@inproceedings{HenkelPaloumpaMuelleretal., author = {Henkel, Karsten and Paloumpa, Ioanna and M{\"u}ller, Klaus and Schmeißer, Dieter}, title = {P(VDF/TrFE) as a ferroelectric dielectric for Organic Field effect Transistors in MFIS structure}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {MFIS structures consisting of metal, ferroelectric poly[vinylidene fluoride trifluoroethylene](P[VDF/TrFE]), insulator, semiconductor (Si) are fabricated and the influence of the polarization of the P(VDF/TrFE) on the CV characteristics of these structures is investigated. We find a characteristic ferroelectric hysteresis in the CV curves upon increasing the voltage scan window (e.g.-U...U,U=6...30V, |UP(VDF/TrFE)|≤15V, dP(VDF/TrFE)=300 nm). A writing process with adequate electric fields causes large shifts in the flatband voltage ( Δ UFB>4V for the quoted example before) which are stable over days. We report on our investigations which focus on the switching behavior by varying the parameters like polymer thickness, writing field strength and time, long time stability, reversing voltage and insulating material (SiO2, PMMA (Polymethylmetacrylate)). This material combination is favorable for transfer into our full organic concept of field effect transistors for application as a nondestructive readout memory (NDRO) cell.}, language = {en} } @inproceedings{MuellerBurkovSchmeisser, author = {M{\"u}ller, Klaus and Burkov, Yevgen and Schmeißer, Dieter}, title = {Surface potential profiling on organic thin film transistors by photoemission-electron-microscopy (PEEM)}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Surface potential imaging with Photoemission-electron-microskopy (PEEM) in high lateral resolution is introduced as a new tool for the characterisation of organic transistor structures. We use source-drain- electrode structures of different organic materials like carbon-black or graphite plotted on a printing foil. Semiconducting regioregular Poly(3-Hexylthiophene-2,5-diyl) (P3HT) was deposited by spin coating. For our measurements we used radiation of a standard high pressure Hg-lamp (4,9 eV) and synchrotron radiation at the BESSYII-U49/2 beam line. In contrast to Kelvin-AFM measurements of the surface potential, PEEM enables a simultaneous analysis of chemical composition by photoelectron spectroscopy. UPS, for example, at zero potential gives information on chemical homogeneity of the organic semiconductor in lateral resolution. PEEM images at applied voltages, compared with UPS-spectra, gives informations on doping profiles in the semiconductor, for example. In conclusion, PEEM should be a complementary method for characterisation of the surface potential with Kelvin-AFM. In addition, PEEM gives opportunities for measurements of chemical composition in the working state of the transistor (applied voltages).}, language = {en} } @inproceedings{MuellerPaloumpaHenkeletal., author = {M{\"u}ller, Klaus and Paloumpa, Ioanna and Henkel, Karsten and Schmeißer, Dieter}, title = {Organic Field Effect Transistors with polymer high-k dielectric insulator}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Organic field effect transistors consisting of the copolymer poly(vinylidene fluoridetrifluoroethylene) (P(VDF-TrFE)) and P3HT (poly(3-hexlythiophene)) as active layer have been fabricated. The influence of P(VDF-TrFE) on the transconductance of organic field effect transistors was investigated and enhanced gate effects are observed compared to similar transistors with PMMA (Polymethylmetacrylate) as gate dielectric. Due to the high dielectric constant of P(VDF-TrFE) (DK=12) an operation voltage smaller than for a conventional organic dielectric like PMMA (DK=3.3) was observed. The thickness of the spincoated dielectric layers is in the range of 2microns and in consequence, no significant hysteresis was found, a prerequisite for transistor operation.}, language = {en} } @inproceedings{GeussMuellerPaloumpaetal., author = {Geuss, Markus and M{\"u}ller, Klaus and Paloumpa, Ioanna and Schmeißer, Dieter}, title = {Surface Potential profiling on operating full organic thin film transistors by Kelvin probe force microscopy}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Kelvin-AFM is employed to study all polymer organic thin film transistors which are promising candidates for low cost - low performance applications like active matrix displays, sensors or single-serving devices. We use bottom contact source-drain- electrode structures of different organic materials like carbon-black or graphite plotted on a printing foil. Semiconducting regioregular Poly(3-Hexylthiophene-2,5-diyl) (P3HT) was subsequently deposited by spin coating. Surface potential profiles across the transistor channel were measured by Kelvin-AFM for various source-drain potential differences and signs. We found that contact resistances cause characteristic steps in the surface potential near the channel edges which vary with the electrode material. Furthermore, nonlinearities appear in the potential gradient which possibly give evidence for lateral inhomogeneities of the carrier mobilities. In summary, surface potential imaging with high lateral resolution ( approx. 100 nm) is introduced as a powerful tool for the characterisation of the transistor performance and the selection of suitable low cost electrode materials.}, language = {en} } @inproceedings{TorcheSchmeisser, author = {Torche, Mohamed and Schmeißer, Dieter}, title = {The interaction of Al, Au, Ag, and Ti metal contacts with Pr2O3 thin films}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Pr2O3 is one of the promising high-k oxides desirable to replace SiO2 for the sub-100nm field-effect transistors (FETs) and dynamic random access memory (DRAM) capacitors. Here we focus on the metallic contacts used for the MOS and MIM based structures. With the thickness of Pr2O3 being around 3nm the metal interaction is crucial to avoid a reduction of the dielectric properties by metal percolation, crack filling or diffusion processes. We use XPS and SRPS to study the initial interaction as well as the thermal stability of metals (Al, Ag, Au, and Ti) on Pr2O3 films. We show that Al, Ag, Au form initial metallic layer which react already at temperatures around 300∘C. In contrast, Ti is found to be more stable than the other metals. We determine the formation of Ti-oxides at the Ti / Pr2O3 interface and its thermal stability. Ti is found to build a good diffusion barrier between the oxide and the metal.}, language = {en} } @inproceedings{SeifarthBurkovSchmeisseretal., author = {Seifarth, Olaf and Burkov, Yevgen and Schmeißer, Dieter and Sydorenko, Alexander and Krenek, Radim and Stamm, Manfred}, title = {Photoelectron spectroscopy and microscopy on magnetic nano particles embedded into block copolymers}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {The formation of metallic nano particles stored in thin films of block copolymers has been investigated by means of synchrotron radiation based photoemission spectroscopy (PES) and microscopy (PEEM). Empty channels in poly(styrene-block-4-vinylpyridine) copolymer with diameters of tens of nanometers filled with CrO2, Cr2O3 and Ni provide ideal bases for performing electron spectroscopy with energy and lateral resolution on magnetic nano particles. We present UPS, XPS, NEXAFS spectra and PEEM images on and off the C 1s, Cr 2p, Ni 2p resonances and discuss the geometric and electronic structure of such compounds. The synchrotron radiation was delivered from the U49/2 beamline at BESSY II.}, language = {en} } @inproceedings{MikaloAppelHoffmannetal., author = {Mikalo, Ricardo Pablo and Appel, G{\"u}nter and Hoffmann, Patrick and Schmeißer, Dieter}, title = {Conducting Polypyrrole doped with Phthalocyaninesulfonates - new materials for chemical sensors}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Polypyrrole - a conducting polymer - is used as an active electrode of a quartz micro ballance and considered as a gate electrode in all-polymer field effect transistors used as chemical sensor. We use substituted phthalocyanines as dopants of polypyrrole as they offer the possibility to enhance the dopant concentration as well as to include functionalized groups. We studied these films by photoelectron spectroscopy, NEXAFS, PEEM, and TEM. These investigations revealed that the electronic structure as well as the morphology are highly dependent on the dopant's structure. We suggest a new charge transport model for 5-ring heterocycle conductive polymers. Whereas in the standard model only the carbon backbone is considered for the charge transport, we found by NEXAFS investigations that the heteroatom has a considerable high participation in the gap states, which are responsible for the charge transport. The dopants π-interactions force the nitrogen lone pair wave functions to contribute to the conducting polymer π-system. This is a novel approach concerning the application as chemical sensors since the reversible interaction of the analyte modifies the dopant and not the matrix.}, language = {en} } @inproceedings{BatchelorFollathSchmeisser, author = {Batchelor, David R. and Follath, Rolf and Schmeißer, Dieter}, title = {Design of a PGM for the U49/2 Undulator at BESSY II}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {This poster describes the beamline proposed for the BESSY II U49/2 Undulator by the Collaborating Research Group of BTU Cottbus, HMI Berlin and the TU Darmstadt. The beamline is designed with both high resolution electron spectroscopy, valence band measurements and PEEM in mind and utilises the wide energy range of the U49 Undulator 40-1500eV. The design chosen is based on a Petersen PGM [1] but with the grating illuminated with parallel light [2]. This modification allows variation of the monochromator higher order content or resolution, spot size without changing the focus. The performance of the beamline was investigated using various programs available at BESSY. The Undulator character- istics were evaluated using both SMUT and WAVE, and the optical performance of the monochromator was checked using REFLEC and RAY. The calculations show a resolving power of 2×104 with a flux of the order 1013 photons s-1 over the energy range covered by the mono- chromator. The maximum nominal second order contributions are ≈ 2\% at 300 eV for the first Undulator harmonic and ≈ 9\% for the third harmonic at 500 eV, both of which can be reduced by increasing the grating incidence angle and, or decreasing the Undulator Pinhole size.}, language = {en} } @inproceedings{HellerSchmeisser, author = {Heller, Thomas and Schmeißer, Dieter}, title = {Polaronen in SrTiO3(100)}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Vorgestellt werden Untersuchungen zur elektronischen Struktur von oxidischen Halbleitern wie SrTiO3(100)-Einkristallen und WO3-Filmen. Die Charakterisierung der Oberfl{\"a}chen erfolgt im Valenzbandbereich mittels Photoelektronenspektroskopie (TGM 7, Bessy I, hν=3D 15-100eV). Zust{\"a}nde entstehen in der Bandl{\"u}cke dieser=20 Materialien durch Dotierung (Heizen oder Natrium-Belegung). Wir untersuchen den Wirkungsquerschnitt speziell f{\"u}r diese Gapzust{\"a}nde. Ohne Dotierung ist der Verlauf des Wirkungsquerschnittes unstrukturiert. Bei Dotierung bilden sich molekulare Resonanzen. Deren Auftreten zeigt, daß diese Gapzust{\"a}nde lokalisiert sind. Weiterhin beobachten wir ausgepr{\"a}gte Feinstrukturen, die die charakteristische Anregung f=FCr Polaronen enthalten.}, language = {de} } @inproceedings{HoffmannBoehmeSchmeisseretal., author = {Hoffmann, Patrick and B{\"o}hme, Oliver and Schmeißer, Dieter and Lloyd Spetz, Anita and M{\aa}rtenson, Per}, title = {Einfluß von Nanopartikeln auf die Funktion von Hochtemperatursensoren}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Es werden Untersuchungen an als Hochtemperatur-Sensoren arbeitenden Schottky-Dioden mit dem Aufbau Metall-Oxidschicht-Siliziumkarbid vorgestellt. Dazu wurden Tiefenprofile mit XPS durch abwechselndes Abtragen durch Sputtern und Messen erstellt. Die Messungen erfolgten an thermisch unterschiedlich vorbehandelten Proben. Dabei konnten dipol-bedingte Verschiebungen der Bindungsenergie von Rumpfniveaus beobachtet werden. Das dazu notwendige Dipol-Moment wird durch das Entstehen von mit einer Oxidschicht {\"u}berzogenen Nanoteilchen erkl{\"a}rt. Die unterschiedlich ausgepr{\"a}gten Dipol-Verschiebungen auf den einzelnen Proben erlaubten eine Erkl{\"a}rung der thermischen Vorbehandlung, die bei Weglassen zu „frischen" und je nach Temperatur zu „aktivierten" oder „toten" Sensoren f{\"u}hrte.}, language = {de} } @inproceedings{MikaloAppelHoffmannetal., author = {Mikalo, Ricardo Pablo and Appel, G{\"u}nter and Hoffmann, Patrick and Schmeißer, Dieter}, title = {Leitf{\"a}higes Polypyrrol als Elektrodenmaterial: Wechselwirkungen mit Silber}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Untersuchungen des metallischen Kontaktes von Silber auf tosylat- und phthalocyanindotiertem Polypyrrol wurden mittels XPS- und µ-NEXAFS vorgenommen. Es wurde festgestellt, daß Silber mit dem Polypyrrol keine Verbindung eingeht. Daraus kann geschlossen werden, daß sowohl das leitf{\"a}hige Polymer, als auch das Silber ihren Leitf{\"a}higkeitsmechanismus beibehalten. Es konnte gezeigt werden, daß bei steigender Silberbelegung die Intensit{\"a}t der Polaronenzust{\"a}nde des Polypyrrol in st{\"a}rkerem Maße abnimmt, als die Intensit{\"a}t der unbesetzten Zust{\"a}nde. Das l{\"a}ßt darauf schließen, daß Silber die Grenzfl{\"a}che stabilisiert.}, language = {de} } @inproceedings{OpreaSchmeisserGoldenblum, author = {Oprea, Alexandru and Schmeißer, Dieter and Goldenblum, A.}, title = {On the charge transfer process in ZnS based ac powder electroluminescent devices}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {The charge transfer process in ZnS based ac powder electroluminescent devices was experimentally and theoretically investigated. The time dependence of active currents and the voltage dependence of the brightness were measured in different operating conditions. This data allowed the hypothesis that each ZnS grain of the ac powder electroluminescent device (PWELD) behaves as a thin films electroluminescent device (TFELD) with metal-insulator-semiconductor-insulator-metal (MISIM) structure. The whole PWELD, itself, can be considered as a sum of many litle MISIM sandwiches electrically conected among them and having the quasi Fermi level of the semiconductor-insulator interface randomly distributed. On this basis, in the frame of a statistical Monte-Carlo like procedure, was developed a quantative semiclassical model, in good agreement with the experimental data.}, language = {en} } @inproceedings{HellerBoehmeSchmeisser, author = {Heller, Thomas and B{\"o}hme, Oliver and Schmeißer, Dieter}, title = {Gap - Zust{\"a}nde in Wolframoxid WO3 - relaxierten Oberfl{\"a}chen}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Vorgestellt werden Arbeiten an d{\"u}nnen WO3-Schichten, die durch Verdampfen aus einer Knudsenzelle im UHV pr{\"a}pariert wurden. Diese Filme sind im Rahmen der XPS-Analysen st{\"o}chiometrisch, ohne Gap-Zust{\"a}nde. Definierte Gap-Zust{\"a}nde bilden sich durch Relaxierung der Oberfl{\"a}che: nach einigen Stunden im UHV, nach Heizen in Argon-Atmosph{\"a}re und nach Belegung mit Natrium. Die Charakterisierung dieser definierten Wolframoxid-Schichten erfolgt durch: 1.)XPS-Intensit{\"a}ten 2.)detailierte Analyse der W4f-Rumpfniveaus durch Synchrotronstrahlung (Bessy, TGM 7) 3.)die Variation der Austrittsarbeit beim Heizen und bei Natrium-Belegung 4.)das Auftreten von Gap-Zust{\"a}nden in der Bandl{\"u}cke}, language = {de} } @inproceedings{HoffmannMikaloSchmeisser, author = {Hoffmann, Patrick and Mikalo, Ricardo Pablo and Schmeißer, Dieter}, title = {PEEM-Untersuchung an Spaltfl{\"a}chen von MoTe2-(0001)}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Molybd{\"a}nditellurid (MoTe2) geh{\"o}rt zu den Schichtgitterverbindung und ist im allgemeinen durch den Herstellungsprozeß n-dotiert. Proben dieses MoTe2 wurden im Ultrahochvakuum gespalten und die so erhaltenen sauberen (0001)-Spaltfl{\"a}chen mit einem Photoemissions-Elektronenmikroskop (PEEM) untersucht. Diese Untersuchung erbrachte nebeneinander auf den Proben- oberfl{\"a}chen liegende stark kontrastierte helle und dunkle Bereiche. Da das PEEM Austrittsarbeitsunterschiede als Kontrast darstellt, k{\"o}nnen diese hellen und dunklen Bereiche auf lokale Unterschiede in der Austrittsarbeit zur{\"u}ckgef{\"u}hrt werden. Weiterhin wird {\"u}ber den Versuch berichtet, eine Zuordnung zwischen dem Kontrast und dem Unterschied in der Austrittsarbeit mit Hilfe eines Elektronenenergie-Analysators (micro-ESCA) zu treffen.}, language = {de} } @misc{SowinskaDasWojciechowskietal., author = {Sowinska, Małgorzata and Das, Chittaranjan and Wojciechowski, Konrad and Rouissi, Zied and Snaith, Henry J. and Schmeißer, Dieter}, title = {Atomic layer deposition of Al2O3 on CH3NH3PbI3 for enhancement of perovskite solar cells stability}, series = {Synchrotron Radiation in Natural Science : Bulletin of the Polish Synchrotron Radiation Society}, volume = {15}, journal = {Synchrotron Radiation in Natural Science : Bulletin of the Polish Synchrotron Radiation Society}, number = {1-2}, issn = {1644-7190}, pages = {S. 33}, language = {en} } @misc{SchmeisserJanowitz, author = {Schmeißer, Dieter and Janowitz, Christoph}, title = {The Cu2p-edge of superconducting BiSrCu-Oxides studed by resonant Photoelectron Spectroscopy}, series = {Synchrotron Radiation in Natural Science : Bulletin of the Polish Synchrotron Radiation Society}, volume = {15}, journal = {Synchrotron Radiation in Natural Science : Bulletin of the Polish Synchrotron Radiation Society}, number = {1-2}, issn = {1644-7190}, pages = {S. 35}, language = {en} } @inproceedings{DasTallaridaSchmeisser, author = {Das, Chittaranjan and Tallarida, Massimo and Schmeißer, Dieter}, title = {TiO2 laminated Silicon microstructures based stable photocathode for water splitting}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, pages = {S. 213}, abstract = {The photoelectrochemical (PEC) water splitting is one of the most efficient ways to obtain hydrogen from water using solar power which can be used as carbon free fuel. The PEC device can bedesigned using semiconducting material that will convert solar radiation to H2. Silicon can be one of the best choices for PEC due to its success in solar cells technology. There are certain issues with Si such as stability in electrochemical medium [1] and higher surface reflectance (25\%) which limits the Si as an ideal candidate for PEC technique [2]. In the present work we addressed these issues by surface structuring and laminating the surface with metal oxide. The microstructuring of Si was done by electrochemical method. The Si microstructure photocathode was stabilized by thin layer of ALD grown TiO2 film. The microstructuring and lamination of Si photocathode by ALD layer of TiO2 decreased the reflectance ofthe surface and shift the onset potential towards anodic direction by 350 mV with a prolonged stability over 60 hours[3]. [1] C. Levy-Clement, J. Electrochem. Soc 1991, 12, 69 [2] J. Oh, et al. Energy Environ. Sci., 2011, 4, 1690 [3] C. Das, et al. Nanoscale 2015,7, 7726}, language = {en} } @misc{HaeberleBrizziGasparetal., author = {Haeberle, J{\"o}rg and Brizzi, Simone and Gaspar, Diana and Barquinha, Pedro and Galazka, Zbigniew and Schulz, Detlev and Schmeißer, Dieter}, title = {A spectroscopic comparison of IGZO thin film and the parent In2O3, Ga2O3, and ZnO single crystals}, series = {Materials Research Express}, volume = {3}, journal = {Materials Research Express}, number = {10}, issn = {2053-1591}, doi = {10.1088/2053-1591/3/10/106302}, pages = {106302-1 -- 106302-17}, abstract = {We use resonant photoelectron spectroscopy at the Zn 2p, Ga 2p, In 3d, and O 1s absorption edges to report on the electronic properties of indium-gallium-zinc-oxide thin films. We also compare the data with the respective data of the corresponding single crystals In2O3, Ga2O3, and ZnO. We focus on the elemental composition and, in particular, find no evidence for oxygen deficiency. The In, Ga, and Zn absorption data at resonance can be used to analyze the conduction band states in detail. We deduce that a configuration interaction between d10s0 and d9s1states is of importance. We provided a novel mechanism in which configuration interaction induced gap states create both, extended unoccupied states around E F as well as localized occupied states within the gap.}, language = {en} } @misc{GhoshBiswasSenetal., author = {Ghosh, Sujoy Kumar and Biswas, Anirban and Sen, Shrabanee and Das, Chittaranjan and Henkel, Karsten and Schmeißer, Dieter and Mandal, Dipankar}, title = {Yb3+ Assisted Self-Polarized PVDF Based Ferroelectretic Nanogenerator: A Facile Strategy of Highly Efficient Mechanical Energy Harvester Fabrication}, series = {Nano Energy}, volume = {2016}, journal = {Nano Energy}, number = {30}, issn = {2211-2855}, doi = {10.1016/j.nanoen.2016.10.042}, pages = {621 -- 629}, abstract = {Ytterbium (Yb3+) assisted porous poly(vinylidene fluoride) (PVDF) composite film comprising flexible ferroelectretic nanogenerator (FTNG) is highlighted where traditional poling treatment is completely avoided. The piezoelectric output of FTNG is realized by the co-operative activity of self-polarized -CH2/-CF2 dipoles with porous electret-like structure in the composite film. Owing to extraordinary ferroelectric and dielectric properties, FTNG is acting as a highly efficient mechanical energy harvester. It is capable to capture several forms of abundant mechanical energy arising from humanfinger movements, machine vibrations and sound waves. As a proof of concept, under compressive deformation, FTNG is enable to instantly powers up several consumer electronics and thus provides a promising strategy for achieving self-powered electronic devices.}, language = {en} } @misc{HenkelKotSchmeisser, author = {Henkel, Karsten and Kot, Małgorzata and Schmeißer, Dieter}, title = {Localized defect states and charge trapping in atomic layer deposited-Al₂O₃ films}, series = {Journal of Vacuum Science and Technology, A : Vacuum, Surfaces, and Films}, volume = {35}, journal = {Journal of Vacuum Science and Technology, A : Vacuum, Surfaces, and Films}, number = {1}, issn = {0734-2101}, doi = {10.1116/1.4971991}, pages = {01B125-1 -- 01B125-18}, abstract = {In this study, the authors compared different Al₂O₃ films grown by atomic layer deposition (ALD) with the same aluminum precursor but on different substrates. The authors employed different process parameters such as thermal-ALD and plasma-enhanced-ALD using different substrate temperatures ranging from 280 °C down to room temperature. They characterized these films by resonant photoelectron spectroscopy and by electrical measurements. They established that generally the ALD-Al₂O₃ films show characteristic features of bulk Al₂O₃. For all films investigated, the authors found intrinsic defect states within the electronic band gap and identified excitonic, polaronic, and charge-transfer defect states. The authors gave an atomistic model to explain these intrinsic defects and found that their relative abundance is subject of the choice of ALD parameters and of the substrate used. They were able to relate the spectroscopic assigned in-gap defect states with the electronic charges as determined in our electrical measurements.}, language = {de} } @misc{KotDasWangetal., author = {Kot, Małgorzata and Das, Chittaranjan and Wang, Zhiping and Henkel, Karsten and Rouissi, Zied and Wojciechowski, Konrad and Snaith, Henry J. and Schmeißer, Dieter}, title = {Room-Temperature Atomic Layer Deposition of Al₂O₃: Impact on Efficiency, Stability and Surface Properties in Perovskite Solar Cells}, series = {ChemSusChem}, volume = {9}, journal = {ChemSusChem}, number = {24}, issn = {1864-5631}, doi = {10.1002/cssc.201601186}, pages = {3401 -- 3406}, abstract = {In this work, solar cells with a freshly made CH₃NH₃PbI₃ perovskite film showed a power conversion efficiency (PCE) of 15.4 \% whereas the one with 50 days aged perovskite film only 6.1 \%. However, when the aged perovskite was covered with a layer of Al₂O₃ deposited by atomic layer deposition (ALD) at room temperature (RT), the PCE value was clearly enhanced. X-ray photoelectron spectroscopy study showed that the ALD precursors are chemically active only at the perovskite surface and passivate it. Moreover, the RT-ALD-Al2O3-covered perovskite films showed enhanced ambient air stability.}, language = {en} } @misc{CuypersFleischmannDorpetal., author = {Cuypers, Daniel and Fleischmann, Claudia and Dorp, Dennis H. von and Brizzi, Simone and Tallarida, Massimo and M{\"u}ller, Matthias and H{\"o}nicke, Philipp and Billen, Arne and Chintala, Ravi and Conard, Thierry and Schmeißer, Dieter and Vandervorst, Wilfried and Elshocht, Sven van and Armini, Silvia and De Gendt, Stefan and Adelmann, Christoph}, title = {Sacrificial Self-Assembled Monolayers for the Passivation of GaAs(100) Surfaces and Interfaces}, series = {Chemistry of Materials}, volume = {28}, journal = {Chemistry of Materials}, number = {16}, issn = {0897-4756}, doi = {10.1021/acs.chemmater.6b01732}, pages = {5689 -- 5701}, abstract = {The use of sacrificial self-assembled monolayers (SAMs) to prepare clean n-type GaAs (100) surfaces without band bending in vacuo is demonstrated. GaAs surface passivation using octadecanethiol SAMs after HCl cleaning is shown to lead to an enhancement of the room-temperature photoluminescence intensity. Synchrotron-radiation photoelectron spectroscopy (SRPES) finds that the interfacial oxide between GaAs and the SAM remains below the detection limit. Evidence for both Ga-S and As-S bonds at the GaAs-thiolate interface is found. The limited thermal stability of the SAM allows the desorption of the alkyl chains by in situ thermal annealing at temperatures above 180 °C, leaving S bonded to Ga behind. The resulting surface contains only a very small amount of O (0.05 ML coverage) and C (about 3\% of the SAM remaining) and shows no band bending with the surface Fermi level close to the conduction band. Atomic layer deposition of Al₂O₃ on this surface occurs via the formation of Al-S bonds without introducing any additional band bending. This indicates that the surface preparation of n-type GaAs (100) using sacrificial octadecanethiol SAMs followed by in situ thermal removal provides a route toward GaAs/oxide interfaces without interfacial oxides and without band bending.}, language = {en} } @misc{CorreaBrizziSchmeisser, author = {Corr{\^e}a, Silma Alberton and Brizzi, Simone and Schmeißer, Dieter}, title = {Depicting the Electronic Structure of HfO₂ Films by Spectroscopic Techniques}, series = {ECS Transactions}, volume = {75}, journal = {ECS Transactions}, number = {6}, issn = {1938-6737}, doi = {10.1149/07506.0145ecst}, pages = {145 -- 153}, abstract = {The electronic structure of HfO₂ films was investigated. The partial density of states for the valence and the conduction bands was determined by the detailed analysis of the O1s resonance profile by resonant photoelectron spectroscopy. The positions of valence band maximum and conduction band minimum, the excitation range for the polaronic states and the range of charge transfer band were found to be not influenced by the preparation conditions. The band gap was determined to be 6.2 eV and the energy of the charge neutrality level (referred to vacuum level) was determined as 4.7 eV. The Fermi level position was observed to vary about 1.2 eV depending on the preparation conditions, which indicates the presence of charges within the films.}, language = {en} } @misc{HenkelDasKotetal., author = {Henkel, Karsten and Das, Chittaranjan and Kot, Małgorzata and Schmeißer, Dieter and Naumann, Franziska and K{\"a}rkk{\"a}nen, Irina and Gargouri, Hassan}, title = {In-gap states in titanium dioxide and oxynitride atomic layer deposited films}, series = {Journal of Vacuum Science and Technology: A}, volume = {35}, journal = {Journal of Vacuum Science and Technology: A}, number = {1}, issn = {0734-2101}, doi = {10.1116/1.4972247}, pages = {01B135-1 -- 01B135-8}, abstract = {Valence band (VB) spectra of titanium dioxide (TiO2) and oxynitride (TiOxNy) films prepared by different atomic layer deposition (ALD) processes are compared and related to electrical characterization [current-voltage (JV) and capacitance-voltage (CV)] results. By increasing the nitrogen amount in the TiO2 film, band-gap narrowing is observed. The band-gap decrease is related to the contribution of the nitrogen density of states, which induces defects within the band-gap and thus reduces its optical band-gap. In-gap states are found in the VB spectra at 1 eV below the Fermi energy in all investigated ALD samples, i.e., in TiO2 as well as in TiOxNy films. An exponential correlation between leakage current density and in-gap state intensity is derived by the combination of JV measurements and VB spectra, whereas the in-gap states seem to have no influence on hysteresis and fixed oxide charges found in the CV data. It is argued that the in-gap states in TiO2 and TiOxNy have an excitonic or polaronic origin. Both, band-gap narrowing and in-gap state intensity can be tuned by the ALD process selection and the variation of its parameters.}, language = {en} } @inproceedings{GarainAdhikaryMandaletal., author = {Garain, Samiran and Adhikary, Prakriti and Mandal, Dipankar and Sen, Shrabanee and Henkel, Karsten and Schmeißer, Dieter}, title = {Electro-active β-Phase Formation in Poly(vinylidene fluoride) Films by Hydrated Rare earth Metal Salt}, series = {Proceeding of the International Conference on Nanotechnology 2013 (ICNT 2013)}, booktitle = {Proceeding of the International Conference on Nanotechnology 2013 (ICNT 2013)}, publisher = {Institute of Technology, Haldia, WB, India}, address = {Haldia}, isbn = {978-81-927756-0-9}, pages = {S. 127}, abstract = {Polyvinylidene fluoride (PVDF) is a typical fluoro-polymer with complicated polymorphisms due to the semi-crystalline nature. Generally, four crystalline phases, α, β, γ and δ may exist in PVDF crystals. The nonpolar α- and δ-phase has a monoclinic lattice with trans-gauche conformation (TGTG⁄), which is thermodynamically most stable for PVDF. The polar β phase with all-trans (TTTT) planar zigzag conformation is attractive for its piezo-, pyro-, and ferroelectric properties. The polar β-Phase and also semi-polar γ-phase (TTTGTTTG⁄) have obtained wide device applications such as acoustic transducers, piezoelectric sensors, energy harvesting generators, pyroelectric sensors, non-volatile memories and energy storage capacitors. In this work, we explore the possibility to nucleate β-phase in PVDF hydrated salt composite films by addition of the hydrated Rare earth metal salt, (NH4)4 Ce (SO4)4, 2H2O) for the piezo- ferro and high dielectric based device applications. It has been found that the water molecules in (NH4)4 Ce (SO4)4, 2H2O could form hydrogen bonds with PVDF during the crystallization process and the hydrogen bonds promoted the electro-active crystalline β- phase in PVDF with all -trans conformations. In addition, the DMF (solvent used for films preparation) can also assist the rare-earth based nanoparticle preparation, as a result the electrostatic interaction of the surface charge of the nanoparticles and molecular dipoles in PVDF can resist the electroactive β- phase in PVDF.}, language = {en} } @inproceedings{SchmeisserMuellerHenkeletal., author = {Schmeißer, Dieter and M{\"u}ller, Sebastian and Henkel, Karsten and M{\"u}ller, Klaus and Wehner, Stefan}, title = {In-situ analysis of moving reaction fronts for the bistable CO oxidation reaction on noble metal catalyst}, series = {Extended Abstracts Book of First International Conference on Materials for Energy}, booktitle = {Extended Abstracts Book of First International Conference on Materials for Energy}, publisher = {Dechema e.V.}, address = {Frankfurt}, isbn = {978-3-89746-117-8}, pages = {S. 932}, abstract = {Experimental data on the reaction kinetics of catalytic processes are prerequisite for modeling of such reactions and their output. We investigate the CO oxidation on some noble metal catalysts, like Iridium(111) and Palladium(111) which is a bistable surface reaction. In a specific range of CO content in the feed gas islands of one or the other adsorbate nucleate and grow, which is recorded with photo electron emission microscopy (PEEM). During these transients the coverage on the surface changes from predominantly oxygen covered to predominantly CO covered resp. vice versa. But the resolution of PEEM and especially its unknown and nonlinear dependence of coverage of the two adsorbates (oxygen and CO) and image intensity make it impossible to extract the changes in coverage. On the other hand the reaction diffusion model based on the Langmuir-Hinshelwood-mechanism delivers the coverage of oxygen and carbon monoxide. The shapeand wall velocity of those islands has been connected perfectly to each other [CPL 423 (2006) 39], but not the absolute coverage and their variation during the reaction. Since the domain wall velocity is small on Iridium(111), this has opened the possibility for a detailed analysis of the changing coverage inside this domain wallutilizing synchrotron radiation and photo electron spectroscopy at BESSY II. The coverage profile of oxygen and CO inside a moving domain wall was measured for both cases using XPS spectra at O1s, C1s and the valence band during thereaction. Comparison with the reaction-diffusion-model and other catalytic surfaces, like Palladium(111) are done.}, language = {en} } @misc{MenezesIndraDasetal., author = {Menezes, Prashanth W. and Indra, Arindam and Das, Chittaranjan and Walter, Carsten and G{\"o}bel, Caren and Gutkin, Vitaly and Schmeißer, Dieter and Driess, Matthias}, title = {Uncovering the Nature of Active Species of Nickel Phosphide Catalysts in High-Performance Electrochemical Overall Water Splitting}, series = {ACS Catalysis}, volume = {7}, journal = {ACS Catalysis}, number = {1}, issn = {2155-5435}, doi = {10.1021/acscatal.6b02666}, pages = {103 -- 109}, abstract = {A systematic structural elucidation of the near-surface active species of the two remarkably active nickel phosphides Ni12P5 and Ni2P on the basis of extensive analytical, microscopic, and spectroscopic investigations is reported. The latter can serve as complementary efficient electrocatalysts in the hydrogen (HER) versus oxygen evolution reaction (OER) in alkaline media. In the OER Ni12P5 shows enhanced performance over Ni2P due to the higher concentration of nickel in this phase, which enables the formation of an amorphous NiOOH/Ni(OH)2 shell on a modified multiphase with a disordered phosphide/phosphite core. The situation is completely reversed in the HER, where Ni2P displayed a significant improvement in electrocatalytic activity over Ni12P5 owing to a larger concentration of phosphide/phosphate species in the shell. Moreover, the efficiently combined use of the two nickel phosphide phases deposited on nickel foam in overall electrocatalytic water splitting is demonstrated by a strikingly low cell voltage and high stability with pronounced current density, and these catalysts could be an apt choice for applications in commercial alkaline water electrolysis.}, language = {en} } @misc{IndraMenezesDasetal., author = {Indra, Arindam and Menezes, Prashanth W. and Das, Chittaranjan and G{\"o}bel, Caren and Tallarida, Massimo and Schmeißer, Dieter and Driess, Matthias}, title = {A facile corrosion approach to the synthesis of highly active CoOxwater oxidation catalysts}, series = {Journal of Materials Chemistry A}, journal = {Journal of Materials Chemistry A}, number = {5}, issn = {2050-7488}, doi = {10.1039/c6ta10650a}, pages = {5171 -- 5177}, abstract = {Ultra-small rock salt cobalt monoxide (CoO) nanoparticles were synthesized and subjected to partial oxidation ('corrosion') with ceric ammonium nitrate (CAN) to form mixed-valence CoOx(1 < x< 2) water oxidation catalysts. Spectroscopic, microscopic and analytical methods evidenced a structural reformation of cubic CoO to active CoOx with a spinel structure. The superior water oxidation activity of CoOx has been established in electrochemical water oxidation under alkaline conditions. Electrochemical water oxidation with CoOx was recorded at a considerably low overpotential of merely 325 mV at a current density of 10 mA cm-2 in comparison to 370 mV for CoO. Transformation of both octahedral CoII and CoIII sites into amorphous Co(OH)2-CoOOH is the key to high electrochemical activity while the presence of a higher amount of octahedral CoIII sites in CoOx is imperative for an efficient oxygen evolution process.}, language = {en} } @inproceedings{ŁobazaKotSchmeisser, author = {Łobaza, Justyna and Kot, Małgorzata and Schmeißer, Dieter}, title = {Analysis of surface oxidation of TiON ALD films}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 202}, abstract = {Titanium oxynitride (TiON) films are interesting due to their remarkable optical and electronic properties which strongly depend on the O/N ratio. However, it is known that films containing Ti are prone to oxidation in contact with the air [1]. In this work, we study the thickness of a surface oxidation layer which is inherently formed on the atomic layer deposition (ALD) grown TiON/TiN films on Si substrate. We use an Ar+ ion bombardment source and X-ray photoelectron spectroscopy (XPS) for this analysis. We calibrate the sputter rate by using substrate signal intensity decay (here Si 2p) in the XPS spectra of the 5 nm thick TiON sample accordingly. This rate is assumed to be constant when films with a larger thickness are analyzed. We find that the surface oxidation layer is about 1 nm thick, independent on the detailed ALD parameters of the films. The TiN films found underneath are close to the stoichiometric values and have a residual O content below 5\%. Finally, we compare these data to our previous results collected with synchrotron-based radiation source [2,3]. References: [1] Sowinska et al., Applied Physics Letters 100, 233509 (2012). [2] M. Sowinska et al., Applied Surface Science 381, 42-47 (2016). [3] M. Sowińska et al., Journal of Vacuum Science and Tech- nology A, 01A12734 (2016).}, language = {en} }