properties.}, language = {en} } @misc{KrammLefevreBogdanoffetal., author = {Kramm, Ulrike Ingrid and Lef{\`e}vre, Michel and Bogdanoff, Peter and Schmeißer, Dieter and Dodelet, Jean-Pol}, title = {Analyzing Structural Changes of Fe-N-C Cathode Catalysts in PEM Fuel Cell by M{\"o}ßbauer Spectroscopy of Complete Membrane-Electrode-Assemblies}, series = {The Journal of Physical Chemistry Letters}, volume = {2014}, journal = {The Journal of Physical Chemistry Letters}, number = {5}, issn = {1948-7185}, doi = {10.1021/jz501955g}, pages = {3750 -- 3756}, abstract = {The applicability of analyzing by M{\"o}ßbauer spectroscopy the structural changes of Fe-N-C catalysts that have been tested at the cathode of membrane electrode assemblies in proton exchange membrane (PEM) fuel cells is demonstrated. The M{\"o}ßbauer characterization of powders of the same catalysts was recently described in our previous publication. A possible change of the iron species upon testing in fuel cell was investigated here by M{\"o}ßbauer spectroscopy, energy-dispersive X-ray cross-sectional imaging, and neutron activation analysis. Our results show that the absorption probability of γ rays by the iron nuclei in Fe-N-C is strongly affected by the presence of Nafion and water content. A detailed investigation of the effect of an oxidizing treatment (1.2 V) of the non-noble cathode in PEM fuel cell indicates that the observed activity decay is mainly attributable to carbon oxidation causing a leaching of active iron sites hosted in the carbon matrix.}, language = {en} } @misc{IndraMenezesSahraieetal., author = {Indra, Arindam and Menezes, Prashanth W. and Sahraie, Nastaran Ranjbar and Bergmann, Arno and Das, Chittaranjan and Tallarida, Massimo and Schmeißer, Dieter and Strasser, Peter and Driess, Matthias}, title = {Unification of Catalytic Water Oxidation and Oxygen Reduction Reactions: Amorphous Beat Crystalline Cobalt Iron Oxides}, series = {Journal of the American Chemical Society}, volume = {2014}, journal = {Journal of the American Chemical Society}, number = {136}, issn = {1520-5126}, doi = {10.1021/ja509348t}, pages = {17530 -- 17536}, abstract = {Catalytic water splitting to hydrogen and oxygen is considered as one of the convenient routes for the sustainable energy conversion. Bifunctional catalysts for the electrocatalytic oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are pivotal for the energy conversion and storage, and alternatively, the photochemical water oxidation in biomimetic fashion is also considered as the most useful way to convert solar energy into chemical energy. Here we present a facile solvothermal route to control the synthesis of amorphous and crystalline cobalt iron oxides by controlling the crystallinity of the materials with changing solvent and reaction time and further utilize these materials as multifunctional catalysts for the unification of photochemical and electrochemical water oxidation as well as for the oxygen reduction reaction. Notably, the amorphous cobalt iron oxide produces superior catalytic activity over the crystalline one under photochemical and electrochemical water oxidation and oxygen reduction conditions.}, language = {en} } @misc{DasHenkelTallaridaetal., author = {Das, Chittaranjan and Henkel, Karsten and Tallarida, Massimo and Schmeißer, Dieter and Gargouri, Hassan and K{\"a}rkk{\"a}nen, Irina and Schneidewind, Jessica and Gruska, Bernd and Arens, Michael}, title = {Thermal and plasma enhanced atomic layer deposition of TiO2: Comparison of spectroscopic and electric properties}, series = {Journal of Vacuum Science and Technology A}, volume = {2015}, journal = {Journal of Vacuum Science and Technology A}, number = {33}, issn = {1520-8559}, doi = {10.1116/1.4903938}, pages = {01A144-1 -- 01A144-8}, abstract = {Titanium oxide (TiO2) deposited by atomic layer deposition (ALD) is used as a protective layer in photocatalytic water splitting system as well as a dielectric in resistive memory switching. The way ALD is performed (thermally or plasma-assisted) may change the growth rate as well as the electronic properties of the deposited films. In the present work, the authors verify the influence of the ALD mode on functional parameters, by comparing the growth rate and electronic properties of TiO2 films deposited by thermal (T-) and plasma-enhanced (PE-) ALD. The authors complete the study with the electrical characterization of selected samples by means of capacitance-voltage and current-voltage measurements. In all samples, the authors found a significant presence of Ti3+ states, with the lowest content in the PE-ALD grown TiO2 films. The observation of Ti3+ states was accompanied by the presence of in-gap states above the valence band maximum. For films thinner than 10 nm, the authors found also a strong leakage current. Also in this case, the PE-ALD films showed the weakest leakage currents, showing a correlation between the presence of Ti3+ states and leakage current density.}, language = {en} } @misc{GarainSinhaAdhikaryetal., author = {Garain, Samiran and Sinha, Tridib Kumar and Adhikary, Prakriti and Henkel, Karsten and Sen, Shrabanee and Ram, Shanker and Sinha, Chittaranjan and Schmeißer, Dieter and Mandal, Dipankar}, title = {Self-Poled Transparent and Flexible UV Light-Emitting Cerium Complex-PVDF Composite: A High-Performance Nanogenerator}, series = {ACS Applied Materials \& Interfaces}, volume = {2015}, journal = {ACS Applied Materials \& Interfaces}, number = {7}, issn = {1944-8244}, doi = {10.1021/am507522r}, pages = {1298 -- 1307}, abstract = {Cerium(III)-,N-dimethylformamide-bisulfate [Ce(DMF)(HSO4)3] complex is doped into poly(vinylidene fluoride) (PVDF) to induce a higher yield (99\%) of the electroactive phases (β- and γ-phases) of PVDF. A remarkable enhancement of the output voltage (∼32 V) of a nano-generator (NG) based on a nonelectrically poled cerium(III) complex containing PVDF composite film is achieved by simple repeated human finger imparting, whereas neat PVDF does not show this kind of behavior. This high electrical output resembles the generation of self-poled electroactiveβ-phase in PVDF due to the electrostatic interactions between the fluoride of PVDF and the surface-active positive charge cloud of the cerium complex via H-bonding and/or bipolar interaction among the opposite poles of cerium complex and PVDF, respectively. The capacitor charging capability of the flexible NG promises its applicability as piezoelectric-based energy harvester. The cerium(III) complex doped PVDF composite film exhibit an intense photoluminescence in the UV region, which might be due to a participation of electron cloud from negative pole of bipolarized PVDF. This fact may open a new area for prospective development of high-performance energy-saving flexible solid-state UV light emitters.}, language = {en} } @inproceedings{KrenekCimrovaSeifarthetal., author = {Krenek, Radim and Cimrova, Vera and Seifarth, Olaf and Bocharova, Vera and Gorodyska, Ganna and Sidorenko, Alexander and Schmeißer, Dieter and Stamm, Manfred}, title = {Electronic Properties of Metals Embedded into Porous Polymeric Nanotemplates}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 41}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 41}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 108}, abstract = {We report on electrical measurements (current-voltage characteristics (CVC)) of metals which are templated via porous polymeric nanotemplates. The nanotemplates are based on self-organization of poly(styrene-block 4-vinylpyridine) (PS-PVP). The cylindrical pores of 8 nm in the diameter are ordered in a hexagonal lattice (24 nm in the period). Chromium and gold were embedded in the nanotemplates by magnetron sputtering, nickel was electrodeposited. These thin films were characterized by AFM, ellipsometry, x-ray reflectivity, XAS, XPS and NEXAFS. CVC were acquired by a connection common for light emitting diodes discussing a further use of nanotemplated metals in these devices. To make the connection, the nanotemplate was deposited on glass with ITO electrodes, then metal was embedded into it and finally Al electrodes were evaporated on the device. Behaviour of space charge limited currents (SCLC) was observed. Also, we deal with the electrical mode of AFM as well. Finally electronic behaviour of the metallic nanorods embedded in polymeric nanotemplates is discussed in respective to the structure and chemical composition obtained by AFM and x-ray techniques.}, language = {en} } @inproceedings{TallaridaSohalSchmeisser, author = {Tallarida, Massimo and Sohal, Rakesh and Schmeißer, Dieter}, title = {Electronic properties of the 2x1 3C-SiC surface reconstruction studied with resonant photoemission}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, isbn = {0420-0195}, pages = {S. 239}, abstract = {We have studied the 2x1 reconstructed surface of the 3C-SiC polytype by means of photoemission spectroscopy. The reconstruction was characterized through Si2p and C1s core level and angle-integrated valence band spectroscopy, and confirmed by the observation of a two-domain 2x1 LEED pattern. The electronic properties of this surface were investigated by collecting valence band spectra at photon energies near the Si2p and C1s absorption edges. The results show a strong dependence of the photoemission intensity on the excitation energy with characteristic resonances for certain valence band features. With a detailed study of the resonances we are able to assign the electronic origin of the resonating states and the nature of the electronic transition near the absorption edges.}, language = {en} } @inproceedings{WehnerHofmannSchmeisseretal., author = {Wehner, Stefan and Hofmann, Patrick and Schmeißer, Dieter and Brand, Helmut R. and K{\"u}ppers, J{\"u}rgen}, title = {Pattern formation in the CO + O reaction on Ir(111) surfaces under the influence of noise}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 708}, abstract = {The rate of CO oxidation on Ir(111) surfaces exhibits bistability at T = 500 K in a range of the CO fraction Y in the CO + O reactant gas flux. Quadrupol mass spectrometer measurements of the CO2 rates as a function of the noise strength imposed on Y are well reproduced by parameter-free modeling. We present Photoelectron emission microscopy (PEEM) measurements and 2D calculations of the spatio-temporal patterns of CO and O rich domains. The role of combined multiplicative and additive noise on Y for CO and O domain wall motion and island nucleation-growth-coalescence processes is analysed. For small noise amplitudes few islands nucleate and grow up to some 100 µ m in diameter, before they merge with another island. With increasing noise amplitudes more islands nucleate. With large noise amplitudes bursts to and switching between the branches is observed. The domain wall velocity is found to be independent of the noise strength and island size.}, language = {en} } @inproceedings{WehnerHoffmannSchmeisseretal., author = {Wehner, Stefan and Hoffmann, Patrick and Schmeißer, Dieter and Brand, Helmut R. and K{\"u}ppers, J{\"u}rgen}, title = {CO oxidation on Ir(111) surfaces: consequences of anisotropic diffusion and noise}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 475}, abstract = {The CO oxidation reaction on Iridium(111) surfaces shows bistability in a limited range of the CO fraction of the reactant gas flux Y and a wide range of temperatures T. The two branches are characterized by their reactivity for CO2 formation. The upper rate (high CO2 formation) rate is related to high oxygen coverage on the surface, the lower rate (little CO2 formation) to high CO coverage. Quadrupol mass spectroscopy and PEEM (photoelectron emission microscopy) was employed to study the influence of a noisy reactant gas flux composition on the spatio-temporal pattern development in the CO oxidation reaction on flat Ir(111) and stepped Ir(977) surfaces. PEEM shows nucleation and growth of few oxygen resp. CO islands at small noise amplitudes. Anisotropic diffusion of CO parallel and normal to the steps causes elliptic shapes of large islands. The long axes of the ellipses are aligned along the steps. At increased noise amplitudes the density of islands becomes larger. 2D modeling of the phenomena based on reaction-diffusion differential equations reproduces the experimental findings quite nicely.}, language = {en} } @inproceedings{SeimeHenkelPaloumpaetal., author = {Seime, Bernd and Henkel, Karsten and Paloumpa, Ioanna and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {Buffer layer investigation of MFIS stacks with an organic ferroelectric layer}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 42}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 42}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 216}, abstract = {Ferroelectric field effect transistors are considered as future non volatile and non destructive readout memory cells. Conventional Perowskite-type ferroelectric materials are shown to work but they need expensive high temperature and high partial pressure processing steps inducing also unintentional and undefined interfacial layers.A possible low cost solution is the use of poly[vinylidene fluoride trifluoroethylene (P[VDF/TrFE]). This is a ferroelectric polymer which can be spin coated at room temperature onto silicon suited with well defined buffer layers. Using P[VDF/TrFE] we focus on metal ferroelectric insulator semi-conductor (MFIS) structures. In MFIS structure a part of the programming voltage drops over the buffering insulator. We report on attempts to minimize this fraction by optimizing the voltage divider over the buffer and the ferroelectric layers. CV measurements for different thickness of the buffer (10-235nm) and the ferroelectric layer(100nm-1μm) and for different permittivity values of the buffer layer(SiO2, Al2O3, HfO2) will be presented. This work is supported by Deutsche Forschungsgemeinschaft within priority program 1157 (DSCH 745/11-1).}, language = {en} } @inproceedings{MandalMuellerSeifarthetal., author = {Mandal, Dipankar and M{\"u}ller, Klaus and Seifarth, Olaf and Hoffman, Patrick and Henkel, Karsten and Schmeißer, Dieter}, title = {Study of reactions at the interface P(VDF/TrFE)/Al and P(VDF/TrFE)/PEDOT:PSS}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 42}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 42}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 797}, abstract = {Due to potential use in non volatile memory application, Poly(vinylidene fluoride/trifluoroethylene) (P(VDF-TrFE)) is a great deal of interest, especially to produce organic field effect transistors (OFET). Right now it was found that Aluminum is one of the cost-effective inorganic electrode candidate. On the other hand, poly(3,4 ethylenedioxythiophene):poly(4-styrenesulfonate)(PEDOT:PSS) shows promising behavior for the application as organic electrode. In part of our investigations we have systematically studied surface interactions of organic ferroelectric thin films (P(VDF-TrFE))with inorganic (Al) and organic layers (PEDOT:PSS). By X-ray photoelectron spectroscopy (XPS) is has been found that there is a interfacial reaction with Al and the copolymer. In contrast, for electrodes, made of PEDOT: PSS, we found not such kind of behavior. In this case, we found no evidence for any surface reaction. Furthermore, we present our results concerning the orientation of permanent dipoles in the co-polymer (formed between hydrogen and fluorine atom). Here, we use Near-edge X-ray absorption fine structure (NEXAFS) analysis at the U 49/2 - PGM2 beam line of the BESSY-II Synchrotron. This work is supported by Deutsche Forschungsgemeinschaft (DFG) within priority program 1157 (DSCH 745/11-1).}, language = {en} } @inproceedings{HenkelSohalTorcheetal., author = {Henkel, Karsten and Sohal, Rakesh and Torche, Mohamed and Schwiertz, Carola and Burkov, Yevgen and Schmeißer, Dieter}, title = {PrOx/AlON stacks as a high-k candidate on SiC}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 42}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 42}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 215}, abstract = {We study the chemical stability and electrical properties of Pr-oxides-SiC MIS stacks. In MISFET devices for high power applications the electric field scaling at the interface between semiconductor and insulator is determined by the ratio of their permittivity values. A high-k material can be used to optimize the performance of such devices. In previous studies we had to understand that the chemical reactivity of the PrOx/SiC interface causes a destructive interaction yielding silicate and graphite formation as well as poor electrical performance after direct deposition of PrOx onto SiC. Therefore we introduced an additional chemically inert layer and in this contribution we focus on PrOx/AlON as a suitable insulator stack. In our spectroscopic investigations we recognized a stable AlON/3C-SiC interface even for annealing steps up to 900∘C. First electrical characterizations are performed on Si substrates and we find a strong improvement in the leakage current by several orders of magnitude down to values of 10-7 A/cm2 at an EOT of 4nm and interface state densities of mean values of 5*1011/eVcm2. We also report on our ongoing electrical characterization of such stacks on SiC substrates. This work is supported by Deutsche Forschungsgemeinschaft within priority program 1157 (DSCH 745/9-2).}, language = {en} } @inproceedings{MuellerSchmeisser, author = {M{\"u}ller, Sebastian and Schmeißer, Dieter}, title = {The initial stages of Chromium growth on Titaniumdioxide-Investigations using synchrotron radiation}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 42}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 42}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 598}, abstract = {We investigate the interface of Cr-TiO2 during the initial stages of Cr deposition. Experiments are carried out at BESSY II (BL U49/2-PGM2). Using XPS, XAS and ResPES we obtain information about electronic structure at the interface. We confirm the results of growth studies by Christian Winde obtained by TEM-EELS. In addition, we find that Cr deposition induces two gap states which appear about 1 eV and 3 eV below EF. Using ResPES, these states can be identified as being Cr-like and Ti-like respectively. Core-level-XPS and CIS-spectra of the lower gap state indicate the existence of mainly Cr4+ at low coverage (< 1 ML). At higher coverage (≈ 2.5 ML) metallic Cr is observed as well as metallic Ti. Oxidized Cr occurs mainly as Cr3+. CIS-spectra of higher gap state show metallic behavior with both Cr- and Ti-like character. CIS-spectra of lower gap-state confirm the existence of Cr3+. Reference: Christian Winde, Herstellung und Charakterisierung von Cr Schichten auf TiO2 (110)Oberfl{\"a}chen, PhD Thesis, University of Stuttgart, 2002}, language = {en} } @inproceedings{NielsenBauerSennetal., author = {Nielsen, Karl-Wilhelm and Bauer, Sebastian and Senn, Konrad and Goennenwein, Sebastian T. B. and Opel, Matthias and Cezar, Julio C. and Schmeißer, Dieter and Gross, Rudolf}, title = {X-ray magnetic circulardichroism in cobalt-doped ZnO}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 42}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 42}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 454}, abstract = {Cobalt-doped ZnO is a diluted magnetic semiconductor with a reported Curie-temperature well above 300 K. Nevertheless, the origin of the ferromagnetic exchange still is under debate. To clearify this issue we have investigated cobalt-doped ZnO thin films with x-ray magnetic circular dichroism (XMCD). The (0001)-oriented Zn0.95Co0.05O thin films were grown on (0001) ZnO, (0001) Al2O3, and (0001) ScAlMgO4 substrates by pulsed laser deposition. The magnetic properties were measured by SQUID magnetometry and XMCD. Room temperature magnetization measurements by SQUID magnetometry and XMCD in the fluorescence yield mode reveal ferromagnetic behavior with similar shape of the magnetization curves, however, with different absolute values. XMCD magnetization in total electron yield, which is surface sensitive, show only small magnetic moments, most likely due to a magnetically dead surface layer. This work is supported by the DFG via SPP1157.}, language = {en} } @inproceedings{KachelRichterPhilipetal., author = {Kachel, Krzysztof and Richter, Matthias and Philip, Shine and Paloumpa, Ioanna and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {Performance of organic solar cells with a ferroelectric component}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 153}, abstract = {Charge dissociation and recombination are important factors for the efficiency of organic solar cells, even in blended systems of different polymers. As a new approach, the influence of additional blended ferroelectric nanoparticles on the solar cell performance is investigated. The ferroelectric dipole of the nanoparticle causes a local field, which could lead to a longer recombination time of the polaron pairs. As solar cell system we use bulk heterojunction cells or bilayer structures based on regioregular poly(3-hexylthiophene) (P3HT) as the donor and phenyl-C61-butyric acid methyl ester (PCBM) as the acceptor molecule. As ferroelectric additive we use the ferroelectric copolymer poly(vinylidene fluoride trifluoroethylene) (P(VDF-TrFE)) or BaTiO3. The copolymer is spincoated as ultrathin film of 20nm, whereas the BaTiO3 is incorporated as nanodispersion into the donor-acceptor blend. We present the solar cell parameters for the different geometries and ferroelectric materials as a function of ferroelectric content and of the alignment of the ferroelectric dipoles after application of an external electric field.}, language = {en} } @inproceedings{KlocekFriedrichZagorodniyetal., author = {Klocek, Jolanta and Friedrich, Daniel and Zagorodniy, Kostyantyn and Schmeißer, Dieter}, title = {Spectroscopic investigations of interaction between C60 fullerene and nitrogen atom from amine group}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 231}, abstract = {We investigated interactions between fullerene molecule and amine group from 3-aminopropyl-trimethoxysilane (3AT). Theoretical calculations show that the material obtained as a result of interactions between 3AT and C60 fullerene may have extremely low dielectric constant around 1.6, so it could be considered as a candidate for ultra low-k (ULK) material applications. We prepared films composed of 3AT and fullerene by using two preparation techniques: spin-coating and evaporation. Interactions between these two components were investigated by using X- ray photoelectron spectroscopy (XPS) and Near Edge X-ray Absorption Fine Structure Spectroscopy (NEXAFS). We found that there are strong chemical reactions between the nucleophilic nitrogen atom from 3AT and electrophilic fullerene molecule. Results of NEXAFS measurements suggest that due to direct interactions between 3AT and C60 the shape of fullerene molecule is changed.}, language = {en} } @inproceedings{KolanekKaravaevTallaridaetal., author = {Kolanek, Krzysztof and Karavaev, Konstantin and Tallarida, Massimo and Schmeißer, Dieter}, title = {Atomic layer deposition of HfO2 onto SiO2 substrates investigated in-situ by non-contact UHV/AFM}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 248}, abstract = {We investigated in-situ the atomic layer deposition (ALD) of HfO2 onto SiO2 substrates with ultra high vacuum (UHV) non-contact atomic force microscope (NC-AFM). The ALD process was started after detailed analysis of the initial Si(001)/SiO2 substrate. The ALD cycles, made by using tetrakis-di-methyl-amido-Hf (TDMAHf) and water as precursors, were performed on the SiO2 substrate maintained at 230 ∘C. We studied the relation between the film growth and the root mean square surface roughness, surface skewness, kurtosis, fractal dimension and correlation length. In the initial stages of the ALD process with our analysis of the surface height histograms we were capable of determination: HfO2 layer thickness, surface coverage and surface roughness of a substrate and deposited material. Observation of the surface height histograms evolution during deposition allowed us to verify conformal and effective ALD growth on SiO2 substrate. With this detailed analysis of the surface topography we confirmed the completion of the first HfO2 layer after four ALD cycles.}, language = {en} } @inproceedings{MichlingTallaridaKolaneketal., author = {Michling, Marcel and Tallarida, Massimo and Kolanek, Krzysztof and Schmeißer, Dieter}, title = {In-situ EELS and UPS measurements on HfO2 ALD layers}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {In this contribution we report on our in-situ cycle-by-cycle (up to 10 cycles) investigations of the HfO2 ALD process using the methods of EELS and UPS. We used TDMA-Hf as a precursor and p-type Si wafer with natural oxide as the substrate. The EELS measurements were done with a primary energy of 52,5 eV and the UPS measurements with He I (21,218 eV). The change in the onset of the loss function is readily observed. Already after two cycles the value approach to the bulk value of HfO2. Upon ALD growth there is a remarkable decrease in the intensity of states within the gap. They are rather smooth and saturate after 10 cycles. With UPS we follow the variation of the VB onset and changes in the secondary electron onset. We summarize our data in a band diagram not based on bulk values but on cycle dependent quantities. With these cycle-by-cycle experiments we study the initial growth of HfO2 especially in the very first cycles.}, language = {en} } @inproceedings{MuellerSchmeisser, author = {M{\"u}ller, Sebastian and Schmeißer, Dieter}, title = {Synchrotron radiation spectroscopy studies of the initial interaction between cobalt and titanium dioxide}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 652}, abstract = {Small metallic particles deposited on oxide surfaces can serve as heterogeneous catalysts, as for example TiO2 supported cobalt is a known Fischer-Tropsch-Catalyst. The goal of the presented studies is to investigate the interaction between cobalt and TiO2 in the initial step of growth by synchrotron radiation based spectroscopy. PES studies of TiO2 supported cobalt show a reduction of the oxide support, accompanied by an oxidation of the deposited material. The oxidation is not complete, but metallic cobalt is found already in the very first step of growth. Uniform decrease of both substrate PES lines indicate very weak interaction between overlayer and TiO2. An atomic multiplet calculation including charge transfer and crystal field effects is applied to simulate the experimental Co 2p XAS and XPS spectra of the oxidized component. The results allow the identification of the local coordination as well as the identification of the oxidation state of cobalt.}, language = {en} } @inproceedings{PhilipRichterFriedrichetal., author = {Philip, Shine and Richter, Matthias and Friedrich, Daniel and Paloumpa, Ioanna and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {Spectroscopic investigations of P3HT/PCBM films for organic BHJ solar cells}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 153}, abstract = {Investigations of the electronic structure and composition of regioregular poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) based films using Near Edge X-Ray Absorption Fine Structure (NEXAFS) are presented. The measurements were performed at the U49/2-PGM2 beam line of BESSY II, Berlin recording TEY (total electron yield) and TFY (total fluorescence yield) data. Samples prepared by spin coating a mixture of P3HT dissolved in chloroform and PCBM dissolved in chlorobenzene onto ITO (indium tin oxide) coated glass slides were analyzed. Upon measuring the pure P3HT and PCBM, all reported excitations were observed, whereas the blended system is a weighted superposition of the related peaks. Analyzing the data we calculate the composition of the mixture. We also show angular dependent NEXAFS measurements of the P3HT/PCBM blend in order to measure the orientation and distribution of the P3HT polymer. Additionally, we show a new approach for organic solar cell application. BaTiO3 nanoparticles were incorporated as nanodispersion into the donor-acceptor blend or the ferroelectric copolymer poly(vinylidene fluoride trifluoroethylene) (P(VDF-TrFE)) was spincoated as an ultrathin film below the blend.}, language = {en} } @inproceedings{RichterFriedrichPhilipetal., author = {Richter, Matthias and Friedrich, Daniel and Philip, Shine and Paloumpa, Ioanna and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {Study of P3HT/PCBM based films by NEXAFS}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 194}, abstract = {In this contribution we report on investigations of the electronic structure and composition of regioregular poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) based films by using Near Edge X-Ray Absorption Fine Structure (NEXAFS). The measurements were done at the U49/2-PGM2 beam line of BESSY II, Berlin using TEY (total electron yield) and TFY (total fluorescence yield) detection. The samples were produced by spin casting a mixture of P3HT (dissolved in chloroform) and PCBM (dissolved in chlorobenzene) on ITO (indium tin oxide) coated glass slides. Measurements of pure P3HT and PCBM show all typical excitations, whereas the blended system is a weighted superposition of the related peaks. Analyzing these weighted superposition, we observe in the surface sensitive TEY data an accumulation of P3HT, whereas in the bulk sensitive TFY signal an as expected mixture is found. We also show angular dependent NEXAFS measurements of the P3HT/PCBM blend in order to measure the orientation and distribution of the P3HT polymer. Additionally, we will show a new approach for organic solar cell application by introducing ferroelectric nanoparticles into the mixture.}, language = {en} } @inproceedings{SchmidtSchmeisser, author = {Schmidt, Stephan and Schmeißer, Dieter}, title = {Cobalt/nickel mixed oxides - cathode materials for Li-Ion-Batteries}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 596}, abstract = {Replacing Co by large amounts of Ni is considered to reduce costs in Li-Ion-Batteries while maintaining their performance. We are interested in whether this replacement causes changes in the valence band (VB) and conduction band (CB) states or not. Samples were prepared as thin films from nitrate solutions on metal substrates and annealed in air and UHV. The Co to Ni ratio was varied from 50/50 over 40/60 and 30/70 up to 20/80. The results are compared to the pure Co-oxide. Experiments were carried out at the U49/2 beamline at BESSYII, Berlin. XPS of the TM2p states reveals the existence of charge transfer ground states and different oxidation states. NEXAS at the Co2p, Ni2p and O1s edges projects the density of unoccupied states while resonant PES at these edges provides the related partial density of states (pDOS) and thus can be used to distinguish between the different contributions of TM3d and O2p states in the valence band region. We find systematic variation of the VB structure, the valence band maximum and a shift at the O1s absorption edge while the TM2p XPS and absorption spectra do not seem to be affected by the mixing.}, language = {en} } @inproceedings{StarzykTallaridaSchmeisser, author = {Starzyk, Łukasz and Tallarida, Massimo and Schmeißer, Dieter}, title = {Electrically optimized high-κ metal gate MOSFET by specific modification of the band alignment}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 231}, abstract = {The electrical optimization of metal/oxide/semiconductor gate stacks by specific modification of the band alignment for advanced MOS technology incorporating high dielectric constant (κ) materials is explored. Because of requirements concerning continued scaling of MOSFET transistors, gate oxides and cobalt electrode have been grown successively on Si substrate respectively by means of atomic layer deposition (ALD) and evaporation. The thicknesses of high-κ films were around 2 nm. In case of work function engineering, interfaces' chemistry plays a fundamental role. We applied synchrotron radiation based x-ray photoelectron spectroscopy (SR XPS) to characterize our samples, which allows step by step in situ investigations. Co 2p, Al 2p, Hf 4f, Si 2p and O 1s core levels spectra were measured and analyzed. From valence band (VB) spectra we determined Schottky barrier height and electronic bands offsets.}, language = {en} } @inproceedings{WyrodekTallaridaSchmeisseretal., author = {Wyrodek, Jakub and Tallarida, Massimo and Schmeißer, Dieter and Weisheit, Martin}, title = {Determination of interfacial layers in high - k ALD nanolaminate materials by ARXPS and SRXPS measurements}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 232}, abstract = {The interfacial layers of high dielectric constant (high - k) nanolaminate films are here explored. Problems concerning ALD nanolaminate layers deals mainly with lack of accurate methods to determine in depth profile of few nm thick stacks. Modified angle resolved XPS(ARXPS) and synchrotron radiation XPS(SRXPS) are proposed as methods suitable in layer profiling. Studied stacks containing ZrO/HfO or AlO/ZrO, were prepared on Si substrates by atomic layer deposition (ALD). Two sets of experiments were covered. First dealt with initial growth (up to 20 cycles, with thickness d < 2nm) of AlO/ZrO and included layer by layer insitu investigation by SRXPS. Second experiment refer to industrial grown ZrO/HfO films ( d ∼ 3nm ) processed with various parameters resulting in both, layer by layer and homogenous depositions. For those samples exsitu XPS, with angle dependent variation of probing depth, measurements were covered. By comparing obtained intensity ratios for different angles with computational developed stack model it was found that no simple layer by layer but some intermixing growth occurred including interaction with silicon substrate.}, language = {en} } @inproceedings{BergholzSchmeisser, author = {Bergholz, Matthias and Schmeißer, Dieter}, title = {Band gap determination of thin Praseodymiumoxide layers on Aluminiumoxynitride films}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 243}, abstract = {High-k dielectrics are important as never bevore in semiconductor industry. We investigate Pr2O3 as one representative of this group on Silicon and Silicon-Aluminium oxynitride substrates. In earlier work we observed the positive influence of this AlOxNy intermediate layer on the electrical properties of the Pr2O3 layer. Now we present in-situ EELS, XPS and UPS measurements of gradually grown thin Pr2O3 on AlOxNy. From these measurements we determine the band structure and find a very fast change of the band gap for the first few {\AA}ngstr{\"o}m, coupled with n-type behaviour for the Pr2O3 film. These results are compared with RIXS measurements of a 5 nm Pr2O3 on a 1 nm thick AlOxNy layer.}, language = {en} } @inproceedings{BurkovHenkelSchmeisser, author = {Burkov, Yevgen and Henkel, Karsten and Schmeißer, Dieter}, title = {X-ray photoemission spectroscopy of Aluminium Oxynitride on Si(001) and the rise as buffer layers}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 243}, abstract = {Praseodymium oxide (PrxOy) is one of the candidate as high-k transistor gate dielectrics, but aluminium oxynitride (AlxONy) as buffer layer is needed to prevent diffusions from the silicon into PrxOy and to hinder charge injection from the semiconductor into the insulator. The thermal stability and thickness dependence of aluminum oxynitride (AlxONy) has been investigated by synchrotron radiation photoemission spectroscopy (SR-PES). AlxONy layers were prepared by low energy ion-beam assisted deposition (LE-IBAD) at room temperature on a silicon substrate cleaned with HF-acid. Aluminium oxynitride is stable till 800∘C. From photoemission spectra we can assess that silicon oxynitride is built as first and then the growth of AlxONy follows. Resonant inelastic X-ray scattering measurements with synchrotron radiation have been performed. The combination of X-ray absorption spectroscopy (XAS) and RIXS make possible to determinate the band gap of AlxONy.}, language = {en} } @inproceedings{HenkelSeimePaloumpaetal., author = {Henkel, Karsten and Seime, Bernd and Paloumpa, Ioanna and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {C(V) and C(t) measurements on MFIS structures consisting P[VDF/TrFE] as ferroelectric layer}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 828}, abstract = {Ferroelectric Field Effect Transistors (FeFETs) are considered as a candidate for future non volatile and non destructive readout memory cells. A possible low cost solution is the use of poly[vinylidene fluoride trifluoroethylene (P[VDF/TrFE]). Using P[VDF/TrFE] we focus on metal ferroelectric insulator semiconductor (MFIS) capacitor structures. In this contribution we will summarize our investigations related to capacitance measurements in dependence of applied bias (C(V)) and time (C(t)). The thickness of the ferroelectric layer as well as the thickness and the material of the buffer layer have been investigated for optimization of the write voltage. CV measurements at higher temperatures deliver decreased flatband voltage shifts within one CV loop resulting in lower memory windows. At temperatures around 100∘C the hysteresis totally vanished, pointing out the ferroelectric behavior of the system. C(t) measurements at a constant bias have been performed for retention analysis of the MFIS stack. After applying a writing pulse we could distinguish between a higher and a lower capacitance state for more than 5 days. This work is supported by Deutsche Forschungsgemeinschaft within priority program 1157 (SCHM 745/11-2).}, language = {en} } @inproceedings{KaravaevTallaridaSchmeisseretal., author = {Karavaev, Konstantin and Tallarida, Massimo and Schmeißer, Dieter and Zschech, Ehrenfried}, title = {In-situ ALD growth of Hafnium oxide films}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 244}, abstract = {We report on a novel system for in-situ atomic layer growth (ALD) of high-k dielectric films. First results were obtained for Hf-oxide samples by using Hf-tetrachloride as precursor and water as oxidizer. We compare the photoelectron spectra of Si2p, O1s and Hf4f of our in-situ prepared films with samples (ex-situ) prepared by industrial ALD reactors and discuss similarities and differences observed in the core level spectra of the various samples by considering the different growth conditions.}, language = {en} } @inproceedings{MandalMuellerSchmeisser, author = {Mandal, Dipankar and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {Dipole orientation of the P[VDF-TrFE] co-polymer films: A NEXAFS study}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 840}, abstract = {Ferroelectric properties of copolymers of vinylidene fluoride with trifluoroethylene (P[VDF-TrFE]) has become great deal of interest due to potential use in non volatile memory technology. Permanent dipoles (formed between the alternating hydrogen and fluorine atom within the copolymer) ordering of orientation are crucial for device efficiency. Here we focus on thickness dependence dipole orientation in these co-polymer films. In our systematic studies, we found there is prominent dipole re-orientation effect also for the intrinsic films (~10 nm thickness) before applying the electric field. It is observed after the application of the field, the dipoles re-oriented in opposite direction. Therefore, we conclude that the lowest thickness of the film should have well grown crystalline lamellae structure. As a result, c-axis of crystallites acts as well define manner in plane of the surface and for that reason the b-axis is more free. Because the b-axis is parallel to the polarization direction, it is easy to get a preferred orientation of the dipoles. For thicker films (here up to 100 nm), the average orientation effect is hindered, so a very low re-orientation effect has been observed. For this investigation, we used Near Edge X-ray Absorption Spectroscopy, at the U 49/2-PGM beam line of BESSY-II, Berlin. This work is supported by DFG within SPP1157 (SCHM 745/11-2).}, language = {en} } @inproceedings{MuellerMandalHenkeletal., author = {M{\"u}ller, Klaus and Mandal, Dipankar and Henkel, Karsten and Paloumpa, Ioanna and Schmeißer, Dieter}, title = {Interface reactions of ferroelectric copolymer layers with different electrode materials}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 830}, abstract = {The ferroelectric copolymer poly(vinylidene fluoride trifluoroethylene) (P(VDF-TrFE)) is a possible material for low cost applications as organic nonvolatile memory element. We present an XPS interface investigation of the copolymer/electrode interface. Below 100nm film thickness, interface phenomena becomes important. Possible interface reactions could lead to a reduction of the ferroelectric functionality.We present a comparative study of the two interfaces Al/P(VDF-TrFE) and PEDOT:PSS/P(VDF-TrFE). The result is a clear indication of a surface reaction in between the Aluminum-electrodes. In contrast, for PEDOT:PSS the measurements shows a layer by layer formation of the interface PEDOT:PSS/PVDF without any reaction. Second, we present a study of remanent polarization of ultrathin spincoated films of the copolymer, in a thickness range from 5 to 100mn, with organic electrodes like PEDOT:PSS. The measurements are carried out by using the flatband shift of a capacitance-voltage (CV) characteristic. This shift of flatband voltage is used as value for the electric polarization of the polymer.}, language = {en} } @inproceedings{MuellerSchmeisser, author = {M{\"u}ller, Sebastian and Schmeißer, Dieter}, title = {Direct Observation of d2L2 Charge Transfer States in TiO2 thin films by Resonant Photoelectron Spectroscopy}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 592}, abstract = {We investigate the electronic structure of TiO2 thin films by SR-PES, NEXAFS and ResPES. The films are prepared in a combined in-situ/ex-situ process that leads to stoichiometric thin films (≈ 10 nm) in Rutile structure. We focus on ResPES at the Ti 2p edge. When the photon energy is close to the Ti 2p absorption edge we observe additional features about 13 eV below the valence band main features. These features show clear spectator auger decay at the resonance leading to d0 final state. From this, we deduce the existence of the d2L2 initial charge transfer state as this is the only possible channel that enables the corresponding spectator auger decay. These features have the same origin as the satellite structures observed in core level spectra, esp. 2p and 3p.}, language = {en} } @inproceedings{TallaridaKaravaevSchmeisseretal., author = {Tallarida, Massimo and Karavaev, Konstantin and Schmeißer, Dieter and Zschech, Ehrenfried}, title = {Photoemission and absorption spectroscopy for in situ investigations of the ALD growth}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 242}, abstract = {We have investigated the growth of Hf-oxide on Si by means of photoemission and X-ray absorption spectroscopy using synchrotron radiation at Bessy, Berlin. The Hf-oxide layers were grown via atomic layer deposition (ALD) using an in-situ ALD reactor attached to the investigation chamber. The XPS and XAS spectra were measured after every deposition cycle by transferring the sample into the investigation chamber without breaking the vacuum. From the experimental data we have obtained information about the early stages of the Hf-oxide growth, concerning in particular the reactivity of the interface with Si. Due to the possibility to study the layers after every cycle and with different oxidation parameters without exposing them to contaminants, the in situ investigation revealed to be a very important method to understand the growth properties of Hf-oxide.}, language = {en} } @inproceedings{OpelNielsenBaueretal., author = {Opel, Matthias and Nielsen, Karl-Wilhelm and Bauer, Sebastian and Goennenwein, Sebastian T. B. and Gross, Rudolf and Cezar, Julio C. and Schmeißer, Dieter and Simon, J{\"u}rgen and Mader, Werner}, title = {Ferromagnetism and magnetic clusters in cobalt-doped ZnO}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 430}, abstract = {Ferromagnetic semiconductors (FMS) - i.e. semiconductors exhibiting long-range magnetic ordering - are intriguing materials. However, in spite of intensive research in the last decade, the existence of homogeneous FMS with a Curie temperature around or above room temperature still is controversial. A particularly tedious issue are local sample inhomogeneities or magnetic clusters, which can yield strong magnetic signals resembling the behaviour expected for a homogeneous FMS. Using pulsed laser deposition, we have grown cobalt-doped ZnO films on single crystalline ZnO substrates. Combining x-ray magnetic circular dichroism, DC magnetometry, and AC susceptibility measurements with a detailed structural analysis by high resolution x-ray diffraction, transmission electron microscopy, and electron-spectroscopic imaging, we can unambigously trace the characteristic, ferromagnetic-like behaviour of our ZnO:Co samples at room-temperature to nanometer-sized superparamagnetic metallic cobalt precipitates.}, language = {en} } @inproceedings{LazarevaKovalMuelleretal., author = {Lazareva, I. and Koval, Yuri and M{\"u}ller, P. and Paloumpa, Ioanna and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {Field effect transistor of graphitized polyimide with P(VDF-TrFE) as gate insulator}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 195}, abstract = {Surfaces of polyimide films were graphitized by low-energy ion irradiation. The conductivity was between 10-5 to 200 S/cm [1]. We prepared field effect transistors using this material. Ferroelectric P(VDF-TrFE) was used as gate insulator. The thickness of P(VDF-TrFE) varied from 120 nm to 1200 nm. Properties of P(VDF-TrFE) were investigated by current-voltage measurements of metal/ P(VDF-TrFE)/metal capacitors. We have found that at room temperature, the coercive field of P(VDF-TrFE) does not depend on the film thickness. At lower temperatures the coercive field increases proportionally to the reciprocal temperature. Remnant polarization is 9.5 µC/cm2. It slightly rises with decreasing temperature. Our recent results of field effect mobility, carrier concentration and threshold voltage are presented. [1] I. Lazareva, Y. Koval, M. Alam, S. Str{\"o}msd{\"o}rfer, P. M{\"u}ller, Appl. Phys. Lett. 90, 262108 (2007)}, language = {en} } @inproceedings{BergholzSohalSchmeisser, author = {Bergholz, Matthias and Sohal, Rakesh and Schmeißer, Dieter}, title = {ELS to determine the band gap of thin dielectric layers}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 156}, abstract = {In ultra thin layers of high-K materials the value of the band gap can be derived not explicitly although it is a key quantity in the electric behavior. We use ELS with a monochromatized (50 meV - 150 meV) electron gun and primary energies between 20 eV and 30 eV. Starting with the native SiO2/Si(001) layers we find that loss function of the substrate dominates for using primary energies beyond 50 eV. In contrast at energies below 50 eV the loss intensity can be used to derived the band gap with an accuracy of ±200 meV. We compare thin (<3 nm) films of HfOx, Pr2O3,Al2O3 and Si-Oxynitrides and discuss the band gap values as well as the scattered intensity observed within the gap.}, language = {en} } @inproceedings{HenkelTorcheSchwiertzetal., author = {Henkel, Karsten and Torche, Mohamed and Schwiertz, Carola and Paloumpa, Ioanna and Sohal, Rakesh and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {Inorganic and organic layers for high-k and organic memory applications}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 127}, abstract = {We report about organic and inorganic MIS stacks for new possibilities for high frequency and high power applications as well as for non volatile memory cell. The organic stack contains a ferroelectric polymer as the functional layer. Poly[vinylidene fluoride trifluoroethylene] (P[VDF/TrFE]) is spin coated from a solution onto oxidised silicon substrates. We report on the polarisation induced flatband voltage shifts. For the inorganic stack our attempt is to combine higk-k dielectrics with high band gap semiconductors (SiC). Praseodymium oxide layers are prepared by electron beam evaporation from Pr6O11 powder and in situ controlling of interface and volume composition (XPS). Praseodymium silicate layers were prepared either by metal evaporation onto a thin ox- ide on top of the semiconductor and following annealing steps or by a wet chemical process out of aqueous Pr(NO3)3 solutions. Using spectro-scopic characterisation we investigate the stability of the various inter-faces within the stacks as well as the reactivity of the metal electrodes on thin Pr2O3. We report the results of electrical characterisation consisting of permittivity values, leakage current and density of interface states.}, language = {en} } @inproceedings{MuellerHenkelPaloumpaetal., author = {M{\"u}ller, Klaus and Henkel, Karsten and Paloumpa, Ioanna and Schmeißer, Dieter}, title = {P(VDF/TrFE) as ferroelectric insulation layer for organic field effect transistors}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 41}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 41}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 101}, abstract = {The ferroelectric polymer poly(vinylidene fluoride trifluoroethylene)(P(VDF-TrFE)) is used as insulating material for organic field effect tran-sistors (OFET) and metal-insulator-semiconductor (MIS)-structures. For the MIS-structures, we find the typical hysteresis in the CV charac-teristic upon increasing the voltage scan window. Based on these results, we fabricate OFET with regioregular poly(3-hexlythiophene)(P3HT) as organic semiconductor. The transistors are constructed in bottom gate architecture with thin layers of spincoated P(VDF-TrFE) as gate insulation (100nm). The drain-source current of the OFET is reversible affected by the polarized gate, which gives opportunities for organic nonvolatile memory elements. We present characteristic features like the hysteretic drain current response or the data retention. Furthermore, we present measurements with Kelvin probe force microscopy, a method which gives informations on the lateral distributions of the surface potential.}, language = {en} } @inproceedings{HoffmannSchmeisserHimpseletal., author = {Hoffmann, Patrick and Schmeißer, Dieter and Himpsel, Franz J. and Engelmann, Hans-J{\"u}rgen and Zschech, Ehrenfried and Stegmann, Heiko and Denlinger, Jonathan D.}, title = {Characterization of Chemical Bonding in Low-K Dielectric Materials for Interconnect Isolation: XAS and EELS Study}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 41}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 41}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 156}, abstract = {The use of low dielectric constant materials in the on-chip interconnect process reduces interconnect delay, power dissipation and crosstalk noise. In CVD deposited organo-silicate glass (OSG) the substitution of oxygen in SiO2 by methyl groups (-CH3) reduces the permittivity significantly (from 4.0 in SiO2 to 2.6-3.3 in the OSG). However, plasma processing removes C and H containing molecular groups. Therefore, compositional analysis and chemical bonding characterization of structured films with nanometer resolution is necessary. OSG thin films as-deposited and after plasma treatment are studied using XAS and EELS. In both techniques, the fine structure near the C1s edge allows to identify C-H, C-C, and C-O bonds. XAS spectra have been recorded for non-patterned films and EELS spectra for patterned structures. The chemical bonding is compared for as-deposited and plasma-treated low-k materials. The flu-orescence and the electron yield recorded while XAS measurement are compared. Examination of the C 1s near-edge structures reveal a mod-ified bonding of the remaining C atoms in the plasma-treated sample regions.}, language = {en} } @inproceedings{MuellerChowdhuryDremovetal., author = {M{\"u}ller, P. and Chowdhury, F. and Dremov, V. and Koval, Yuri and Lichtenberg, F. and M{\"u}ller, S. and Schmeißer, Dieter and Pentcheva, R.}, title = {Resistive memory switching in perovskite-derivative single crystals}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 818}, abstract = {We investigated several layered perovskite derivatives of the family AnBnO3n+2, such as LaTiO3.41, CaNbO3.41 and SrNbO3.41, which can be considered as a stacking of blocks consisting of 5 perovskite layers. Electric transport across these layers takes place via intrinsic tunnelling. Mesa devices with a cross-sectional area of 50 to 200 µm2 and a height between 30 and 500 nm were fabricated by electron-beam lithography and ion-beam etching. Both dc I-V characteristics and pulsed current injection have shown switching between different resistive states in these materials. The resistive states have long-term stability, which makes them interesting for memory applications. The transport experiments suggest that switching and resistive memory are controlled by trapping and release of charge carriers. Furthermore, photoelectron and NEXAFS spectroscopy of cleaved LaTiO3.41 surfaces have been performed. The results are compared to recent correlated band theory (LDA+U) calculations.}, language = {en} } @inproceedings{SeifarthWalczykLupinaetal., author = {Seifarth, Olaf and Walczyk, Christian and Lupina, Grzegorz and Dabrowski, Jaroslaw and Weidner, G{\"u}nter and Zaumseil, Peter and Schmeißer, Dieter and Storck, Peter and M{\"u}ssig, Hans-Joachim and Schroeder, Thomas}, title = {On the electronic and dielectric characterisation of thin cubic PrO2 layers on Silicon}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 196}, abstract = {For the integration of 100 \% Ge onto the Si platform, a buffer oxide approach has been developed recently, using rare earth oxides to tune the lattice constant between the Si and the Ge. Among these buffer oxides, PrO2 is a prospective candidate with high quality crystalline growth on Si, moderated by an interfacial Pr-silicate between. In order to specify electronic properties of thin PrO2 and its interface on Si(111), especially the width of the band gap, we performed synchrotron radiation based XPS, UPS and XAS measurements at the U49/2 PGM 2 beamline at BESSY II and correlate the results with our structural characterisation performed by TEM and XRD. In order to evaluate the dielectric properties of thin PrO2 layers on Si(111), we performed temperature-, time-, voltage-, and layer thickness-dependent leakage current measurements (J-V). Here, we identified relaxation behaviour in the leakage current, successfully addressed to defect like states inside the Pr-silicate interface layer, corroborated by frequency dependent capacitance versus voltage (C-V) measurements.}, language = {en} } @inproceedings{FriedrichMichlingKloceketal., author = {Friedrich, Daniel and Michling, Marcel and Klocek, Jolanta and Schmeißer, Dieter and Avdoshenko, Stas and Chumakov, Dmytro and Zschech, Ehrenfried}, title = {Study of C60 based films formation by NEXAFS}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 145}, abstract = {The C60 fullerenes and some of its -OH, -CF3 and -Cl derivates are candidates for application as ultra-low-k insulators in the semiconductor industry. Future preparation of thin films based on these materials requires the stability of the substituted fullerenes against chemical handling and processing steps. The latter issue was addressed by our NEXAFS studies that were done by synchrotron radiation at the beam line U49/2-PGM2 at BESSY II. Performed were the C K-edge NEXAFS studies in total fluorescence and total electron yield modes. The C60 based films were deposited on silicon by spraying from solutions. The influence of the different substitutional groups with C60 molecules was studied. The data were compared to the reference spectra of a pure C60 film. For C60(OH)24, C60-Cl2 and C60(CF3)12 a variance of the intensity of the π*-resonance as well as shift to higher energies of 0.5 eV (-OH), 0.6 eV (-F), 0.7 eV (-Cl) were observed. The results confirm the necessary stability of the used C60 derivatives and shall be used for optimization of the film deposition chemistry and conditions.}, language = {en} } @inproceedings{KaravaevTallaridaSchmeisser, author = {Karavaev, Konstantin and Tallarida, Massimo and Schmeißer, Dieter}, title = {Evolution of the interfacial layer during the atomic layer deposition of HfO2 on Si/SiO2 substrates}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 160}, abstract = {We studied the formation of the interfacial layer in the Si/SiO2/HfO2 system using the in-situ Atomic Layer Deposition (ALD) reactor developed in our group [1,2]. We measured the X-ray photoelectron and X-ray absorption spectra with synchrotron radiation at the beamline U49-2/PGM2-BESSY II. The ALD growth was obtained using different Hf-precursors (HfCl4,TEMAHf and TDMAHf) on various prepared substrates at different temperatures. The investigation was carried out in-situ giving the possibility to determine the properties of the grown film after every ALD cycle without breaking the vacuum. We observed the evolution of the Si/SiO2/HfO2 system during the formation of first three Hf-oxide layers, detecting the interfacial growth of SiO2 during the initial ALD cycles from the XPS spectra of Si2p. We discuss how the interfacial layer growth depends on the various ALD parameters. [1] M. Tallarida, K. Karavaev, and D. Schmeisser, J. Appl. Phys. 104, 064116 (2008); [2] M. Tallarida, K. Karavaev, and D. Schmeisser, J. Vac. Sci. Technol. B, accepted for publication.}, language = {en} } @inproceedings{KolanekKaravaevTallaridaetal., author = {Kolanek, Krzysztof and Karavaev, Konstantin and Tallarida, Massimo and Schmeißer, Dieter}, title = {In-situ investigations of the atomic layer deposition of HfO2 with UHV/AFM}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 160}, abstract = {We studied in-situ the atomic layer deposition (ALD) of HfO2 with ultra high vacuum (UHV) atomic force microscope (AFM), using the ALD reactor developed by our group [1, 2]. The reactor was attached to the Omicron Large Sample-UHV/AFM system in the AFM-Lab of the Angewandte Physik-Sensorik chair at the BTU-Cottbus. We investigated different Si(001)/SiO2 substrates and surface preparation techniques performed before the ALD process. After each ALD cycle (using TDMAHf and H2O as precursors), we studied the influence of the HfO2 growth on the root mean square (RMS) roughness; the surface fractal dimension and the height histogram: the surface skewness and kurtosis. We focused on the influence of the substrate temperature on the surface topography during the ALD. The in-situ studies of the ALD process with the UHV/AFM system correlated with the experiments performed with photoelectron spectroscopy can be used for understanding the fundamental properties of the ALD of HfO2 on Si(001). [1] M. Tallarida, K. Karavaev, and D. Schmeisser, J. Appl. Phys. 104, 064116 (2008); [2] M. Tallarida, K. Karavaev, and D. Schmeisser, J. Vac. Sci. Technol. B, accepted for publication.}, language = {en} } @inproceedings{KraatzSchmeisserZschechetal., author = {Kraatz, Matthias and Schmeißer, Dieter and Zschech, Ehrenfried and Ho, Paul S.}, title = {Electromigration simulation for on-chip Cu interconnects}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 161}, abstract = {We are investigating the influence of copper microstructure on electromigration degradation effects and interconnect lifetimes using computer simulation. The simulation is carried out in three dimensions. For the copper microstructure, a Monte Carlo technique was used to model the Cu grain growth. Different diffusivities where applied to grain boundaries and top interface of the interconnect model according to the qualitative crystallographic orientation of adjacent grains. The grain boundary network and the top interface form the diffusion paths for the electromigration mass transport. Along the diffusion paths, the fluxes of vacancies where calculated including mechanical stress and electromigration driving forces using a finite difference method. Positive flux divergent sites of the FDM lattice are treated as void nucleation sites after a critical vacancy concentration is reached. The resistance increase due to void growth was calculated using a cellular automaton, masking current free regions as quasi voids and adding the resistance of the slices of the lattice normal to the electron flow direction in series. A parallel computing environment was used to generate large numbers of interconnect models in order to obtain a pool of data for statistical analysis of interconnect lifetimes. The results of this analysis will be shown}, language = {en} } @inproceedings{MichlingFriedrichSchmeisseretal., author = {Michling, Marcel and Friedrich, Daniel and Schmeißer, Dieter and Koval, Yuri and M{\"u}ller, Paul}, title = {Study of polyimide after graphitization with low-energy Ar+ Ion irradiation by NEXAFS}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 147}, abstract = {In this contribution we report on investigations of the electronic structure of Ar+ irradiated polyimide samples by using NEXAFS. The NEXAFS measurements were done at the U49/2-PGM2 beam line of BESSY II, Berlin using TEY and TFY detection. Polyimide samples are prepared using low Ar+ dose while the temperature of the samples is varied between 300K and 700K. In the NEXAFS data at the Carbon K-edge we see substantial changes between different samples. The differences appear in particular in the more surface sensitive TEY-Signal. The NEXFS data are consistent with the graphitization of the surface upon Ar+ bombardment as we identify the characteristic absorption bands of graphitic carbon. Its relative content increases with increasing sample temperature. In contrast, in the more bulk sensitive TFY data, the emission characteristic of polyimide is maintained. The possibility to cover insulating polymers with a conducting layer is a great demand for many applications. Because of the relative low price of the basic materials, the irradiation with low-energy Ions will play an important roll in the microelectronic of the future.}, language = {en} } @inproceedings{MuellerSchmeisser, author = {M{\"u}ller, Sebastian and Schmeißer, Dieter}, title = {Investigation of ultra-thin Chromium layers on Titanium Dioxide by resonant photoemission}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 453}, abstract = {Oxide supported metal films and clusters offer interesting properties with a wide range of possible applications. In this context, Titanium Dioxide is chosen as a model substrate due to its simple electronic structure with a d0 configuration. We study the interaction of ultrathin Chromium films deposited on TiO2 film with focus on the modifications of the valence band and band gap region. Normal photoemission in bulk and surface sensitive modes as well as resonant photoemission at the Cr 2p and Ti 2p edges are used to distinguish the different Cr 3d and Ti 3d contributions to the valence band. In the initial step we find to gap states of distinct character with a sharp resonance of the Cr 3d related state at the Cr 2p edge. With increasing layer thickness we observe that this resonance extends to about 20 eV below the Fermi-Energy. Datasets of valence band spectra measured around the Cr 2p edge show 2 resonant mechanisms in this case i.e. a participator channel for the 3d state accompanied by a spectator channel at fixed kinetic energy.}, language = {en} } @inproceedings{RichterMuellerPhilipetal., author = {Richter, Matthias and M{\"u}ller, Klaus and Philip, Shine and Paloumpa, Ioanna and Henkel, Karsten and Schmeißer, Dieter}, title = {Temperature dependence of organic solar cell parameters}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 44}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 44}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 671}, abstract = {The influence of an annealing step on the parameters of bulk heterojunction organic solar cells is investigated. In order to fabricate the solar cells we use glass coated with ITO (Indiumtinoxide) as a substrate on which the active layer consisting of P3HT and PCBM is spincoated. Al-electrodes are evaporated on top of the active layer. We use PEDOT:PSS as buffer layer. Each sample is annealed at different temperatures for a short time. Between every temperature step the I-V characteristic of the cell is measured. The following parameters are derived afterwards: FF, Isc (density), Voc. Also the efficiency is estimated. The results show a maximum cell efficiency for drying at 100°C for 20sec. A further important step for preparation is the drying procedure of the PEDOT:PSS layer. Here an improvement of about 50\% in cell efficiency is measured after drying at 50°C for 5 days under inert gas atmosphere.}, language = {en} } @inproceedings{TallaridaKaravaevKolaneketal., author = {Tallarida, Massimo and Karavaev, Konstantin and Kolanek, Krzysztof and Schmeißer, Dieter}, title = {Basics of the atomic layer deposition of HfO2 onto Si/SiO2 substrates: in-situ investigations with XPS, XAS and UHV-AFM}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 44}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 44}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 159}, abstract = {We developed a reactor for investigating in-situ the atomic layer deposition (ALD) of HfO2. X-ray photoelectron and X-ray absorption spectra were collected after each ALD cycle using synchrotron radiation at the beamline U49-2/PGM2 - BESSY II, Berlin. The morphology of the substrate and thin film surfaces was investigated after each ALD cycle with an UHV-AFM microscopy attached to the ALD reactor. We studied the ALD on differently prepared substrates, at different substrate temperatures, and using different Hf-precursors (HfCl4, TEMAHf, TDMAHf). We observed the evolution of the Si/SiO2/HfO2 system during the formation of the first three Hf-oxide layers [1]; we detected the incorporation of Cl into the Hf-oxide films and proposed a mechanism responsible for the Cl contamination [2]; we found evidence of the interfacial-SiO2 growth during the initial ALD cycles and of dipole formation at the HfO2/SiO2 interface. In this contribution we illustrate the basics of the technique used, and discuss the physical-chemical properties of ALD on the basis of the experimental results. [1] M. Tallarida, K. Karavaev, and D. Schmeisser, J. Appl. Phys. 104, 064116 (2008); [2] M. Tallarida, K. Karavaev, and D. Schmeisser, J. Vac. Sci. Technol. B, accepted for publication.}, language = {en} } @inproceedings{TallaridaKaravaevKolaneketal., author = {Tallarida, Massimo and Karavaev, Konstantin and Kolanek, Krzysztof and Schmeißer, Dieter}, title = {In-situ experimental approach to the study of atomic layer deposition with atomic force microscope, X-ray photoelectron and X-ray absorption spectroscopy}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 44}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 44}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S.176}, abstract = {We describe our experimental approach to the investigation of atomic layer deposition (ALD). ALD is a powerful deposition technique for growing conformal thin films of composite materials with atomically accurate thickness on large area [1]. Despite the enormous industrial interest growing around ALD, its fundamental properties were not yet properly studied. We developed an ALD reactor for the in-situ investigations using XPS, XAS and AFM as experimental techniques. We studied the chemical-physical properties of the growing thin films after each deposition cycle. Here, we illustrate the recent results concerning the ALD of HfO2 obtained using different Hf-precursors on various substrates [2]. We show how the in-situ investigations could deliver an important insight into the fundamental characteristics of ALD and how these information could be used to modify and optimize the deposition parameters. [1] M. Leskel{\"a}, M. Ritala, Thin Solid Films, 409, 138, 2002; [2] M. Tallarida, K. Karavaev, and D. Schmeisser, J. Appl. Phys. 104, 064116 (2008).}, language = {en} } @inproceedings{SeifarthWalczykLupinaetal., author = {Seifarth, Olaf and Walczyk, Christian and Lupina, Grzegorz and Zaumseil, Peter and Schmeißer, Dieter and M{\"u}ssig, Hans-Joachim and Schroeder, Thomas}, title = {The electronic band diagram of thin PrO2(111) / Pr-silicate buffers on Si(111) and its relevance to dielectric properties}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 136}, abstract = {Thin dielectric buffers of cubic PrO2(111) on Si(111) are ideally suited to integrate Ge onto Si by moderating the lattice mismatch between the materials. The leakage current across this dielectric buffer is strongly influenced by the electronic band diagram and defects inside the band gap. Therefore, we measured the band offsets, band gaps and defect positions by means of synchrotron radiation based photoemission spectroscopy techniques (XPS and XAS) with special emphasis on the Pr-silicate interface. In a next step we compare the spectroscopic data with information from dielectric studies, based on temperature dependent leakage current studies. We observe a close relation between dielectric properties and the electronic structure.}, language = {en} } @inproceedings{FriedrichMichlingSchmeisseretal., author = {Friedrich, Daniel and Michling, Marcel and Schmeißer, Dieter and Koval, Yuri and M{\"u}ller, Paul}, title = {Characterization of ion beam modified polyimide layers}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 247}, abstract = {Ion beam modified polyimide show high conductivity. In our investigation we focus on the electronic structure and the element composition, in order to understand the mechanism of conductivity. In our experiments we use the methods NEXAFS and PES. The measurements were done at the U49/2-PGM2 beam line of BESSY II, Berlin. We find an increase of the sp2 hybridized graphite contribution, after low Ar+ ion doses bombardment while the temperature of the samples is varied from 300 K to 650 K. In addition we follow the He+ bombardment induced changes by in-situ monitoring of the O1s, N1s content in the polyimide films.}, language = {en} } @inproceedings{DudekLupinaKozłowskietal., author = {Dudek, Peter and Lupina, Grzegorz and Kozłowski, Grzegorz and Dabrowski, Jarek Marek and Lippert, Gunther and M{\"u}ssig, Hans-Joachim and Schmeißer, Dieter and Schroeder, Thomas}, title = {Band structure and electrical properties of MBE grown HfO2 - based alkaline earth perovskites}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 232}, abstract = {Ultra thin dielectric films (<20 nm) deposited on TiN electrodes are interesting for MIM capacitor application. High capacitance density and dielectric permittivity must be accompanied by extremely low leakage currents (10-8 A/cm2) at bias 0.5 V. To achieve such low leakage currents, high band gap and proper band alignment is required. Occupied electronic states can be probed with standard laboratory photoemission methods. Probing of unoccupied states is more challenging. Synchrotron based PES in combination with XAS forms a powerful method to study the band alignment. ASAM end station located at the U 49/2 PGM 2 beamline of BESSY II (Berlin) offers excellent conditions for performing such measurements. We investigated HfO2 - based alkaline earth perovskite - BaHfO3 with subsequent admixture of TiO2, resulting in formation of BaHf0.5Ti0.5O3 compound. The analysis of data indicates that band gap for HfO2 is similar to BaHfO3 and amounts 5.8 eV; for BaHf0.5Ti0.5O3 it decreases to 3.8 eV. We conclude that the addition of TiO2 to BaHfO3 increases significantly the dielectric permittivity but also impacts the band gap alignment. The conduction band offset shrinks, influencing the leakage current behavior.}, language = {en} } @inproceedings{FriedrichKovalMuelleretal., author = {Friedrich, Daniel and Koval, Yuri and M{\"u}ller, Paul and Schmeißer, Dieter}, title = {Electronic structure of thin spin-coated polyimide layers}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 311}, abstract = {The conductivity of polyimide layers can be modified by several orders of magnitude by ion beam radiation. In order to understand the electronic structure of the pure polyimide before ion beam modification we focus in our preliminary experiments on spectroscopic investigations of thin as prepared polyimide films. The films were made by spin coating from a PMDA/ODA solution with subsequent vacuum annealing at 350°C. The layer thickness can be controlled by changing the concentration of PMDA/ODA in the solution realizing a thickness down to 3.5nm. For the characterization of the as prepared thin polyimide films the techniques NEXAFS, ResPES, XPS and CIS were applied at the U49/2-PGM2 beam line of Bessy II, Berlin. Our data including the valence band, core levels and absorption spectrum were compared with theoretical LCAO calculations. Based on these results we are able to attribute all spectral features to the specific atomic bonds in the molecule.}, language = {en} } @inproceedings{HoffmannbeckRichterStaedteretal., author = {Hoffmannbeck, David and Richter, Matthias and St{\"a}dter, Matthias and Paloumpa, Ioanna and Henkel, Karsten and Schmeißer, Dieter}, title = {Spectroscopic and microscopic characterization of potential catalysts for the hydrogenation of CO2}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 483}, abstract = {The reduction of CO2 emissions is a general demand of the society in order to avoid irreversible climate changes. We are investigating potential catalysts for the hydrogenation of CO2 in particular for its application in the so called oxyfuel combustion process. In order to understand the catalytic behavior of the investigated materials we use the techniques X-Ray Photoemission (XPS) and -absorption (XAS) Spectroscopy as well as X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The prospective of our work is to figure out the electronic and structural properties of the material and to optimize proper catalysts or design new ones for best catalytic activity. Beside the spectro-microscopic investigations the catalysts are tested under Sabatier reaction conditions in terms of activity, stability and sensitivity against poisoning. In our preliminary work we constructed a Sabatier reactor system with analytical parts based on infrared absorption and mass spectroscopy modules. First spectroscopic and catalytic results achieved on a commercially available Ru/Al2O3 catalyst will be presented.}, language = {en} } @inproceedings{KraatzZhangSchmeisseretal., author = {Kraatz, Matthias and Zhang, Lijuan and Schmeißer, Dieter and Zschech, Ehrenfried and Ho, Paul S.}, title = {Statistical Analysis of Computer-simulated On-Chip Interconnect Electromigration Lifetimes under the Influence of Microstructure and Strengthened Top Interface}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 292}, abstract = {We are investigating the statistics of computer-simulated interconnect electromigration (EM) lifetimes with regard to the effects of microstructure and a strengthened top interface. The degradation process of EM once threatened the entire existence of integrated circuit industry in the 1960s and has remained a major reliability concern. Ongoing miniaturization and the introduction of new materials further complicate the task of EM-resistant chip manufacturing. We have developed a simple two-dimensional finite difference simulation that models the mass transport by electromigration along the grain boundaries and the top interface of interconnect segments that allows us to do calculations of void nucleation and growth. A parallel computer simulates hundreds of interconnects simultaneously and statistical analysis becomes feasible. A Monte Carlo grain growth algorithm (a modified Potts version) is applied to model the grain structure of the interconnect segments. We will show that the simulation can be used to compare simulation and experiment qualitatively. Four cases have been studied: interconnect segments with small/large grains and weak/strong top interface.}, language = {en} } @inproceedings{MbuaMuellerRichteretal., author = {Mbua, Roy and M{\"u}ller, Klaus and Richter, Matthias and Henkel, Karsten and Paloumpa, Ioanna and Schmeißer, Dieter and Kramm, Ulricke}, title = {Investigation of new Catalysts for PEM Fuel Cells}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 483}, abstract = {Increasing green house emissions amplify global warming concerns worldwide. Fuel cells, based on polymer electrolyte membranes (PEM) are part of the solution to this issue. We aim at developing and testing new catalysts for fuel cells. Platinum catalysts perform best in PEM fuel cells to date but they are very expensive. For fuel cells to be perfectly applicable and economically affordable, an alternative catalyst with similar or even greater efficiency should be developed. Metal phthalocyanines are known to be good oxygen reduction catalysts and are associated with high electron transfer properties. We investigated Cobalt Phthalocyanine in its pure state mixed with Carbon Black (CoPc:Carbon Black=1:9) untreated and also after a treatment in N2 at several temperatures, up to 1000°C for 30 minutes. Results of XPS and EDX analyses reveal that the treatment at higher temperatures causes a rearrangement in the chemical states of Co, N and C atoms. Furthermore, results of cycling voltammetry (CV) analysis reveal that CoPc treated in N2 at 800°C exhibited a higher current density, in conclusion, a higher catalytic activity than the untreated CoPc.}, language = {en} } @inproceedings{MichlingKolanekSchmeisseretal., author = {Michling, Marcel and Kolanek, Krzysztof and Schmeißer, Dieter and Tallarida, Massimo}, title = {A growth model for the HfO2 ALD process}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 294}, abstract = {In this contribution we report on our in-situ2 cycle-by-cycle (up to the 25 cycles) investigation of the HfO2 atomic layer deposition (ALD) process using the method of x-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS). We used Tetrakis-Dimethyl-Amino-Hafnium (TDMA-Hf) and H2O as precursors and p-type Si wafer with native oxide as a substrate. The XPS measurements were carried out at BESSY II in Berlin with primary energies of 150 eV and 640 eV and the EELS measurements were done with a primary energy of 50 eV. We measured the O1s, Si2p core level and the valence band including the Hf 4f core level. From the Hf4f to Si2p ratios taken at each energy we developed a growth model for the first monolayer and for the following layers too. From our data we conclude, that in the first monolayer up to the fourth ALD cycle an island growth occurs. The height of these islands is about 0,5nm. After the first monolayer is completed, a layer- by-layer growth can be expected. In order to proof this observation we have simulated the Hf/Si ratio for different excitation energies and found a very good agreement with our measurement data. The EELS data especially the evaluation of the loss function onset confirm our growth model.}, language = {en} } @inproceedings{PhilipMartinezMuelleretal., author = {Philip, Shine and Martinez, Elias and M{\"u}ller, Klaus and Kunst, Marinus and Schmeißer, Dieter}, title = {Time resolved microwave conductivity measurements of Bulk Heterojunction solar cells}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 301}, abstract = {The time resolved microwave conductivity (TRMC) method was used in order to study the generation and decay kinetics of charge carriers in the Bulk Heterojunction (BHJ) solar cells. The charge carriers were generated with 532nm laser pulses of 10ns FWHM (Full Width at Half Maximum) induced in the cells. The BHJ solar cells used for the measurements had a photoactive layer consisting of a mixture of Poly (3-Hexylthiophene) P3HT and Phenyl-C61-butyric acid methyl ester (PCBM) which was spin coated onto Indium tin oxide (ITO)/glass substrates. In the field of Organic photovoltaic blends, TRMC method is introduced as a new method of direct investigation of the charge carrier lifetime as well as the charge carrier mobility and we were successful in studying the charge carrier lifetime of the reference BHJ solar cells. We also studied the influence of aligned ferroelectric fields on the charge separation in BHJ solar cells. As ferroelectric material, we used the copolymer Poly (vinylidene fluoride - trifluoroethylene) P(VDF-TrFE).}, language = {en} } @inproceedings{RichterSchmeisser, author = {Richter, Matthias and Schmeißer, Dieter}, title = {Electronic structure and optical properties of P3HT - Evidence of 2D-polarons in P3HT}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 311}, abstract = {In this contribution we report on investigations of the electronic structure and optical characteristics of poly(3-hexylthiophene) (P3HT) based films. Various techniques like NEXAFS, SRXPS, UPS, UV-VIS and FTIR were used. X-Ray based measurements were done at the U49/2-PGM2 beam line at BESSYII. The samples were produced by spin casting P3HT dissolved in chloroform and other suitable solvents on ITO (indium tin oxide) coated glass slides and silicon substrates. Regioregular-P3HT is known to form thin films with nanocrystalline lamellae. This 2D structure give rise to additional electronic excitations in photoinduced absorption measurements, which are attributed to 2D-polarons [1]. In the Total Electron Yield (surface sensitive) and Total Fluorescence Yield (bulk sensitive) NEXAFS spectra of regioregular-P3HT three additional features can be found prior to the first typical π* excitation. The nature of these features was further investigated by means of SRXPS and UPS measurements. Energy differences relative to π*-peak maximum (0.54eV, 0.87eV and 2.24eV) suggest that these features are due to 2D-polarons. This presence of polarons is further confirmed by our FTIR and UV-VIS results. [1] Osterbacka et al., Synth. Met. 116 (2001) 317}, language = {en} } @inproceedings{SchmidtSchmeisser, author = {Schmidt, Stefan and Schmeißer, Dieter}, title = {Localized gap states in cobalt/nickel mixed oxides}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 486}, abstract = {Replacing Co by large amounts of Ni is considered to reduce costs in Li-Ion-Batteries while maintaining their performance. We investigate the electronic structure of Co/Ni compounds because of their direct impact on battery operation. Thin Co/Ni oxide films on metal substrates were prepared by dropping/spin-coating from nitrate solutions followed by subsequent annealing in air and UHV. The following Co to Ni ratios have been investigated: 50/50, 40/60, 30/70, and 20/80. The results are compared with the pure Co-oxide and magnetron sputtered LiCoO2 reference samples. Spectroscopic measurements on these samples were carried out at the U49/2 beamline at BESSYII, Berlin. XPS of the transition metal (TM) 2p states reveals the existence of charge transfer ground states and different oxidation states. NEXAFS at the Co L3, Ni L3 and O K edges reflects the density of unoccupied states while resonant PES at these edges provides the related partial density of states (pDOS). Therefore, these techniques can be used in order to distinguish between the different contributions of TM3d and O2p states in the valence band region. We find sharp localized features at the valence band edge and at the O K and Co L3 absorption edges that are discussed to originate from the strong hybridization between metal and oxygen states in that region.}, language = {en} } @inproceedings{TallaridaDessmannStaedteretal., author = {Tallarida, Massimo and Deßmann, Nils and St{\"a}dter, Matthias and Friedrich, Daniel and Michling, Marcel and Schmeißer, Dieter}, title = {Atomic layer deposition of TiO}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {We present a study of the initial growth of TiO2 on Si(111) by atomic layer deposition (ALD). The Si substrate was etched with NH4F before ALD to remove the native oxide film and to produce a Si-H termination. In-situ experiments by means of photoemission and X-ray absorption spectroscopy were conducted with synchrotron radiation on Ti-oxide films produced using Ti-tetra-iso-propoxide (TTIP) and water as precursors. O1s, Ti2p, C1s, and Si2p core level, and O1s and Ti2p absorption edges show the transition of the Ti-oxide properties during the first layers. The growth starts with a very small growth rate (0.03nm/cycle) due to the growth inhibition of the Si-H termination and proceeds with higher growth rate (0.1nm/cycle) after 1.5nm Ti-oxide has been deposited.}, language = {en} } @inproceedings{DasStaedterTallaridaetal., author = {Das, Chittaranjan and St{\"a}dter, Matthias and Tallarida, Massimo and Schmeißer, Dieter}, title = {Investigation of Linear Dichroism in ALD layers of TiO2}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Titanium dioxide is on the most studied material due to its wide range of applications in various fields such as self cleaning, photocatalysis, solar cell, water splitting, bio-implants, etc. In order to increase its efficiency in water splitting and solar cell, it is necessary to understand the crystal structure and electronic properties in thin films. In our approach we are investigating the X-ray linear dichroism (XLD) of thin layers of TiO2. XLD studies have been done in multiferroics, antiferromagnetic, and ferromagnetic materials, but a very less amount of work have been done in studying XLD effect of TiO2 thin films. These layers are grown by in-situ atomic layer deposition (ALD) system and are investigated with X-ray absorption spectroscopy (XAS) at BESSY II, Berlin. ALD is a promising technique to grow thin films on different substrates conveniently due to its uniform deposition property. XAS study will also help us to better understand the interfacial electronic properties of thin films of TiO2.}, language = {en} } @inproceedings{MuellerHoffmannbeckKirneretal., author = {M{\"u}ller, Klaus and Hoffmannbeck, David and Kirner, Georg and St{\"a}dter, Matthias and Schmeißer, Dieter}, title = {CO2-Methanation by Catalytic Conversion}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {The utilization of CO2 as raw material is an important component of a program for CO2 reduction. A possibility is the production of methane. At a moderate temperature of around 350°C, hydrogenation of CO2 to methane is possible by the Sabatier reaction CO2 + 4H2 ->CH4 +2H2O. Prerequisite for an efficient kinetics of the Sabatier reaction is the application and optimization of catalysts. In this contribution, we present investigations of Ru and Ni catalysts on different substrates. For Ru/Al2O3 catalysts, we found stable operation without degradation within 500 hours with a conversion rate of 80\% at 350°C. For NiO/SiO2 catalysts, a conversion rate of 90\% was found for temperatures of 350-405°C. We also show the investigation of cross sensitivities against SOx and NOx, which are typical contaminations of CO2, generated by the industrial oxyfuel process. In our work the morphology (REM, AFM, specific surface), chemical composition (FTIR, XPS) and phase composition (XRD) of the catalysts are characterized. In addition, we report on thermodesorption (TDS) measurements at atmospheric pressure to determine the amount of adsorbed CO2 under real conditions. The project is funded by the German Ministry of Research and Education (BMBF-GeoEn).}, language = {en} } @inproceedings{PhilipMuellerRichteretal., author = {Philip, Shine and M{\"u}ller, Klaus and Richter, Matthias and Kunst, Marinus and Schmeißer, Dieter}, title = {Study of excited states and a model for exciton-polaron interaction in P3HT}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Organic semiconductors efficiently harvest light in the region of the solar spectrum due to a high absorption/extinction coefficient.In our work we study the electronic structure and the charge carrier dynamics of polymeric organic semiconductor regioregular poly(3-hexylthiophen-2,5-diyl) (P3HT), an ideal p-type semiconductor and a widely used conjugated polymer, and blends with the fullerene derivative phenyl-C61-butyric acid methyl ester (PCBM), an electron acceptor material. The study was done with the help of time resolved microwave conductivity (TRMC) for contactless investigation of bulk carrier dynamics, optical spectroscopy, ultraviolet photoelectron spectroscopy(UPS) and high resolution X-ray absorption spectroscopy(XAS) which investigates excited states of rr-P3HT. From the data obtained we could infer the positions of the valence and conduction band, the existence of two excitons as well as the co-existence of one dimensional and two dimensional polarons. Based on our spectroscopic data we propose a model in which the scattering of virtual polarons and excitons are shown to create mobile polaronic charge carriers.}, language = {en} } @inproceedings{RichterFriedrichSchmeisser, author = {Richter, Matthias and Friedrich, Daniel and Schmeißer, Dieter}, title = {3h-Auger decay in the π-band of HOPG}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {In this contribution we report on the electronic structure of highly oriented pyrolitic graphite (HOPG). HOPG is a model system because of the clear separation between π- and σ-bands in the valence band regime. X-ray based measurements were done at the U49/2-PGM2 beam line at BESSYII in Berlin. The resonant photoemission spectra (resPES) at the carbon K-edge give a complete picture of the occupied and unoccupied states in these sp2 hybridized system. Above the K-edge the resPES data are dominated by the Auger process causing a C2p4 final state. The Auger lines appear at constant kinetic energy (spectator, 2h) or constant binding energy (participator, 1h). For the features right at the resonance we observe a different Auger decay mechanism. We attribute it to the decay out of an excitonic intermediate state with a long lifetime. It involves three valence hole states. The original primary core hole is filled by a normal KLL Auger decay. The excited electron rests in the excitonic intermediate state and decays later. We discuss the spectral features of such combined spectator-participator decays in detail which are found only close to resonance and only in the localized valence states of excitonic excitation i.e.C1s - 1π* transitions [1, 2, 3]. [1] Richter et al. (2011) BioNanoScience, submitted. [2] Michling et al. (2011) IOP C Ser Mater Sci Eng, submitted. [3] Schmidt et al. (2011) Solid State Ionics, submitted.}, language = {en} } @inproceedings{StaedterSchmeisser, author = {St{\"a}dter, Matthias and Schmeißer, Dieter}, title = {AP-TDS characterization of CO2 methanation catalysts}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Development of new catalysts and their characterization by TDS (thermal desorption spectroscopy) is used in a wide field of applications. In our group we focus on catalysts usable to convert CO2 towards methane by the Sabatier reaction (CO2 + 4H2 → CH4 + 2H2O at 375∘C). For measuring large numbers of samples we designed an AP-TDS (ambient pressure TDS) chamber where various desorption experiments can be performed without bringing the catalyst into vacuum. The well-defined reaction chamber, in terms of temperature, pressure and gas composition (Ar atmosphere), is separated by a pin hole (∅ = 6 µ m) from an external UHV chamber. Evolving species and their composition are monitored by a mass spectrometer attached to the UHV chamber. Our first measurement results on commercially available NiO/SiO2 and Ru/Al2O3 based catalysts, with focus on the identification and enumeration of different adsorption sites for CO2, will be presented. CO2 saturated samples were heated from RT to 1100∘C (heating rate β = 0.3 K/s) while measuring the evolution of the CO2 content. Our measurements show large numbers of different adsorption sites for NiO (200-750∘C) whereas Ru shows only few different sites around 440∘C. For both catalysts, most of the formerly adsorbed CO2 remains at the surface (at 375∘C) available for methanation.}, language = {en} } @inproceedings{TallaridaMichlingDasetal., author = {Tallarida, Massimo and Michling, Marcel and Das, Chittaranjan and Friedrich, Daniel and St{\"a}dter, Matthias and Schmeißer, Dieter}, title = {Role of substrate chemistry in ALD revealed by in-situ techniques}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {We show recent results of our in-situ investigations where the role of substrate chemistry in ALD is outlined. While the usual strategy to develop new properties of ALD films is to find new precursors or new procedures, the influence of substrate chemistry on the growth properties of ALD films has been often underestimated. This has principally a technical reason, as the usual characterization methods (QMS, FTIR, ellipsometry) are only weakly sensitive to the substrate, and a characterization of substrates before ALD is often not possible. Thanks to the use of in-situ characterization methods, including photoemission and X-ray absorption spectroscopy with synchrotron radiation, we are able to determine chemical properties of substrates before ALD and after either half or complete ALD cycles. The substrate chemistry influences the standard Al2O3 ALD with TMA and water [1,2], as well as the TiO2 ALD with TTIP and either water, O2 or O2-plasma. [1] M. Tallarida, K. Kukli, M. Michling, M. Ritala, M. Leskel{\"a} and D. Schmeisser, Chem. Mater. 23, 3159 (2011); [2] M. Tallarida, C. Adelmann, A. Delabie, S. van Elshocht, M. Caymax, and D. Schmeisser, Appl. Phys. Lett. 92, 042906 (2011).}, language = {en} } @inproceedings{FischerRohrbeckWehneretal., author = {Fischer, Christian B. and Rohrbeck, Magdalena and Wehner, Stefan and Richter, Matthias and Schmeißer, Dieter}, title = {Diamond-Like Carbon Coatings on Selected Plastic Materials}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {The manufacturing of synthetic materials and their wide range of use for daily life is accompanied by essential requirements. Besides the basic performance of materials such as flexibility, elasticity, fracture strength and chemical resistance, further determinants are long term stability or biocompatibility. To overcome mismatches in surface characteristics of optimal parent material they can be customized for their intended use resulting in suitable coatings for profitable applications. The determining factor for such modifications is the preservation of basic material performance in addition to the benefit of further advantages like changed adhesive, improved repellent or antibacterial behavior. Protective coatings of selected plastic materials have been realized by depositing a few layers of diamond-like carbon (DLC). The assembly of soft plastic material and robust DLC coating is important for the resulting material characteristics. The detailed understanding of materials interphasing between these unequal materials and the conjunction of carbon centers in chemically different neighborhood is part of the presented work. Results will be transferable to other plastic materials with diverse needs, e.g. energy storage devices, water treatments and coatings for everyday commodities or industrial parts.}, language = {en} } @inproceedings{RohrbeckFischerWehneretal., author = {Rohrbeck, Magdalena and Fischer, Christian B. and Wehner, Stefan and Richter, Matthias and Schmeißer, Dieter}, title = {Diamond-Like Carbon Coatings on Industrial Polyethylene Surfaces}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Synthetic materials are used in a wide variety of fields. Depending on the intended application the plastic material must meet specific requirements. Since the material always interacts with its environment, particular attention is required regarding the surface. Possible damage of the plastic material and further risks could be caused by the adhesion of bacteria, biofilm formation and encrustations. Therefore, bacteria-repellent coatings and surface-modified materials that allow for an effective removal of adhered bacteria are of extremely high interest for many applications. In this study Polyethylene (PE) is chosen as simplest model for relevant plastic materials. Surface modification of PE samples is accomplished by plasma-deposited diamond-like carbon (DLC) coatings to achieve increased abrasion strength and bacterial resistance. Two types of nanometer-scaled DLC films with different layer thicknesses are compared by multiscale microscopic analysis. Further spectroscopic measurements with synchrotron radiation are performed. These results will provide an enhanced understanding of layer formation at the interface between the basic plastic material and the DLC coating and will possibly lead to optimal parameters for the surface coating to achieve improved product characteristics.}, language = {en} } @misc{DasTallaridaSchmeisser, author = {Das, Chittaranjan and Tallarida, Massimo and Schmeißer, Dieter}, title = {Si microstructures laminated with a nanolayer of TiO2 as long-term stable and effective photocathodes in PEC devices}, series = {Nanoscale}, journal = {Nanoscale}, number = {7}, issn = {2040-3364}, doi = {10.1039/C5NR00764J}, pages = {7726 -- 7733}, abstract = {Photoelectrochemical (PEC) water splitting is one of the most emerging fields for green energy generation and storage. Here we show a study of microstructured Si covered by a TiO2 nano-layer. The microstructures are prepared by galvanostatic selective etching of Si. The TiO2 nano-layer was deposited by atomic layer deposition (ALD) to protect the microstructured photocathode against corrosion. The obtained microstructured photocathode showed a shift in the onset potential of 400 mV towards the anodic direction compared to bare Si. The Si microstructures laminated with a nano-layer of TiO2 show stability over 60 hours of measurement.}, language = {en} } @inproceedings{HenkelDasSowinskaetal., author = {Henkel, Karsten and Das, Chittaranjan and Sowinska, Małgorzata and Tallarida, Massimo and Schmeißer, Dieter and Gargouri, Hassan and K{\"a}rkk{\"a}nen, Irina and Schneidewind, Jessica and Gruska, Bernd and Arens, Michael}, title = {Charakterisierung von TiO2-ALD-Schichten und deren Nutzung f{\"u}r die Passivierung von Si-Photokathoden}, series = {Tagungsband Photovoltaik-Meeting: Anwendungen-Qualit{\"a}t-Perspektiven, Senftenberg, 15.04.2015}, booktitle = {Tagungsband Photovoltaik-Meeting: Anwendungen-Qualit{\"a}t-Perspektiven, Senftenberg, 15.04.2015}, editor = {Gl{\"u}ck, B. K. and Schmidt, S. and Stein, E. and Raschke, J{\"o}rg-Uwe and Richter, H.}, publisher = {BTU Cottbus-Senftenberg}, address = {Senftenberg}, pages = {3 -- 8}, abstract = {Wir berichten zun{\"a}chst {\"u}ber den Einfluss der Methode der Atomlagenabscheidung auf die TiO2-Schichteigenschaften. Insbesondere wird der Zusammenhang zwischen Ti3+- sowie Interbandzust{\"a}nden mit elektrischen Kennlinien und deren Einfluss auf funktionale Schichteigenschaften diskutiert. Anschließend werden Mikrostrukturierung, Grenzfl{\"a}chen-Engineering und konforme Abscheidung einer TiO2-ALD-Schutzschicht effektiv zur Performance-Steigerung von p-Si-Photokathoden angewendet.}, language = {de} } @misc{NourbakhshAdelmannSongetal., author = {Nourbakhsh, Amirhasan and Adelmann, Christoph and Song, Yi and Lee, Chang Seung and Asselberghs, Inge and Huyghebaert, Cedric and Brizzi, Simone and Tallarida, Massimo and Schmeißer, Dieter and Elshocht, Sven van and Heyns, Marc and Kong, Jing and Palacios, Tom{\´a}s and De Gendt, Stefan}, title = {Graphene oxide monolayers as atomically thin seeding layers for atomic layer deposition of metal oxides}, series = {Nanoscale}, volume = {2015}, journal = {Nanoscale}, number = {7}, issn = {2040-3364}, doi = {10.1039/C5NR01128K}, pages = {10781 -- 10789}, abstract = {Graphene oxide (GO) was explored as an atomically-thin transferable seed layer for the atomic layer deposition (ALD) of dielectric materials on any substrate of choice. This approach does not require specific chemical groups on the target surface to initiate ALD. This establishes GO as a unique interface which enables the growth of dielectric materials on a wide range of substrate materials and opens up numerous prospects for applications. In this work, a mild oxygen plasma treatment was used to oxidize graphene monolayers with well-controlled and tunable density of epoxide functional groups. This was confirmed by synchrotron-radiation photoelectron spectroscopy. In addition, density functional theory calculations were carried out on representative epoxidized graphene monolayer models to correlate the capacitive properties of GO with its electronic structure. Capacitance-voltage measurements showed that the capacitive behavior of Al2O3/GO depends on the oxidation level of GO. Finally, GO was successfully used as an ALD seed layer for the deposition of Al2O3 on chemically inert single layer graphene, resulting in high performance top-gated field-effect transistors.}, language = {en} } @misc{TamangGhoshGarainetal., author = {Tamang, Abiral and Ghosh, Sujoy Kumar and Garain, Samiran and Alam, Md. Mehebub and Haeberle, J{\"o}rg and Henkel, Karsten and Schmeißer, Dieter and Mandal, Dipankar}, title = {DNA-Assisted β‑phase Nucleation and Alignment of Molecular Dipoles in PVDF Film: A Realization of Self-Poled Bioinspired Flexible Polymer Nanogenerator for Portable Electronic Devices}, series = {ACS Applied Materials \& Interfaces}, journal = {ACS Applied Materials \& Interfaces}, number = {7}, issn = {1944-8244}, doi = {10.1021/acsami.5b04161}, pages = {16143 -- 16147}, abstract = {A flexible nanogenerator (NG) is fabricated with a poly(vinylidene fluoride) (PVDF)film, where deoxyribonu-cleic acid (DNA) is the agent for the electroactive β-phase nucleation. Denatured DNA is co-operating to align the molecular-CH2/-CF2 dipoles of PVDF causing piezo- electricity without electrical poling. The NG is capable of harvesting energy from a variety of easily accessible mechanical stress such as human touch, machine vibration, football juggling, and walking. The NG exhibits high piezoelectric energy conversion efficiency facilitating the instant turn-on of several green or blue light-emitting diodes. The generated energy can be used to charge capacitors providing a wide scope for the design of self-powered portable devices.}, language = {en} } @misc{SchmeisserHaeberleRichteretal., author = {Schmeißer, Dieter and Haeberle, J{\"o}rg and Richter, Matthias and Brazda, Petr}, title = {Spin State and Satellite Structures of ε-Fe₂O₃ as determined by Resonant Photoelectron Spectroscopy}, series = {Nuclear Instruments and Methods in Physics Research B}, volume = {2015}, journal = {Nuclear Instruments and Methods in Physics Research B}, number = {364}, issn = {0168-583X}, doi = {10.1016/j.nimb.2015.08.062}, pages = {127 -- 131}, abstract = {We use resonant photoelectron spectroscopy at the Fe2p and the O1s absorption edges to report on spectroscopic investigation of Fe-oxides nanoparticles. We discuss the spectroscopic details like multiple Auger decays, satellite emission in the X-ray absorption process and the core level data. We explain these data by a novel mechanism in which the resonant excitation between Fe3d and Fe4s states are involved. This mechanism is observed when the photo-excited electron becomes polarized by the electron-hole pairs existing in the conduction and valence bands.}, language = {en} } @misc{AlbertonCorreaBrizziSchmeisser, author = {Alberton Corr{\^e}a, Silma and Brizzi, Simone and Schmeißer, Dieter}, title = {Spectroscopic investigation of the electronic structure of thin atomic layer deposition HfO2 films}, series = {Journal of Vacuum Science \& Technology A}, volume = {34}, journal = {Journal of Vacuum Science \& Technology A}, number = {1}, issn = {0734-2101}, doi = {10.1116/1.4935338}, pages = {01A117-1 -- 01A117-8}, abstract = {The electronic structure of HfO2 thin films is investigated employing resonant photoelectron spectroscopy (resPES). The detailed analysis of the O1s resonance profile enables the determination of the partial density of states for the valence and the conduction bands as well as the electronic band gap to be 6.2 eV. The position of the charge neutrality level is evaluated. Thereby, it is demonstrated that the resPES data are able to combine information both for the valence as well as for the conduction band states. In addition, evidences for intrinsic in-gap states attributed to polaronic and charge transfer states are given. Electronic charges within the atomic layer deposition-HfO2films are identified, pointing out that the amount of charges is essential to determine the accurate position of the surface potentials.}, language = {en} } @misc{SowińskaHenkelSchmeisseretal., author = {Sowińska, Małgorzata and Henkel, Karsten and Schmeißer, Dieter and K{\"a}rkk{\"a}nen, Irina and Schneidewind, Jessica and Naumann, Franziska and Gruska, Bernd and Gargouri, Hassan}, title = {Plasma-enhanced atomic layer deposition of titanium oxynitrides films: A comparative spectroscopic and electrical study}, series = {Journal of Vacuum Science and Technology A}, journal = {Journal of Vacuum Science and Technology A}, number = {34}, issn = {0734-2101}, doi = {10.1116/1.4936227}, pages = {01A127-1 -- 01A127-9}, abstract = {The process parameters' impact of the plasma-enhanced atomic layer deposition (PE-ALD) method on the oxygen to nitrogen (O/N) ratio in titanium oxynitride (TiOxNy) films was studied. Titanium(IV)isopropoxide in combination with NH3 plasma and tetrakis(dimethylamino) titanium by applying N2 plasma processes were investigated. Samples were characterized by the in situ spectroscopic ellipsometry, x-ray photoelectron spectroscopy, and electrical characterization (current-voltage: I-V and capacitance-voltage: C-V) methods. The O/N ratio in the TiOxNy films is found to be very sensitive for their electric properties such as conductivity, dielectric breakdown, and permittivity. Our results indicate that these PE-ALD film properties can be tuned, via the O/N ratio, by the selection of the process parameters and precursor/coreactant combination.}, language = {en} } @misc{PitthandosReisAlbertonCorreaetal., author = {Pitthan, E. and dos Reis, R. and Alberton Corr{\^e}a, Silma and Schmeißer, Dieter and Boudinov, H. I. and Stedile, F. C.}, title = {Influence of CO annealing in metal-oxide-semiconductor capacitors with SiO2 films thermally grown on Si and on SiC}, series = {Journal of Applied Physics}, journal = {Journal of Applied Physics}, number = {119}, issn = {0021-8979}, doi = {10.1063/1.4939836}, pages = {025307-1 -- 025307-6}, abstract = {Understanding the influence of SiC reaction with CO, a by-product of SiC thermal oxidation, is a key point to elucidate the origin of electrical defects in SiC metal-oxide-semiconductor (MOS) devices. In this work, the effects on electrical, structural, and chemical properties of SiO2/Si and SiO2/SiC structures submitted to CO annealing were investigated. It was observed that long annealing times resulted in the incorporation of carbon from CO in the Si substrate, followed by deterioration of the SiO2/Si interface, and its crystallization as SiC. Besides, this incorporated carbon remained in the Si surface (previous SiO2/Si region) after removal of the silicon dioxide film by HF etching. In the SiC case, an even more defective surface region was observed due to the CO interaction. All MOS capacitors formed using both semiconductor materials presented higher leakage current and generation of positive effective charge after CO annealings. Such results suggest that the negative fixed charge, typically observed in SiO2/SiC structures, is not originated from the interaction of the CO by-product, formed during SiC oxidation, with the SiO2/SiC interfacial region.}, language = {en} } @misc{SchmeisserHaeberle, author = {Schmeißer, Dieter and Haeberle, J{\"o}rg}, title = {Intrinsic localized gap states in IGZO and its parent single crystalline TCOs}, series = {Thin Solid Films}, journal = {Thin Solid Films}, number = {603}, issn = {0040-6090}, doi = {10.1016/j.tsf.2016.02.010}, pages = {206 -- 211}, abstract = {We report on the X-ray absorption data for Indium-Gallium-Zink-Oxide thin films, amorphous ZnO films, amorphous SnOx films, and single crystalline In2O3, Ga2O3, ZnO, and SnO2 data. These absorption data probe the empty conduction band states explicitly. Also they allow for an elemental assignment using resonant excitation to derive the contributions of each metal ion. We find that the lowest states appear right at the Fermi energy and result from configuration interaction induced charge transfer states which we consider as intrinsic gap states.}, language = {en} } @inproceedings{AlbertonCorreaBrizziTallaridaetal., author = {Alberton Corr{\^e}a, Silma and Brizzi, Simone and Tallarida, Massimo and Schmeißer, Dieter}, title = {Charging effect in HfO2 films deposited on SiO2/Si by atomic layer deposition}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Thin films of hafnium oxide (HfO2) deposited by atomic layer deposition (ALD) have been studied extensively as a high-k replacement for the SiO2 gate in field effect transistors. The use of ALD process allows one to grow homogeneous thin films at low temperatures with a precise control of thickness [1]. Some important electrical considerations for the application of a high-k dielectric include the presence of fixed charge (Qf) and charge trapping in the dielectric. For instance, in the case of Al2O3 thin films deposited on Si, the thickness of the interfacial SiO2 layer was identified as a key fundamental parameter determining Qf [2]. A similar trend can be also expected in HfO2/Si structures. Therefore, in this work, we proposed an in situ evaluation of photon induced charge trapping in HfO2 films deposited on SiO2/Si structures. For that, tetrakis-di-methyl-amino-hafnium (TDMAHf) and H2O were employed as precursors to deposit HfO2 films on SiO2/Si samples with variable thickness of the SiO2 interlayer. Measurements were performed by Synchrotron Radiation Photoemission Spectroscopy (SR-PES). Results indicated that the charging process is dependent on the thickness of the SiO2 interlayer and on the quality of the HfO2 film. [1] M. Leskel{\"a} and M. Ritala, Thin Solid Films 409, 138 (2002). [2] G. Dingemans et al., J. Appl. Phys. 110, 093715 (2011).}, language = {en} } @inproceedings{BrizziTallaridaAdelmannetal., author = {Brizzi, Simone and Tallarida, Massimo and Adelmann, Christoph and Ragnarsson, Lars-{\AA}ke and Elshocht, Sven van and Schmeißer, Dieter}, title = {Structural changes in HfO2 thin films: thickness and doping dependence}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {In this work we show results regarding MOCVD and ALD HfO2 as well as Al-doped HfO2. We use Synchrotron Radiation Photoemission Spectroscopy (SRPES) to determine Hf/O atomic ratios and X-ray Absorption Spectroscopy (XAS) to investigate the electronic properties related to their crystallization. MOCVD films are synthesized at temperatures ranging from ambient to 400∘C and show structures from completely amorphous to monoclinic. ALD films are amorphous as deposited, and can crystallize after post-deposition anneal depending on the percentage of Al-doping. We discuss PES results in order to determine how close to stoichiometry the Hf/O atomic ratios of the films are, as well as the doping level. From XAS data, instead, we can point out how orbital hybridizations are related to structural and physical properties.}, language = {en} } @inproceedings{DasTallaridaSchmeisser, author = {Das, Chittaranjan and Tallarida, Massimo and Schmeißer, Dieter}, title = {X-ray linear dichroism in atomic layer deposited Titanium dioxide layers}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Among the various metal oxides TiO2 has been investigated because of its wide range of applications in various fields such as self-cleaning, photocatalysis, solar cell, water splitting, bio-implants. In order to increase its efficiency in water splitting and solar cell energy conversion, it is necessary to understand the crystal structure and electronic properties of thin films. Generally the process of synthesis may modify the electronic properties of TiO2. In the present work we show X-ray linear dichroism (XLD) measurements of TiO2 thin films of different polymorphs. Titania thin films were produced by atomic layer deposition (ALD) and were characterized in-situ with X-ray photoelectron and absorption spectroscopy at synchrotron radiation center BESSY-II. We found that that all titania phases show XLD at Ti-L and O-K edges, but the intensity of XLD is different for different phases. We discuss our data in terms of the partial density of states.}, language = {en} } @inproceedings{DasTallaridaSchmeisser, author = {Das, Chittaranjan and Tallarida, Massimo and Schmeißer, Dieter}, title = {Control of thickness of SiO2 interfacial layer for photocatalytic water splitting on Si photocathodes}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Silicon with a band gap of 1.1eV is an excellent candidate for visible photocatalytic water splitting. But p-type Si has a low quantum yield and are less efficient for water splitting [1]. It has been shown that preventing oxidation of Si surface can shift the onset potential for water reduction by about 300mV towards more positive [2]. We investigated in detail the influence of the SiO2 layer thickness on the onset potential for water splitting on Si photocathodes: we used p-type Si substrates covered with SiO2 layers of varying thickness. Then, we deposited a thin TiO2 film on using atomic layer deposition (ALD) to inhibit Si oxidation during the electrochemical experiment. In this way we could shift the onset potential up to 200mV, depending on the SiO2 thickness. [1]E. L. Warren, S. W. Boettcher, M. G. Walter, H. A. Atwater, and N. S. Lewis: J. Phys. Chem. C 115 (2011) 594. [2]B. Seger, Anders B. Laursen, P. C. K. Vesborg, T. Pedersen, O. Hansen, S. Dahl, I. Chorkendorff, Angew. Chem. Int. Ed. 2012, 51, 9128}, language = {en} } @inproceedings{HaeberleGasparBarquinhaetal., author = {Haeberle, J{\"o}rg and Gaspar, Diana and Barquinha, Pedro and Machulik, Stephan and Janowitz, Christoph and Galazka, Zbigniew and Schmeißer, Dieter}, title = {A spectroscopic comparison of AOS thin films and TCO single crystals}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Amorphous oxide semiconductors (AOS) and transparent conductive oxides (TCO) are today one of most attractive fields of research in many industrial products, like e.g. high definition, low cost, transparent, and flexible displays. We got the unique possibility to measure a-GIZO and a-SnOx thin films and compare their electronic properties with those of In2O3, Ga2O3, ZnO, and SnO2 single crystals. We use resPES to study the electronic properties. We report on the core levels, the VB PES data, partial Integrated Yield (pIY) and the XAS absorption data. From these we are able to derive the elemental ratio, the pDOS as well as the band scheme. At the O1s resonance we observe multiple Auger processes from which we deduce that a band of localized defect states is located between the Fermi energy and the CBM. The resonant profiles taken at the corresponding metal edges indicate that metal states are involved in the DOS.}, language = {en} } @inproceedings{TallaridaHenkelGargourietal., author = {Tallarida, Massimo and Henkel, Karsten and Gargouri, Hassan and Haeberle, J{\"o}rg and Gruska, Bernd and Arens, Matthias and Schmeißer, Dieter}, title = {New opportunities with Plasma enhanced atomic layer deposition (PE-ALD) of oxides}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Thermal Atomic layer deposition (T-ALD) of oxides is obtained by the pulsed alternation of a metal precursor and an oxygen source, typically H2O or O3, and the reactions leading to ALD are thermally activated. With plasma enhanced ALD (PE-ALD), instead, the oxygen source is represented by an oxygen-containing plasma. The higher reactivity of the plasma-generated species extend the capabilities of ALD: improved film quality and increased flexibility in process conditions, such as growth at low temperature, are typical advantages of PE-ALD over T-ALD. We report on results on the preparation of thin (<100 nm) aluminum oxide (Al2O3) films on silicon substrates using T-ALD and PE-ALD in the SENTECH SI ALD LL system. Films were deposited in the temperature range between room temperature (RT) and 200∘C. We characterized the films with spectroscopic ellipsometry (thickness, refractive index, growth rate) over 4" wafers and with X-ray photoelectron spectroscopy. All films resulted in a high degree of homogeneity, independent of the deposition temperature. Investigations with capacitance-voltage and conductance-voltage measurements showed a very low interface states density for the PE-ALD films.}, language = {en} } @inproceedings{RoeskenRohrbeckCatenaetal., author = {R{\"o}sken, Liz M. and Rohrbeck, Magdalena and Catena, Alberto and Wehner, Stefan and Fischer, Christian B. and Richter, Matthias and St{\"a}dter, Matthias and Schmeißer, Dieter}, title = {Characterization of diamond-like carbon (DLC) coatings on industrial polyethylene and polyoxymethylene by SEM, AFM and NEXAFS}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Diamond-like carbon (DLC) coatings are often utilized to change the base properties of raw materials, e. g. to gain robust or chemically inert surfaces. Here the deposition of hard DLC layers on soft polymers is tested. The common industrial polymers polyethylene (PE) and polyoxymethylene (POM) serve as model substrates in the present work. In order to examine the effect of the carbonaceous layers on PE and POM thin diamond-like carbon films were realized via PECVD. The topography of the different coatings was detected by AFM and SEM uncovering the different influence of the substrate material, e. g. interlayer formation for PE. The composition of the surface structures were analyzed in more detail by NEXAFS, showing the hybridization of carbon atoms in chemical different surroundings from the pure polymer to the carbon coating. The comparison of carbon coated PE- and POM-composites enables valuable insights into the interaction between soft substrates and hard coatings. For the chosen settings in PECVD, POM showed incomplete coating, while on PE a very stable and robust composite has formed.}, language = {en} } @inproceedings{AlbertonCorreaBrizziTallaridaetal., author = {Alberton Corr{\^e}a, Silma and Brizzi, Simone and Tallarida, Massimo and Schmeißer, Dieter}, title = {Spectroscopic investigation of the electronic structure of HfO2 thin films}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 211}, abstract = {HfO2 is of current interest as a material for memristive and ferroelectric devices. In this work, we used spectroscopic techniques to evaluate the electronic structure and defects mechanisms in thin HfO2 films deposited by atomic layer deposition and by metal-organic chemical vapour deposition. The partial density of states for the valence and the conduction bands was determined by the detailed analysis of the O1s resonance profile by resonant photoelectron spectroscopy. From the relative contributions we find a CNL 6.5 eV referred to Evac. We also find that the positions of valence band maximum and conduction band minimum, the excitation range for the polaronic states and the range of charge transfer band were not influenced by the preparation conditions. All films exhibit a band gap of 6.2 eV. However, the Fermi level position was found to vary within about 1.2 eV depending on the preparation conditions, which we argue that is due to the presence of charges within the films. This explains why the position of the Fermi level depends on the individual preparation parameters.}, language = {en} } @inproceedings{DasTallaridaSchmeisser, author = {Das, Chittaranjan and Tallarida, Massimo and Schmeißer, Dieter}, title = {Determination of charge neutrality level in TiO2 films from res-PES measurements}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 415}, abstract = {Titanium dioxide is one of the metal oxides which have versatile application in different fields. The applications of TiO2 are in the field of cosmetics, electronics (memory resistive switching), dye, photonics and photocatalysis. In the present paper we study the resPES data of TiO2 films prepared by atomic layer deposition. The measurements are done in in-situ system at beam line U49/2-PGM2 in BESSY-II. The density of state in valence band and conduction band is obtained from the resonance photo electron spectroscopy (res-PES) of the O1s and the Ti2p edge. The data allow to determine the position of the VBM and CBM with respect to the Fermi energy. Also the existence of localized O2p and Ti2p derived states is deduced which appear in the gap. In addition we determine the charge neutrality level (CNL).The CNL is the position where the weight of the density of state from valence band and conduction band are equal. This is an important quantity for the discussion of interface properties.}, language = {en} } @inproceedings{HaeberleGasparBarquinhaetal., author = {Haeberle, J{\"o}rg and Gaspar, Diana and Barquinha, Pedro and Pereira, Lu{\´i}s and Martins, Rodrigo and Fortunato, Elvira and Machulik, Stephan and Janowitz, Christoph and Manzke, Recardo and Schmeißer, Dieter}, title = {The Electronic Structure of amorphuos SnOx thin films and SnO2 single crystals}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 271}, abstract = {We compare the electronic properties of amorphous p-type SnOx thin film grown by rf magnetron sputtering with those of n-type SnO2 single crystals grown by cvt. We use resPES to study the electronic band structure. We measure the core levels, the VB PES data, partial Integrated Yield (pIY) and the XAS absorption data. From the resPES data recorded at the O1s and the Sn3d edges we derive the VB pDOS and the CB pDOS . The differences are most pronounced in the position of the VBM as for the a-SnOx films there appears a band closer to the Fermi energy. In addition for the SnOx we find in the XAS and pIY data a significant peak that appears right at the Fermi energy. This peak is absent in the single crystalline data. We attribute this to a change in the configuration of the Sn4d states to form a 4d8 configuration instead of 4d9 and 4d10 configurations which are identified in the single crystalline data.}, language = {en} } @inproceedings{IsraelRachowSchwiertzetal., author = {Israel, Johannes and Rachow, Fabian and Schwiertz, Carola and Charlafti, Evgenia and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {Self restriction oft the Sabatier reaction in large scale}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {A main goal for a sustainable energy supply is a long term energy storage system. One opportunity in this research field is the power to gas concept, where the produced gas can be fed in the existing network of natural gas. Here we show in a technical scale how the direct CO2 conversion to methane according the Sabatier reaction, CO2 + 4 H2 → CH4 + 2H2O , is self organized. At a certain limit of gas flow, a steady state equilibrium of exothermic heat production and thermal flow is reached and the reaction needs no further external annealing. We find for the maximum volume rate at the steady state equilibirum a shift of around 250 ∘C above the optimized temperature of the catalytic supported chemical equilibrium. It is shown that also with this setup the used catalyst works with a stable conversion higher than 80 \% under the reached temperature and given pressure conditions.}, language = {en} } @inproceedings{MandalHenkelSchmeisser, author = {Mandal, Dipankar and Henkel, Karsten and Schmeißer, Dieter}, title = {A polymer nanogenerator based on silver nanoparticles doped electrospun P(VDF-HFP) nanofibers}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 208}, abstract = {The rising energy demand within the increasing mobility of human society has driven the development of new alternative power sources for portable devices with ultra-low electric power consumption. Based on its piezoelectric properties poly-vinylidene fluoride (PVDF) is a good candidate for mechanical energy harvesting for such devices. Moreover the copolymer poly(vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] offers better film flexibility and cost-effectiveness than pure PVDF. We report on a polymer nanogenerator (PNG) based on electrospun P(VDF-HFP) nanofibers doped with silver nanoparticles (Ag-NPs). The electrospun fibers were characterized by FTIR, XPS, SEM and pressure imparting probe. It has been found that the yield of the piezoelectric phase is increased by the addition of Ag-NPs due to an interaction between surface charges of Ag-NPs and the molecular dipoles. Furthermore, defects in the P(VDF-HFP) electrospun fibers are removed. Accordingly, a significant enhancement in the output power of the PNG was found. Similar trends were also observed with Pd-NPs.}, language = {en} } @inproceedings{RachowIsraelSchwiertzetal., author = {Rachow, Fabian and Israel, Johannes and Schwiertz, Carola and Charlafti, Evgenia and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {CO2 Methanation with different gas mixtures}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 539}, abstract = {A key issue in the Energiewende in Germany is the storage of excess energy, as it enables energy management systems to react to fluctuating sources and enhances the flexibility of an energy mix. Power to Gas may be the most reasonable approach to store the energy in the form of hydrogen or synthetic natural gas. We study the direct conversion of CO2 by the Sabatier reaction to gain a methane based mixture which can replace natural gas in CHP plants and gas motors and can help to partially reduce the CO2 emission. In laboratory scale we investigated the performance (with IR and QMS) of Ni-based catalyst for different sources of CO2 like clean CO2, CO2 emitted as flue gas from an Oxyfuel power plant or a synthetic mixture with O2, N2 and SO2 in concentration typical for conventional power plants. Measurements from an up-scaled system are also presented, showing data important for a technical application. Here, we are able to convert more than 200kg CO2/day with conversion rates up to 90\%.}, language = {en} } @inproceedings{RouissiTallaridaSchmeisser, author = {Rouissi, Zied and Tallarida, Massimo and Schmeißer, Dieter}, title = {Study of atomic layer deposition with scanning tunneling microscopy}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 401}, abstract = {We present a work concerning the study of the initial steps of atomic layer deposition (ALD) with scanning tunneling microscopy (STM). We focus on the role of the substrates which has been often neglected.However, the detailed knowledge of precursor-substrate reactions is important for the understanding of how ALD proceeds. We report on the reaction of the Al-precursor, trimethyl-Al (TMA), on nanostructured surfaces such as Ag nanoclusters and nanostripes prepared by thermal evaporation on HOPG. We characterized the surface before and after one TMA adsorption pulse at room temperature, observing that the morphology of step edges changes after TMA creating a new terraces with a width of 7-10 nm, translated in the direction of the TMA deposition. This shows that, in case of a regular stepped surface, the substrate morphology would keep the same regularity with the translation in a direction privileged by the precursor absorption.}, language = {en} } @inproceedings{RouissiBrizziAlbertonCorreaetal., author = {Rouissi, Zied and Brizzi, Simone and Alberton Corr{\^e}a, Silma and Tallarida, Massimo and Schmeißer, Dieter}, title = {Comparison of charge neutrality level of Cu/CuO/HfO2 and Si/SiO2/HfO2}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {208}, abstract = {Copper Oxide (CuO) is a promising metal oxide semiconductor, which can be used in different applications, such as catalysis, solar energy conversion, and water splitting. In this work, we use resonance photoemission spectroscopy (ResPES) to analyse the electronics properties of HfO2 films deposited on Cu/CuO and Si/SiO2. For that, we deposited 10 cycles of HfO2 by atomic layer deposition (ALD) on Cu/CuO and Si/SiO2 samples and investigated the density states for the valence and conduction bands which were determined by the detailed analysis of the O1s resonance profile obtained by ResPES. We compared the positions of valence band maximum and conduction band minimum, the excitation range for the polaronic states and the range of charge transfer band in Cu/CuO/HfO2 and Si/SiO2/HfO2. Also, we determined the band gap and the charge neutrality level (CNL).}, language = {en} } @misc{KrammZanaVoschetal., author = {Kramm, Ulrike Ingrid and Zana, Alessandro and Vosch, Tom and Fiechter, Sebastian and Arenz, Matthias and Schmeißer, Dieter}, title = {On the structural composition and stability of Fe-N-C catalysts prepared by an intermediate acid leaching}, series = {Journal of Solid State Electrochemistry}, volume = {20}, journal = {Journal of Solid State Electrochemistry}, number = {4}, issn = {1432-8488}, doi = {10.1007/s10008-015-3060-z}, pages = {969 -- 981}, abstract = {The development of highly active and stable non-noble metal catalysts (NNMC) for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEM-FC) becomes of importance in order to enable cost reduction. In this work, we discuss the structural composition as derived from Fe-57M{\"o}ßbauer spectroscopy and X-ray diffraction, catalytic performance determined by a rotating (ring)disk electrode (RRDE) technique and stability evaluation of our Fe-N-C catalysts prepared by an intermediate acid leaching (IAL). The advantage of this IAL is given by a high density of active sites within the catalyst, as even without sulphur addition, an iron carbide formation and related disintegration of active sites are inhibited. In addition, our accelerated stress tests illustrate better stability of the sulphur-free IAL catalyst in comparison to the sulphur-added one.}, language = {en} } @misc{MuellerGoryachkoBurkovetal., author = {M{\"u}ller, K. and Goryachko, Andriy and Burkov, Yevgen and Schwiertz, Carola and Ratzke, Markus and K{\"o}ble, J. and Reif, J{\"u}rgen and Schmeißer, Dieter}, title = {Scanning Kelvin probe and photoemission electron microscopy of organic source-drain structures}, series = {Synthetic Metals}, volume = {146}, journal = {Synthetic Metals}, number = {3}, pages = {377 -- 382}, language = {en} } @misc{KraatzGallZschechetal., author = {Kraatz, Matthias and Gall, Martin and Zschech, Ehrenfried and Schmeißer, Dieter and Ho, Paul S.}, title = {A model for statistical electromigration simulation with dependence on capping layer and Cu microstructure in two dimensions}, series = {Computational Materials Science}, volume = {120}, journal = {Computational Materials Science}, issn = {1879-0801}, doi = {10.1016/j.commatsci.2016.04.020}, pages = {29 -- 35}, abstract = {A model has been developed to simulate electromigration degradation in an interconnect segment in two dimensions using finite differences. The model was deployed on a parallel computer to statistically assess the lifetimes. The simulation takes into account the diffusion paths for electromigration mass transport along the grain boundaries and the capping layer. The microstructure is generated with a Monte Carlo algorithm, using a modified Potts model. Diffusivities along the grain boundaries and the capping layers were applied as multiples of a base diffusivity and were statistically scattered. The simulation results correlate well with electromigration tests.}, language = {en} } @misc{SowinskaBrizziDasetal., author = {Sowinska, Małgorzata and Brizzi, Simone and Das, Chittaranjan and K{\"a}rkk{\"a}nen, Irina and Schneidewind, Jessica and Naumann, Franziska and Gargouri, Hassan and Henkel, Karsten and Schmeißer, Dieter}, title = {Analysis of nitrogen species in titanium oxynitride ALD films}, series = {Applied Surface Science}, volume = {381}, journal = {Applied Surface Science}, issn = {0169-4332}, doi = {10.1016/j.apsusc.2016.02.096}, pages = {42 -- 47}, abstract = {Titanium oxynitride films are prepared by plasma enhanced atomic layer deposition method using two different precursors and nitrogen sources. Synchrotron radiation-based X-ray photoelectron spectroscopy and X-ray absorption spectroscopy are used to characterize the nitrogen species incorporated within these films depending on the deposition parameters. It is found that nitrogen atoms in these films are differently bonded. In particular, it can be distinguished between Ti-ON and Ti-N bonding configurations and molecular nitrogen species caused by precursor fragments.}, language = {en} } @misc{DasRichterTallaridaetal., author = {Das, Chittaranjan and Richter, Matthias and Tallarida, Massimo and Schmeißer, Dieter}, title = {Electronic properties of atomic layer deposited films, anatase and rutile TiO2 studied by resonant photoemission spectroscopy}, series = {Journal of Physics D: Applied Physics}, volume = {49}, journal = {Journal of Physics D: Applied Physics}, number = {27}, issn = {0022-3727}, doi = {10.1088/0022-3727/49/27/275304}, pages = {275304-1 -- 275304-17}, abstract = {The TiO2 films are prepared by atomic layer deposition (ALD) method using titanium isopropoxide precursors at 250 °C and analyzed using resonant photoemission spectroscopy (resPES). We report on the Ti2p and O1s core levels, on the valence band (VB) spectra and x-ray absorption spectroscopy (XAS) data, and on the resonant photoelectron spectroscopy (resPES) profiles at the O1s and the Ti3p absorption edges. We determine the elemental abundance, the position of the VB maxima, the partial density of states (PDOS) in the VB and in the conduction band (CB) and collect these data in a band scheme. In addition, we analyze the band-gap states as well as the intrinsic states due to polarons and charge-transfer excitations. These states are found to cause multiple Auger decay processes upon resonant excitation. We identify several of these processes and determine their relative contribution to the Auger signal quantitatively. As our resPES data allow a quantitative analysis of these defect states, we determine the relative abundance of the PDOS in the VB and in CB and also the charge neutrality level. The anatase and rutile polymorphs of TiO2 are analyzed in the same way as the TiO2 ALD layer. The electronic properties of the TiO2ALD layer are compared with the anatase and rutile polymorphs of TiO2. In our comparative study, we find that ALD has its own characteristic electronic structure that is distinct from that of anatase and rutile. However, many details of the electronic structure are comparable and we benefit from our spectroscopic data and our careful analysis to find these differences. These can be attributed to a stronger hybridization of the O2p and Ti3d4s states for the ALD films when compared to the anatase and rutile polymorphs.}, language = {en} } @misc{DasKotHenkeletal., author = {Das, Chittaranjan and Kot, Małgorzata and Henkel, Karsten and Schmeißer, Dieter}, title = {Engineering of Sub-Nanometer SiOₓ Thickness in Si Photocathodes for Optimized Open Circuit Potential}, series = {ChemSusChem}, volume = {9}, journal = {ChemSusChem}, number = {17}, issn = {1864-5631}, doi = {10.1002/cssc.201600777}, pages = {2332 -- 2336}, abstract = {Silicon is one of the most promising materials to be used for tandem-cell water-splitting devices. However, the electrochemical instability of bare Si makes it difficult to be used for stable devices. Besides that, the photovoltage loss in Si, caused by several factors (e.g., metal oxide protection layer and/or SiO₂/Si or catalyst/Si interface), limits its use in these devices. In this work, we present that an optimized open circuit potential (OCP) of Si can be obtained by controlling the SiOₓ thickness in sub-nanometer range. It can be done by means of a simple and cost-effective way using the combination of a wet chemical etching and the low temperature atomic layer deposition (ALD) of TiO₂. We have found that a certain thickness of the native SiOₓ is necessary to prevent further oxidation of the Si photocathode during the ALD growth of TiO₂. Moreover, covering the Si photocathode with an ALD TiO₂ layer enhances its stability.}, language = {en} } @misc{HaeberleMachulikJanowitzetal., author = {Haeberle, J{\"o}rg and Machulik, Stephan and Janowitz, Christoph and Manzke, Recardo and Gaspar, Diana and Barquinha, Pedro and Schmeißer, Dieter}, title = {Gap states in the electronic structure of SnO2 single crystals and amorphous SnOxthin films}, series = {Journal of Applied Physics}, volume = {120}, journal = {Journal of Applied Physics}, number = {10}, issn = {0021-8979}, doi = {10.1063/1.4962313}, pages = {105101-1 -- 105101-13}, abstract = {The electronic structure of a SnO2 single crystal is determined by employing resonant photoelectron spectroscopy. We determine the core level, valence band, and X-ray absorption (XAS) data and compare these with those of amorphous SnOx thin films. We find similar properties concerning the data of the core levels, the valence band features, and the absorption data at the O1s edge. We find strong signals arising from intrinsic in-gap states and discuss their origin in terms of polaronic and charge-transfer defects. We deduce from the XAS data recorded at the Sn3d edge that the Sn4d10 ground state has contributions of 4d9 and 4d8 states due to configuration interaction. We identify localized electronic states depending on the strength of the 4d-5s5p interaction and of the O2p-to-Sn4d charge-transfer processes, both appear separated from the extended band-like states of the conduction band. For the amorphous SnOx thin films, significant differences are found only in the absorption data at the Sn3d-edge due to a stronger localization of the in-gap states.}, language = {en} }