@misc{TallaridaDasCibrevetal., author = {Tallarida, Massimo and Das, Chittaranjan and Cibrev, Dejan and Kukli, Kaupo and Tamm, Aile and Ritala, Mikko and Lana-Villarreal, Teresa and Gómez, Roberto and Leskel{\"a}, Markku and Schmeißer, Dieter}, title = {Modification of Hematite Electronic Properties with Trimethyl Aluminum to Enhance the Efficiency of Photoelectrodes}, series = {The Journal of Physical Chemistry Letters}, volume = {5}, journal = {The Journal of Physical Chemistry Letters}, number = {20}, doi = {10.1021/jz501751w}, pages = {3582 -- 3587}, abstract = {The electronic properties of hematite were investigated by means of synchrotron radiation photoemission (SR-PES) and X-ray absorption spectroscopy (XAS). Hematite samples were exposed to trimethyl aluminum (TMA) pulses, a widely used Al-precursor for the atomic layer deposition (ALD) of Al2O3. SR-PES and XAS showed that the electronic properties of hematite were modified by the interaction with TMA. In particular, the hybridization of O 2p states with Fe 3d and Fe 4s4p changed upon TMA pulses due to electron inclusion as polarons. The change of hybridization correlates with an enhancement of the photocurrent density due to water oxidation for the hematite electrodes. Such an enhancement has been associated with an improvement in charge carrier transport. Our findings open new perspectives for the understanding and utilization of electrode modifications by very thin ALD films and show that the interactions between metal precursors and substrates seem to be important factors in defining their electronic and photoelectrocatalytic properties.}, language = {en} } @misc{IndraMenezesSahraieetal., author = {Indra, Arindam and Menezes, Prashanth W. and Sahraie, Nastaran Ranjbar and Bergmann, Arno and Das, Chittaranjan and Tallarida, Massimo and Schmeißer, Dieter and Strasser, Peter and Driess, Matthias}, title = {Unification of Catalytic Water Oxidation and Oxygen Reduction Reactions: Amorphous Beat Crystalline Cobalt Iron Oxides}, series = {Journal of the American Chemical Society}, volume = {2014}, journal = {Journal of the American Chemical Society}, number = {136}, issn = {1520-5126}, doi = {10.1021/ja509348t}, pages = {17530 -- 17536}, abstract = {Catalytic water splitting to hydrogen and oxygen is considered as one of the convenient routes for the sustainable energy conversion. Bifunctional catalysts for the electrocatalytic oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are pivotal for the energy conversion and storage, and alternatively, the photochemical water oxidation in biomimetic fashion is also considered as the most useful way to convert solar energy into chemical energy. Here we present a facile solvothermal route to control the synthesis of amorphous and crystalline cobalt iron oxides by controlling the crystallinity of the materials with changing solvent and reaction time and further utilize these materials as multifunctional catalysts for the unification of photochemical and electrochemical water oxidation as well as for the oxygen reduction reaction. Notably, the amorphous cobalt iron oxide produces superior catalytic activity over the crystalline one under photochemical and electrochemical water oxidation and oxygen reduction conditions.}, language = {en} } @misc{DasHenkelTallaridaetal., author = {Das, Chittaranjan and Henkel, Karsten and Tallarida, Massimo and Schmeißer, Dieter and Gargouri, Hassan and K{\"a}rkk{\"a}nen, Irina and Schneidewind, Jessica and Gruska, Bernd and Arens, Michael}, title = {Thermal and plasma enhanced atomic layer deposition of TiO2: Comparison of spectroscopic and electric properties}, series = {Journal of Vacuum Science and Technology A}, volume = {2015}, journal = {Journal of Vacuum Science and Technology A}, number = {33}, issn = {1520-8559}, doi = {10.1116/1.4903938}, pages = {01A144-1 -- 01A144-8}, abstract = {Titanium oxide (TiO2) deposited by atomic layer deposition (ALD) is used as a protective layer in photocatalytic water splitting system as well as a dielectric in resistive memory switching. The way ALD is performed (thermally or plasma-assisted) may change the growth rate as well as the electronic properties of the deposited films. In the present work, the authors verify the influence of the ALD mode on functional parameters, by comparing the growth rate and electronic properties of TiO2 films deposited by thermal (T-) and plasma-enhanced (PE-) ALD. The authors complete the study with the electrical characterization of selected samples by means of capacitance-voltage and current-voltage measurements. In all samples, the authors found a significant presence of Ti3+ states, with the lowest content in the PE-ALD grown TiO2 films. The observation of Ti3+ states was accompanied by the presence of in-gap states above the valence band maximum. For films thinner than 10 nm, the authors found also a strong leakage current. Also in this case, the PE-ALD films showed the weakest leakage currents, showing a correlation between the presence of Ti3+ states and leakage current density.}, language = {en} } @inproceedings{TallaridaSohalSchmeisser, author = {Tallarida, Massimo and Sohal, Rakesh and Schmeißer, Dieter}, title = {Electronic properties of the 2x1 3C-SiC surface reconstruction studied with resonant photoemission}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 41}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, isbn = {0420-0195}, pages = {S. 239}, abstract = {We have studied the 2x1 reconstructed surface of the 3C-SiC polytype by means of photoemission spectroscopy. The reconstruction was characterized through Si2p and C1s core level and angle-integrated valence band spectroscopy, and confirmed by the observation of a two-domain 2x1 LEED pattern. The electronic properties of this surface were investigated by collecting valence band spectra at photon energies near the Si2p and C1s absorption edges. The results show a strong dependence of the photoemission intensity on the excitation energy with characteristic resonances for certain valence band features. With a detailed study of the resonances we are able to assign the electronic origin of the resonating states and the nature of the electronic transition near the absorption edges.}, language = {en} } @inproceedings{KolanekKaravaevTallaridaetal., author = {Kolanek, Krzysztof and Karavaev, Konstantin and Tallarida, Massimo and Schmeißer, Dieter}, title = {Atomic layer deposition of HfO2 onto SiO2 substrates investigated in-situ by non-contact UHV/AFM}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 248}, abstract = {We investigated in-situ the atomic layer deposition (ALD) of HfO2 onto SiO2 substrates with ultra high vacuum (UHV) non-contact atomic force microscope (NC-AFM). The ALD process was started after detailed analysis of the initial Si(001)/SiO2 substrate. The ALD cycles, made by using tetrakis-di-methyl-amido-Hf (TDMAHf) and water as precursors, were performed on the SiO2 substrate maintained at 230 ∘C. We studied the relation between the film growth and the root mean square surface roughness, surface skewness, kurtosis, fractal dimension and correlation length. In the initial stages of the ALD process with our analysis of the surface height histograms we were capable of determination: HfO2 layer thickness, surface coverage and surface roughness of a substrate and deposited material. Observation of the surface height histograms evolution during deposition allowed us to verify conformal and effective ALD growth on SiO2 substrate. With this detailed analysis of the surface topography we confirmed the completion of the first HfO2 layer after four ALD cycles.}, language = {en} } @inproceedings{MichlingTallaridaKolaneketal., author = {Michling, Marcel and Tallarida, Massimo and Kolanek, Krzysztof and Schmeißer, Dieter}, title = {In-situ EELS and UPS measurements on HfO2 ALD layers}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {In this contribution we report on our in-situ cycle-by-cycle (up to 10 cycles) investigations of the HfO2 ALD process using the methods of EELS and UPS. We used TDMA-Hf as a precursor and p-type Si wafer with natural oxide as the substrate. The EELS measurements were done with a primary energy of 52,5 eV and the UPS measurements with He I (21,218 eV). The change in the onset of the loss function is readily observed. Already after two cycles the value approach to the bulk value of HfO2. Upon ALD growth there is a remarkable decrease in the intensity of states within the gap. They are rather smooth and saturate after 10 cycles. With UPS we follow the variation of the VB onset and changes in the secondary electron onset. We summarize our data in a band diagram not based on bulk values but on cycle dependent quantities. With these cycle-by-cycle experiments we study the initial growth of HfO2 especially in the very first cycles.}, language = {en} } @inproceedings{StarzykTallaridaSchmeisser, author = {Starzyk, Łukasz and Tallarida, Massimo and Schmeißer, Dieter}, title = {Electrically optimized high-κ metal gate MOSFET by specific modification of the band alignment}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 231}, abstract = {The electrical optimization of metal/oxide/semiconductor gate stacks by specific modification of the band alignment for advanced MOS technology incorporating high dielectric constant (κ) materials is explored. Because of requirements concerning continued scaling of MOSFET transistors, gate oxides and cobalt electrode have been grown successively on Si substrate respectively by means of atomic layer deposition (ALD) and evaporation. The thicknesses of high-κ films were around 2 nm. In case of work function engineering, interfaces' chemistry plays a fundamental role. We applied synchrotron radiation based x-ray photoelectron spectroscopy (SR XPS) to characterize our samples, which allows step by step in situ investigations. Co 2p, Al 2p, Hf 4f, Si 2p and O 1s core levels spectra were measured and analyzed. From valence band (VB) spectra we determined Schottky barrier height and electronic bands offsets.}, language = {en} } @inproceedings{WyrodekTallaridaSchmeisseretal., author = {Wyrodek, Jakub and Tallarida, Massimo and Schmeißer, Dieter and Weisheit, Martin}, title = {Determination of interfacial layers in high - k ALD nanolaminate materials by ARXPS and SRXPS measurements}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 45}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 232}, abstract = {The interfacial layers of high dielectric constant (high - k) nanolaminate films are here explored. Problems concerning ALD nanolaminate layers deals mainly with lack of accurate methods to determine in depth profile of few nm thick stacks. Modified angle resolved XPS(ARXPS) and synchrotron radiation XPS(SRXPS) are proposed as methods suitable in layer profiling. Studied stacks containing ZrO/HfO or AlO/ZrO, were prepared on Si substrates by atomic layer deposition (ALD). Two sets of experiments were covered. First dealt with initial growth (up to 20 cycles, with thickness d < 2nm) of AlO/ZrO and included layer by layer insitu investigation by SRXPS. Second experiment refer to industrial grown ZrO/HfO films ( d ∼ 3nm ) processed with various parameters resulting in both, layer by layer and homogenous depositions. For those samples exsitu XPS, with angle dependent variation of probing depth, measurements were covered. By comparing obtained intensity ratios for different angles with computational developed stack model it was found that no simple layer by layer but some intermixing growth occurred including interaction with silicon substrate.}, language = {en} } @inproceedings{KaravaevTallaridaSchmeisseretal., author = {Karavaev, Konstantin and Tallarida, Massimo and Schmeißer, Dieter and Zschech, Ehrenfried}, title = {In-situ ALD growth of Hafnium oxide films}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 43}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 244}, abstract = {We report on a novel system for in-situ atomic layer growth (ALD) of high-k dielectric films. First results were obtained for Hf-oxide samples by using Hf-tetrachloride as precursor and water as oxidizer. We compare the photoelectron spectra of Si2p, O1s and Hf4f of our in-situ prepared films with samples (ex-situ) prepared by industrial ALD reactors and discuss similarities and differences observed in the core level spectra of the various samples by considering the different growth conditions.}, language = {en} } @inproceedings{TallaridaKaravaevSchmeisseretal., author = {Tallarida, Massimo and Karavaev, Konstantin and Schmeißer, Dieter and Zschech, Ehrenfried}, title = {Photoemission and absorption spectroscopy for in situ investigations of the ALD growth}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 43}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 242}, abstract = {We have investigated the growth of Hf-oxide on Si by means of photoemission and X-ray absorption spectroscopy using synchrotron radiation at Bessy, Berlin. The Hf-oxide layers were grown via atomic layer deposition (ALD) using an in-situ ALD reactor attached to the investigation chamber. The XPS and XAS spectra were measured after every deposition cycle by transferring the sample into the investigation chamber without breaking the vacuum. From the experimental data we have obtained information about the early stages of the Hf-oxide growth, concerning in particular the reactivity of the interface with Si. Due to the possibility to study the layers after every cycle and with different oxidation parameters without exposing them to contaminants, the in situ investigation revealed to be a very important method to understand the growth properties of Hf-oxide.}, language = {en} } @inproceedings{KaravaevTallaridaSchmeisser, author = {Karavaev, Konstantin and Tallarida, Massimo and Schmeißer, Dieter}, title = {Evolution of the interfacial layer during the atomic layer deposition of HfO2 on Si/SiO2 substrates}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 160}, abstract = {We studied the formation of the interfacial layer in the Si/SiO2/HfO2 system using the in-situ Atomic Layer Deposition (ALD) reactor developed in our group [1,2]. We measured the X-ray photoelectron and X-ray absorption spectra with synchrotron radiation at the beamline U49-2/PGM2-BESSY II. The ALD growth was obtained using different Hf-precursors (HfCl4,TEMAHf and TDMAHf) on various prepared substrates at different temperatures. The investigation was carried out in-situ giving the possibility to determine the properties of the grown film after every ALD cycle without breaking the vacuum. We observed the evolution of the Si/SiO2/HfO2 system during the formation of first three Hf-oxide layers, detecting the interfacial growth of SiO2 during the initial ALD cycles from the XPS spectra of Si2p. We discuss how the interfacial layer growth depends on the various ALD parameters. [1] M. Tallarida, K. Karavaev, and D. Schmeisser, J. Appl. Phys. 104, 064116 (2008); [2] M. Tallarida, K. Karavaev, and D. Schmeisser, J. Vac. Sci. Technol. B, accepted for publication.}, language = {en} } @inproceedings{KolanekKaravaevTallaridaetal., author = {Kolanek, Krzysztof and Karavaev, Konstantin and Tallarida, Massimo and Schmeißer, Dieter}, title = {In-situ investigations of the atomic layer deposition of HfO2 with UHV/AFM}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 44}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 160}, abstract = {We studied in-situ the atomic layer deposition (ALD) of HfO2 with ultra high vacuum (UHV) atomic force microscope (AFM), using the ALD reactor developed by our group [1, 2]. The reactor was attached to the Omicron Large Sample-UHV/AFM system in the AFM-Lab of the Angewandte Physik-Sensorik chair at the BTU-Cottbus. We investigated different Si(001)/SiO2 substrates and surface preparation techniques performed before the ALD process. After each ALD cycle (using TDMAHf and H2O as precursors), we studied the influence of the HfO2 growth on the root mean square (RMS) roughness; the surface fractal dimension and the height histogram: the surface skewness and kurtosis. We focused on the influence of the substrate temperature on the surface topography during the ALD. The in-situ studies of the ALD process with the UHV/AFM system correlated with the experiments performed with photoelectron spectroscopy can be used for understanding the fundamental properties of the ALD of HfO2 on Si(001). [1] M. Tallarida, K. Karavaev, and D. Schmeisser, J. Appl. Phys. 104, 064116 (2008); [2] M. Tallarida, K. Karavaev, and D. Schmeisser, J. Vac. Sci. Technol. B, accepted for publication.}, language = {en} } @inproceedings{TallaridaKaravaevKolaneketal., author = {Tallarida, Massimo and Karavaev, Konstantin and Kolanek, Krzysztof and Schmeißer, Dieter}, title = {Basics of the atomic layer deposition of HfO2 onto Si/SiO2 substrates: in-situ investigations with XPS, XAS and UHV-AFM}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 44}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 44}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 159}, abstract = {We developed a reactor for investigating in-situ the atomic layer deposition (ALD) of HfO2. X-ray photoelectron and X-ray absorption spectra were collected after each ALD cycle using synchrotron radiation at the beamline U49-2/PGM2 - BESSY II, Berlin. The morphology of the substrate and thin film surfaces was investigated after each ALD cycle with an UHV-AFM microscopy attached to the ALD reactor. We studied the ALD on differently prepared substrates, at different substrate temperatures, and using different Hf-precursors (HfCl4, TEMAHf, TDMAHf). We observed the evolution of the Si/SiO2/HfO2 system during the formation of the first three Hf-oxide layers [1]; we detected the incorporation of Cl into the Hf-oxide films and proposed a mechanism responsible for the Cl contamination [2]; we found evidence of the interfacial-SiO2 growth during the initial ALD cycles and of dipole formation at the HfO2/SiO2 interface. In this contribution we illustrate the basics of the technique used, and discuss the physical-chemical properties of ALD on the basis of the experimental results. [1] M. Tallarida, K. Karavaev, and D. Schmeisser, J. Appl. Phys. 104, 064116 (2008); [2] M. Tallarida, K. Karavaev, and D. Schmeisser, J. Vac. Sci. Technol. B, accepted for publication.}, language = {en} } @inproceedings{TallaridaKaravaevKolaneketal., author = {Tallarida, Massimo and Karavaev, Konstantin and Kolanek, Krzysztof and Schmeißer, Dieter}, title = {In-situ experimental approach to the study of atomic layer deposition with atomic force microscope, X-ray photoelectron and X-ray absorption spectroscopy}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 44}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft ; Reihe 6, Bd. 44}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S.176}, abstract = {We describe our experimental approach to the investigation of atomic layer deposition (ALD). ALD is a powerful deposition technique for growing conformal thin films of composite materials with atomically accurate thickness on large area [1]. Despite the enormous industrial interest growing around ALD, its fundamental properties were not yet properly studied. We developed an ALD reactor for the in-situ investigations using XPS, XAS and AFM as experimental techniques. We studied the chemical-physical properties of the growing thin films after each deposition cycle. Here, we illustrate the recent results concerning the ALD of HfO2 obtained using different Hf-precursors on various substrates [2]. We show how the in-situ investigations could deliver an important insight into the fundamental characteristics of ALD and how these information could be used to modify and optimize the deposition parameters. [1] M. Leskel{\"a}, M. Ritala, Thin Solid Films, 409, 138, 2002; [2] M. Tallarida, K. Karavaev, and D. Schmeisser, J. Appl. Phys. 104, 064116 (2008).}, language = {en} } @inproceedings{MichlingKolanekSchmeisseretal., author = {Michling, Marcel and Kolanek, Krzysztof and Schmeißer, Dieter and Tallarida, Massimo}, title = {A growth model for the HfO2 ALD process}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 294}, abstract = {In this contribution we report on our in-situ2 cycle-by-cycle (up to the 25 cycles) investigation of the HfO2 atomic layer deposition (ALD) process using the method of x-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS). We used Tetrakis-Dimethyl-Amino-Hafnium (TDMA-Hf) and H2O as precursors and p-type Si wafer with native oxide as a substrate. The XPS measurements were carried out at BESSY II in Berlin with primary energies of 150 eV and 640 eV and the EELS measurements were done with a primary energy of 50 eV. We measured the O1s, Si2p core level and the valence band including the Hf 4f core level. From the Hf4f to Si2p ratios taken at each energy we developed a growth model for the first monolayer and for the following layers too. From our data we conclude, that in the first monolayer up to the fourth ALD cycle an island growth occurs. The height of these islands is about 0,5nm. After the first monolayer is completed, a layer- by-layer growth can be expected. In order to proof this observation we have simulated the Hf/Si ratio for different excitation energies and found a very good agreement with our measurement data. The EELS data especially the evaluation of the loss function onset confirm our growth model.}, language = {en} } @inproceedings{TallaridaDessmannStaedteretal., author = {Tallarida, Massimo and Deßmann, Nils and St{\"a}dter, Matthias and Friedrich, Daniel and Michling, Marcel and Schmeißer, Dieter}, title = {Atomic layer deposition of TiO}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 46}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {We present a study of the initial growth of TiO2 on Si(111) by atomic layer deposition (ALD). The Si substrate was etched with NH4F before ALD to remove the native oxide film and to produce a Si-H termination. In-situ experiments by means of photoemission and X-ray absorption spectroscopy were conducted with synchrotron radiation on Ti-oxide films produced using Ti-tetra-iso-propoxide (TTIP) and water as precursors. O1s, Ti2p, C1s, and Si2p core level, and O1s and Ti2p absorption edges show the transition of the Ti-oxide properties during the first layers. The growth starts with a very small growth rate (0.03nm/cycle) due to the growth inhibition of the Si-H termination and proceeds with higher growth rate (0.1nm/cycle) after 1.5nm Ti-oxide has been deposited.}, language = {en} } @inproceedings{DasStaedterTallaridaetal., author = {Das, Chittaranjan and St{\"a}dter, Matthias and Tallarida, Massimo and Schmeißer, Dieter}, title = {Investigation of Linear Dichroism in ALD layers of TiO2}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Titanium dioxide is on the most studied material due to its wide range of applications in various fields such as self cleaning, photocatalysis, solar cell, water splitting, bio-implants, etc. In order to increase its efficiency in water splitting and solar cell, it is necessary to understand the crystal structure and electronic properties in thin films. In our approach we are investigating the X-ray linear dichroism (XLD) of thin layers of TiO2. XLD studies have been done in multiferroics, antiferromagnetic, and ferromagnetic materials, but a very less amount of work have been done in studying XLD effect of TiO2 thin films. These layers are grown by in-situ atomic layer deposition (ALD) system and are investigated with X-ray absorption spectroscopy (XAS) at BESSY II, Berlin. ALD is a promising technique to grow thin films on different substrates conveniently due to its uniform deposition property. XAS study will also help us to better understand the interfacial electronic properties of thin films of TiO2.}, language = {en} } @inproceedings{TallaridaMichlingDasetal., author = {Tallarida, Massimo and Michling, Marcel and Das, Chittaranjan and Friedrich, Daniel and St{\"a}dter, Matthias and Schmeißer, Dieter}, title = {Role of substrate chemistry in ALD revealed by in-situ techniques}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Bd. 47}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {We show recent results of our in-situ investigations where the role of substrate chemistry in ALD is outlined. While the usual strategy to develop new properties of ALD films is to find new precursors or new procedures, the influence of substrate chemistry on the growth properties of ALD films has been often underestimated. This has principally a technical reason, as the usual characterization methods (QMS, FTIR, ellipsometry) are only weakly sensitive to the substrate, and a characterization of substrates before ALD is often not possible. Thanks to the use of in-situ characterization methods, including photoemission and X-ray absorption spectroscopy with synchrotron radiation, we are able to determine chemical properties of substrates before ALD and after either half or complete ALD cycles. The substrate chemistry influences the standard Al2O3 ALD with TMA and water [1,2], as well as the TiO2 ALD with TTIP and either water, O2 or O2-plasma. [1] M. Tallarida, K. Kukli, M. Michling, M. Ritala, M. Leskel{\"a} and D. Schmeisser, Chem. Mater. 23, 3159 (2011); [2] M. Tallarida, C. Adelmann, A. Delabie, S. van Elshocht, M. Caymax, and D. Schmeisser, Appl. Phys. Lett. 92, 042906 (2011).}, language = {en} } @misc{DasTallaridaSchmeisser, author = {Das, Chittaranjan and Tallarida, Massimo and Schmeißer, Dieter}, title = {Si microstructures laminated with a nanolayer of TiO2 as long-term stable and effective photocathodes in PEC devices}, series = {Nanoscale}, journal = {Nanoscale}, number = {7}, issn = {2040-3364}, doi = {10.1039/C5NR00764J}, pages = {7726 -- 7733}, abstract = {Photoelectrochemical (PEC) water splitting is one of the most emerging fields for green energy generation and storage. Here we show a study of microstructured Si covered by a TiO2 nano-layer. The microstructures are prepared by galvanostatic selective etching of Si. The TiO2 nano-layer was deposited by atomic layer deposition (ALD) to protect the microstructured photocathode against corrosion. The obtained microstructured photocathode showed a shift in the onset potential of 400 mV towards the anodic direction compared to bare Si. The Si microstructures laminated with a nano-layer of TiO2 show stability over 60 hours of measurement.}, language = {en} } @inproceedings{HenkelDasSowinskaetal., author = {Henkel, Karsten and Das, Chittaranjan and Sowinska, Małgorzata and Tallarida, Massimo and Schmeißer, Dieter and Gargouri, Hassan and K{\"a}rkk{\"a}nen, Irina and Schneidewind, Jessica and Gruska, Bernd and Arens, Michael}, title = {Charakterisierung von TiO2-ALD-Schichten und deren Nutzung f{\"u}r die Passivierung von Si-Photokathoden}, series = {Tagungsband Photovoltaik-Meeting: Anwendungen-Qualit{\"a}t-Perspektiven, Senftenberg, 15.04.2015}, booktitle = {Tagungsband Photovoltaik-Meeting: Anwendungen-Qualit{\"a}t-Perspektiven, Senftenberg, 15.04.2015}, editor = {Gl{\"u}ck, B. K. and Schmidt, S. and Stein, E. and Raschke, J{\"o}rg-Uwe and Richter, H.}, publisher = {BTU Cottbus-Senftenberg}, address = {Senftenberg}, pages = {3 -- 8}, abstract = {Wir berichten zun{\"a}chst {\"u}ber den Einfluss der Methode der Atomlagenabscheidung auf die TiO2-Schichteigenschaften. Insbesondere wird der Zusammenhang zwischen Ti3+- sowie Interbandzust{\"a}nden mit elektrischen Kennlinien und deren Einfluss auf funktionale Schichteigenschaften diskutiert. Anschließend werden Mikrostrukturierung, Grenzfl{\"a}chen-Engineering und konforme Abscheidung einer TiO2-ALD-Schutzschicht effektiv zur Performance-Steigerung von p-Si-Photokathoden angewendet.}, language = {de} } @misc{NourbakhshAdelmannSongetal., author = {Nourbakhsh, Amirhasan and Adelmann, Christoph and Song, Yi and Lee, Chang Seung and Asselberghs, Inge and Huyghebaert, Cedric and Brizzi, Simone and Tallarida, Massimo and Schmeißer, Dieter and Elshocht, Sven van and Heyns, Marc and Kong, Jing and Palacios, Tom{\´a}s and De Gendt, Stefan}, title = {Graphene oxide monolayers as atomically thin seeding layers for atomic layer deposition of metal oxides}, series = {Nanoscale}, volume = {2015}, journal = {Nanoscale}, number = {7}, issn = {2040-3364}, doi = {10.1039/C5NR01128K}, pages = {10781 -- 10789}, abstract = {Graphene oxide (GO) was explored as an atomically-thin transferable seed layer for the atomic layer deposition (ALD) of dielectric materials on any substrate of choice. This approach does not require specific chemical groups on the target surface to initiate ALD. This establishes GO as a unique interface which enables the growth of dielectric materials on a wide range of substrate materials and opens up numerous prospects for applications. In this work, a mild oxygen plasma treatment was used to oxidize graphene monolayers with well-controlled and tunable density of epoxide functional groups. This was confirmed by synchrotron-radiation photoelectron spectroscopy. In addition, density functional theory calculations were carried out on representative epoxidized graphene monolayer models to correlate the capacitive properties of GO with its electronic structure. Capacitance-voltage measurements showed that the capacitive behavior of Al2O3/GO depends on the oxidation level of GO. Finally, GO was successfully used as an ALD seed layer for the deposition of Al2O3 on chemically inert single layer graphene, resulting in high performance top-gated field-effect transistors.}, language = {en} } @inproceedings{AlbertonCorreaBrizziTallaridaetal., author = {Alberton Corr{\^e}a, Silma and Brizzi, Simone and Tallarida, Massimo and Schmeißer, Dieter}, title = {Charging effect in HfO2 films deposited on SiO2/Si by atomic layer deposition}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Thin films of hafnium oxide (HfO2) deposited by atomic layer deposition (ALD) have been studied extensively as a high-k replacement for the SiO2 gate in field effect transistors. The use of ALD process allows one to grow homogeneous thin films at low temperatures with a precise control of thickness [1]. Some important electrical considerations for the application of a high-k dielectric include the presence of fixed charge (Qf) and charge trapping in the dielectric. For instance, in the case of Al2O3 thin films deposited on Si, the thickness of the interfacial SiO2 layer was identified as a key fundamental parameter determining Qf [2]. A similar trend can be also expected in HfO2/Si structures. Therefore, in this work, we proposed an in situ evaluation of photon induced charge trapping in HfO2 films deposited on SiO2/Si structures. For that, tetrakis-di-methyl-amino-hafnium (TDMAHf) and H2O were employed as precursors to deposit HfO2 films on SiO2/Si samples with variable thickness of the SiO2 interlayer. Measurements were performed by Synchrotron Radiation Photoemission Spectroscopy (SR-PES). Results indicated that the charging process is dependent on the thickness of the SiO2 interlayer and on the quality of the HfO2 film. [1] M. Leskel{\"a} and M. Ritala, Thin Solid Films 409, 138 (2002). [2] G. Dingemans et al., J. Appl. Phys. 110, 093715 (2011).}, language = {en} } @inproceedings{BrizziTallaridaAdelmannetal., author = {Brizzi, Simone and Tallarida, Massimo and Adelmann, Christoph and Ragnarsson, Lars-{\AA}ke and Elshocht, Sven van and Schmeißer, Dieter}, title = {Structural changes in HfO2 thin films: thickness and doping dependence}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {In this work we show results regarding MOCVD and ALD HfO2 as well as Al-doped HfO2. We use Synchrotron Radiation Photoemission Spectroscopy (SRPES) to determine Hf/O atomic ratios and X-ray Absorption Spectroscopy (XAS) to investigate the electronic properties related to their crystallization. MOCVD films are synthesized at temperatures ranging from ambient to 400∘C and show structures from completely amorphous to monoclinic. ALD films are amorphous as deposited, and can crystallize after post-deposition anneal depending on the percentage of Al-doping. We discuss PES results in order to determine how close to stoichiometry the Hf/O atomic ratios of the films are, as well as the doping level. From XAS data, instead, we can point out how orbital hybridizations are related to structural and physical properties.}, language = {en} } @inproceedings{DasTallaridaSchmeisser, author = {Das, Chittaranjan and Tallarida, Massimo and Schmeißer, Dieter}, title = {X-ray linear dichroism in atomic layer deposited Titanium dioxide layers}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Among the various metal oxides TiO2 has been investigated because of its wide range of applications in various fields such as self-cleaning, photocatalysis, solar cell, water splitting, bio-implants. In order to increase its efficiency in water splitting and solar cell energy conversion, it is necessary to understand the crystal structure and electronic properties of thin films. Generally the process of synthesis may modify the electronic properties of TiO2. In the present work we show X-ray linear dichroism (XLD) measurements of TiO2 thin films of different polymorphs. Titania thin films were produced by atomic layer deposition (ALD) and were characterized in-situ with X-ray photoelectron and absorption spectroscopy at synchrotron radiation center BESSY-II. We found that that all titania phases show XLD at Ti-L and O-K edges, but the intensity of XLD is different for different phases. We discuss our data in terms of the partial density of states.}, language = {en} } @inproceedings{DasTallaridaSchmeisser, author = {Das, Chittaranjan and Tallarida, Massimo and Schmeißer, Dieter}, title = {Control of thickness of SiO2 interfacial layer for photocatalytic water splitting on Si photocathodes}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Silicon with a band gap of 1.1eV is an excellent candidate for visible photocatalytic water splitting. But p-type Si has a low quantum yield and are less efficient for water splitting [1]. It has been shown that preventing oxidation of Si surface can shift the onset potential for water reduction by about 300mV towards more positive [2]. We investigated in detail the influence of the SiO2 layer thickness on the onset potential for water splitting on Si photocathodes: we used p-type Si substrates covered with SiO2 layers of varying thickness. Then, we deposited a thin TiO2 film on using atomic layer deposition (ALD) to inhibit Si oxidation during the electrochemical experiment. In this way we could shift the onset potential up to 200mV, depending on the SiO2 thickness. [1]E. L. Warren, S. W. Boettcher, M. G. Walter, H. A. Atwater, and N. S. Lewis: J. Phys. Chem. C 115 (2011) 594. [2]B. Seger, Anders B. Laursen, P. C. K. Vesborg, T. Pedersen, O. Hansen, S. Dahl, I. Chorkendorff, Angew. Chem. Int. Ed. 2012, 51, 9128}, language = {en} } @inproceedings{TallaridaHenkelGargourietal., author = {Tallarida, Massimo and Henkel, Karsten and Gargouri, Hassan and Haeberle, J{\"o}rg and Gruska, Bernd and Arens, Matthias and Schmeißer, Dieter}, title = {New opportunities with Plasma enhanced atomic layer deposition (PE-ALD) of oxides}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Thermal Atomic layer deposition (T-ALD) of oxides is obtained by the pulsed alternation of a metal precursor and an oxygen source, typically H2O or O3, and the reactions leading to ALD are thermally activated. With plasma enhanced ALD (PE-ALD), instead, the oxygen source is represented by an oxygen-containing plasma. The higher reactivity of the plasma-generated species extend the capabilities of ALD: improved film quality and increased flexibility in process conditions, such as growth at low temperature, are typical advantages of PE-ALD over T-ALD. We report on results on the preparation of thin (<100 nm) aluminum oxide (Al2O3) films on silicon substrates using T-ALD and PE-ALD in the SENTECH SI ALD LL system. Films were deposited in the temperature range between room temperature (RT) and 200∘C. We characterized the films with spectroscopic ellipsometry (thickness, refractive index, growth rate) over 4" wafers and with X-ray photoelectron spectroscopy. All films resulted in a high degree of homogeneity, independent of the deposition temperature. Investigations with capacitance-voltage and conductance-voltage measurements showed a very low interface states density for the PE-ALD films.}, language = {en} } @inproceedings{AlbertonCorreaBrizziTallaridaetal., author = {Alberton Corr{\^e}a, Silma and Brizzi, Simone and Tallarida, Massimo and Schmeißer, Dieter}, title = {Spectroscopic investigation of the electronic structure of HfO2 thin films}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 211}, abstract = {HfO2 is of current interest as a material for memristive and ferroelectric devices. In this work, we used spectroscopic techniques to evaluate the electronic structure and defects mechanisms in thin HfO2 films deposited by atomic layer deposition and by metal-organic chemical vapour deposition. The partial density of states for the valence and the conduction bands was determined by the detailed analysis of the O1s resonance profile by resonant photoelectron spectroscopy. From the relative contributions we find a CNL 6.5 eV referred to Evac. We also find that the positions of valence band maximum and conduction band minimum, the excitation range for the polaronic states and the range of charge transfer band were not influenced by the preparation conditions. All films exhibit a band gap of 6.2 eV. However, the Fermi level position was found to vary within about 1.2 eV depending on the preparation conditions, which we argue that is due to the presence of charges within the films. This explains why the position of the Fermi level depends on the individual preparation parameters.}, language = {en} } @inproceedings{DasTallaridaSchmeisser, author = {Das, Chittaranjan and Tallarida, Massimo and Schmeißer, Dieter}, title = {Determination of charge neutrality level in TiO2 films from res-PES measurements}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 415}, abstract = {Titanium dioxide is one of the metal oxides which have versatile application in different fields. The applications of TiO2 are in the field of cosmetics, electronics (memory resistive switching), dye, photonics and photocatalysis. In the present paper we study the resPES data of TiO2 films prepared by atomic layer deposition. The measurements are done in in-situ system at beam line U49/2-PGM2 in BESSY-II. The density of state in valence band and conduction band is obtained from the resonance photo electron spectroscopy (res-PES) of the O1s and the Ti2p edge. The data allow to determine the position of the VBM and CBM with respect to the Fermi energy. Also the existence of localized O2p and Ti2p derived states is deduced which appear in the gap. In addition we determine the charge neutrality level (CNL).The CNL is the position where the weight of the density of state from valence band and conduction band are equal. This is an important quantity for the discussion of interface properties.}, language = {en} } @inproceedings{RouissiTallaridaSchmeisser, author = {Rouissi, Zied and Tallarida, Massimo and Schmeißer, Dieter}, title = {Study of atomic layer deposition with scanning tunneling microscopy}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 401}, abstract = {We present a work concerning the study of the initial steps of atomic layer deposition (ALD) with scanning tunneling microscopy (STM). We focus on the role of the substrates which has been often neglected.However, the detailed knowledge of precursor-substrate reactions is important for the understanding of how ALD proceeds. We report on the reaction of the Al-precursor, trimethyl-Al (TMA), on nanostructured surfaces such as Ag nanoclusters and nanostripes prepared by thermal evaporation on HOPG. We characterized the surface before and after one TMA adsorption pulse at room temperature, observing that the morphology of step edges changes after TMA creating a new terraces with a width of 7-10 nm, translated in the direction of the TMA deposition. This shows that, in case of a regular stepped surface, the substrate morphology would keep the same regularity with the translation in a direction privileged by the precursor absorption.}, language = {en} } @inproceedings{RouissiBrizziAlbertonCorreaetal., author = {Rouissi, Zied and Brizzi, Simone and Alberton Corr{\^e}a, Silma and Tallarida, Massimo and Schmeißer, Dieter}, title = {Comparison of charge neutrality level of Cu/CuO/HfO2 and Si/SiO2/HfO2}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {208}, abstract = {Copper Oxide (CuO) is a promising metal oxide semiconductor, which can be used in different applications, such as catalysis, solar energy conversion, and water splitting. In this work, we use resonance photoemission spectroscopy (ResPES) to analyse the electronics properties of HfO2 films deposited on Cu/CuO and Si/SiO2. For that, we deposited 10 cycles of HfO2 by atomic layer deposition (ALD) on Cu/CuO and Si/SiO2 samples and investigated the density states for the valence and conduction bands which were determined by the detailed analysis of the O1s resonance profile obtained by ResPES. We compared the positions of valence band maximum and conduction band minimum, the excitation range for the polaronic states and the range of charge transfer band in Cu/CuO/HfO2 and Si/SiO2/HfO2. Also, we determined the band gap and the charge neutrality level (CNL).}, language = {en} } @misc{DasRichterTallaridaetal., author = {Das, Chittaranjan and Richter, Matthias and Tallarida, Massimo and Schmeißer, Dieter}, title = {Electronic properties of atomic layer deposited films, anatase and rutile TiO2 studied by resonant photoemission spectroscopy}, series = {Journal of Physics D: Applied Physics}, volume = {49}, journal = {Journal of Physics D: Applied Physics}, number = {27}, issn = {0022-3727}, doi = {10.1088/0022-3727/49/27/275304}, pages = {275304-1 -- 275304-17}, abstract = {The TiO2 films are prepared by atomic layer deposition (ALD) method using titanium isopropoxide precursors at 250 °C and analyzed using resonant photoemission spectroscopy (resPES). We report on the Ti2p and O1s core levels, on the valence band (VB) spectra and x-ray absorption spectroscopy (XAS) data, and on the resonant photoelectron spectroscopy (resPES) profiles at the O1s and the Ti3p absorption edges. We determine the elemental abundance, the position of the VB maxima, the partial density of states (PDOS) in the VB and in the conduction band (CB) and collect these data in a band scheme. In addition, we analyze the band-gap states as well as the intrinsic states due to polarons and charge-transfer excitations. These states are found to cause multiple Auger decay processes upon resonant excitation. We identify several of these processes and determine their relative contribution to the Auger signal quantitatively. As our resPES data allow a quantitative analysis of these defect states, we determine the relative abundance of the PDOS in the VB and in CB and also the charge neutrality level. The anatase and rutile polymorphs of TiO2 are analyzed in the same way as the TiO2 ALD layer. The electronic properties of the TiO2ALD layer are compared with the anatase and rutile polymorphs of TiO2. In our comparative study, we find that ALD has its own characteristic electronic structure that is distinct from that of anatase and rutile. However, many details of the electronic structure are comparable and we benefit from our spectroscopic data and our careful analysis to find these differences. These can be attributed to a stronger hybridization of the O2p and Ti3d4s states for the ALD films when compared to the anatase and rutile polymorphs.}, language = {en} } @inproceedings{RouissiTallaridaSchmeisser, author = {Rouissi, Zied and Tallarida, Massimo and Schmeißer, Dieter}, title = {HfO2 grow by ALD on Si(111)-H terminated stepped surface}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, pages = {S. 419}, abstract = {We studied by STM the growth of HfO2 on Si (111)-H stepped surface (miscut by 0.5∘). The steps are aligned in the [11-2] direction. In order to obtain well defined steps and terraces we prepare the sample by chemical etching in 40\% Nh4F. In our in-situ study we investigate the ALD growth of HfO2 by TDMAH and H2O [1-2]. We follow for the first four ALD cycles the distribution of the nucleation sites. We also study the influence of the substrate temperature by comparing the growth within the ALD window at 300K and 580K. We observed that at RT the as-grown HfO2 forms stripes which are oriented normal to the step orientations. Further growth starts from the step edges and proceeds towards the terraces. Defects created by the etching processes act as nucleation sites for 3D islands. Based on our STM data we are able to correlate the structural changes on that inert and stepped Si(111)-H surface during ALD with experimental [3] and theoretical [4] results obtained for planar Si(100) surfaces. [1] M. Tallarida et al., Semicond. Sci. Technol. 27, 074010 (2012) [2] K. Kolanek et al., Thin Solid Films 518, 4688 (2010) [3] K. Kolanek et al., J. Vac. Sci. Technol. A 31, 01A104 (2013) [4]L. Riikka et al., J. Appl. Phys.96, 7686 (2004)}, language = {en} } @inproceedings{RouissiHenkelTallaridaetal., author = {Rouissi, Zied and Henkel, Karsten and Tallarida, Massimo and Schmeißer, Dieter}, title = {ALD growth of Al2O3 on Stepped Surface of HOPG and Ag-HOPG}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, pages = {S. 419}, abstract = {Atomic Layer Deposition (ALD) is an excellent deposition technique to grow thin film with high homogeneity coverage on ideal surfaces. Here we are interested in the growth properties on non-ideal (stepped, inert) surfaces. Using STM we studied the growth of Al2O3 by ALD on stepped surface of HOPG and silver covered HOPG (Ag-HOPG). The HOPG sample was cleaved to and then cleaned by N2 in vacuum. We obtain regular steps with terrace widths of 50nm - 500nm. Ag was deposited by thermal deposition on the HOPG. The Al2O3 growth at RT was studies after the first, third, and fifth cycle. Silver evaporation leads to step decoration with island of 1nm-7nm. On the terraces we find the formation of 2D domain of Ag chains. The features caused by the individual ALD cycles of Al2O3 depend on the terrace widths of the HOPG substrate. For small terraces (<100nm) we obtain a growth of 2D domains ( 20nm-25nm) on the edge steps and in the middle of the terrace. For large terraces (>100nm) we find agglomeration of the precursors on individual nucleation sites. Here 3D islands are formed with a height of up to 5nm in the fifth ALD cycle.}, language = {en} } @inproceedings{BrizziTallaridaSchmeisser, author = {Brizzi, Simone and Tallarida, Massimo and Schmeißer, Dieter}, title = {CVD and ALD deposited hafnia: an XPS study}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {In this work we report on Hafnium oxide deposited on silicon by means of chemical vapour deposition (CVD) and atomic layer deposition (ALD) using tetrakis-di-methyl-amino-Hf (TDMAHf) and water as precursors. We have studied the behavior of ALD and CVD at intermediate temperatures: ALD was performed outside the ALD window (T>300∘C), whereas CVD was performed at low temperatures, approaching the ALD window (T<400∘C). In this way we wanted to elucidate about the possibility of taking advantage of the conformality of ALD films and the high growth rate of CVD at the same time. Comparable sets of samples prepared with the two methods were measured by X-ray photoelectron spectroscopy and atomic force microscopy in order to determine differences between them: growth rate, Hf/O ratio, valence band positions and roughness are discussed and compared as a function of deposition temperature and process parameters.}, language = {en} } @inproceedings{ChoudhuryTallaridaDasetal., author = {Choudhury, Sakeb Hasan and Tallarida, Massimo and Das, Chittaranjan and Schmeißer, Dieter}, title = {Atomic layer deposition of Ga2O3 using Tri-methyl-Gallium and H2O}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {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.}, language = {en} } @inproceedings{DasTallaridaSkorupskaetal., author = {Das, Chittaranjan and Tallarida, Massimo and Skorupska, Katarzyna and Lewerenz, Hans-Joachim and Schmeißer, Dieter}, title = {An efficient Si photo cathode for a wide range of electrolyte pH values}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {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.}, language = {en} } @inproceedings{TallaridaAballeKumaretal., author = {Tallarida, Massimo and Aballe, Lucia and Kumar, Ashwani and Barman, Sudipto Roy and Horn, Karsten}, title = {Characterisation of nearly free electron bands in thin Al-Mg alloy films on Si(111)}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, abstract = {Thin films of Al-Mg alloys have been grown on Si(111) by MBE over a wide range of compositions, and were characterized by angle-resolved photoemission. For Al-rich alloys, electron confinement leads to the occurrence of quantum well states, and a surface state similar to that in the Al/Si(111) film is found. For Mg-rich compositions, only a broad surface state is observed. The occurrence of quantum well states and the surface state, and their binding energy dependence on alloy composition is explained in terms of the virtual crystal approximation, with an average electron density in the alloy system. The dispersion of the quantum well states in a direction parallel to the film shows a nearly free electron behaviour similar to that found in Al/Si(111). The variation of electron density in these alloy films open the way for a study of more complex metallic systems, e.g. an investigation of the influence of electron density of the electromagnetic response.}, 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{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{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} } @misc{CibrevTallaridaDasetal., author = {Cibrev, Dejan and Tallarida, Massimo and Das, Chittaranjan and Lana-Villarreal, Teresa and Schmeißer, Dieter and Gómez, Roberto}, title = {New insights into water photooxidation on reductively pretreated hematite photoanodes}, series = {Physical Chemistry Chemical Physics}, volume = {19}, journal = {Physical Chemistry Chemical Physics}, number = {32}, issn = {1463-9076}, doi = {10.1039/C7CP03958A}, pages = {21807 -- 21817}, abstract = {It has been recently demonstrated that the photoactivity toward oxygen evolution of a number of n-type metal oxides can be substantially improved by a reductive electrochemical pretreatment. Such an enhancement has been primarily linked to the formation of low valent metal species that increase electrode conductivity. In this work, we report new insights into the electrochemical doping using highly ordered (110)-oriented hematite nanorods directly grown on FTO. The reductive pretreatment consists in applying negative potentials for a controlled period of time. Such a pretreatment was optimized in both potentiostatic and potentiodynamic regimes. We show that the optimized pretreatment enhances electrode conductivity due to an increase in charge carrier density. However, it additionally triggers changes in the morphologic, catalytic and electronic properties that facilitate the separation and collection of the photogenerated charge carriers causing an up to 8-fold enhancement in the photocurrent for water oxidation. The reductive pretreatment can be considered as a highly controllable electrochemical n-type doping with the amount of generated Fe2+/polaron species and the change in film morphology as the main factors determining the final efficiency for water photooxidation of the resulting electrodes.}, language = {en} } @incollection{HenkelKotRichteretal., author = {Henkel, Karsten and Kot, Małgorzata and Richter, Matthias and Tallarida, Massimo and Schmeißer, Dieter}, title = {An (In Situ)² Approach: ALD and resPES Applied to Al₂O₃, HfO₂, and TiO₂ Ultrathin Films}, series = {Encyclopedia of Interfacial Chemistry: Surface Science and Electrochemistry, Vol. 3.1}, booktitle = {Encyclopedia of Interfacial Chemistry: Surface Science and Electrochemistry, Vol. 3.1}, editor = {Wandelt, Klaus}, publisher = {Elsevier}, address = {Oxford}, isbn = {978-0-12-809739-7}, doi = {10.1016/B978-0-12-409547-2.13852-1}, pages = {18 -- 26}, abstract = {Oxide surface coatings are of importance in tailoring interface properties with respect to surface passivation, adjustment of surface potentials, or providing active centers for surface reactions. In this contribution, we report about surface coatings prepared by the atomic layer deposition (ALD) method. ALD is known for its conformal growth of ultrathin, dense films which exhibit a low concentration of pinholes.}, language = {en} } @misc{DorpNynsCuypersetal., author = {Dorp, Dennis H. von and Nyns, Laura and Cuypers, Daniel and Ivanov, Tsvetan and Brizzi, Simone and Tallarida, Massimo and Fleischmann, Claudia and H{\"o}nicke, Philipp and M{\"u}ller, Matthias and Richard, Olivier and Schmeißer, Dieter and De Gendt, Stefan and Lin, Dennis H. C. and Adelmann, Christoph}, title = {Amorphous Gadolinium Aluminate as a Dielectric and Sulfur for Indium Phosphide Passivation}, series = {ACS Applied Electronic Materials}, volume = {1}, journal = {ACS Applied Electronic Materials}, number = {11}, issn = {2637-6113}, doi = {10.1021/acsaelm.9b00388}, pages = {2190 -- 2201}, abstract = {The passivation of n-type InP (100) using sulfur in combination with a gadolinium aluminate (GAO) dielectric layer has been studied. Photoluminescence, minority-carrier lifetime, and capacitance-voltage measurements indicate that a (NH4)2S vapor passivation step prior to atomic layer deposition of the oxide effectively lowers the interface state density. Surface and interface chemistry were studied by synchrotron radiation photoemission spectroscopy (SRPES). The effect of ex situ surface passivation after native oxide removal in HCl solution was examined. It was observed that surface reoxidation occurred during (NH4)2S vapor exposure, leading to the formation of Inx(HPO4)y. S was present on the surface as a sulfide in both surface and subsurface sites. After atomic layer deposition of GAO, sulfates were detected in addition to Inx(HPO4)y, which was confirmed by near-edge X-ray absorptionfine structure analysis. The S in the stack was quantified using reference-free grazing incidence X-rayfluorescence analysis. X-ray absorption spectroscopy showed that Gd was oxidized and present in the 3+ oxidation state, most likely as a phosphate close to the InP interface and possibly mixed with sulfates. Energy-dependent SRPES measurements of Al 2p and Gd 4d core levels, complemented by transmission electron microscopy, further suggest that the dielectric layer was segregated. Valence band measurements confirm the effective passivation of InP, indicating unpinning of the surface Fermi level.}, language = {en} } @misc{KotKegelmannKoebleretal., author = {Kot, Małgorzata and Kegelmann, Lukas and K{\"o}bler, Hans and Vorokhta, Mykhailo and Escudero, Carlos and K{\´u}š, Peter and Šm{\´i}d, Břetislav and Tallarida, Massimo and Albrecht, Steve and Abate, Antonio and Matol{\´i}nov{\´a}, Iva and Schmeißer, Dieter and Flege, Jan Ingo}, title = {In situ Near-Ambient Pressure X-ray Photoelectron Spectroscopy Reveals the Influence of Photon Flux and Water on the Stability of Halide Perovskite}, series = {ChemSusChem}, volume = {13}, journal = {ChemSusChem}, number = {21}, issn = {1864-5631}, doi = {10.1002/cssc.202001527}, pages = {5722 -- 5730}, abstract = {For several years, scientists have been trying to understand the mechanisms that reduce the long-term stability of perovskite solar cells. In this work, we examined the effect of water and photon flux on the stability of CH3NH3PbI3 perovskite films and solar cells using in situ near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), field emission scanning electron microscopy (FESEM), and current density-voltage (J-V) characterization. The used amount of water vapor (up to 1 mbar) had a negligible impact on the perovskite film. The higher the photon flux, the more prominent were the changes in the NAP-XPS and FESEM data; also, a faster decline in power conversion efficiency (PCE) and a more substantial hysteresis in the J-V characteristics were observed. Based on our results, it can be concluded that the PCE decrease originates from the creation of Frenkel pair defects in the perovskite film under illumination. The stronger the illumination, the higher the number of Frenkel defects, leading to a faster PCE decline and more substantial hysteresis in the J-V sweeps.}, language = {en} }