naiem ali | United Arab Emirates University (original) (raw)
Papers by naiem ali
ACS Applied Materials & Interfaces, 2021
The intrinsic stability of the 5 V LiCoPO4-LiCo2P3O10 thin-film (carbon-free) cathode material co... more The intrinsic stability of the 5 V LiCoPO4-LiCo2P3O10 thin-film (carbon-free) cathode material coated with MoO3 thin layer is studied using a comprehensive synchrotron electron spectroscopy in situ approach combined with first-principle calculations. The atomic-molecular level study demonstrates fully reversible electronic properties of the cathode after the first electrochemical cycle. The polyanionic oxide is not involved in chemical reactions with the fluoroethylene-containing liquid electrolyte even when charged to 5.1 V vs Li+/Li. The high stability of the cathode is explained on the basis of the developed energy level model. In contrast, the chemical composition of the cathode-electrolyte interface evolves continuously by involving MoO3 in the decomposition reaction with consequent leaching of oxide from the surface. The proposed mechanisms of chemical reactions are attributed to external electrolyte oxidation via charge transfer from the relevant electron level to the MoO3 valence band state and internal electrolyte oxidation via proton transfer to the solvents. This study provides a deeper insight into the development of both a doping strategy to enhance the electronic conductivity of high-voltage cathode materials and an efficient surface coating against unfavorable interfacial chemical reactions.
Advanced Materials Interfaces, 2020
Advanced Materials Interfaces, 2020
Applied Surface Science, 2018
Abstract The electronic and chemical structure of two types of nearly lattice-matched InAs/(Cd,Zn... more Abstract The electronic and chemical structure of two types of nearly lattice-matched InAs/(Cd,Zn)(Se,Te) heterovalent interfaces grown coherently by molecular beam epitaxy are investigated by soft x-ray photoelectron spectroscopy (SXPS) and secondary ion mass-spectroscopy (SIMS). The valence band offset (VBO) at the CdSe/InAs heterointerface formed close to the Cd/Se ∼ 1:1 stoichiometric conditions is determined to be 1.02 ± 0.08 eV. The incorporation of a 3-monolayer-thick ZnTe intermediate layer between InAs and CdSe leads to an increase in the VBO between InAs and CdSe by approximately 0.17 eV. The dominant chemical bonds at the interface have been established to be InsbndSe or InsbndTe ones from analysis of SXPS spectra recorded at different excitation energies (100 – 650 eV) and surface sensitive SIMS study, while the signals from Cd(Zn)sbndAs bonds are negligible. The diffusion of the InAs substrate components to the CdSe layer is rather weak: in particular, the concentration of In and As atoms drops in the CdSe layer down to 1% at the distance from the interface of 1 nm. Introduction of the 1-nm-thick ZnTe layer slows down the As surface segregation even more.
Journal of The Electrochemical Society, 2019
Journal of Materials Chemistry A, 2018
The novel LiCoPO4–LiCo2P3O10 cathode material: a rigid band behavior of the electronic structure.
The Journal of Chemical Physics, 2016
Understanding the mechanism of the interaction of lithium ion conductors with water is crucial fo... more Understanding the mechanism of the interaction of lithium ion conductors with water is crucial for both fundamental and technological points of view. Despite the generally accepted fact that water is one of main sources of the degradation of Li-ion recharge batteries, the physicochemical processes occurring at the water-lithium ion conductor interface are not fully understood. By using synchrotron X-ray photoelectron spectroscopy (SXPS) and O K- and Co L- X-ray absorption near edge structure (XANES), we evidence that H2O is dissociatively adsorbed on LiCoO2 thin film at room temperature resulting in the formation of OH groups and the accumulation of the negative charge at the surface accompanied by electron transfer to the initial empty Co3d (eg (*)) state. By considering the experimentally obtained energy diagram of the ionic conductor and water, direct charge transfer is not favorable due to a high difference in the chemical potential of the ionic conductor and electronic levels of the molecule. Here, we develop the model for the dissociative water adsorption which explains the electron transfer to LiCoO2 by using the atomistic approach. The model takes into account the intrinsic defects found on the surface (<2 nm depth) by using the depth resolved photoemission experiments and can be explored to other layered transition metal oxides to interpret the interaction of water with the surface of ionic conductors.
Materials Letters, 2016
A method is presented which leads to a higher sputter rate as compared to the sputtering of the s... more A method is presented which leads to a higher sputter rate as compared to the sputtering of the surface of a bulk sample under the same sputtering conditions: the target is coated beforehand by a separate process to produce a nanostructured film on its surface. In the case of silver, the sputter yield under ion bombardment is 1.7 times higher. If the ions for the bombardment are generated by a voltage applied to the sample, then improvements up to a factor of five can be realized.
Journal of the European Ceramic Society, 2016
In the present work, novel V8C7/SiC(O) ceramic nanocomposites were synthesized upon thermal trans... more In the present work, novel V8C7/SiC(O) ceramic nanocomposites were synthesized upon thermal transformation of a polymer-derived single-source-precursor, which was obtained by the chemical modification of a polycarbosilane with vanadyl acetylacetonate. High-temperature treatment of the precursor in argon atmosphere first leads to an amorphous SiVOC single-phase ceramic which subsequently undergoes phase-separation, crystallization and finally converts into V8C7/SiC(O) ceramic nanocomposites. Interestingly, the high-temperature stability of V8C7/SiC(O) was shown to strongly depend on the oxygen content present either in the SiC(O) matrix or in the atmosphere during the annealing process. Thus, larger oxygen contents induce a conversion of the V8C7 phase into V5Si3. The specific surface area (SSA) of the obtained nanocomposite powders depends on the processing temperature: The SSA decreases from 64 to 4 m2/g as the pyrolysis temperature increases from 600 to 1300 °C, respectively. Whereas it increases again to ca. 50 m2/g as the sample is exposed to 1700 °C (6 h annealing), due to the evolution of CO. Preliminary results of the catalytic activity of the V8C7/SiC(O)-based materials show that they are active for the decomposition of the ammonia. The maximum ammonia conversion efficiency was found to be 35% at around 650 °C, which is higher than that of the pure vanadium carbide reported in the literature (ca. 13%).
J. Mater. Chem. C, 2016
The melt-shear organization technique for tailor-made polystyrene-co-polyacrylonitrile (PSAN) she... more The melt-shear organization technique for tailor-made polystyrene-co-polyacrylonitrile (PSAN) shell and silica core particles is investigated yielding easy-scalable carbonaceous porous films after etching and appropriate thermal treatment.
Chemistry of Materials, 2014
In this study, a comprehensive experimental in situ analysis of the evolution of the occupied and... more In this study, a comprehensive experimental in situ analysis of the evolution of the occupied and unoccupied density of states as a function of the charging state of the Li x≤1 CoO 2 films has been done by using synchrotron X-ray photoelectron spectroscopy (SXPS), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and O K-and Co L 3,2-edges XANES. Our experimental data demonstrate the change of the Fermi level position and the Co3d−O2p hybridization under the Li + removal and provide the evidence for the involvement of the oxygen states in the charge compensation. Thus, the rigid band model fails to describe the observed changes of the electronic structure. The Co site is involved in a Co 3+ → Co 4+ oxidation at the period of the Li deintercalation (x ∼ 0.5), while the electronic configuration at the oxygen site is stable up to 4.2 V. Further lowering of the Fermi level promoted by Li + extraction leads to a deviation of the electronic density of states due to structural distortions, and the top of the O2p bands overlaps the Co3d state which is accompanied by a hole transfer to the O2p states. The intrinsic voltage limit of LiCoO 2 has been determined, and the energy band diagram of Li x≤1 CoO 2 vs the evolution of the Fermi level has been built. It was concluded that Li x CoO 2 cannot be stabilized at the deep Li deintercalation even with chemically compatible solid electrolytes.
Frontiers of Multifunctional Integrated Nanosystems
The growth of fullerene C60 films on InP(001)-(2×4) was studied by a set of surface science techn... more The growth of fullerene C60 films on InP(001)-(2×4) was studied by a set of surface science techniques under ultra-high vacuum (UHV) conditions. Spectral signature measured by photoelectron and electron energy-loss spectroscopies (UPS, XPS, EELS, HREELS) corresponds to that of bulk C60 both at low (1–2 monolayers (ML)) and high (10 ML) coverage. The result shows a weak bonding, most probably
Chemistry of Materials, 2015
ABSTRACT In recent years, there have been significant efforts to understand the role of the elect... more ABSTRACT In recent years, there have been significant efforts to understand the role of the electronic structure of redox active materials according to their performance and thermodynamic stability in electrochemical storage devices and to develop novel materials with higher energy density and higher power. It is generally recognized that transition metal compounds used as a positive electrode determine the specific capacity and the energy density of rechargeable batteries, while the charge transfer resistance at electrolyte-electrode interface plays a key role in delivering the power of the electrochemical cell. In the present work, we study the stability of LixNi0.2Co0.7Mn0.1O2 thin films through the evolution of the occupied and unoccupied density of states as a function of the charging state of the electrode as well as the physicochemical conditions influencing the ionic transport across the electrode-electrolyte interface. A comprehensive experimental quasi in-situ approach has been applied by using synchrotron X-ray photoelectron spectroscopy (SXPS) and O K- and Ni L-, Co L-, Mn L - edges XANES. Our experimental data demonstrate the change of the Fermi level position with the Li+ removal and Ni2+ → Ni4+ and Co3+ → Co4+ changes of oxidation state for the charge compensation in the bulk of the material. As is evidenced by the experimentally determined energy band diagram of Lix≦1.0Ni0.2Co0.7Mn0.1O2 vs the evolution of the Fermi level, no hole transfer to the O2p bands is observed up to a charging state of 4.8 V which evidences the thermodynamic stability of Lix≦1.0Ni0.2Co0.7Mn0.1O2 under high charging voltage in contrast to LiCoO2. A very thin solid electrolyte interface layer (less than 30 Å thickness) on the Lix≦1.0Ni0.2Co0.7Mn0.1O2 film is formed in a decomposition reaction of the electrolyte also involving the transition metal oxide. The enhanced concentration of lithium in the interface layer correlates evidently with the electron transfer to the transition metal sites changing their electronic configuration. It is concluded that Lix≦1.0Ni0.2Co0.7Mn0.1O2 can serve as high energy density cathode material, but the delivery of high power, which is a critical parameter for an electric vehicle, is strongly influenced by the physicochemical conditions at the solid electrolyte interface, which can suppress Li+ diffusion or even block the Li+ paths across the interface.
![Research paper thumbnail of Erratum to “Surface phonons of clean and hydrogen terminated Si(110) surfaces” [Surface Science 582 (2005) 159–172]](https://attachments.academia-assets.com/85133334/thumbnails/1.jpg)
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Surface Science, 2005
We report an investigation of the dynamical properties of clean and monohydride-terminated Si(1 1... more We report an investigation of the dynamical properties of clean and monohydride-terminated Si(1 1 0) surfaces, measured by means of high resolution electron energy loss spectroscopy (HREELS). On both surfaces a number of surface phonons is observed and successfully assigned to predicted modes. A (1 • 5) reconstruction is found to be the stable surface phase corresponding to monohydride coverage of Si(1 1 0). For the Si-H stretching and bending bands of this monohydride Si(1 1 0) surface we find a relatively strong dispersion along the [1 1 0] direction. Apparently, this is related to the coupling of oscillators along the Si chains of the (1 1 0) surface. In addition, surface vibrations induced by adsorbed residual gases are measured and analysed.
Surface and Interface Analysis, 2004
ABSTRACT Viscosity measurements of GaInSn eutectic alloys were performed in a homebuilt device fo... more ABSTRACT Viscosity measurements of GaInSn eutectic alloys were performed in a homebuilt device for low (9%) and high (95%) relative humidity for shorter (450 min) and longer (1800 min) time periods. At constant exposure time a characteristic increase of viscosity is observed with increasing humidity. For high humidity, high viscosity is obtained after a short time.Assuming that the measured viscosity change is strongly related to the absorption of oxygen, XPS was applied to the chemical and quantitative analysis of differently prepared samples. In all cases, Ga is predominantly oxidized at the surface whereas Ga atoms in the metallic state are located deeper inside. Besides Ga2O3 (the most stable oxide phase), the less stable Ga2O is detected. Indium and tin are almost stable in their metallic state. With increasing humidity the thickness of the oxide film increases in our case from about 19 Å to 25 Å, assuming a layer-by-layer model. The presented results confirm our assumption of the increase in viscosity of the GaInSn system as a consequence of the preferential oxidation of gallium in the near-surface region. Copyright © 2004 John Wiley & Sons, Ltd.
physica status solidi (b), 2006
ABSTRACT The responsivity and the decay time of AlGaN solar blind UV-detectors have been studied.... more ABSTRACT The responsivity and the decay time of AlGaN solar blind UV-detectors have been studied. The photodetectors have shown a good spectral responsivity in a narrow spectral range (220 < λ < 300 nm) and a short time response with the best estimated characteristic time constant of τ ∼ 30 ms measured at room temperature. Possible mechanisms responsible for the persistent photoconductivity (PPC) effect in AlxGa1–xN (x = 0.51) are analyzed. A shape of the spectral response as a function of the applied voltage is analyzed in the frameworks of the space-charge limited current model. It has been shown that the main source of PPC is traps above the Fermi level. PPC occurs when the density of free carriers equals the density of the traps. The model attributing PPC to the spatial separation of the photoexcited electrons and holes by the macroscopic potential barrier is not supported by our photocurrent studies. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Ionics, 2010
The electronic structure of a solid electrolyte/solid electrode interface (SESEI) of an all-solid... more The electronic structure of a solid electrolyte/solid electrode interface (SESEI) of an all-solid-state thin film battery was investigated. The thin film battery consisted of a LiPON solid electrolyte and a LiCoO2 cathode. The lithium phosphorus oxynitride (LiPON) electrolyte was RF sputtered in a step-by-step procedure onto the cathode and investigated by photoelectron X-ray-induced spectroscopy after each deposition step. An intermediate
ACS Applied Materials & Interfaces, 2021
The intrinsic stability of the 5 V LiCoPO4-LiCo2P3O10 thin-film (carbon-free) cathode material co... more The intrinsic stability of the 5 V LiCoPO4-LiCo2P3O10 thin-film (carbon-free) cathode material coated with MoO3 thin layer is studied using a comprehensive synchrotron electron spectroscopy in situ approach combined with first-principle calculations. The atomic-molecular level study demonstrates fully reversible electronic properties of the cathode after the first electrochemical cycle. The polyanionic oxide is not involved in chemical reactions with the fluoroethylene-containing liquid electrolyte even when charged to 5.1 V vs Li+/Li. The high stability of the cathode is explained on the basis of the developed energy level model. In contrast, the chemical composition of the cathode-electrolyte interface evolves continuously by involving MoO3 in the decomposition reaction with consequent leaching of oxide from the surface. The proposed mechanisms of chemical reactions are attributed to external electrolyte oxidation via charge transfer from the relevant electron level to the MoO3 valence band state and internal electrolyte oxidation via proton transfer to the solvents. This study provides a deeper insight into the development of both a doping strategy to enhance the electronic conductivity of high-voltage cathode materials and an efficient surface coating against unfavorable interfacial chemical reactions.
Advanced Materials Interfaces, 2020
Advanced Materials Interfaces, 2020
Applied Surface Science, 2018
Abstract The electronic and chemical structure of two types of nearly lattice-matched InAs/(Cd,Zn... more Abstract The electronic and chemical structure of two types of nearly lattice-matched InAs/(Cd,Zn)(Se,Te) heterovalent interfaces grown coherently by molecular beam epitaxy are investigated by soft x-ray photoelectron spectroscopy (SXPS) and secondary ion mass-spectroscopy (SIMS). The valence band offset (VBO) at the CdSe/InAs heterointerface formed close to the Cd/Se ∼ 1:1 stoichiometric conditions is determined to be 1.02 ± 0.08 eV. The incorporation of a 3-monolayer-thick ZnTe intermediate layer between InAs and CdSe leads to an increase in the VBO between InAs and CdSe by approximately 0.17 eV. The dominant chemical bonds at the interface have been established to be InsbndSe or InsbndTe ones from analysis of SXPS spectra recorded at different excitation energies (100 – 650 eV) and surface sensitive SIMS study, while the signals from Cd(Zn)sbndAs bonds are negligible. The diffusion of the InAs substrate components to the CdSe layer is rather weak: in particular, the concentration of In and As atoms drops in the CdSe layer down to 1% at the distance from the interface of 1 nm. Introduction of the 1-nm-thick ZnTe layer slows down the As surface segregation even more.
Journal of The Electrochemical Society, 2019
Journal of Materials Chemistry A, 2018
The novel LiCoPO4–LiCo2P3O10 cathode material: a rigid band behavior of the electronic structure.
The Journal of Chemical Physics, 2016
Understanding the mechanism of the interaction of lithium ion conductors with water is crucial fo... more Understanding the mechanism of the interaction of lithium ion conductors with water is crucial for both fundamental and technological points of view. Despite the generally accepted fact that water is one of main sources of the degradation of Li-ion recharge batteries, the physicochemical processes occurring at the water-lithium ion conductor interface are not fully understood. By using synchrotron X-ray photoelectron spectroscopy (SXPS) and O K- and Co L- X-ray absorption near edge structure (XANES), we evidence that H2O is dissociatively adsorbed on LiCoO2 thin film at room temperature resulting in the formation of OH groups and the accumulation of the negative charge at the surface accompanied by electron transfer to the initial empty Co3d (eg (*)) state. By considering the experimentally obtained energy diagram of the ionic conductor and water, direct charge transfer is not favorable due to a high difference in the chemical potential of the ionic conductor and electronic levels of the molecule. Here, we develop the model for the dissociative water adsorption which explains the electron transfer to LiCoO2 by using the atomistic approach. The model takes into account the intrinsic defects found on the surface (<2 nm depth) by using the depth resolved photoemission experiments and can be explored to other layered transition metal oxides to interpret the interaction of water with the surface of ionic conductors.
Materials Letters, 2016
A method is presented which leads to a higher sputter rate as compared to the sputtering of the s... more A method is presented which leads to a higher sputter rate as compared to the sputtering of the surface of a bulk sample under the same sputtering conditions: the target is coated beforehand by a separate process to produce a nanostructured film on its surface. In the case of silver, the sputter yield under ion bombardment is 1.7 times higher. If the ions for the bombardment are generated by a voltage applied to the sample, then improvements up to a factor of five can be realized.
Journal of the European Ceramic Society, 2016
In the present work, novel V8C7/SiC(O) ceramic nanocomposites were synthesized upon thermal trans... more In the present work, novel V8C7/SiC(O) ceramic nanocomposites were synthesized upon thermal transformation of a polymer-derived single-source-precursor, which was obtained by the chemical modification of a polycarbosilane with vanadyl acetylacetonate. High-temperature treatment of the precursor in argon atmosphere first leads to an amorphous SiVOC single-phase ceramic which subsequently undergoes phase-separation, crystallization and finally converts into V8C7/SiC(O) ceramic nanocomposites. Interestingly, the high-temperature stability of V8C7/SiC(O) was shown to strongly depend on the oxygen content present either in the SiC(O) matrix or in the atmosphere during the annealing process. Thus, larger oxygen contents induce a conversion of the V8C7 phase into V5Si3. The specific surface area (SSA) of the obtained nanocomposite powders depends on the processing temperature: The SSA decreases from 64 to 4 m2/g as the pyrolysis temperature increases from 600 to 1300 °C, respectively. Whereas it increases again to ca. 50 m2/g as the sample is exposed to 1700 °C (6 h annealing), due to the evolution of CO. Preliminary results of the catalytic activity of the V8C7/SiC(O)-based materials show that they are active for the decomposition of the ammonia. The maximum ammonia conversion efficiency was found to be 35% at around 650 °C, which is higher than that of the pure vanadium carbide reported in the literature (ca. 13%).
J. Mater. Chem. C, 2016
The melt-shear organization technique for tailor-made polystyrene-co-polyacrylonitrile (PSAN) she... more The melt-shear organization technique for tailor-made polystyrene-co-polyacrylonitrile (PSAN) shell and silica core particles is investigated yielding easy-scalable carbonaceous porous films after etching and appropriate thermal treatment.
Chemistry of Materials, 2014
In this study, a comprehensive experimental in situ analysis of the evolution of the occupied and... more In this study, a comprehensive experimental in situ analysis of the evolution of the occupied and unoccupied density of states as a function of the charging state of the Li x≤1 CoO 2 films has been done by using synchrotron X-ray photoelectron spectroscopy (SXPS), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and O K-and Co L 3,2-edges XANES. Our experimental data demonstrate the change of the Fermi level position and the Co3d−O2p hybridization under the Li + removal and provide the evidence for the involvement of the oxygen states in the charge compensation. Thus, the rigid band model fails to describe the observed changes of the electronic structure. The Co site is involved in a Co 3+ → Co 4+ oxidation at the period of the Li deintercalation (x ∼ 0.5), while the electronic configuration at the oxygen site is stable up to 4.2 V. Further lowering of the Fermi level promoted by Li + extraction leads to a deviation of the electronic density of states due to structural distortions, and the top of the O2p bands overlaps the Co3d state which is accompanied by a hole transfer to the O2p states. The intrinsic voltage limit of LiCoO 2 has been determined, and the energy band diagram of Li x≤1 CoO 2 vs the evolution of the Fermi level has been built. It was concluded that Li x CoO 2 cannot be stabilized at the deep Li deintercalation even with chemically compatible solid electrolytes.
Frontiers of Multifunctional Integrated Nanosystems
The growth of fullerene C60 films on InP(001)-(2×4) was studied by a set of surface science techn... more The growth of fullerene C60 films on InP(001)-(2×4) was studied by a set of surface science techniques under ultra-high vacuum (UHV) conditions. Spectral signature measured by photoelectron and electron energy-loss spectroscopies (UPS, XPS, EELS, HREELS) corresponds to that of bulk C60 both at low (1–2 monolayers (ML)) and high (10 ML) coverage. The result shows a weak bonding, most probably
Chemistry of Materials, 2015
ABSTRACT In recent years, there have been significant efforts to understand the role of the elect... more ABSTRACT In recent years, there have been significant efforts to understand the role of the electronic structure of redox active materials according to their performance and thermodynamic stability in electrochemical storage devices and to develop novel materials with higher energy density and higher power. It is generally recognized that transition metal compounds used as a positive electrode determine the specific capacity and the energy density of rechargeable batteries, while the charge transfer resistance at electrolyte-electrode interface plays a key role in delivering the power of the electrochemical cell. In the present work, we study the stability of LixNi0.2Co0.7Mn0.1O2 thin films through the evolution of the occupied and unoccupied density of states as a function of the charging state of the electrode as well as the physicochemical conditions influencing the ionic transport across the electrode-electrolyte interface. A comprehensive experimental quasi in-situ approach has been applied by using synchrotron X-ray photoelectron spectroscopy (SXPS) and O K- and Ni L-, Co L-, Mn L - edges XANES. Our experimental data demonstrate the change of the Fermi level position with the Li+ removal and Ni2+ → Ni4+ and Co3+ → Co4+ changes of oxidation state for the charge compensation in the bulk of the material. As is evidenced by the experimentally determined energy band diagram of Lix≦1.0Ni0.2Co0.7Mn0.1O2 vs the evolution of the Fermi level, no hole transfer to the O2p bands is observed up to a charging state of 4.8 V which evidences the thermodynamic stability of Lix≦1.0Ni0.2Co0.7Mn0.1O2 under high charging voltage in contrast to LiCoO2. A very thin solid electrolyte interface layer (less than 30 Å thickness) on the Lix≦1.0Ni0.2Co0.7Mn0.1O2 film is formed in a decomposition reaction of the electrolyte also involving the transition metal oxide. The enhanced concentration of lithium in the interface layer correlates evidently with the electron transfer to the transition metal sites changing their electronic configuration. It is concluded that Lix≦1.0Ni0.2Co0.7Mn0.1O2 can serve as high energy density cathode material, but the delivery of high power, which is a critical parameter for an electric vehicle, is strongly influenced by the physicochemical conditions at the solid electrolyte interface, which can suppress Li+ diffusion or even block the Li+ paths across the interface.
Surface Science, 2005
We report an investigation of the dynamical properties of clean and monohydride-terminated Si(1 1... more We report an investigation of the dynamical properties of clean and monohydride-terminated Si(1 1 0) surfaces, measured by means of high resolution electron energy loss spectroscopy (HREELS). On both surfaces a number of surface phonons is observed and successfully assigned to predicted modes. A (1 • 5) reconstruction is found to be the stable surface phase corresponding to monohydride coverage of Si(1 1 0). For the Si-H stretching and bending bands of this monohydride Si(1 1 0) surface we find a relatively strong dispersion along the [1 1 0] direction. Apparently, this is related to the coupling of oscillators along the Si chains of the (1 1 0) surface. In addition, surface vibrations induced by adsorbed residual gases are measured and analysed.
Surface and Interface Analysis, 2004
ABSTRACT Viscosity measurements of GaInSn eutectic alloys were performed in a homebuilt device fo... more ABSTRACT Viscosity measurements of GaInSn eutectic alloys were performed in a homebuilt device for low (9%) and high (95%) relative humidity for shorter (450 min) and longer (1800 min) time periods. At constant exposure time a characteristic increase of viscosity is observed with increasing humidity. For high humidity, high viscosity is obtained after a short time.Assuming that the measured viscosity change is strongly related to the absorption of oxygen, XPS was applied to the chemical and quantitative analysis of differently prepared samples. In all cases, Ga is predominantly oxidized at the surface whereas Ga atoms in the metallic state are located deeper inside. Besides Ga2O3 (the most stable oxide phase), the less stable Ga2O is detected. Indium and tin are almost stable in their metallic state. With increasing humidity the thickness of the oxide film increases in our case from about 19 Å to 25 Å, assuming a layer-by-layer model. The presented results confirm our assumption of the increase in viscosity of the GaInSn system as a consequence of the preferential oxidation of gallium in the near-surface region. Copyright © 2004 John Wiley & Sons, Ltd.
physica status solidi (b), 2006
ABSTRACT The responsivity and the decay time of AlGaN solar blind UV-detectors have been studied.... more ABSTRACT The responsivity and the decay time of AlGaN solar blind UV-detectors have been studied. The photodetectors have shown a good spectral responsivity in a narrow spectral range (220 < λ < 300 nm) and a short time response with the best estimated characteristic time constant of τ ∼ 30 ms measured at room temperature. Possible mechanisms responsible for the persistent photoconductivity (PPC) effect in AlxGa1–xN (x = 0.51) are analyzed. A shape of the spectral response as a function of the applied voltage is analyzed in the frameworks of the space-charge limited current model. It has been shown that the main source of PPC is traps above the Fermi level. PPC occurs when the density of free carriers equals the density of the traps. The model attributing PPC to the spatial separation of the photoexcited electrons and holes by the macroscopic potential barrier is not supported by our photocurrent studies. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Ionics, 2010
The electronic structure of a solid electrolyte/solid electrode interface (SESEI) of an all-solid... more The electronic structure of a solid electrolyte/solid electrode interface (SESEI) of an all-solid-state thin film battery was investigated. The thin film battery consisted of a LiPON solid electrolyte and a LiCoO2 cathode. The lithium phosphorus oxynitride (LiPON) electrolyte was RF sputtered in a step-by-step procedure onto the cathode and investigated by photoelectron X-ray-induced spectroscopy after each deposition step. An intermediate