Showing papers on "Chemical state published in 2008"
TL;DR: In this paper, the authors used X-ray photoelectron spectroscopy (XPS) depth profiling and high-resolution Xray diffraction to analyze 10 samples of crystalline aluminum nitride (AlN) film.
Abstract: Ten samples of crystalline aluminum nitride (AlN) film were deposited on sapphire and silicon substrates by a plasma source molecular beam method. The samples were analyzed using X-ray photoelectron spectroscopy (XPS) depth profiling and high-resolution X-ray diffraction. Oxygen levels were observed to decrease exponentially from the surface into the bulk film. Aluminum, nitrogen and oxygen peaks were fitted with subpeaks in a consistent manner and the subpeaks were assigned to chemical states. AlN subpeaks were observed at 73.5 eV for Al2p and 396.4 eV for N1s. An N1s subpeak at 395.0 eV was assigned to NN defects. No direct NO bonds are assigned; rather it is proposed that an NAlO bond sequence is the source of higher binding energy N1s subpeaks. The observations in this study support a model in which oxygen is bound only to aluminum in the form of AlO octahedral complexes dispersed or clustered throughout the main AlN matrix or as AlO bonds on the crystal grain boundaries. The data also suggest that the AlN lattice parameters are related to oxygen content, since the c-axis is observed to increase with increasing oxygen content. Copyright © 2008 John Wiley & Sons, Ltd.
256 citations
TL;DR: Definite assignment of the boron oxidation state will contribute to the preparation, characterization, and understanding of B-TiO2 photoactivity under visible light which has been the subject of extensive work in the past few years.
Abstract: Boron is diamagnetic in B-doped anatase TiO2 nanoparticles which exhibit photocatalytic activities in the visible light range. Using N as a paramagnetic probe for the formal oxidation state of boron in N/B-codoped TiO2, with more than 90% unpaired spin density in the N2p orbital, we infer that boron enters the oxygen vacancy substitutionally in the form of B1-. Combination of spin-Hamiltonian analysis and interpretation of light dependent EPR spectra in terms of a charge compensating mechanism supports a model of [N2-B1-]+1 for the new EPR active center which acts as a trap for electrons liberated from [N1-] centers under blue light irradiation. Definite assignment of the boron oxidation state will contribute to the preparation, characterization, and understanding of B−TiO2 photoactivity under visible light which has been the subject of extensive work in the past few years.
109 citations
TL;DR: In this paper, the authors combined electrochemical and XPS surface analytical methods to gain a deeper insight into the mechanisms underlying the corrosion resistance of electroless deposited Ni-P alloys with phosphorus content between 18 and 22.
Abstract: Electroless Ni–P alloys are produced as coatings on a broad variety of substrates. They exhibit a corrosion resistance that is superior to pure nickel but do not form a NiO oxide film (passive film) as pure nickel does. Despite the fact that many mechanisms have been proposed to explain this superior corrosion behaviour, no consensus has yet been reached. In this work electrochemical and XPS surface analytical methods have been combined in order to gain a deeper insight into the mechanisms underlying the corrosion resistance of electroless deposited Ni–P alloys with phosphorus content between 18 and 22 at.%. The anodic polarization curves in acidic and neutral solutions confirm a broad current plateau followed by a region with increasing current density. During potentiostatic polarization in the plateau region the current decays according to a power law with exponent ca. −0.5 indicating diffusion-limited dissolution of nickel. XPS/XAES measurements performed after potentiostatic polarization show that phosphorus is present in three different chemical environments. Based on the Auger parameter concept and on the chemical state plot, the three phosphorus states were assigned to phosphorus in the bulk alloy, phosphates and an intermediate phosphorus compound attributed to elemental phosphorus. Angle-resolved XPS analysis has shown that the elemental phosphorus is enriched at the interface between the alloy and the outermost surface in contact with the corrosive solution. These results suggest the following conclusions: the high corrosion resistance of electroless deposited Ni–P alloys can be explained by a strong enrichment of elemental phosphorus at the interface which limits the dissolution of nickel via a diffusion mechanism. A complementary explanation––not yet advanced––for the high corrosion resistance may lie in the electronic state of nickel in the Ni–P alloys.
102 citations
TL;DR: In this article, the catalytically important Mn/CeO2−TiO2 (MCT) solid solutions were synthesized by solution combustion technique using glycine, urea, or PEG as fuel.
Abstract: The catalytically important Mn/CeO2−TiO2 (MCT) solid solutions were synthesized by solution combustion technique using glycine, urea, or PEG as fuel. These samples along with those prepared by coprecipitation and wet impregnation methods were characterized for its structural, textural and redox properties using various physical and spectroscopic techniques, viz., powder X-ray diffraction, high-resolution transmission electron microscopy, temperature-programmed reduction, diffuse reflectance UV−visible, electron paramagnetic resonance, and X-ray photoelectron spectroscopy. The samples prepared by the solution combustion method showed high thermal stability, even at temperatures of 1323 K, whereas the samples synthesized by conventional routes lost its structural integrity at higher temperatures due to fast sintering. The combustion and coprecipitation methods stabilize Mn species both in +2 and +3 oxidation states, while in the MCT sample prepared by wet impregnation, Mn ions are present in +3 state exclus...
97 citations
TL;DR: In this paper, the performance of a 100°C-annealed Mn-Fe binary oxide was evaluated by cyclic voltammetry at a potential sweep rate of 5mV s −1, with an optimum specific capacitance of 280 F g −1.
81 citations
TL;DR: In this paper, an iron oxide thin film grown with atomic layer deposition for a gas sensor application was investigated, and the results indicated that the film has a granular structure and that it has grown mainly on the glass substrate leaving the platinum electrodes uncovered.
77 citations
TL;DR: In this article, a series of Ce-TiO 2 /SiO 2 coatings on SiO 2 were prepared by the sol-gel process and characterized by TG-DTA, XRD, SEM, XPS and DRS.
Abstract: A series of Ce-TiO 2 /SiO 2 (Ce-TiO 2 coatings on SiO 2 ) were prepared by the sol–gel process and characterized by TG–DTA, XRD, SEM, XPS and DRS. The photocatalytic activities of Ce-TiO 2 /SiO 2 for the oxidation of formaldehyde irradiated by 250 W high-pressure mercury lamp were investigated. According to XPS investigation, the Ti element mainly existed as the chemical state of Ti 4+ , and Ce is present mainly in the +4 oxidation state and a little in the +3 oxidation state. The effect of cerium content on the photocatalytic activities was studied, and the result reveals that 0.10%Ce-TiO 2 /SiO 2 exhibits highest photoactivity. The light absorption of Ce-TiO 2 /SiO 2 increases with increasing cerium content, and cerium doping causes absorption spectra of Ce-TiO 2 /SiO 2 to shift to the visible region. The high photocatalytic activity of Ce-TiO 2 /SiO 2 can be explained by the effective separation of photogenerated electron–hole pairs, which are trapped by Ce 4+ and hydroxyl groups balancing the positive charge generated by the incorporation of Si in a Ti matrix, respectively.
61 citations
TL;DR: In this paper, the nano-HA in the electrolyte has effects on the surface character and apatite-forming ability of the PEO coating; however, it has no obvious influence on those of the CT-PEO coatings.
60 citations
01 Jan 2008
TL;DR: The adsorption behavior of carbons is affected to a considerable extent by the chemical state of their surfaces, which is also of great practical importance in many other applications of carbon materials such as for catalysts and catalyst supports, and carbon polymer composites.
Abstract: The adsorption behavior of carbons is affected to a considerable extent by the chemical state of their surfaces, which is also of great practical importance in many other applications of carbon materials such as for catalysts and catalyst supports, and carbon-polymer composites. In the surface of carbon materials, the regular network of covalent C-C bonds is broken, and reactive sites result as a consequence. Usually “free valences,” also called “dangling bonds,” are saturated with foreign elements, in first line hydrogen and oxygen. In the case of carbon structures derived from the graphite lattice, the surface is inhomogeneous and is constituted to variable fractions of basal faces, i.e., honeycomb-like graphene layers, and of the edges of the graphene layers. While the basal faces are quite inert, the edge sites are reactive and can chemisorb other elements such as hydrogen, oxygen, nitrogen species, and halogens. In contrast, the surface of diamond is much more homogeneous and has a comparatively simpler chemical behavior.
59 citations
TL;DR: It is shown that this electronegativity scale can be successfully applied to predict the hardness of covalent and polar covalents in crystals, which will be very useful for studying various chemical and physical properties ofcovalent materials.
Abstract: A new electronegativity table of elements in covalent crystals with different bonding electrons and the most common coordination numbers is suggested on the basis of covalent potentials of atoms in crystals. For a given element, the electronegativity increases with increasing number of bonding electrons and decreases with increasing coordination number. Particularly, the ionicity of a covalent bond in different environments can be well-reflected by current electronegativity values; that is, the ionicity of chemical bonds increases as the coordination number of the bonded atoms increases. We show that this electronegativity scale can be successfully applied to predict the hardness of covalent and polar covalent crystals, which will be very useful for studying various chemical and physical properties of covalent materials.
42 citations
TL;DR: In the present investigations, highly textured ZnO thin films with a preferential (002)-orientation were prepared on glass substrates and deposition conditions were optimized to obtain device-quality films for practical applications.
TL;DR: In this paper, the influence of the cooling procedure applied at the end of the CCVD synthesis of carbon nanotubes has been investigated, and the structure and chemical state of the iron-based particles were compared through complementary local and global investigations involving X-ray diffraction, electron microscopy, electron diffraction as well as electron energy loss spectroscopy.
Abstract: The true chemical nature and physical state of the catalyst particles in Catalytic Chemical Vapor Deposition (CCVD) synthesis of carbon nanotubes are the subject of intense discussions, as it is one of the keys to understand their growth mechanisms The CCVD method considered in this article involves pyrolysis of mixed liquid aerosols and leads to the synthesis of large carpets of multiwalled nanotubes (MWNTs) partially filled with iron-based materials The experimental approach consists in studying the influence of the cooling procedure applied at the end of the synthesis Both slow standard cooling or quenching were performed, and the structure and chemical state of the iron-based particles were compared through complementary local and global investigations involving X-ray diffraction, electron microscopy, electron diffraction, as well as electron energy loss spectroscopy We clearly demonstrate that iron-based catalyst particles are carbon-rich and oxygen-free in quenched samples, and that they oxidize during the slow cooling step It is inferred that they are very probably molten supersaturated carbon-metal particles during the NT growth
TL;DR: In this article, it was shown that elemental boron powder with a purity of 95-99% can be produced using a high temperature molten salt electrowinning process using X-ray photoelectron spectroscopy (XPS).
TL;DR: In this article, the valence band maximum (VBM) spectrum taken by ultraviolet photoelectron spectroscopy (UPS) indicates that the Fermi energy of ZnO:As:O2 films shifts toward the VBM by 0.37
Abstract: Arsenic-doped ZnO (ZnO:As) films were grown by metal–organic chemical vapor deposition (MOCVD) on GaAs layers, which were deposited on sapphire substrates by sputtering using a GaAs target. The As doping was obtained by thermal diffusion. The ZnO:As films were annealed in nitrogen (ZnO:As:N2) and oxygen (ZnO:As:O2) atmosphere, respectively. X-ray photoelectron spectroscopy (XPS) measurements showed that annealing in oxygen facilitated even As doping in ZnO films and the content of As remains around 3.4% after Ar+ bombardment. However, annealing in N2 leads to the aliquation of As at the surface for ZnO:As films. Core level results show that there are two chemical states of As in ZnO:As:O2 films including AsZn–2VZn and AsZn, while four types exist in ZnO:As:N2 films including AsZn, AsZn–2VZn, Asi, and AsO. The contribution centered at around 43.9 eV of the As 3d peak is ascribed to AsZn–2VZn. The valence band maximum (VBM) spectrum taken by ultraviolet photoelectron spectroscopy (UPS) indicates that the Fermi energy of ZnO:As:O2 films shifts toward the VBM by 0.37 eV compared with undoped ZnO films, which proves AsZn–2VZn is an acceptor in ZnO:As:O2 films, but the ZnO:As films still show n-type conductivity, which is possibly due to the compensation of As-related donor and native defects. Detailed analysis of the chemical states of As may help point toward paths for growing high-quality ZnO:As films.
TL;DR: In this article, the early stages of the ALD were investigated with high-resolution photoelectron spectroscopy and x-ray absorption spectra, and the growth properties of HfO2 were deduced from the analysis of those variations.
Abstract: We have grown HfO2 on Si(001) by atomic layer deposition (ALD) using HfCl4 and H2O as precursors. The early stages of the ALD were investigated with high-resolution photoelectron spectroscopy and x-ray absorption spectroscopy. We observed the changes occurring in the Si2p, O1s, Hf4f, Hf4d, and Cl2p core level lines after each ALD cycle up to the complete formation of two layers of HfO2. From the analysis of those variations, we deduced the growth properties of HfO2. The first layer consists of a sparse and Cl-contaminated oxide because of the incomplete oxidation, and the second layer is denser than the first one and with an almost stoichiometric O∕Hf ratio. At the completion of the second layer, the x-ray absorption spectra revealed the change of the Hf-oxide chemical state due to the transition from the thin Hf-oxide to the bulklike HfO2.
TL;DR: In this paper, the chemical state of Si(111) surfaces upon anisotropic etching in concentrated NH4F solution was investigated and minute amounts of oxidized silicon were detected and attributed to the fast Si-H-OH formation at atomic steps.
Abstract: Synchrotron radiation photoelectron spectroscopy was employed to investigate the chemical state of Si(111) surfaces upon anisotropic etching in concentrated NH4F solution. Minute amounts of oxidized silicon were detected and attributed to the fast Si–H–OH formation at atomic steps. Combining in situ optical and scanning probe techniques, consecutive chemical treatments were developed to achieve optimized morphological and chemical surface properties. Native oxides and a stressed SiO2/Si layer are removed by a two-step NH4F treatment leading to a terraced surface without triangular etch pits; subsequently, silicon in the Si1+/2+/3+ valence states is dissolved by HF (50%) while the surface topography is preserved.
TL;DR: X-ray photoelectron spectroscopic (XPS) studies were carried out on wet-chemically synthesized cubic BaTiO3, Ba09Nd01TiO 3 and BaTi09Fe01O3−δ powders.
TL;DR: In this article, the chemical etch rate, etched surface morphology and the surface chemical state depend on the texture of the (0 0 2) and (1 0 0) planes.
Abstract: The chemical etching of AlN films with the texture of the (0 0 2) and (1 0 0) planes has been investigated. The chemical states of the films before and after etching were particularly focused on. The AlN films were prepared by sputtering and etched in KOH solution. It is found that the etch rate, etched surface morphology and the surface chemical state depend on the film's different textures. The etch rate of the film with (1 0 0) texture is higher than that of the (0 0 2) orientated film, while the latter exhibits homogeneous pyramids of triangular shape on the etched surface. Some changes were observed in the x-ray photoelectron spectroscopy (XPS) after etching, including the reduction of the Al–O component, the enhancement of the O–H component and the appearance of the N–H component. Based on the XPS results, the appropriate mechanisms of the chemical etching for films with (0 0 2) and (1 0 0) textures have been proposed. The etching can be continued by the attractive effect between OH− ions and Al atoms as well as dissolving the in-process product of aluminium oxide.
TL;DR: In this article, three common Al-Au intermetallics, Al2Au, AlAu2, and alAu4, were oxidized in the air and characterized using x-ray photoelectron spectroscopy in terms of the elemental chemical state.
Abstract: Three common Al–Au intermetallics, Al2Au, AlAu2, and AlAu4, were oxidized in the air and characterized using x-ray photoelectron spectroscopy in terms of the elemental chemical state. It was found that there is an increasing trend of oxidation in these intermetallics as the Au content increases. AlAu4 shows the greatest tendency to oxidize with two extra peaks appearing on the Au 4f spectra after long exposure time in air. The surface of AlAu2, although fully oxidized, reveals only one Au 4f peak shift as depth increases. Al2Au was the least oxidizing compound, and the oxide is thin. The binding energies of Al 2p and Au 4f peaks were measured and reported. The Au atoms trapped in the oxide layers exhibit higher binding energy emissions compared to those of elemental Au.
TL;DR: A systematic study ofX-ray intensity ratios of the K-series lines was made on compounds of nickel and cobalt to examine the influence of chemical state and 0.6 and 1.2 T external magnetic fields on energy-dispersive X-ray fluorescence analysis.
TL;DR: The chemical states of chromium, arsenic, and selenium in sewage sludge incineration ash were determined by X-ray absorption fine structure (XAFS) spectroscopy and it was speculated that the chemical state of As changed into As(V) during the incineration process.
TL;DR: In this article, the formation and growth of a self-organized nanotube layer can be achieved directly by anodization in NH4-containing electrolytes, and the diameter, length, and wall thickness of the nanotubes are significantly affected by anodicizing conditions such as applied voltage, current density, and anodizing time.
Abstract: TiO2 nanotube-type oxide film on Ti substrate has been fabricated using an electrochemical method, and the chemical bonding state, ultra-fine structures, and surface characteristics of the TiO2 nanotube layer have been investigated. The formation and growth of a self-organized nanotube layer can be achieved directly by anodization in NH4-containing electrolytes. The diameter, length, and wall thickness of the nanotube are significantly affected by anodizing conditions such as applied voltage, current density, and anodizing time. The length limiting factor of nanotube growth was found to be the diffusion of ionic species in the electrolyte. XRD investigations revealed that annealed nanotubes have anatase and rutile structure, and some Ti-peaks from the Ti substrate were observed. From the compositional analysis of TiO2 nanotubes layer using Energy Dispersive Spectroscopy (EDS), Ti, O, and P elements were obtained in the wall nanotube layer. For incorporated P-containing in the TiO2 nanotube layer, various chemical states were presented, which were revealed mostly in the forms of H2PO4, HPO4
2-, and PO4
3-.
TL;DR: In this article, the nature, the chemical state and electrocatalytic activity of Ni overlayers electrochemically prepared on a polycrystalline Mo surface were studied by means of X-ray and UV photoelectron spectroscopies (XPS, UPS) and steady state potentiostatic polarization measurements for the H2 evolution reaction in 1M NaOH solution.
TL;DR: In this paper, the microstructure of the oxide film of the tritium penetration barrier formed on 316L stainless steel, which was prepared by a combined process, namely, aluminizing and oxidizing treatments using a double glow plasma technology, was examined by scanning electronic microscope (SEM), X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM).
TL;DR: In this paper, the chemical bonding states of nitrogen doped ZnO films under monodoping, codoping, and cluster doping with Ga were investigated and it was found that the N/Ga flux ratio in the doping process has a critical influence on the chemical bond of nitrogen in ZnOs.
Abstract: Fabrication of high quality p-type ZnO is the main challenge in recent ZnO research that prevents the practical application of ZnO-based devices in optoelectronics. The mechanism behind is thought to be due to self-compensation of native defects and/or dopant-induced donors. In this report, we investigated the chemical bonding states of nitrogen doped ZnO films under monodoping, codoping, and cluster doping with Ga. It was found that the N/Ga flux ratio in the doping process has a critical influence on the chemical bonding of nitrogen in ZnO. By tuning the N/Ga doping ratio, it is expected to create appropriate chemical environments to enhance the formation of desired dopant species: Ga–N2O2 (codoping), Ga–N3O and Ga–N4 (cluster doping) for p-type ZnO.
TL;DR: In this paper, chemical state information on contamination-free Ge2Sb2Te5 thin film using high-resolution x-ray photoelectron spectroscopy (HRXPS) and the corresponding theoretical understanding of the chemical states, on both amorphous and metastable phases, illuminating the phase-change mechanism of the system.
Abstract: We present chemical state information on contamination-free Ge2Sb2Te5 thin film using high-resolution x-ray photoelectron spectroscopy (HRXPS) and the corresponding theoretical understanding of the chemical states, on both amorphous and metastable phases, illuminating the phase-change mechanism of the system. HRXPS data revealed that the Sb 4d shallow core level was split into two components having different binding energies and that the spin-orbit splitting feature of the Ge 3d level was enhanced as the system became metastable. Negligible change was observed in the Te 4d shallow core level, and in contrary to the previous report’s prediction less change in valance band spectra was observed. The results imply that Sb movement is also involved in the phase-change mechanism and that acquisition of shallow core-level spectra can be a useful measure for understanding phase-change mechanism. Hydrogenated SbTe6 octahedral-like cluster model was introduced to schematically interpret the generation of the two co...
TL;DR: In this article, the chemical transformations of supported Rh particles, ranging in size from a few micrometers to a few nanometers, and nanocrystalline Rh films have been studied under identical oxidizing and reduction conditions by means of scanning photoelectron microscopy (SPEM), which allows determination of the chemical state of single Rh microparticles.
Abstract: The chemical transformations of supported Rh particles, ranging in size from a few micrometers to a few nanometers, and nanocrystalline Rh films have been studied under identical oxidizing and reduction conditions by means of scanning photoelectron microscopy (SPEM), which allows determination of the chemical state of single Rh microparticles. Comparing the oxidation states attained by the Rh particles revealed substantial reactivity differences with particle size, as well as variations in the reactivity of particles with similar dimensions and within the same particle. The results are interpreted in terms of the variable morphology of the particles as verified by secondary electron microscopy and atomic force microscopy.
TL;DR: This work reports on an ab initio simulation of chemisorption of the D-alaninol on Cu (100) which indicates that both chemical functions, the NH(2) and the dehydrogenated hydroxyl, are involved in the bonding to the surface at low coverage.
Abstract: In recent years, an increasing interest has been focused on the adsorption of molecules on surfaces due to the importance of technologies based on the interaction of organic systems with metals and oxides for biosensors, catalysis, and molecularly imprinted polymer technology A particularly attractive area is the study of chiral surfaces, as these can act as heterogeneous catalysts and sensors in the stereochemical industrial processes This work reports on an ab initio simulation of chemisorption of the D-alaninol on Cu (100) This system has been investigated systematically by using the Vienna ab initio simulation Package (VASP) which performs density functional theory (DFT) calculations in periodic boundary conditions Molecular dynamics at 300 K is performed to explore all the possible geometries, finally, optimized at 0 K to obtain the adsorption modes C 1s, O 1s, and N 1s, core level shift (CLS) calculations of those adsorption modes have been evaluated and compared with x-ray photoelectron spectroscopy experimental data Energetic and CLS indicate that both chemical functions, the NH(2) and the dehydrogenated hydroxyl, are involved in the bonding to the surface at low coverage Atomic hydrogen coadsorbs in a fourfold hollow site An atomistic thermodynamics approach suggests that at room temperature under UHV conditions, coadsorbed hydrogen has recombined as H(2) and desorbed from the surface
TL;DR: In this paper, a glow discharge cell was used to produce a continuous plasma with a majority of N atomic species, and a theoretical model based on stacked layers allowed to determine the optimal temperature of nitridation.
TL;DR: In this article, the process of low energy N 2 + implantation and annealing of a Cu(0, 0, 1) surface was studied by means of Auger electron spectroscopy (AES), X-ray photoelectron (XPS), and low energy ion spectrometry (LEIS) techniques.