TY - THES A1 - Müller, Sebastian T1 - Synchrotron radiation spectroscopy studies of the initial interaction of Chromium and Cobalt with the surface of Titanium Dioxide N2 - In the framework of this thesis, synchrotron radiation based spectroscopy methods are applied to study the electronic structures of stoichiometric Rutile single crystals and TiO2 thin films, and the initial stage of chromium and cobalt growth on TiO2 thin films. Resonance photoemission spectroscopy of clean TiO2 at the Ti L2,3 edges led to Auger-like features, with kinetic energies corresponding to the Ti L2,3M4,5M4,5 Auger decay channels. The presence of these features is assigned to origin from a d2L2 charge transfer state. The resonance of the Ti L3M2,3V Auger channel at the Ti L2 edge is assigned to the L2L3V Coster-Kronig Auger, followed by the normal L3M2,3V Auger decay. The deposition of chromium on the TiO2 film causes a strong interaction at the interface, in which TiO(2-x) is formed together with chromium in the Cr 3+ state. Besides the oxidized component, contribution of metallic chromium is found as well. In the ultra-low coverage regime, post-deposition oxidation is observed, in which metallic chromium is oxidized to Cr2O3, accompanied by re-oxidation of the substrate to TiO2. The interface reaction is also reflected by the appearance of two defect states in the band gap. Resonant photo-emission at the Cr 2p and Ti 2p edges shows well distinguishable Cr 3d respectively Ti 3d character of the respective states. Indications for self-cleaning properties are found by removal of surface carbon during storage in UHV, but the influence of chromium on these properties is not studied in detail. The interaction between cobalt and TiO2 is weaker than that of chromium and TiO2. Nevertheless, an interface reaction is found, in which some of the deposited cobalt is oxidized, while the oxide support is partly reduced. The particular oxidation state of Cobalt is identified by means of multiplet calculation including charge transfer and crystal field effects. The calculated XAS and XPS spectra indicate Co 2+ in a tetrahedral coordination with four oxygen atoms. The metallic component of cobalt gives rise to a broad resonance in the valence band down to -20 eV, with a pronounced satellite feature that reflects the oxidized component. KW - Titanium dioxide KW - Metal/metal-oxide interaction KW - Multiplet-calculation KW - Resonant photoemission Y1 - 2010 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:co1-opus-18914 UR - http://opus.kobv.de/btu/volltexte/2010/1891/ ER - TY - THES A1 - Henkel, Karsten T1 - Electrical Investigations on Praseodymium Oxide/Aluminum Oxynitride Containing Metal-Insulator-Semiconductor Stacks and on Metal-Ferroelectric-Insulator-Semiconductor Structures Consisting of Poly[vinylidene fluoride trifluoroethylene] N2 - In this thesis electrical characterizations on metal-insulator-semiconductor (MIS) and metal-ferroelectric-insulator-semiconductor (MFIS) stacks are presented. The results are discussed in terms of the increase of the performance of these stacks in order to optimize the characteristics of devices like the field effect transistor (FET) for logic applications and the ferroelectric field effect transistor (FeFET) for non-volatile and non-destructive readout memory applications. Therefor, two material classes are investigated. Firstly, this work focuses on praseodymium oxide (PrxOy) films as a high-kmaterial on silicon (Si) and silicon carbide in MISsamples. In particular the improvement of the performance by the introduction of an aluminum oxynitride buffer layer, which acts as an interdiffusion barrier and reduces the leakage current, the interface state density and the equivalent oxide thickness, is demonstrated. Secondly, in this work the very attractive ferroelectric material poly[vinylidene fluoride trifluoroethylene] (P[VDF/TrFE]) is introduced in MFIS stacks on Si. The way of successive improvements of the MFIS stack is extensively discussed. Here, the optimization of the preparation of the samples as well as of the layer parameters in the sequence of the MFIS stacks is depicted. An improved long time stability of the memory functionof the MFIS stack with a partially optimized layer sequence is exhibited. The electrical results are correlated to spectroscopic findings on both material systems. Strong interfacial reactions between the PrxOy and Si as well as between the aluminum electrode and the P[VDF/TrFE] layer are observed. For both systems the importance of a buffer layer is discussed and its optimization is addressed, too. On both systems a very nice, as consistent, chain of improvements is shown caused by the spectroscopic controlled preparation combined with electrical measurements in order to obtain the functionality of a given material system. KW - Pr2O3 KW - P(VDF-TrFE) KW - capacitance-voltage KW - conductance-voltage KW - current-voltage KW - dielectric properties KW - high-k KW - feFET Y1 - 2009 SN - 978-3-8322-8404-6 PB - Shaker CY - Aachen ER - TY - THES A1 - Torche, Mohamed T1 - Praseodymium oxide as dielectric in MIS stacks KW - high-k KW - Pr2O3 KW - X-ray photoelectron spectroscopy KW - XPS Y1 - 2006 CY - Cottbus ER - TY - THES A1 - Seifarth, Olaf T1 - Properties of chromium, cobalt and nickel nanoparticles embedded into ordered block copolymers and conducting polymers KW - block copolymers KW - chromium nanoparticles KW - cobalt nanoparticles KW - nickel nanoparticles Y1 - 2006 CY - Cottbus ER - TY - GEN A1 - Haeberle, Jörg A1 - Henkel, Karsten A1 - Gargouri, Hassan A1 - Naumann, Franziska A1 - Gruska, Bernd A1 - Arens, Michael A1 - Tallarida, Massimo A1 - Schmeißer, Dieter T1 - Ellipsometry and XPS comparative studies of thermal and plasma enhanced atomic layer deposited Al2O3-films T2 - Beilstein Journal of Nanotechnology N2 - We report on results on the preparation of thin (<100 nm) aluminum oxide (Al2O3) films on silicon substrates using thermal atomic layer deposition (T-ALD) and plasma enhanced atomic layer deposition (PE-ALD) in the SENTECH SI ALD LL system. The T-ALD Al2O3layers were deposited at 200 °C, for the PE-ALD films we varied the substrate temperature range between room temperature (rt) and 200 °C. We show data from spectroscopic ellipsometry (thickness, refractive index, growth rate) over 4” wafers and correlatethem to X-ray photoelectron spectroscopy (XPS) results. The 200°C T-ALD and PE-ALD processes yield films with similar refractive indices and with oxygen to aluminum elemental ratios very close to the stoichiometric value of 1.5. However, in both also fragments of the precursor are integrated into the film. The PE-ALD films show an increased growth rate and lower carbon contaminations. Reducing the deposition temperature down to rt leads to a higher content of carbon and CH-species. We also find a decrease of the refractive index and of the oxygen to aluminum elemental ratio as well as an increase of the growth rate whereas the homogeneity of the film growth is not influenced significantly. Initial state energy shifts in all PE-ALD samples are observed which we attribute to a net negative charge within the films. KW - Al2O3 KW - ALD KW - ellipsometry KW - PE-ALD KW - XPS Y1 - 2013 U6 - https://doi.org/10.3762/bjnano.4.83 SN - 2190-4286 VL - 2013 IS - 4 SP - 732 EP - 742 ER - TY - CHAP A1 - Cuypers, Daniel A1 - Dorp, Dennis H. von A1 - Tallarida, Massimo A1 - Brizzi, Simone A1 - Rodriguez, Leonard A1 - Conard, Thierry A1 - Arnauts, Sophia A1 - Schmeißer, Dieter A1 - Adelmann, Christoph A1 - De Gendt, Stefan T1 - Study of InP Surfaces After Wet Chemical Treatments T2 - Meeting Abstracts-Electrochemical Society, San Francisco, 2013 KW - Synchrotron Radiation Photoelectron Spectroscopy KW - InP KW - Wet chemical treatment Y1 - 2013 UR - http://ma.ecsdl.org/content/MA2013-02/30/2132.full.pdf+html N1 - MA2013-02(30) SP - S. 2132 PB - The Electrochemical Society ER - TY - GEN A1 - Cuypers, Daniel A1 - Dorp, Dennis H. von A1 - Tallarida, Massimo A1 - Brizzi, Simone A1 - Rodriguez, Leonard A1 - Conard, Thierry A1 - Arnauts, Sophia A1 - Schmeißer, Dieter A1 - Adelmann, Christoph A1 - De Gendt, Stefan T1 - Study of InP Surfaces after Wet Chemical Treatments T2 - ECS Transactions N2 - In this work synchrotron radiation photoemission spectroscopy (SRPES) is used to study InP surfaces after different wet chemical treatments. All results are compared to a typical fingerprint of surface components present on an as received InP sample. It is shown that acidified (HCl and H₂SO₄) treatments efficiently remove the native phosphate, although components like Pᴼ, Inᴼ and P(2±∆)+ remain present. In alkaline solution (NH₄OH) oxide remains present at the surface. As an alternative treatment, the immersion into (NH₄)₂S was studied. This passivation treatment results in fewer surface components which suggests that a higher quality surface is obtained. KW - Synchrotron Radiation Photoelectron Spectroscopy KW - InP KW - Wet chemical treatment Y1 - 2013 U6 - https://doi.org/10.1149/05806.0297ecst SN - 1938-6737 SN - 1938-5862 VL - 58 IS - 6 SP - 297 EP - 303 ER - TY - GEN A1 - Cuypers, Daniel A1 - Dorp, Dennis H. von A1 - Tallarida, Massimo A1 - Brizzi, Simone A1 - Conard, Thierry A1 - Rodriguez, Leonard A1 - Mees, M. A1 - Arnauts, Sophia A1 - Schmeißer, Dieter A1 - Adelmann, Christoph A1 - De Gendt, Stefan T1 - Study of InP Surfaces after Wet Chemical Treatments T2 - ECS Journal of Solid State Science and Technology N2 - The influence of different wet chemical treatments (HCl, H₂SO₄, NH₄OH) on the composition of InP surfaces is studied by using synchrotron radiation photoemission spectroscopy (SRPES). It is shown that a significant amount of oxide remains present after immersion in a NH₄OH solution which is ascribed to the insolubility of In³⁺ at higher pH values. Acidic treatments efficiently remove the native oxide, although components like Pᴼ, Inᴼ and P(2±Δ)+ suboxides are observed. Alternatively, the influence of a passivation step in (NH₄)₂S solution on the surface composition was investigated. The InP surface after immersion into (NH₄)₂S results in fewer surface components, without detection of Pᴼ and P(2±Δ)+ suboxides. Finally, slight etching of InP surfaces in HCl/H₂O₂ solution followed by a native oxide removal step, showed no significant effect on the surface composition. KW - Synchrotron Radiation Photoelectron Spectroscopy KW - Scanning Tunneling Microscopy KW - InP KW - Wet chemical treatment Y1 - 2014 U6 - https://doi.org/10.1149/2.005401jss SN - 2162-8777 SN - 2162-8769 VL - 3 IS - 1 SP - N3016 EP - N3022 ER - TY - GEN A1 - Müller, Klaus A1 - Städter, Matthias A1 - Rachow, Fabian A1 - Hoffmannbeck, David A1 - Schmeißer, Dieter T1 - Sabatier-based CO2-methanation by catalytic conversion T2 - Environmental Earth Sciences N2 - The catalytic conversion of CO2is an important component for the reintegration of secondary products like CO2 or H2 into the energy supply. An example is the "power to gas’" concept with a conversion of CO2 into CH4. The CO2 is transferred into a carrier of chemical energy, with the possibility to feed the produced CH4 into the existing network of natural gas. At temperatures of around 350 °C, hydrogenation of CO2 to CH4 is possible by the Sabatier reaction CO2+4H2->CH4+H2O. One prerequisite for efficient kinetics of the Sabatier reaction is the application and optimization of catalysts. The focus of catalyst development is given to their performance under the conditions to be expected in the special application. As a part of the project Geoenergy-Research (GeoEn), we address questions related to the catalytic utilization of CO2 produced in the course of the oxyfuel combustion of lignite. In this contribution, we report on the experimental setup in laboratory scale, which enables an advanced characterization of the catalytic performance, including thermodesorption measurements at atmospheric pressure in order to determine the amount of adsorbed CO2 under real conditions. We also show data for activation energies, the catalytic performance as function of temperature and the long time stability of a commercial Ru-based catalyst. KW - CO2 KW - Sabatier reaction KW - Catalysis KW - RuO2 Y1 - 2013 U6 - https://doi.org/10.1007/s12665-013-2609-3 SN - 1866-6280 VL - 70 IS - 8 SP - 3771 EP - 3778 ER - TY - GEN A1 - Das, Chittaranjan A1 - Tallarida, Massimo A1 - Schmeißer, Dieter T1 - Linear dichroism in ALD layers of TiO₂ T2 - Environmental Earth Sciences N2 - We prepare TiO₂film by ALD and study their electronic properties by soft X-ray absorption spectroscopy (XAS) and photoelectron spectroscopy. We focus on XAS and X-ray linear dichroism to indentify band onset and learn about local distortion of the Ti–O octahedral atomic and about defects which cause Ti-based electronic states within the band gap. KW - Anatase KW - Dichroism KW - Amorphous Y1 - 2013 U6 - https://doi.org/10.1007/s12665-013-2836-7 SN - 1866-6280 VL - 70 IS - 8 SP - 3785 EP - 3795 ER - TY - GEN A1 - Städter, Matthias A1 - Müller, Klaus A1 - Rachow, Fabian A1 - Richter, Matthias A1 - Schmeißer, Dieter T1 - Ambient pressure thermal desorption spectroscopy (AP-TDS) of NiO/SiO2 catalysts T2 - Environmental Earth Sciences N2 - The Sabatier reaction is a key process in the "power-to-gas" application which is considered to con-tribute to future chemical energy storage systems. In this contribution we focus on the catalytic active sites of a NiO catalyst supported on SiO2(NiO/SiO2) which is commonly used in the Sabatier reaction. A novel technique for the characterization of the active sites is presented and dis-cussed using thermal desorption spectroscopy at ambient pressure. This analytical tool is operated under reaction conditions and allows element specific measurements during the catalytic process of CO2 reforming towards methane. Beside the desorption experiments, XPS and XAS measurements of pristine and catalytically used samples are performed to determine the influence of the Sabatier reaction conditions on the surface structure of the catalyst. KW - CO2 KW - NiO KW - TDS KW - XAS KW - XPS Y1 - 2013 U6 - https://doi.org/10.1007/s12665-013-2835-8 SN - 1866-6280 VL - 70 IS - 8 SP - 3779 EP - 3784 ER - TY - GEN A1 - Scheck-Wenderoth, Magdalena A1 - Schmeißer, Dieter A1 - Mutti, Maria A1 - Kolditz, Olaf A1 - Huenges, Ernst A1 - Schultz, Hans-Martin A1 - Liebscher, Axel A1 - Bock, Michaela T1 - Geoenergy: new concepts for utilization of geo-reservoirs as potential energy sources T2 - Environmental Earth Sciences KW - Geothermal technologies KW - capturing and storing and utilizing CO2 KW - hydraulic fracturing Y1 - 2013 U6 - https://doi.org/10.1007/s12665-013-2877-y SN - 1866-6280 VL - 70 IS - 8 SP - 3427 EP - 3431 ER - TY - GEN A1 - Gerlich, Lukas A1 - Ohsiek, Susanne A1 - Klein, Christoph A1 - Geiß, Mario A1 - Friedemann, Michael A1 - Kücher, Peter A1 - Schmeißer, Dieter T1 - Interface engineering for the TaN/Ta barrier film deposition process to control Ta-crystal growth T2 - Microelectronic Engineering N2 - As a consequence of device shrinking the resistivity of the widely used TaN/Ta double barrier layer becomes an increasingly important parameter for device speed beyond the 32 nm technology node. In this study we describe the optimization of the deposition of TaN/Ta stacks in such a way that tantalum nitride layer thickness is minimized and tantalum grows in the favorable conducting alpha-phase. In the first part of the study we usedin situ ARXPS to investigate the growth of different tantalum nitride layers on SiO2 and SiOCH as a function of deposition time, nitrogen flow and deposition power. In the second part we analyzed the crystalline phase of a 20 nm thick tantalum layer deposited on top of the same series of tantalum nitride layers characterized in the growth study. The main findings are the appearance of tan-talum carbide and tantalum silicide as interface species for the deposition on SiOCH and only tantalum silicide for the deposition on SiO2. We found that alpha-tantalum grows preferably on tantalum carbide and nitrogen rich intermediate layers whereas silicide at the interface promotes the growth of beta-tantalum. To verify these findings we studied two additional modifications of the interface. A lower bias power for a deposition of tantalum nitride on SiO2 was used to confirm the role of tantalum silicide and a thermal treatment of a thin tantalum layer on SiOCH was applied to confirm the role of tantalum carbide. Finally, the contact resistance in via chains on patterned wafers for four selected processes showed the same trends as the sheet resistance of the corresponding barrier films on blanket wafer experiments. KW - Tantalum KW - in situ XPS KW - Ta-phase KW - TaNx KW - Barrier KW - Interface Y1 - 2013 U6 - https://doi.org/10.1016/j.mee.2013.01.017 VL - Vol. 106 SP - 63 EP - 68 ER - TY - GEN A1 - Henkel, Karsten A1 - Gargouri, Hassan A1 - Gruska, Bernd A1 - Arens, Michael A1 - Tallarida, Massimo A1 - Schmeißer, Dieter T1 - Capacitance and conductance versus voltage characterization of Al2O3 layers prepared by PE-ALD at 25°C ≤ T ≤ 200°C T2 - Journal of Vacuum Science and Technology A N2 - In this work, plasma enhanced atomic layer deposited (PE-ALD) samples were prepared at substrate temperatures in the range between room temperature (RT) and 200 °C and investigated by capacitance–voltage and conductance–voltage recordings. The measurements are compared to standard thermal atomic layer deposition (T-ALD) at 200 °C. Very low interface state density (D it) ~1011 eV−1 cm−2 could be achieved for the PE-ALD process at 200 °C substrate temperature after postdeposition anneal (PDA) in forming gas at 450 °C. The PDA works very effectively for both the PE-ALD and T-ALD at 200 °C substrate temperature delivering also similar values of negative fixed charge density (N fix) around −2.5 × 1012 cm−2. At the substrate temperature of 150 °C, highest N fix (−2.9 × 1012 cm−2) and moderate D it (2.7 × 1011 eV−1 cm−2) values were observed. The as deposited PE-ALD layer at RT shows both low D it in the range of (1 to 3) × 1011 eV−1 cm−2 and low N fix (−4.4 × 1011 cm−2) at the same time. The dependencies of N fix, D it, and relative permittivity on the substrate temperatures and its adjustability are discussed. KW - Atomic layer deposition (ALD) KW - Al2O3 KW - dielectric properties KW - interface state density KW - fixed oxide charge KW - permittivity Y1 - 2014 UR - http://link.aip.org/link/?JVA/32/01A107&aemail=author U6 - https://doi.org/10.1116/1.4831897 VL - 1 IS - 32 SP - 01A107-1 EP - 01A107-10 ER - TY - THES A1 - Hoffmann, Patrick T1 - Untersuchungen zu Inhomogenitäten an der Halbleitergrenzfläche Silizium-Siliziumoxynitrid KW - Grenzflächeneigenschaften KW - SiO2 KW - SiON KW - Synchrotron-basierte Röntgen-Spektroskopie KW - XPS KW - XAS Y1 - 2003 SN - 3-8322-1982-X PB - Shaker-Verlag CY - Aachen ER - TY - THES A1 - Mikalo, Ricardo Pablo T1 - Elektronische Eigenschaften von leitfähigen konjugierten Polymeren und deren Grenzflächenreaktionen im elektrischen Kontakt mit Metallen KW - konjugierte Polymere KW - Photoelektronenspektroskopie KW - XPS KW - XAS Y1 - 2003 SN - 3-89959-115-1 PB - Der Andere Verlag CY - Osnarbrück ER - TY - THES A1 - Heller, Thomas T1 - Molekulare Resonanzen im Wirkungsquerschnitt der Photoemission in den Valenzzuständen der stöchiometrischen und der mit Natrium belegten WO3 und TiO2 (110) 1x1 Oberfläche KW - WO3 KW - TiO2 KW - Photoelektronenspektroskopie KW - Natriumadsorption Y1 - 2002 SN - 3-8322-0742-2 PB - Shaker CY - Aachen ER - TY - THES A1 - Yfantis, Alexandros D. T1 - Development and Characterisation of Corrosion Resistent Layers of Conducting Polymers on Aluminium Alloys KW - corrosion protection KW - conducting polymers KW - X-ray photoelectron spectroscopy Y1 - 2001 SN - 960-394-115-8 PB - Parissianou CY - Athen ER - TY - THES A1 - Appel, Günter T1 - Untersuchungen zur mesoskopischen und elektronischen Struktur von Polypyrroltosylat und Polypyrrolkupferphthalocyaninsulfonat KW - Polypyrroltosylat KW - Polypyrrolkupferphthalocyaninsulfonat KW - elektronische Struktur KW - XPS KW - XAS Y1 - 1999 SN - 3-8265-4830-2 PB - Shaker CY - Aachen ER - TY - THES A1 - Hofmann, Andreas T1 - Elektronische Struktur epitaktischer Chalkopyrite und deren Heterokontakte für die Photovoltaik Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:co1-opus-24434 N1 - Prof. Schmeißer, Gutachter, Arbeit am HZB CY - Cottbus ER - TY - THES A1 - Zimmer, Fabian T1 - Herstellung und Charakterisierung hocheffzienter, mikromechanischer NIR-Beugungsgitter für den Einsatz in miniaturisierten Spektrometern KW - Mikrosystemtechnik KW - MEMS KW - Mikrooptik KW - Mikrospiegel KW - Spektrometer Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:co1-opus-25224 UR - http://opus.kobv.de/btu/volltexte/2012/2522/ ER - TY - THES A1 - Dudek, Piotr T. T1 - Atomic scale engineering of HfO2–based dielectrics for future DRAM applications N2 - Modern dielectrics in combination with appropriate metal electrodes have a great potential to solve many difficulties associated with continuing miniaturization process in the microelectronic industry. One significant branch of microelectronics incorporates dynamic random access memory (DRAM) market. The DRAM devices scaled for over 35 years starting from 4 kb density to several Gb nowadays. The scaling process led to the dielectric material thickness reduction, resulting in higher leakage current density, and as a consequence higher power consumption. As a possible solution for this problem, alternative dielectric materials with improved electrical and material science parameters were intensively studied by many research groups. The higher dielectric constant allows the use of physically thicker layers with high capacitance but strongly reduced leakage current density. This work focused on deposition and characterization of thin insulating layers. The material engineering process was based on Si cleanroom compatible HfO2 thin films deposited on TiN metal electrodes. A combined materials science and dielectric characterization study showed that Ba added HfO2 (BaHfO3) films and Ti added BaHfO3 (BaHf0.5Ti0.5O3) layers are promising candidates for future generation of state of the art DRAMs. In especial a strong increase of the dielectric permittivity k was achieved for thin films of cubic BaHfO3 (k~38) and BaHf0.5Ti0.5O3 (k~90) with respect to monoclinic HfO2 (k~19). Meanwhile the CET values scaled down to 1 nm for BaHfO3 and ~0.8 nm for BaHf0.5Ti0.5O3 with respect to HfO2 (CET=1.5 nm). The Hf4+ ions substitution in BaHfO3 by Ti4+ ions led to a significant decrease of thermal budget from 900°C for BaHfO3 to 700°C for BaHf0.5Ti0.5O3. Future studies need to focus on the use of appropriate metal electrodes (high work function) and on film deposition process (homogeneity) for better current leakage control. KW - Dielectrics KW - High-k materials KW - Atomic Scale Engineering KW - HfO2-based materials KW - XPS Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:co1-opus-22775 UR - http://opus.kobv.de/btu/volltexte/2011/2277/ ER - TY - THES A1 - Rauscher, Stefan T1 - Dynamische Modifizierung von Silizium-Elektrolyt-Grenzflächen und deren oberflächenphysikalischen Eigenschaften Y1 - 2004 PB - Brandenburgische Techn. Univ. CY - Cottbus ER - TY - GEN A1 - Richter, Matthias A1 - Starke, Ulrich A1 - Schmeißer, Dieter T1 - Multiple Auger processes in Graphene T2 - Journal of Electron Spectroscopy and Related Phenomena N2 - Resonant Auger decay processes have been studied by resonant photoemission spectroscopy (resPES) and X-ray absorption spectroscopy (XAS) in Graphene systems. The pi*-resonance is used to identify the degree of localization of the lowest pi*-orbitals in the conduction band. Localization and lifetime of the photo-excited intermediate state cause the formation of multiple Auger processes. For the Graphene systems we identify two novel Auger decay combinations with a four hole final state: the (S+S) and the(S+S)* decay. We demonstrate that these processes are sensitive for interlayer coupling and interactions with the metallic free electrons of the substrate. KW - Graphene KW - X-Ray absorption spectroscopy KW - XAS KW - resonant photoemission spectroscopy KW - resPES KW - multiple hole Auger Y1 - 2014 U6 - https://doi.org/10.1016/j.elspec.2013.12.009 SN - 0368-2048 IS - Vol. 192 SP - 1 EP - 6 ER - TY - GEN A1 - Tallarida, Massimo A1 - Das, Chittaranjan A1 - Schmeißer, Dieter T1 - Quantum size effects in TiO2 thin films grown by atomic layer deposition T2 - Beilstein Journal of Nanotechnology N2 - We study the atomic layer deposition of TiO2 by means of X-ray absorption spectroscopy. The Ti precursor, titanium isopropoxide, was used in combination with H2O on Si/SiO2 substrates that were heated at 200 °C. The low growth rate (0.15 Å/cycle) and the in situ characterization permitted to follow changes in the electronic structure of TiO2 in the sub-nanometer range, which are influenced by quantum size effects. The modified electronic properties may play an important role in charge carrier transport and separation, and increase the efficiency of energy conversion systems. KW - atomic layer deposition (ALD) KW - charge transfer multiplet KW - covalency KW - energy conversion KW - quantum size effects KW - titanium dioxide (TiO2) KW - water splitting KW - X-ray absorption spectroscopy (XAS) Y1 - 2014 U6 - https://doi.org/10.3762/bjnano.5.7 SN - 2190-4286 IS - 5 SP - 77 EP - 82 ER - TY - GEN A1 - Richter, Matthias A1 - Friedrich, Daniel A1 - Schmeißer, Dieter T1 - Interlayer-exciton mediated three-hole-Auger-decay in the pi-band of highly oriented pyrolytic graphite T2 - Physica E N2 - Resonant photoemission spectroscopy(resPES) is used to probe the occupied pi- and unoccupied pi*-bands of carbon thin films with particular focus on the Auger decay. Highly Oriented Pyrolytic Graphite (HOPG) is studied at the C1s edge. We find strong resonant features at 285.5 eV and 292 eV in the resPES diagram. The normal two-hole Auger decay proceeds under constant kinetic energy (451)only in the sigma*-region. In the pi*-region, however, it proceeds under 67.5° in terms of a Ebind(w) diagram. We attribute this to a multiple Auger decay with a net three hole final state. For this novel decay process we propose a model.We discuss the long lifetime of the first resonant excitation and conclude that it arises from the strong excitonic character of the first resonant state. We use HOPG as a reference system and suggest that this novel process is a tool to identify interlayer–substrate interaction of the carbon layers involved. KW - resonant excitation KW - three hole Auger decay KW - X-ray photoelectron spectroscopy KW - HOPG Y1 - 2014 U6 - https://doi.org/10.1016/j.physe.2013.01.015 SN - 1386-9477 VL - Vol. 56 SP - 441 EP - 446 ER - TY - THES A1 - Michling, Marcel Frank T1 - Spektroskopische Untersuchungen an organischen Materialien und Metalloxiden N2 - Im Rahmen der vorliegenden Arbeit wurde mit Synchrotron-basierenden, optischen und Elektronen-basierenden Methoden die elektronischen Eigenschaften zweier unterschiedlicher Materialklassen untersucht. Der Fokus lag dabei im besonderen auf der Bestimmung der Größe der Bandlücke/HOMO-LUMO-Lücke und ihre Abhängigkeit der verwendeten Methode. Die zwei unterschiedliche Materialklassen, welche untersucht wurden sind folgende: Erstens die organischen Systeme Cobalt-Phthalocyanin und Fulleren. An Ihnen wird der Einfluss der verwendeten Messmethoden aufgezeigt und die sich draus ergebenen HOMO- LUMO-Lücken (elektronisch, Volumen, Oberfläche, optisch) diskutiert. Es zeigt sich, dass die optische Methode (Ellipsometrie) generell den kleinsten Wert und die elektronischen Methoden (XPS, XAS) den größten Wert ergeben. Die Gründe dafür werden ausführlich diskutiert. Durch die Kombination von XPS- , XAS- und Ellipsometrie-Messungen war es möglich die Orientierung der aufgedampften CoPc-Moleküle auf den SiO2-Substrat zu bestimmen. Zweitens wurden die Metalloxide HfO2, Al2O3, In2O3 und Ga2O3 aufgrund ihrer großen technologischen Bedeutung untersucht. Mit Hilfe von ALD Zyklus-für-Zyklus Experimenten konnten die elektronischen Eigenschaften von HfO2 in Abhängigkeit der ALD- Zyklenzahl und das Wachstum von HfO2 in den ersten Zyklen studiert werden. Auf Basis der XPS- und EELS-Ergebnisse wurde ein Wachstumsmodell entwickelt. Es wird ebenfalls der Einfluss einer Dipolschicht an der Grenzfläche HfO2/SiO2 auf die Größe der Bandlücke in den EELS-Messungen diskutiert. Mittels resonanten Photoemission wurde ein neuer Auger-Mechanismus (3-Loch-Auger-Prozess) in den Oxiden gefunden. Dieser hat seine Ursache in Defekten. Defekte führen auch zu einer Fano-Anti-Resonanz, welche an der O1s-Absorptions-Kante beobachtet und diskutiert wird. KW - Spektroskopie KW - Organik KW - Metalloxide KW - Bandlücke KW - 3h-Auger Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:co1-opus-29014 UR - http://opus.kobv.de/btu/volltexte/2013/2901/ ER - TY - THES A1 - Richter, Matthias T1 - Excitons and Polarons in resonant Auger decay processes N2 - In the framework of this thesis synchrotron radiation spectroscopy is applied to study the electronic structure of organic semiconductors, of Graphene, and of transition metal (TM) oxide water splitting catalysts (Co-PI) with emphasis on excitonic and polaronic effects. For a correct theoretical description of the electronic structure of these material classes electron-phonon and electron-electron coupling as well as polarization and excitonic effects have to be considered. Excitons and Polarons are localized in-gap states. They are known to affect the optical properties of the material. Their influence can also be revealed in the resonant Auger decay profile. Even in TM-oxides Polarons and Excitons are observed as a consequence of an oxygen 2p to TM3d charge transfer. Therefor, the following three material classes are chosen for the fundamental study of Excitons and Polarons in resonant Auger decay processes. First, the existence of localized polaronic and excitonic states is investigated for regioregular-Poly(3 hexylthiophene-2,5-diyl) (rr-P3HT) and Phenyl-C61-butyric acid methyl ester (PCBM) used as a light absorber in organic solar cells. The existence of 2D-Polarons, singlet Exciton, and triplet Exciton is demonstrated for rr-P3HT whereas for PCBM only singlet Excitons are observed. Singlet Excitons show an influence on the resonant Auger decay by a combined spectator-participator (S+P) Auger decay in the π*-band. Second, for a more detailed study of the (S+P) decay Highly Ordered Pyrolytic Graphite (HOPG) is chosen. For Graphene as a single layer of HOPG without van der Waals force another combination of Auger decays can be observed: a double spectator Auger (S+S) and a double spectator Auger-Gain (S+S)* decay. Third, Co-PI (cobalt oxide compound) is investigated. It is a TM-oxide catalyst used for the oxygen evolution reaction in photo-electrochemical cells. Self-trapped Excitons formed by resonant core electron excitation into self-trapped hole states give rise to a combined Auger decay process (S+P). For all three novel Auger decay processes {(S+P), (S+S), and (S+S)*} a model is proposed. KW - Exciton KW - Polaron KW - X-Ray absorption spectroscopy (XAS) KW - resonant photoemission spectroscopy (resPES) KW - Auger decay Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:co1-opus-29816 UR - http://opus.kobv.de/btu/volltexte/2014/2981/ ER - TY - GEN A1 - Haeberle, Jörg A1 - Richter, Matthias A1 - Galazka, Zbigniew A1 - Janowitz, Christoph A1 - Schmeißer, Dieter T1 - Resonant Photoemission at the O1s threshold to characterize In2O3 single crystals T2 - Thin Solid Films N2 - We report on spectroscopic investigations on In2O3 single crystals. We focus on the detailed analysis of the O1s resonance profile by resonant photoelectron spectroscopy. We analyze the electronic structure and assign the O2p to build the valence band and both, O2p and In5s5p states to contribute to the conduction band (CB). We determine the partial density of states for the valence and CBs and find a strong hybridization of O2p and In5s states. This is deduced from constant final state spectra on the O-KLL-Auger over the O K-edge and In M4,5-edge and a comparison to the corresponding X-ray absorption spectroscopy data.We also identify several types of defects. A broad band of oxygen derived defects is identified that extends throughout the gap. These are attributed to small polarons which cause an anti-resonance in the valence states around the O1s threshold. In addition, a separate Auger decay at resonance indicates the existence of localized charge transfer states which involves localized In5s5p states. KW - In2O3 KW - TCO KW - X-ray spectroscopy KW - Small polaron KW - Charge transfer Y1 - 2014 U6 - https://doi.org/10.1016/j.tsf.2013.03.036 SN - 0040-6090 SN - 1879-2731 VL - 2014 IS - 555 SP - 53 EP - 56 ER - TY - GEN A1 - Kramm, Ulrike Ingrid A1 - Herrmann-Geppert, Iris A1 - Fiechter, Sebastian A1 - Zehl, Gerald A1 - Zizak, Ivo A1 - Dorbandt, Iris A1 - Schmeißer, Dieter A1 - Bogdanoff, Peter T1 - Effect of iron carbide formation on the number of active sites in Fe-N-C catalysts for the oxygen reduction reaction in acidic media T2 - Journals of materials chemistry A KW - Oxygen reduction reaction (ORR) KW - Fe-N-C catalyst KW - acidic media KW - high-temperature X-ray diffraction (HT-XRD) KW - thermogravimetry coupled with mass-spectroscopy (TG-MS) Y1 - 2014 U6 - https://doi.org/10.1039/c3ta13821f SN - 2050-7488 SN - 2050-7496 IS - 8 SP - 2663 EP - 2670 ER - TY - GEN A1 - Kramm, Ulrike Ingrid A1 - Lefèvre, Michel A1 - Larouche, Nicholas A1 - Schmeißer, Dieter A1 - Dodelet, Jean-Pol T1 - Correlations between Mass Activity and Physicochemical Properties of Fe/N/C Catalysts for the ORR in PEM Fuel Cell via 57 Fe Mössbauer Spectroscopy and Other Techniques T2 - Journal of the American Chemica Society N2 - The aim of this work is to clarify the origin of the enhanced PEM-FC performance of catalysts prepared by the procedures described in Science 2009, 324, 71 and Nat. Commun. 2011, 2, 416. Catalysts were characterized after a first heat treatment in argon at 1050 °C (Ar) and a second heat treatment in ammonia at 950 °C (Ar + NH3). For the NC catalysts a variation of the nitrogen precursor was also implemented. 57Fe Mössbauer spectroscopy, X-ray photoelectron spectroscopy, neutron activation analysis, and N2 sorption measurements were used to characterize all catalysts. The results were correlated to the mass activity of these catalysts measured at 0.8 V in H2/O2 PEM-FC. It was found that all catalysts contain the same FeN4-like species already found in INRS Standard (Phys. Chem. Chem. Phys. 2012, 14, 11673). Among all FeN4-like species, only D1 sites, assigned to FeN4/C, and D3, assigned to N-FeN2+2 /C sites, were active for the oxygen reduction reaction (ORR). The difference between INRS Standard and the new catalysts is simply that there are many more D1 and D3 sites available in the new catalysts. All (Ar + NH3)-type catalysts have a much larger porosity than Ar-type catalysts, while the maximum number of their active sites is only slightly larger after a second heat treatment in NH3. The large difference in activity between the Ar-type catalysts and the Ar + NH3 ones stems from the availability of the sites to perform ORR, as many sites of the Ar-type catalysts are secluded in the material, while they are available at the surface of the Ar + NH3-type catalysts. KW - Fe-N-C catalyst KW - 57 Fe Mössbauer Spectroscopy KW - X-ray photo-electron spectroscopy KW - neutron activation analysis KW - nitrogen sorption measurements KW - oxygen reduction reaction (ORR) KW - PEM Fuel Cell Y1 - 2014 U6 - https://doi.org/10.1021/ja410076f SN - 0002-7863 SN - 1520-5126 VL - 136 IS - 3 SP - 978 EP - 985 ER - TY - THES A1 - Gerlich, Lukas T1 - In situ ARXPS Charakterisierung von tantalbasierten Barriereschichten N2 - Als eine Folge der Miniaturisierung aller integrierten elektrischen Bauteile wird der spezifische Widerstand der TaN/Ta Doppelsperrschichten ein zunehmend wichtiger Parameter für die Schaltgeschwindigkeit beim 32 nm Technologieknoten. In Rahmen dieser Arbeit wird die Optimierung der Abscheidung von TaN/Ta Stapeln durchgeführt, mit dem Ziel die Tantalnitridschichtdicke zu minimieren und das Tantal in der leitfähigeren alpha-Phase wachsen zu lassen. Im ersten Teil der Studie wurde in situ ARXPS verwendet, um das Wachstum von verschiedenen Tantalnitridschichten auf SiO2 und SiCOH in Abhängigkeit der Abscheidezeit, des Stickstoffflusses und der Abscheideleistung zu untersuchen. Im zweiten Teil wurde die kristalline Phase 20 nm dicken Tantal Schichten abgeschieden auf verschiedenen Tantalnitridschichten, die in der Wachstumsstudie vorgestellt worden sind, untersucht. Die wichtigsten Erkenntnisse sind das Auftreten von Tantalkarbid und Tantalsilizid als Zwischenschichtverbindungen bei der Abscheidung auf SiCOH und nur Tantalsilizid für die Abscheidung auf SiO2. Demzufolge wächst alpha-Tantal vorzugsweise auf Tantalkarbid und stickstoffreichen Zwischenschichten, während Silizid an der Schnittstelle das Wachstum von beta-Tantal fördert. Um die Ergebnisse zu überprüfen, wurden zwei weitere Modifikationen des Interfaces untersucht. So wurde eine kleinere Bias-Leistung für eine Abscheidung von Tantalnitrid auf SiO2 benutzt, um die Rolle des Tantalsilizids zu bestätigen. Außerdem wurde eine thermische Behandlung einer dünnen Tantalschicht auf SiCOH durchgeführt, um die Rolle des Tantalkarbids zu bestätigen. Schließlich ergab die Kontaktwiderstandsmessung in Viaketten auf strukturierten Wafern für vier ausgewählte Prozesse tendenziell den gleichen Verlauf wie die Schichtwiderstandsergebnisse der entsprechenden Barrierenaufbauten der Experimente auf blanken Testwafern. KW - Photoelektronenspektroskopie KW - Tantal KW - ARXPS KW - Barriere KW - Interface Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:co1-opus-28485 UR - http://opus.kobv.de/btu/volltexte/2013/2848/ ER - TY - GEN A1 - Adelmann, Christoph A1 - Schram, Tom A1 - Chew, Soon Aik A1 - Woicik, J. C. A1 - Brizzi, Simone A1 - Tallarida, Massimo A1 - Schmeißer, Dieter A1 - Horiguchi, Naoto A1 - Elshocht, Sven van A1 - Ragnarsson, Lars-Åke T1 - On the scalability of doped hafnia thin films T2 - Applied Physics Letters N2 - The scaling behavior of Gd- and Al-doped HfO2 films as gate dielectrics in metal-oxide-semiconductor (MOS) capacitors was studied. For equivalent oxide thicknesses (EOTs) in the range of 10 Å, crystallized Gd:HfO2 showed higher leakage current densities than crystallized Al:HfO2, with undoped HfO2 in between. Ultimately, the scalability of Al:HfO2 was limited by the ability to crystallize the films at a given thermal budget. As a result, for post-deposition annealing at 800 °C, the EOT of Al:HfO2 based MOS capacitors was limited to ∼8 Å. However, for such an EOT, leakage current densities were reduced by about 100× with respect to HfO2. This demonstrates the high potential of Al:HfO2 for low-standby-power MOS devices. KW - scalability KW - hafnia thin films KW - Al:HfO2 KW - Gd:HfO2 KW - EXAFS KW - equivalent oxide thickness (EOT) KW - leakage current KW - X-ray absorption spectroscopy (XAS) Y1 - 2014 U6 - https://doi.org/10.1063/1.4870075 SN - 0003-6951 SN - 1077-3118 IS - 104 SP - 122906-1 EP - 122906-4 ER - TY - CHAP A1 - Henkel, Karsten A1 - Tallarida, Massimo A1 - Haeberle, Jörg A1 - Gargouri, Hassan A1 - Naumann, Franziska A1 - Gruska, Bernd A1 - Arens, Michael A1 - Schmeißer, Dieter ED - Glück, Bernhard K. ED - Schmidt, Sindy ED - Stein, Erhard ED - Raschke, Jörg-Uwe ED - Richter, Hans T1 - PE-ALD-Al2O3-Schichten für die Passivierung von Solarzellen T2 - Tagungsband Photovoltaik-Meeting: Anwendungen-Qualität-Perspektiven, Senftenberg, 16.04.2014 N2 - Dünne Al2O3-Schichten wurden bei Substrattemperaturen zwischen Raumtemperatur und 200°C mittels PE-ALD auf Si-Substraten abgeschieden und ellipsometrisch, spektroskopisch und elektrisch charakterisiert. Ihr Potenzial für die chemische und Feldeffektpassivierung der Oberflächenrekombination wird bewertet. KW - Al2O3 KW - Atomlagenabscheidung (ALD) KW - Passivierung KW - PE-ALD KW - negative fixe Oxidladungen Y1 - 2014 SP - 7 EP - 14 PB - Cottbus-Senftenberg CY - BTU ER - TY - GEN A1 - Mandal, Dipankar A1 - Henkel, Karsten A1 - Schmeißer, Dieter T1 - Improved performance of a polymer nanogenerator based on silver nanoparticles doped electrospun P(VDF–HFP) nanofibers T2 - Physical Chemistry Chemical Physics N2 - We report on the electrospinning of poly(vinylidene fluoride–hexafluoropropylene) [P(VDF–HFP)] nanofibers doped with silver nanoparticles for the preparation of a polymer based nanogenerator (PNG). It has been found that the yield of the piezoelectric phase is increased by the addition of silver nanoparticles. Furthermore, defects in the P(VDF–HFP) electrospun fibers are removed resulting in a significant enhancement in the output power of the PNG. A maximum generated PNG output voltage of 3 V with a current density of 0.9 μA cm−2 is achieved. KW - piezoelectric thin polymer film KW - FTIR KW - nanogenerator KW - PVDF KW - P(VDF-HFP) KW - nanofibers Y1 - 2014 U6 - https://doi.org/10.1039/C3CP55238A SN - 1463-9084 SN - 1463-9076 VL - 2014 IS - 16 SP - 10403 EP - 10407 ER - TY - GEN A1 - Schmeißer, Dieter A1 - Haeberle, Jörg A1 - Barquinha, Pedro A1 - Gaspar, Diana A1 - Pereira, Luís A1 - Martins, Rodrigo A1 - Fortunato, Elvira T1 - Electronic structure of amorphous ZnO films T2 - Physica Status Solidi C N2 - 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. KW - a-ZnO thin films KW - intrinsic defects KW - resonant PES KW - amorphous oxide semiconductors (AOS) KW - transparent conducting oxides (TCO) KW - charge transfer Y1 - 2014 U6 - https://doi.org/10.1002/pssc.201400010 SN - 1610-1642 VL - 11 IS - 9-10 SP - 1476 EP - 1480 ER - TY - GEN A1 - Tallarida, Massimo A1 - Das, Chittaranjan A1 - Cibrev, Dejan A1 - Kukli, Kaupo A1 - Tamm, Aile A1 - Ritala, Mikko A1 - Lana-Villarreal, Teresa A1 - Gómez, Roberto A1 - Leskelä, Markku A1 - Schmeißer, Dieter T1 - Modification of Hematite Electronic Properties with Trimethyl Aluminum to Enhance the Efficiency of Photoelectrodes T2 - The Journal of Physical Chemistry Letters N2 - 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. KW - Hematite KW - Atomic Layer deposition KW - Photoelectrode KW - electro-catalysis KW - TMA KW - efficiency enhancement Y1 - 2014 U6 - https://doi.org/10.1021/jz501751w VL - 5 IS - 20 SP - 3582 EP - 3587 ER - TY - GEN A1 - Kramm, Ulrike Ingrid A1 - Lefèvre, Michel A1 - Bogdanoff, Peter A1 - Schmeißer, Dieter A1 - Dodelet, Jean-Pol T1 - Analyzing Structural Changes of Fe-N-C Cathode Catalysts in PEM Fuel Cell by Mößbauer Spectroscopy of Complete Membrane-Electrode-Assemblies T2 - The Journal of Physical Chemistry Letters N2 - The applicability of analyzing by Mößbauer 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 Mößbauer 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 Mößbauer 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. KW - iron-based catalyst KW - iron−nitrogen−carbon catalyst KW - non-noble metal catalyst KW - nonprecious metal catalyst KW - oxygen reduction reaction KW - ORR KW - polymer electrolyte membrane fuel cell KW - PEM-FC KW - degradation Y1 - 2014 U6 - https://doi.org/10.1021/jz501955g SN - 1948-7185 VL - 2014 IS - 5 SP - 3750 EP - 3756 ER - TY - GEN A1 - Szakacs, Csaba E. A1 - Lefèvre, Michel A1 - Kramm, Ulrike Ingrid A1 - Dodelet, Jean-Pol A1 - Vidal, François T1 - A density functional theory study of catalytic sites for oxygen reduction in Fe/N/C catalysts used in H2/O2 fuel cells T2 - Physical Chemistry Chemical Physics N2 - The oxygen reduction catalytic activity of carbon-supported FeN4 moieties bridging micropores between two graphene sheets was investigated by density functional theory (DFT). Based on the FeN2+2/C structure proposed earlier by our group, two types of FeN2+2/C structures were considered: one mostly planar and one in which the Fe ion is significantly displaced out of the graphitic plane. A structure in which the FeN4 moiety is embedded in an extended graphene sheet (FeNpyri4/C) was also considered. In addition, we have investigated the influence of an axial pyridine group approaching the Fe centre. The formation energy is lowest for the planar FeN2+2/C structure. The overall downhill behaviour of the relative free energy vs. the reaction step suggests that most structures have catalytic activity near zero potential. This conclusion is further supported by calculations of the binding energies of adsorbed O2 and H2O and of the O–O bond lengths of adsorbed O2 and OOH. The side-on interaction of adsorbed O2 is preferred over the end-on interaction for the three basic structures without the axial pyridine. The pyridine coordination produces a stronger binding of O2 for the planar FeN2+2/C and the FeNpyri4/C structures as well as a dominant end-on interaction of O2. The energy levels of the planar FeN2+2/C structure with and without the pyridine ligand are nearly equal for iron spin states S = 1 and S = 2, suggesting that both configurations are formed with similar concentration during the preparation process, as also previously found for two of the iron sites by Mössbauer spectroscopy experiments. KW - density functional theory (DFT) KW - iron-based catalyst KW - iron−nitrogen−carbon catalyst KW - non-noble metal catalyst KW - oxygen reduction reaction (ORR) KW - polymer electrolyte membrane fuel cell (PEM-FC) Y1 - 2014 U6 - https://doi.org/10.1039/C3CP55331K SN - 1463-9076 SN - 1463-9084 VL - 2014 IS - 16 SP - 13654 EP - 13661 ER - TY - GEN A1 - Indra, Arindam A1 - Menezes, Prashanth W. A1 - Sahraie, Nastaran Ranjbar A1 - Bergmann, Arno A1 - Das, Chittaranjan A1 - Tallarida, Massimo A1 - Schmeißer, Dieter A1 - Strasser, Peter A1 - Driess, Matthias T1 - Unification of Catalytic Water Oxidation and Oxygen Reduction Reactions: Amorphous Beat Crystalline Cobalt Iron Oxides T2 - Journal of the American Chemical Society N2 - 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. KW - photochemical KW - electrochemical KW - catalyst KW - water oxidation reaction KW - oxygen reduction reaction KW - cobalt iron oxides KW - control of crytallinity Y1 - 2014 U6 - https://doi.org/10.1021/ja509348t SN - 1520-5126 SN - 0002-7863 VL - 2014 IS - 136 SP - 17530 EP - 17536 ER - TY - GEN A1 - Das, Chittaranjan A1 - Henkel, Karsten A1 - Tallarida, Massimo A1 - Schmeißer, Dieter A1 - Gargouri, Hassan A1 - Kärkkänen, Irina A1 - Schneidewind, Jessica A1 - Gruska, Bernd A1 - Arens, Michael T1 - Thermal and plasma enhanced atomic layer deposition of TiO2: Comparison of spectroscopic and electric properties T2 - Journal of Vacuum Science and Technology A N2 - 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. KW - titanium oxide (TiO2) KW - atomic layer deposition KW - plasma enhanced atomic layer deposition KW - synchrotron radiation photoelectron spectroscopy (SR-PES) KW - x-ray absorption spectroscopy KW - capacitance-voltage (CV) KW - current-voltage (IV) KW - ellipsometry KW - in-gap states Y1 - 2015 U6 - https://doi.org/10.1116/1.4903938 SN - 1520-8559 SN - 0734-2101 VL - 2015 IS - 33 SP - 01A144-1 EP - 01A144-8 ER - TY - THES A1 - Städter, Matthias T1 - Untersuchungen zu Fanoresonanzen in der resonanten Photoelektronenspektroskopie N2 - Im Mittelpunkt der vorliegenden Arbeit stehen die Untersuchung von Fanointerferenzen innerhalb der wissenschaftlichen Methode der resonanten Photoelektronenspektroskopie. Basis dieser Methode ist die Interpretation aus dem Festkörper emittierter Elektronen. Die detektierten Elektronen können dabei aus direkten Photoemissionen oder Deaktivierungsprozessen (Spectator-/Participator-Zerfälle) nach resonanten Anregungen von Rumpfelektronen stammen. Führen beide Prozesse zum selben Systemendzustand, können die emittierten Elektronen interferieren, was sich in der Ausprägung eines charakteristischen Intensitätsprofils, dem Fano-Profil, äußert. Die Form des Intensitätsprofils kann dabei über den Fanoparameter q beschrieben werden. Im Rahmen dieser Arbeit erfolgte die Diskussion von Fanointerferenzen an organischen (HOPG, Graphenflocken) und oxidischen (CuO, In2O3, SiO2) Materialsystemen. Im HOPG und den untersuchten Graphenflocken konnten mittels der Analyse der Fanoprofile exzitonische Zustände innerhalb der Bandlücke nachgewiesen werden. Durch die Untersuchungen am CuO konnte die Variation des Fanoparameters in Abhängigkeit vom Grundzustand des Systems gezeigt werden. Die für die untersuchten In2O3 Einristalle beobachteten Interferenzen beruhen auf der Existenz besetzter Zustände an der Fermienergie. Abschließend konnte eine Korrelation des jeweils auftretenden Fanoparameters mit den beobachteten multi-hole-Auger-Zerfällen nachgewiesen werden. KW - Fano KW - Fanointerferenzen KW - Festkörperphysik KW - In-gap Zustände KW - Resonante Photoelektronenspektroskopie Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:co1-opus4-31860 UR - http://opus4.kobv.de/opus4-btu/frontdoor/index/index/docId/3186 ER - TY - GEN A1 - Garain, Samiran A1 - Sinha, Tridib Kumar A1 - Adhikary, Prakriti A1 - Henkel, Karsten A1 - Sen, Shrabanee A1 - Ram, Shanker A1 - Sinha, Chittaranjan A1 - Schmeißer, Dieter A1 - Mandal, Dipankar T1 - Self-Poled Transparent and Flexible UV Light-Emitting Cerium Complex–PVDF Composite: A High-Performance Nanogenerator T2 - ACS Applied Materials & Interfaces N2 - 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. KW - PVDF KW - electroactive phase KW - nanogenerator KW - cerium charge transfer complex KW - piezoelectric energy harvester KW - UV-emitter Y1 - 2015 U6 - https://doi.org/10.1021/am507522r SN - 1944-8244 SN - 1944-8252 VL - 2015 IS - 7 SP - 1298 EP - 1307 ER - TY - CHAP A1 - Krenek, Radim A1 - Cimrova, Vera A1 - Seifarth, Olaf A1 - Bocharova, Vera A1 - Gorodyska, Ganna A1 - Sidorenko, Alexander A1 - Schmeißer, Dieter A1 - Stamm, Manfred T1 - Electronic Properties of Metals Embedded into Porous Polymeric Nanotemplates T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 41 N2 - 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. Y1 - 2006 UR - http://www.dpg-verhandlungen.de/year/2006/conference/dresden/part/cpp/session/25/contribution/2 SN - 0420-0195 SP - S. 108 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Tallarida, Massimo A1 - Sohal, Rakesh A1 - Schmeißer, Dieter T1 - Electronic properties of the 2x1 3C-SiC surface reconstruction studied with resonant photoemission T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41 N2 - 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. Y1 - 2006 UR - http://www.dpg-verhandlungen.de/year/2006/conference/dresden/part/hl/session/5/contribution/2 SN - 0420-0195 SP - S. 239 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Wehner, Stefan A1 - Hofmann, Patrick A1 - Schmeißer, Dieter A1 - Brand, Helmut R. A1 - Küppers, Jürgen T1 - Pattern formation in the CO + O reaction on Ir(111) surfaces under the influence of noise T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41 N2 - 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. Y1 - 2006 UR - http://www.dpg-verhandlungen.de/year/2006/conference/dresden/part/syss/session/1/contribution/9 SN - 0420-0195 SP - S. 708 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Wehner, Stefan A1 - Hoffmann, Patrick A1 - Schmeißer, Dieter A1 - Brand, Helmut R. A1 - Küppers, Jürgen T1 - CO oxidation on Ir(111) surfaces: consequences of anisotropic diffusion and noise T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41 N2 - 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. Y1 - 2006 UR - http://www.dpg-verhandlungen.de/year/2006/conference/dresden/part/o/session/14/contribution/37 SN - 0420-0195 SP - S. 475 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Seime, Bernd A1 - Henkel, Karsten A1 - Paloumpa, Ioanna A1 - Müller, Klaus A1 - Schmeißer, Dieter T1 - Buffer layer investigation of MFIS stacks with an organic ferroelectric layer T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 42 N2 - 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). Y1 - 2007 UR - http://www.dpg-verhandlungen.de/year/2007/conference/regensburg/part/df/session/11/contribution/1 SN - 0420-0195 SP - S. 216 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Mandal, Dipankar A1 - Müller, Klaus A1 - Seifarth, Olaf A1 - Hoffman, Patrick A1 - Henkel, Karsten A1 - Schmeißer, Dieter T1 - Study of reactions at the interface P(VDF/TrFE)/Al and P(VDF/TrFE)/PEDOT:PSS T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 42 N2 - 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). Y1 - 2007 UR - http://www.dpg-verhandlungen.de/year/2007/conference/regensburg/part/syoe/session/8/contribution/18 SN - 0420-0195 SP - S. 797 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Henkel, Karsten A1 - Sohal, Rakesh A1 - Torche, Mohamed A1 - Schwiertz, Carola A1 - Burkov, Yevgen A1 - Schmeißer, Dieter T1 - PrOx/AlON stacks as a high-k candidate on SiC T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 42 N2 - 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). Y1 - 2007 UR - http://www.dpg-verhandlungen.de/year/2007/conference/regensburg/part/df/session/10/contribution/8 SN - 0420-0195 SP - S. 215 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Müller, Sebastian A1 - Schmeißer, Dieter T1 - The initial stages of Chromium growth on Titaniumdioxide-Investigations using synchrotron radiation T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 42 N2 - 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)Oberflächen, PhD Thesis, University of Stuttgart, 2002 Y1 - 2007 UR - http://www.dpg-verhandlungen.de/year/2007/conference/regensburg/part/o/session/33/contribution/8 SN - 0420-0195 SP - S. 598 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Nielsen, Karl-Wilhelm A1 - Bauer, Sebastian A1 - Senn, Konrad A1 - Goennenwein, Sebastian T. B. A1 - Opel, Matthias A1 - Cezar, Julio C. A1 - Schmeißer, Dieter A1 - Gross, Rudolf T1 - X-ray magnetic circulardichroism in cobalt-doped ZnO T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 42 N2 - 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. Y1 - 2007 UR - http://www.dpg-verhandlungen.de/year/2007/conference/regensburg/part/ma/session/15/contribution/13 SN - 0420-0195 SP - S. 454 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Kachel, Krzysztof A1 - Richter, Matthias A1 - Philip, Shine A1 - Paloumpa, Ioanna A1 - Müller, Klaus A1 - Schmeißer, Dieter T1 - Performance of organic solar cells with a ferroelectric component T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45 N2 - 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. Y1 - 2010 UR - http://www.dpg-verhandlungen.de/year/2010/conference/regensburg/part/cpp/session/27/contribution/6 SN - 0420-0195 SP - S. 153 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Klocek, Jolanta A1 - Friedrich, Daniel A1 - Zagorodniy, Kostyantyn A1 - Schmeißer, Dieter T1 - Spectroscopic investigations of interaction between C60 fullerene and nitrogen atom from amine group T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45 N2 - 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. Y1 - 2010 UR - http://www.dpg-verhandlungen.de/year/2010/conference/regensburg/part/ds/session/23/contribution/1 SN - 0420-0195 SP - S. 231 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Kolanek, Krzysztof A1 - Karavaev, Konstantin A1 - Tallarida, Massimo A1 - Schmeißer, Dieter T1 - Atomic layer deposition of HfO2 onto SiO2 substrates investigated in-situ by non-contact UHV/AFM T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45 N2 - 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. Y1 - 2010 SN - 0420-0195 SP - S. 248 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Michling, Marcel A1 - Tallarida, Massimo A1 - Kolanek, Krzysztof A1 - Schmeißer, Dieter T1 - In-situ EELS and UPS measurements on HfO2 ALD layers T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45 N2 - 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. Y1 - 2010 UR - http://www.dpg-verhandlungen.de/year/2010/conference/regensburg/part/ds/session/24/contribution/5 SN - 0420-0195 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Müller, Sebastian A1 - Schmeißer, Dieter T1 - Synchrotron radiation spectroscopy studies of the initial interaction between cobalt and titanium dioxide T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45 N2 - 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. Y1 - 2010 SN - 0420-0195 SP - S. 652 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Philip, Shine A1 - Richter, Matthias A1 - Friedrich, Daniel A1 - Paloumpa, Ioanna A1 - Müller, Klaus A1 - Schmeißer, Dieter T1 - Spectroscopic investigations of P3HT/PCBM films for organic BHJ solar cells T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45 N2 - 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. Y1 - 2010 SN - 0420-0195 SP - S. 153 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Richter, Matthias A1 - Friedrich, Daniel A1 - Philip, Shine A1 - Paloumpa, Ioanna A1 - Müller, Klaus A1 - Schmeißer, Dieter T1 - Study of P3HT/PCBM based films by NEXAFS T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45 N2 - 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. Y1 - 2010 UR - http://www.dpg-verhandlungen.de/year/2010/conference/regensburg/part/df/session/7/contribution/4 SN - 0420-0195 SP - S. 194 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Schmidt, Stephan A1 - Schmeißer, Dieter T1 - Cobalt/nickel mixed oxides - cathode materials for Li-Ion-Batteries T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45 N2 - 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. Y1 - 2010 UR - http://www.dpg-verhandlungen.de/year/2010/conference/regensburg/part/o/session/45/contribution/6 SN - 0420-0195 SP - S. 596 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Starzyk, Łukasz A1 - Tallarida, Massimo A1 - Schmeißer, Dieter T1 - Electrically optimized high-κ metal gate MOSFET by specific modification of the band alignment T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45 N2 - 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. Y1 - 2010 UR - http://www.dpg-verhandlungen.de/year/2010/conference/regensburg/part/ds/session/23/contribution/3 SN - 0420-0195 SP - S. 231 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Wyrodek, Jakub A1 - Tallarida, Massimo A1 - Schmeißer, Dieter A1 - Weisheit, Martin T1 - Determination of interfacial layers in high - k ALD nanolaminate materials by ARXPS and SRXPS measurements T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45 N2 - 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. Y1 - 2010 UR - http://www.dpg-verhandlungen.de/year/2010/conference/regensburg/part/ds/session/24/contribution/6 SN - 0420-0195 SP - S. 232 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Bergholz, Matthias A1 - Schmeißer, Dieter T1 - Band gap determination of thin Praseodymiumoxide layers on Aluminiumoxynitride films T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43 N2 - 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 Ångström, 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. Y1 - 2008 UR - http://www.dpg-verhandlungen.de/year/2008/conference/berlin/part/ds/session/23/contribution/4 SN - 0420-0195 SP - S. 243 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Burkov, Yevgen A1 - Henkel, Karsten A1 - Schmeißer, Dieter T1 - X-ray photoemission spectroscopy of Aluminium Oxynitride on Si(001) and the rise as buffer layers T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43 N2 - 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. Y1 - 2008 UR - http://www.dpg-verhandlungen.de/year/2008/conference/berlin/part/ds/session/23/contribution/5 SN - 0420-0195 SP - S. 243 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Henkel, Karsten A1 - Seime, Bernd A1 - Paloumpa, Ioanna A1 - Müller, Klaus A1 - Schmeißer, Dieter T1 - C(V) and C(t) measurements on MFIS structures consisting P[VDF/TrFE] as ferroelectric layer T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43 N2 - 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). Y1 - 2008 UR - http://www.dpg-verhandlungen.de/year/2008/conference/berlin/part/sysa/session/4/contribution/7 SN - 0420-0195 SP - S. 828 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Karavaev, Konstantin A1 - Tallarida, Massimo A1 - Schmeißer, Dieter A1 - Zschech, Ehrenfried T1 - In-situ ALD growth of Hafnium oxide films T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43 N2 - 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. Y1 - 2008 UR - http://www.dpg-verhandlungen.de/year/2008/conference/berlin/part/ds/session/23/contribution/12 SN - 0420-0195 SP - S. 244 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Mandal, Dipankar A1 - Müller, Klaus A1 - Schmeißer, Dieter T1 - Dipole orientation of the P[VDF-TrFE] co-polymer films: A NEXAFS study T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43 N2 - 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). Y1 - 2008 UR - http://www.dpg-verhandlungen.de/year/2008/conference/berlin/part/sysa/session/5/contribution/76 SN - 0420-0195 SP - S. 840 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Müller, Klaus A1 - Mandal, Dipankar A1 - Henkel, Karsten A1 - Paloumpa, Ioanna A1 - Schmeißer, Dieter T1 - Interface reactions of ferroelectric copolymer layers with different electrode materials T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43 N2 - 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. Y1 - 2008 UR - http://www.dpg-verhandlungen.de/year/2008/conference/berlin/part/sysa/session/5/contribution/16 SN - 0420-0195 SP - S. 830 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Müller, Sebastian A1 - Schmeißer, Dieter T1 - Direct Observation of d2L2 Charge Transfer States in TiO2 thin films by Resonant Photoelectron Spectroscopy T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43 N2 - 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. Y1 - 2008 UR - http://www.dpg-verhandlungen.de/year/2008/conference/berlin/part/o/session/32/contribution/3 SN - 0420-0195 SP - S. 592 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Tallarida, Massimo A1 - Karavaev, Konstantin A1 - Schmeißer, Dieter A1 - Zschech, Ehrenfried T1 - Photoemission and absorption spectroscopy for in situ investigations of the ALD growth T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43 N2 - 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. Y1 - 2008 UR - http://www.dpg-verhandlungen.de/year/2008/conference/berlin/part/ds/session/22/contribution/5 SN - 0420-0195 SP - S. 242 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Opel, Matthias A1 - Nielsen, Karl-Wilhelm A1 - Bauer, Sebastian A1 - Goennenwein, Sebastian T. B. A1 - Gross, Rudolf A1 - Cezar, Julio C. A1 - Schmeißer, Dieter A1 - Simon, Jürgen A1 - Mader, Werner T1 - Ferromagnetism and magnetic clusters in cobalt-doped ZnO T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43 N2 - 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. Y1 - 2008 UR - http://www.dpg-verhandlungen.de/year/2008/conference/berlin/part/ma/session/3/contribution/6 SN - 0420-0195 SP - S. 430 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Lazareva, I. A1 - Koval, Yuri A1 - Müller, P. A1 - Paloumpa, Ioanna A1 - Müller, Klaus A1 - Schmeißer, Dieter T1 - Field effect transistor of graphitized polyimide with P(VDF-TrFE) as gate insulator T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43 N2 - 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. Strömsdörfer, P. Müller, Appl. Phys. Lett. 90, 262108 (2007) Y1 - 2008 UR - http://www.dpg-verhandlungen.de/year/2008/conference/berlin/part/df/session/11/contribution/6 SN - 0420-0195 SP - S. 195 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Bergholz, Matthias A1 - Sohal, Rakesh A1 - Schmeißer, Dieter T1 - ELS to determine the band gap of thin dielectric layers T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41 N2 - 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. Y1 - 2006 UR - http://www.dpg-verhandlungen.de/year/2006/conference/dresden/part/ds/session/8/contribution/2 SN - 0420-0195 SP - S. 156 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Henkel, Karsten A1 - Torche, Mohamed A1 - Schwiertz, Carola A1 - Paloumpa, Ioanna A1 - Sohal, Rakesh A1 - Müller, Klaus A1 - Schmeißer, Dieter T1 - Inorganic and organic layers for high-k and organic memory applications T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41 N2 - 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. Y1 - 2006 UR - http://www.dpg-verhandlungen.de/year/2006/conference/dresden/part/df/session/1/contribution/4 SN - 0420-0195 SP - S. 127 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Müller, Klaus A1 - Henkel, Karsten A1 - Paloumpa, Ioanna A1 - Schmeißer, Dieter T1 - P(VDF/TrFE) as ferroelectric insulation layer for organic field effect transistors T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 41 N2 - 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. Y1 - 2006 UR - http://www.dpg-verhandlungen.de/year/2006/conference/dresden/part/cpp/session/23/contribution/28 SN - 0420-0195 SP - S. 101 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Hoffmann, Patrick A1 - Schmeißer, Dieter A1 - Himpsel, Franz J. A1 - Engelmann, Hans-Jürgen A1 - Zschech, Ehrenfried A1 - Stegmann, Heiko A1 - Denlinger, Jonathan D. T1 - Characterization of Chemical Bonding in Low-K Dielectric Materials for Interconnect Isolation: XAS and EELS Study T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 41 N2 - 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. Y1 - 2006 SN - 0420-0195 SP - S. 156 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Müller, P. A1 - Chowdhury, F. A1 - Dremov, V. A1 - Koval, Yuri A1 - Lichtenberg, F. A1 - Müller, S. A1 - Schmeißer, Dieter A1 - Pentcheva, R. T1 - Resistive memory switching in perovskite-derivative single crystals T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43 N2 - 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. Y1 - 2008 UR - http://www.dpg-verhandlungen.de/year/2008/conference/berlin/part/synf/session/1/contribution/11 SN - 0420-0195 SP - S. 818 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Seifarth, Olaf A1 - Walczyk, Christian A1 - Lupina, Grzegorz A1 - Dabrowski, Jaroslaw A1 - Weidner, Günter A1 - Zaumseil, Peter A1 - Schmeißer, Dieter A1 - Storck, Peter A1 - Müssig, Hans-Joachim A1 - Schroeder, Thomas T1 - On the electronic and dielectric characterisation of thin cubic PrO2 layers on Silicon T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43 N2 - 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. Y1 - 2008 UR - http://www.dpg-verhandlungen.de/year/2008/conference/berlin/part/df/session/12/contribution/6 SN - 0420-0195 SP - S. 196 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Friedrich, Daniel A1 - Michling, Marcel A1 - Klocek, Jolanta A1 - Schmeißer, Dieter A1 - Avdoshenko, Stas A1 - Chumakov, Dmytro A1 - Zschech, Ehrenfried T1 - Study of C60 based films formation by NEXAFS T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44 N2 - 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. Y1 - 2009 SN - 0420-0195 SP - S. 145 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Karavaev, Konstantin A1 - Tallarida, Massimo A1 - Schmeißer, Dieter T1 - Evolution of the interfacial layer during the atomic layer deposition of HfO2 on Si/SiO2 substrates T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44 N2 - 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. Y1 - 2009 SN - 0420-0195 SP - S. 160 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Kolanek, Krzysztof A1 - Karavaev, Konstantin A1 - Tallarida, Massimo A1 - Schmeißer, Dieter T1 - In-situ investigations of the atomic layer deposition of HfO2 with UHV/AFM T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44 N2 - 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. Y1 - 2009 UR - http://www.dpg-verhandlungen.de/year/2009/conference/dresden/part/ds/session/11/contribution/6 SN - 0420-0195 SP - S. 160 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Kraatz, Matthias A1 - Schmeißer, Dieter A1 - Zschech, Ehrenfried A1 - Ho, Paul S. T1 - Electromigration simulation for on-chip Cu interconnects T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44 N2 - 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 Y1 - 2009 UR - http://www.dpg-verhandlungen.de/year/2009/conference/dresden/part/ds/session/13/contribution/4 SN - 0420-0195 SP - S. 161 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Michling, Marcel A1 - Friedrich, Daniel A1 - Schmeißer, Dieter A1 - Koval, Yuri A1 - Müller, Paul T1 - Study of polyimide after graphitization with low-energy Ar+ Ion irradiation by NEXAFS T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44 N2 - 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. Y1 - 2009 UR - http://www.dpg-verhandlungen.de/year/2009/conference/dresden/part/df/session/15/contribution/5 SN - 0420-0195 SP - S. 147 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Müller, Sebastian A1 - Schmeißer, Dieter T1 - Investigation of ultra-thin Chromium layers on Titanium Dioxide by resonant photoemission T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44 N2 - 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. Y1 - 2009 UR - http://www.dpg-verhandlungen.de/year/2009/conference/dresden/part/o/session/3/contribution/5 SN - 0420-0195 SP - S. 453 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Richter, Matthias A1 - Müller, Klaus A1 - Philip, Shine A1 - Paloumpa, Ioanna A1 - Henkel, Karsten A1 - Schmeißer, Dieter T1 - Temperature dependence of organic solar cell parameters T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 44 N2 - 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. Y1 - 2009 UR - http://www.dpg-verhandlungen.de/year/2009/conference/dresden/part/syop/session/4/contribution/2 SN - 0420-0195 SP - S. 671 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Tallarida, Massimo A1 - Karavaev, Konstantin A1 - Kolanek, Krzysztof A1 - Schmeißer, Dieter T1 - Basics of the atomic layer deposition of HfO2 onto Si/SiO2 substrates: in-situ investigations with XPS, XAS and UHV-AFM T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 44 N2 - 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. Y1 - 2009 UR - http://www.dpg-verhandlungen.de/year/2009/conference/dresden/part/ds/session/11/contribution/4 SN - 0420-0195 SP - S. 159 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Tallarida, Massimo A1 - Karavaev, Konstantin A1 - Kolanek, Krzysztof A1 - Schmeißer, Dieter T1 - In-situ experimental approach to the study of atomic layer deposition with atomic force microscope, X-ray photoelectron and X-ray absorption spectroscopy T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 44 N2 - 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. Leskelä, M. Ritala, Thin Solid Films, 409, 138, 2002; [2] M. Tallarida, K. Karavaev, and D. Schmeisser, J. Appl. Phys. 104, 064116 (2008). Y1 - 2009 UR - http://www.dpg-verhandlungen.de/year/2009/conference/dresden/part/ds/session/26/contribution/15 SN - 0420-0195 SP - S.176 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Seifarth, Olaf A1 - Walczyk, Christian A1 - Lupina, Grzegorz A1 - Zaumseil, Peter A1 - Schmeißer, Dieter A1 - Müssig, Hans-Joachim A1 - Schroeder, Thomas T1 - The electronic band diagram of thin PrO2(111) / Pr-silicate buffers on Si(111) and its relevance to dielectric properties T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44 N2 - 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. Y1 - 2009 UR - http://www.dpg-verhandlungen.de/year/2009/conference/dresden/part/df/session/6/contribution/5 SN - 0420-0195 SP - S. 136 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Friedrich, Daniel A1 - Michling, Marcel A1 - Schmeißer, Dieter A1 - Koval, Yuri A1 - Müller, Paul T1 - Characterization of ion beam modified polyimide layers T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45 N2 - 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. Y1 - 2010 UR - http://www.dpg-verhandlungen.de/year/2010/conference/regensburg/part/ds/session/38/contribution/10 SN - 0420-0195 SP - S. 247 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Dudek, Peter A1 - Lupina, Grzegorz A1 - Kozłowski, Grzegorz A1 - Dabrowski, Jarek Marek A1 - Lippert, Gunther A1 - Müssig, Hans-Joachim A1 - Schmeißer, Dieter A1 - Schroeder, Thomas T1 - Band structure and electrical properties of MBE grown HfO2 - based alkaline earth perovskites T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45 N2 - 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. Y1 - 2010 UR - http://www.dpg-verhandlungen.de/year/2010/conference/regensburg/part/ds/session/24/contribution/4 SN - 0420-0195 SP - S. 232 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Friedrich, Daniel A1 - Koval, Yuri A1 - Müller, Paul A1 - Schmeißer, Dieter T1 - Electronic structure of thin spin-coated polyimide layers T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46 N2 - 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. Y1 - 2011 UR - http://www.dpg-verhandlungen.de/year/2011/conference/dresden/part/ds/session/63/contribution/3 SN - 0420-0195 SP - S. 311 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Hoffmannbeck, David A1 - Richter, Matthias A1 - Städter, Matthias A1 - Paloumpa, Ioanna A1 - Henkel, Karsten A1 - Schmeißer, Dieter T1 - Spectroscopic and microscopic characterization of potential catalysts for the hydrogenation of CO2 T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46 N2 - 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. Y1 - 2011 UR - http://www.dpg-verhandlungen.de/year/2011/conference/dresden/part/o/session/60/contribution/123 SN - 0420-0195 SP - S. 483 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Kraatz, Matthias A1 - Zhang, Lijuan A1 - Schmeißer, Dieter A1 - Zschech, Ehrenfried A1 - Ho, Paul S. T1 - Statistical Analysis of Computer-simulated On-Chip Interconnect Electromigration Lifetimes under the Influence of Microstructure and Strengthened Top Interface T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46 N2 - 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. Y1 - 2011 UR - http://www.dpg-verhandlungen.de/year/2011/conference/dresden/part/ds/session/7/contribution/2 SN - 0420-0195 SP - S. 292 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Mbua, Roy A1 - Müller, Klaus A1 - Richter, Matthias A1 - Henkel, Karsten A1 - Paloumpa, Ioanna A1 - Schmeißer, Dieter A1 - Kramm, Ulricke T1 - Investigation of new Catalysts for PEM Fuel Cells T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46 N2 - 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. Y1 - 2011 UR - http://www.dpg-verhandlungen.de/year/2011/conference/dresden/part/o/session/60/contribution/119 SN - 0420-0195 SP - S. 483 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Michling, Marcel A1 - Kolanek, Krzysztof A1 - Schmeißer, Dieter A1 - Tallarida, Massimo T1 - A growth model for the HfO2 ALD process T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46 N2 - 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. Y1 - 2011 UR - http://www.dpg-verhandlungen.de/year/2011/conference/dresden/part/ds/session/12/contribution/1 SN - 0420-0195 SP - S. 294 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Philip, Shine A1 - Martinez, Elias A1 - Müller, Klaus A1 - Kunst, Marinus A1 - Schmeißer, Dieter T1 - Time resolved microwave conductivity measurements of Bulk Heterojunction solar cells T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46 N2 - 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). Y1 - 2011 UR - http://www.dpg-verhandlungen.de/year/2011/conference/dresden/part/ds/session/42/contribution/31 SN - 0420-0195 SP - S. 301 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Richter, Matthias A1 - Schmeißer, Dieter T1 - Electronic structure and optical properties of P3HT - Evidence of 2D-polarons in P3HT T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46 N2 - 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 Y1 - 2011 UR - http://www.dpg-verhandlungen.de/year/2011/conference/dresden/part/ds/session/64/contribution/3 SN - 0420-0195 SP - S. 311 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Schmidt, Stefan A1 - Schmeißer, Dieter T1 - Localized gap states in cobalt/nickel mixed oxides T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46 N2 - 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. Y1 - 2011 UR - http://www.dpg-verhandlungen.de/year/2011/conference/dresden/part/o/session/69/contribution/2 SN - 0420-0195 SP - S. 486 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Tallarida, Massimo A1 - Deßmann, Nils A1 - Städter, Matthias A1 - Friedrich, Daniel A1 - Michling, Marcel A1 - Schmeißer, Dieter T1 - Atomic layer deposition of TiO T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46 N2 - 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. Y1 - 2011 UR - http://www.dpg-verhandlungen.de/year/2011/conference/dresden/part/ds/session/12/contribution/2 SN - 0420-0195 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Das, Chittaranjan A1 - Städter, Matthias A1 - Tallarida, Massimo A1 - Schmeißer, Dieter T1 - Investigation of Linear Dichroism in ALD layers of TiO2 T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47 N2 - 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. Y1 - 2012 UR - http://www.dpg-verhandlungen.de/year/2012/conference/berlin/part/ds/session/44/contribution/59 SN - 0420-0195 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Müller, Klaus A1 - Hoffmannbeck, David A1 - Kirner, Georg A1 - Städter, Matthias A1 - Schmeißer, Dieter T1 - CO2-Methanation by Catalytic Conversion T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - 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). Y1 - 2012 UR - http://www.dpg-verhandlungen.de/year/2012/conference/berlin/part/ds/session/37/contribution/45 SN - 0420-0195 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER -