Showing papers on "Oxide published in 1983"

A study of the core level electrons in iron and its three oxides by means of X-ray photoelectron spectroscopy

Abstract: The core level electrons in iron and its three oxides FeO, Fe3O4 and alpha -Fe2O3 have been studied by means of X-ray photoelectron spectroscopy. The main features of the spectra have been identified and electron binding energies have been measured. The Fe 2p peaks of the oxide spectra are broadened (FWHM approximately 4.5 eV) due to unresolved multiplet splitting, and shake-up satellites can be observed for both FeII and FeIII species. For all the samples studied the O 1s spectra consist of two overlapping peaks, one due to the oxide and a higher binding energy peak due to an adsorbed species. The higher binding energy peak was frequently dominant indicating a high degree of absorption on the oxide surfaces. The effect of argon ion etching on the surfaces has also been investigated and the results indicate that the analysis of surfaces by means of ion etching in conjunction with XPS can give misleading results.

Electrochemistry and photoelectrochemistry of iron(III) oxide

Abstract: Iron(III) oxide has been extensively studied as a possible n-type semiconductor for use in solar photoelectrolysis cells However, its properties have remained curiously elusive; even such fundamental properties as bandgap and flat-band potential are still controversial, and this uncertainty has hindered any rational evaluation of the use of the material in solar cells In this paper, an extensive study of the surface and bulk properties of both single-crystal and polycrystalline Fe2O3 is reported Surface pretreatment is found to have a major effect on the photoelectrochemical properties Even in properly treated samples, however, the photocurrent onset is found to be delayed due to the small value of the faradaic rate constant for the oxidation of water, and a semi-quantitative treatment of this case is provided Improper surface treatment is shown to lead to a substantial conversion of the surface of Fe2O3 to Fe3O4; this introduces a large fraction of recombination sites at the surface that not only delay dc photocurrent onset to very anodic potentials but also reduce the observed efficiency to remarkably low values

Characterization and Reactivity of Molecular Oxygen Species on Oxide Surfaces

Abstract: Publisher Summary This chapter discusses the characterization and reactivity of mononuclear oxygen species on oxide surfaces. Measurement of the electron paramagnetic resonance (EPR) parameters gives information which at the simplest level indicates the presence of a paramagnetic species but which can be sufficiently detailed to identify and characterize the adsorbed species. Measurements of the variation of the intensity of the signal with time can give kinetic data on reactions occurring at the surface. Although most of the EPR measurements have been carried out at low temperatures, there is evidence from the examples for some of the species that are stable at much higher temperatures and may play an important role in catalytic reactions.

Study of the K edges of 3 d transition metals in pure and oxide form by x-ray-absorption spectroscopy

Abstract: The metal $K$-edge absorption spectra of $3d$ transition metals and oxides are measured by x-ray-absorption spectroscopy. Experiments are performed on metal foils or fine powders dusted onto Scotch tape, at the Cornell High Energy Synchrotron Source. Comparisons to theory are made for both the metal and oxide data. We concentrate on the spectral nearedge structure (NES) and attempt to interpret its origins. For the metals, we find excellent agreement between the data and one-electron calculations. This agreement is much closer than previously found for the ${L}_{23}$ edges in the same materials. The picture for the oxide near-edge structure is not so auspicious. Although symmetry-based molecular-orbital (MO) theory has been widely invoked, it is probably inadequate. Recent calculations indicate that while some of the near-edge peaks are indeed attributable to one-electron MO-type transitions whose energies are modified by the presence of the core hole, other features have no such simple origin. Finally we compare the oxide NES of the metal ${L}_{23}$,$K$ edges and the oxygen $K$ edge altogether. These are found to agree with each other and to MO theory only for Ti${\mathrm{O}}_{2}$. The mismatch of the three NES's in the other oxides indicates the failure of one-electron theory for insulators. Instead, the near-edge structure must be dominated by core excitons, as previously shown for NiO. The presence of excitons explains the lack of agreement between the NES for core excitations of different atoms in the same solid.

XPS Studies of Oxygen Evolution on Ru and RuO2 Anodes

Abstract: Anodic oxidation of Ru and electrodes in has been investigated using x‐ray photoelectron spectroscopy. During evolution on Ru a highly defective hydrated oxide film is formed as a result of corrosion. At a temperature of 310°C in vacuum this film decomposes to metallic ruthenium. The surface of anodes prepared by thermal decomposition of contains some , which is stable during anodic polarization. A reaction path for evolution and corrosion on Ru and anodes is proposed.

Properties of tin doped indium oxide thin films prepared by magnetron sputtering

Abstract: Indium tin oxide (ITO) films have been prepared by the magnetron sputtering technique from a target of a mixture of In2O3 and SnO2 in the proportion 9:1 by weight. By optimizing the deposition conditions it has been possible to produce highly transparent (transmission ∼90%) and conducting (resistivity ∼10−5 Ω cm) ITO films. A resistivity ∼10−4 Ω cm has been obtained for films of thickness ∼1000 A at a comparatively low substrate temperature of 50 °C and without using oxygen in the sputtering chamber. To characterize the films, the following properties have been studied, viz., electrical conductivity, thermoelectric power, Hall effect, optical transmission, and band gap. The effect of annealing in air and vacuum on the properties of the films have also been studied.

Method of making structures with dimensions in the sub-micrometer range

Abstract: Following the method of making structures with dimensions in the submicrometer range, structures of a polymeric layer with horizontal and substantially vertical surfaces are first made on a substrate. Thereupon, a silicon nitride or oxide layer is plasma deposited. This layer is subjected to reactive ion etching methods in such a manner that its horizontal regions and the polymeric structures are removed, with merely the narrow regions of the silicon nitride or oxide layer that had originally been arranged adjacent the vertical surfaces of the polymeric structures remaining. In the case of positive lithography, the silicon nitride or oxide walls are converted into a mask with the same dimensions but consisting of a different mask material. In the case of negative lithography the silicon nitride or oxide walls are converted in a mask reversal process into openings in a mask material layer through which by means of reactive ion etching vertical trenches approximately 0.5 μm deep can be etched in the silicon substrate. The trenches are filled by thermal oxidation or with a synthetic material as e.g. polyimide. The method as disclosed by the invention can also be applied to other processes than recessed isolation in semiconductor technology.

Low emissivity coatings on transparent substrates

Abstract: A low emissivity coating on a transparent substrate of glass or plastics material is produced by cathode sputtering a layer of silver and thereafter reactively sputtering an anti-reflection metal oxide layer over the silver in the presence of oxygen or an oxidizing gas, wherein a small amount of an additional metal other than silver is sputtered onto the silver before the overlying anti-reflection metal oxide layer is applied. The process produces a new low emissivity coated product comprising a glass or plastics substrate with a low emissivity coating comprising a silver layer, a small amount of additional metal dispersed non-uniformly in the silver layer and possibly extending over the silver layer, and an overlying anti-reflection metal oxide coating.

Preparation and properties of oxynitride glasses

Abstract: Mixtures of oxides and nitrides can be melted and quenched to form glasses that contain up to 20 at % nitrogen. Adding nitrogen to an oxide glass increases its Tg, hardness, fracture toughness, elastic modulus, and chemical durability. Those changes suggest that nitrogen substitutes for oxygen in the network to produce a more highly cross-linked structure. Nitrides will be stable in oxide melts only if they are not oxidized by other components. To a first approximation, the possibility of redox reaction between a given oxide and nitride can be predicted by comparing ΔG° for the oxide with ΔG° for oxidation of the nitride. In agreement with experiment, the analysis predicts Al2O3, Li2O, CaO, Y2O3, and La2O3 will not cause decomposition in melts containing Si3N4 and SiO2, whereas K2O, Na2O, P2O5, and B2O3 will bw unstable.

Electrodeposition of Conducting Transition Metal Oxide/Hydroxide Films from Aqueous Solution

Abstract: Donnees sur une methode generale de depot electrolytique de couches minces d'oxyde-hydroxyde de Cu, Ni, Co, Fe et Mn, a partir d'une solution aqueuse, sur une electrode a disque tournant de Pt, soit sous tension constant, soit sous tension variant cycliquement

Influence of silicon additions on the oxidation resistance of a stainless steel

Abstract: Oxidation tests in a CO2-based atmosphere at 1123 K have been conducted on a series of 20Cr-25Ni stainless steels containing a dispersion of TiN particles and with silicon contents ranging from 0.05 to 2.35 wt.%. In all cases, a chromia surface film whose thickness increased parabolically with time was formed. The parabolic rate constant was a minimum at an intermediate alloy silicon content when an interlayer of silica was formed between the outer oxide and the metal. The significance of this duplex structure on the processes determining the oxidation rate and the extent of oxide spalling is discussed. An additional feature of the attack was the formation of subsurface voidage whose depth again increased parabolically with time. The appropriate rate constant also showed a minimum at an intermediate silicon level and the relationships between this form of attack and the development of the surface oxides are highlighted.

Surface characterization of copper(II) oxide-zinc oxide methanol-synthesis catalysts by x-ray photoelectron spectroscopy. 1. Precursor and calcined catalysts

Abstract: A surface characterization of the precursor and calcined copper oxide-zinc oxide (CuO-ZnO) catalysts prepared both by coprecipitation and by impregnation methods was carried out by using x-ray photoelectron spectroscopy (XPS). Strong oxide-oxide interactions were found to result in the formation of several surface copper species in the coprecipitated catalysts. With the catalysts containing 80-30 wt % CuO, it is proposed that the CuO structure is distorted to produce amorphous copper oxide phases in the surface layer. The copper species in the catalysts with > 80 wt % CuO are composed of the Cu/sup 2 +/ ions in crystalline CuO and the amorphous phases. As for the catalysts containing less than 30 wt % CuO XPS results showed the presence of Cu/sup 2 +/ ions, which dissolved substitutionally in the ZnO lattice and formed highly covalent bondings with oxygen anions. In contrast to the coprecipitated catalysts, the impregnated catalysts showed no appreciable interactions between copper and zinc oxides. The surface copper species in the precursor catalysts were attributed to copper hydroxycarbonate in the high copper content catalysts and to the copper in zinc hydroxycarbonate in the low copper content catalysts. 5 figures, 3 tables.

Hydrogen migration under avalanche injection of electrons in Si metal‐oxide‐semiconductor capacitors

Abstract: Aluminum/silicon dioxide/silicon capacitors in which the oxide has been grown thermally under ultra‐dry (≲1 ppm H2O) conditions and subsequently treated by low temperature water diffusion have been characterized electrically and chemically. Avalanche injection of electrons has been observed to produce the complex charging behavior previously observed in similar systems, which includes electron trapping and interface positive charge generation. Secondary ion mass spectrometry depth profiling of these structures has shown that electron injection also results in hydrogen transport. This is the first direct observation of hydrogen redistribution under the influence of an electron current. We demonstrate a linear relationship between injected charge fluence and areal density of hydrogen localized at the SiO2/Si interface. These results indicate that hydrogen release correlates with interface state generation, but not with bulk oxide trapping.

Surface characterization of copper(II) oxide-zinc oxide methanol-synthesis catalysts by x-ray photoelectron spectroscopy. 2. Reduced catalysts

Abstract: The surface state of the coprecipitated cupric oxide-zinc oxide (CuO-ZnO) catalysts reduced at 250/sup 0/C with H/sub 2/ was investigated by x-ray photoelectron spectroscopy (XPS). It was found that a monovalent copper species was present in the surface of the catalysts with low copper contents. It was revealed that two distinct types of copper metal species, both of them being negatively charged by electron transfer from ZnO, were produced in the catalyst surface upon the reduction. In the high copper content catalysts (> 25 wt % CuO), the predominant Cu metal species is described by well-dispersed metal particles, whereas in the low copper content catalysts (< 10 wt % CuO), the major copper metal species is best characterized by a two-dimensional epitaxial copper layer over ZnO. It is concluded that both the two-dimensional copper metal and Cu/sup +/ are formed from Cu/sup 2 +/ dissolved in a ZnO lattice, while the copper metal particles are originating mainly from crystalline and amorphous copper oxide phases. The two-dimensional copper metal species was found to be preferentially reoxidized to Cu/sup +/ when exposed to air at room temperature. The two-dimensional Cu/sup 0/-Cu/sup +/ species are suggested to be catalytically active for the methanolmore » synthesis at low temperature and pressure. The reduction of ZnO was observed only when reduced at 500/sup 0/C and in the presence of copper. In the case of the impregnated catalysts, no appreciable interactions were found between Cu metal and ZnO, in contrast to the coprecipitated catalysts. 7 figures, 2 tables.« less