TY - CHAP A1 - Das, Chittaranjan A1 - Tallarida, Massimo A1 - Schmeißer, Dieter T1 - Control of thickness of SiO2 interfacial layer for photocatalytic water splitting on Si photocathodes T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - Silicon with a band gap of 1.1eV is an excellent candidate for visible photocatalytic water splitting. But p-type Si has a low quantum yield and are less efficient for water splitting [1]. It has been shown that preventing oxidation of Si surface can shift the onset potential for water reduction by about 300mV towards more positive [2]. We investigated in detail the influence of the SiO2 layer thickness on the onset potential for water splitting on Si photocathodes: we used p-type Si substrates covered with SiO2 layers of varying thickness. Then, we deposited a thin TiO2 film on using atomic layer deposition (ALD) to inhibit Si oxidation during the electrochemical experiment. In this way we could shift the onset potential up to 200mV, depending on the SiO2 thickness. [1]E. L. Warren, S. W. Boettcher, M. G. Walter, H. A. Atwater, and N. S. Lewis: J. Phys. Chem. C 115 (2011) 594. [2]B. Seger, Anders B. Laursen, P. C. K. Vesborg, T. Pedersen, O. Hansen, S. Dahl, I. Chorkendorff, Angew. Chem. Int. Ed. 2012, 51, 9128 KW - photocatalysis KW - water splitting KW - Si photocathodes KW - atomic layer depsoition (ALD) KW - passivation layer KW - TiO2 Y1 - 2014 UR - http://www.dpg-verhandlungen.de/year/2014/conference/dresden/part/ds/session/49/contribution/5?lang=en SN - 0420-0195 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Das, Chittaranjan A1 - Tallarida, Massimo A1 - Schmeißer, Dieter T1 - Determination of charge neutrality level in TiO2 films from res-PES measurements T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - Titanium dioxide is one of the metal oxides which have versatile application in different fields. The applications of TiO2 are in the field of cosmetics, electronics (memory resistive switching), dye, photonics and photocatalysis. In the present paper we study the resPES data of TiO2 films prepared by atomic layer deposition. The measurements are done in in-situ system at beam line U49/2-PGM2 in BESSY-II. The density of state in valence band and conduction band is obtained from the resonance photo electron spectroscopy (res-PES) of the O1s and the Ti2p edge. The data allow to determine the position of the VBM and CBM with respect to the Fermi energy. Also the existence of localized O2p and Ti2p derived states is deduced which appear in the gap. In addition we determine the charge neutrality level (CNL).The CNL is the position where the weight of the density of state from valence band and conduction band are equal. This is an important quantity for the discussion of interface properties. KW - charge neutrality level KW - resonant photoelectron spectroscopy KW - TiO2 Y1 - 2015 UR - http://www.dpg-verhandlungen.de/year/2015/conference/berlin/part/o/session/58/contribution/12?lang=en SN - 0420-0195 SP - S. 415 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Sowinska, Małgorzata A1 - Brizzi, Simone A1 - Das, Chittaranjan A1 - Kärkkänen, Irina A1 - Schneidewind, Jessica A1 - Naumann, Franziska A1 - Gargouri, Hassan A1 - Henkel, Karsten A1 - Schmeißer, Dieter T1 - Analysis of nitrogen species in titanium oxynitride ALD films T2 - Applied Surface Science N2 - Titanium oxynitride films are prepared by plasma enhanced atomic layer deposition method using two different precursors and nitrogen sources. Synchrotron radiation-based X-ray photoelectron spectroscopy and X-ray absorption spectroscopy are used to characterize the nitrogen species incorporated within these films depending on the deposition parameters. It is found that nitrogen atoms in these films are differently bonded. In particular, it can be distinguished between Ti-ON and Ti-N bonding configurations and molecular nitrogen species caused by precursor fragments. KW - titanium oxynitride KW - X-ray photoelectron spectroscopy KW - X-ray absorption spectroscopy KW - ALD process parameters Y1 - 2016 U6 - https://doi.org/10.1016/j.apsusc.2016.02.096 SN - 0169-4332 SN - 1873-5584 VL - 381 SP - 42 EP - 47 ER - TY - GEN A1 - Das, Chittaranjan A1 - Richter, Matthias A1 - Tallarida, Massimo A1 - Schmeißer, Dieter T1 - Electronic properties of atomic layer deposited films, anatase and rutile TiO2 studied by resonant photoemission spectroscopy T2 - Journal of Physics D: Applied Physics N2 - The TiO2 films are prepared by atomic layer deposition (ALD) method using titanium isopropoxide precursors at 250 °C and analyzed using resonant photoemission spectroscopy (resPES). We report on the Ti2p and O1s core levels, on the valence band (VB) spectra and x-ray absorption spectroscopy (XAS) data, and on the resonant photoelectron spectroscopy (resPES) profiles at the O1s and the Ti3p absorption edges. We determine the elemental abundance, the position of the VB maxima, the partial density of states (PDOS) in the VB and in the conduction band (CB) and collect these data in a band scheme. In addition, we analyze the band-gap states as well as the intrinsic states due to polarons and charge-transfer excitations. These states are found to cause multiple Auger decay processes upon resonant excitation. We identify several of these processes and determine their relative contribution to the Auger signal quantitatively. As our resPES data allow a quantitative analysis of these defect states, we determine the relative abundance of the PDOS in the VB and in CB and also the charge neutrality level. The anatase and rutile polymorphs of TiO2 are analyzed in the same way as the TiO2 ALD layer. The electronic properties of the TiO2ALD layer are compared with the anatase and rutile polymorphs of TiO2. In our comparative study, we find that ALD has its own characteristic electronic structure that is distinct from that of anatase and rutile. However, many details of the electronic structure are comparable and we benefit from our spectroscopic data and our careful analysis to find these differences. These can be attributed to a stronger hybridization of the O2p and Ti3d4s states for the ALD films when compared to the anatase and rutile polymorphs. KW - titanium dioxide (TiO2) KW - resonant photoemission spectroscopy (resPES) KW - defect states KW - partial density of states (pDOS) KW - charge neutrality level (CNL) Y1 - 2016 U6 - https://doi.org/10.1088/0022-3727/49/27/275304 SN - 0022-3727 SN - 1361-6463 VL - 49 IS - 27 SP - 275304-1 EP - 275304-17 ER - TY - GEN A1 - Das, Chittaranjan A1 - Kot, Małgorzata A1 - Henkel, Karsten A1 - Schmeißer, Dieter T1 - Engineering of Sub-Nanometer SiOₓ Thickness in Si Photocathodes for Optimized Open Circuit Potential T2 - ChemSusChem N2 - Silicon is one of the most promising materials to be used for tandem-cell water-splitting devices. However, the electrochemical instability of bare Si makes it difficult to be used for stable devices. Besides that, the photovoltage loss in Si, caused by several factors (e.g., metal oxide protection layer and/or SiO₂/Si or catalyst/Si interface), limits its use in these devices. In this work, we present that an optimized open circuit potential (OCP) of Si can be obtained by controlling the SiOₓ thickness in sub-nanometer range. It can be done by means of a simple and cost-effective way using the combination of a wet chemical etching and the low temperature atomic layer deposition (ALD) of TiO₂. We have found that a certain thickness of the native SiOₓ is necessary to prevent further oxidation of the Si photocathode during the ALD growth of TiO₂. Moreover, covering the Si photocathode with an ALD TiO₂ layer enhances its stability. KW - atomic layer deposition KW - open circuit potential KW - Si photocathodes KW - silica KW - stability Y1 - 2016 U6 - https://doi.org/10.1002/cssc.201600777 SN - 1864-5631 SN - 1864-564X VL - 9 IS - 17 SP - 2332 EP - 2336 ER - TY - CHAP A1 - Sowinska, Małgorzata A1 - Das, Chittaranjan A1 - Wojciechowski, Konrad A1 - Snaith, Henry J. A1 - Schmeißer, Dieter T1 - XPS study of the ALD growth of Al₂O₃ on the CH₃NH₃PbI₃ T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - Organic-inorganic lead halide perovskites have emerged as very attractive absorber materials for the fabrication of low cost and high efficiency solar cells, but a delicate nature of these films is one of the main challenges for a successful commercialization. Typically, when exposed to air or moisture, perovskite films degrade within a couple of hours or days. Moreover, the methylammonium lead triiodide (CH₃NH₃PbI₃) perovskite cannot sustain a prolonged annealing at temperatures around 85∘C. In this work, we are investigating stability (upon air and thermal exposure) of a CH₃NH₃PbI₃ perovskite film coated with a thin layer of Al₂O₃ deposited by atomic layer deposition (ALD). In particular, the chemical and electronic changes occurred at the Al₂O₃/CH₃NH₃PbI₃ interface during the first 50 ALD cycles were monitored ex-situ by high-resolution and surface-sensitive synchrotron-based X-ray photoelectron spectroscopy (SR-XPS). The advantage of the ALD as a deposition method is that it can produce extremely dense layers with a very precise thickness control at room temperature. Detailed SR-XPS data analysis and a stability test of the perovskite film with alumina will be presented. KW - atomic layer deposition KW - perovskite solar cells KW - Al₂O₃ KW - X-Ray photoelectron spectroscopy KW - synchrotron Y1 - 2016 UR - http://www.dpg-verhandlungen.de/year/2016/conference/regensburg/part/cpp/session/31/contribution/6?lang=en SP - S. 206 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Sowinska, Małgorzata A1 - Das, Chittaranjan A1 - Wojciechowski, Konrad A1 - Snaith, Henry J. A1 - Schmeißer, Dieter T1 - Spectroscopic investigation of the nitrogen role in organic-inorganic perovskite films T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - Over the past few years, a wide range of device architectures employing organic-inorganic metal halide perovskite absorbers has been reported, with efficiencies exceeding 20%. Despite the tremendous progress, a number of key issues must be resolved before the wide-spread com- mercialization will be possible. Some of the primary challenges include lead toxicity, long-term stability, and fast degradation upon exposure to humid atmosphere. Recent computational and experimental studies suggest that hybrid metal-halide perovskites act as an ionic-electronic conductor. The study of vacancy-mediated migration of I−, Pb2+ and CH3NH3− ions and their relative activation energies suggests that migration of halide vacancies, to and from the interfaces in the solar cell during its operation, is the main conduction mechanism. In this work, we are presenting high resolution synchrotron-based spectroscopic study, which indicates that the contribution of nitrogen into the conduction mechanism of methyl ammonium lead iodide-based (CH3NH3PbI3) perovskite films should not be neglected. The N1s core level and resonant X-ray photoelectron spectroscopy at the N1s-egde of the CH3NH3PbI3 films are discussed in detail. KW - perovskite solar cells KW - X-ray photoelectron spectroscopy KW - nitrogen Y1 - 2016 UR - http://www.dpg-verhandlungen.de/year/2016/conference/regensburg/part/cpp/session/11/contribution/7?lang=en SP - S. 150 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Choudhury, Sakeb Hasan A1 - Tallarida, Massimo A1 - Das, Chittaranjan A1 - Schmeißer, Dieter T1 - Atomic layer deposition of Ga2O3 using Tri-methyl-Gallium and H2O T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - Considering numerous applications such as transparent conducting oxides, gas sensors, photovoltaic applications, deep UV photo detectors, field effect transistors and spintronics gallium oxide (Ga2O3) has earned quite a lot of focus recently. Various techniques have already been demonstrated to produce Ga2O3 naming evaporation, sputtering, pulsed laser deposition, chemical vapor deposition and atomic layer deposition (ALD). Among them, ALD gives the possibility of controlling the thickness at the atomic level, good step coverage and delivers dense and homogeneous films. In this contribution, we report on the growth of ALD Ga2O3 using trimethylgallium (TMG) and H2O as metal and oxygen precursors, respectively. We deposited thin Ga2O3 films on Si, TiO2, Al2O3 and RuO2 over a temperature range of 150-300°C and characterized them by X-ray photo emission spectroscopy and atomic force microscopy. From this study, we are able to discuss the influence of the temperature on the growth dynamics of Ga2O3 and its chemical composition. KW - atomic layer deposition KW - Ga2O3 KW - X-ray photoelectron spectroscopy (XPS) KW - Si, TiO2 , Al2O3 and RuO2 substrates Y1 - 2013 UR - http://www.dpg-verhandlungen.de/year/2013/conference/regensburg/part/ds/session/4/contribution/2?lang=de PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - CHAP A1 - Das, Chittaranjan A1 - Tallarida, Massimo A1 - Skorupska, Katarzyna A1 - Lewerenz, Hans-Joachim A1 - Schmeißer, Dieter T1 - An efficient Si photo cathode for a wide range of electrolyte pH values T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - Hydrogen fuel cells, being environmental friendly to produce energy, are a technology of future. One of the efficient ways to produce hydrogen is solar driven photocatalysis using semiconducting materials as photo electrodes. The choice of electrodes is a crucial factor and is done on the basis of photo corrosion stability, light absorption efficiency, and photocarrier lifetime. P-type Si can be used as photo cathode to produce H2 by direct photocatalysis. Si cathodes can be used in acidic electrolytes to have efficient photo catalytic activity but they are unstable in alkaline electrolytes. Therefore, to use both Si electrodes in the same electrolyte, their chemical stability should be extended over a wide range of pH. To this purpose we modified the surface of a p-type Si photocathode with very thin films of TiO2 grown by atomic layer deposition (ALD). We found that the modified Si cathode shows an increased photoresponse and a lower onset potential with respect to the pristine surface and an increased stability at various pH values. KW - Si photoelectrode KW - water splitting KW - atomic layer deposition (ALD) KW - TiO2 Y1 - 2013 UR - http://www.dpg-verhandlungen.de/year/2013/conference/regensburg/part/ds/session/4/contribution/3?lang=de PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Sowinska, Małgorzata A1 - Das, Chittaranjan A1 - Wojciechowski, Konrad A1 - Rouissi, Zied A1 - Snaith, Henry J. A1 - Schmeißer, Dieter T1 - Atomic layer deposition of Al2O3 on CH3NH3PbI3 for enhancement of perovskite solar cells stability T2 - Synchrotron Radiation in Natural Science : Bulletin of the Polish Synchrotron Radiation Society KW - atomic layer deposition KW - perovskite soloar cells KW - X-ray photoelectron spectroscopy (XPS) KW - Atomic foce microscopy (AFM) Y1 - 2016 SN - 1644-7190 VL - 15 IS - 1-2 SP - S. 33 ER - TY - CHAP A1 - Das, Chittaranjan A1 - Tallarida, Massimo A1 - Schmeißer, Dieter T1 - TiO2 laminated Silicon microstructures based stable photocathode for water splitting T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft N2 - 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 KW - water splitting KW - TiO2 KW - atomic layer deposition (ALD) KW - Si photoelectrodes Y1 - 2016 UR - http://www.dpg-verhandlungen.de/year/2016/conference/regensburg/part/ds/session/48/contribution/4?lang=en SP - S. 213 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Ghosh, Sujoy Kumar A1 - Biswas, Anirban A1 - Sen, Shrabanee A1 - Das, Chittaranjan A1 - Henkel, Karsten A1 - Schmeißer, Dieter A1 - Mandal, Dipankar T1 - Yb3+ Assisted Self-Polarized PVDF Based Ferroelectretic Nanogenerator: A Facile Strategy of Highly Efficient Mechanical Energy Harvester Fabrication T2 - Nano Energy N2 - 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. KW - PVDF KW - Yb 3+ KW - Porous ferroelectret material KW - Self-polarization KW - Ferroelectretic nanogenerator KW - Mechanical energy harvester KW - Self-powered electronics Y1 - 2016 U6 - https://doi.org/10.1016/j.nanoen.2016.10.042 SN - 2211-2855 VL - 2016 IS - 30 SP - 621 EP - 629 ER -