A. Ignatiev

Electric-pulse-induced reversible resistance change effect in magnetoresistive films

A large electric-pulse-induced reversible resistance change active at room temperature and under zero magnetic field has been discovered in colossal magnetoresistive (CMR) Pr0.7Ca0.3MnO3 thin films. Electric field-direction-dependent resistance changes of more than 1700% were observed under applied pulses of ∼100 ns duration and as low as ±5 V magnitude. The resistance changes were cumulative with pulse number, were reversible and nonvolatile. This electrically induced effect, observed in CMR materials at room temperature has both the benefit of a discovery in materials properties and the promise of applications for thin film manganites in the electronics arena including high-density nonvolatile memory.

Interactions of ion beams with surfaces. Reactions of nitrogen with silicon and its oxides

Ion beam studies of chemical reactions between nitrogen and surfaces of silicon and its oxides are reported. A spectrometer system designed for these studies which combines the techniques of x‐ray and uv photoelectron spectroscopy, Auger electron spectroscopy, secondary ion mass spectroscopy, low energy electron diffraction, and ion bombardment is described. This work employs XPS and UPS to examine the products induced by 500 eV N+2 beams on targets of elemental Si, SiO, and SiO2. The N+2 ions undergo charge exchange and dissociation at the surface of the target to form hot N atoms. Reaction with Si, produces nitrides which are similar to those of the type Si3N4. Reaction with SiO and SiO2 forms nitrides, with no evidence of nitrate or nitrite formation. The chemical nature of the reaction is suggested by identification of the reaction products through XPS and UPS and energy level shifts. The thickness of the silicon nitride layer on Si(111) formed by 500 eV N+2 bombardment has been determined to be ∼19 A...

Leed investigations of xenon single crystal films and their use in studying the Ir(100) surface

Abstract Well-ordered, chemically pure, xenon crystals of the (111) surface orientation were grown on Ir (100) 1 × 1 and 1 × 5 type substrates at 55°K. Because of the strongly kinematic character of the xenon LEED intensity-energy spectra, it was possible to use the scattering spectra from adsorbed xenon to investigate the surface structures of Ir (100). The combination of information from the Auger spectra of the iridium, from the differences in orientation of the xenon crystals grown on the two Ir (100) structures, and from the positions of the Bragg-type interlayer scattering peaks in the adsorbed xenon-Ir (100) intensityenergy spectra, indicated in a self-consistent manner that the occurrence of the thermally stable 1 × 5 structure is associated with no identifiable surface impurity whereas it is consistent with the presence of a distorted hexagonal overlayer of iridium on a (100) plane typical of the fcc crystal.

Solar selective black cobalt: preparation, structure, and thermal stability

In the quest for an electroplated selective black coating stable to 500 °C in air, black cobalts have been prepared by three techniques to yield (a) plated cobalt sulphides, (b) plated cobalt oxide‐hydroxide, and (c) cobalt oxide prepared by thermal oxidation of electropolated cobalt metal. The optical properties of the various coatings are analyzed before and after exposure to air for extended periods of time at temperatures in the 300 °–500 °C range. The sulfide black cobalt is not acceptable as a high‐temperature selective absorber due to severe thermal degradation. The plated oxide is a good selective absorber to about 400 °C, and the thermally oxidized black to a slightly higher temperature, but degrades at 500 °C. Structure studies via scanning electron microscopy (SEM), Auger electron spectroscopy (AES), and x‐ray photoemission spectroscopy (XPS) are reported which yield a full account of the coating chemistry before and after heating. The studies reveal that the high solar absorptance of the accep...

Formation and characterization of thin film vanadium oxides: Auger electron spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, and optical reflectance studies

Abstract The growth of thin film vanadium oxides on a vanadium substrate under oxygen partial pressure has been investigated over a range of temperatures and times. A variety of oxide structures in the range VO2V2O5 have been grown. Chemical composition, phase identification and structure of the oxides have been characterized using several analytical techniques including Auger electron spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction (XRD), scanning electron microscopy, and optical reflectance and have been supported by thermodynamic calculations. Small grain crystalline V2O5 was successfully grown under a reproducible recipe. A visible band gap energy Eg ≈ 2.38 eV and an XRD morphological factor ƒ ≈ 0.94 were measured for the grown V2O5 film. Ultrahigh vacuum thermally induced reduction of V2O5 into a lower oxide has been observed. The various properties (structural, electronic, optical, and electrical) of V2O5 have also been reviewed.

Electrical conductivity relaxation studies of an epitaxial La0.5Sr0.5CoO3−δ thin film

Abstract The oxygen surface exchange coefficient kchem of a La0.5Sr0.5CoO3−δ (LSCO) thin film has been determined from electrical conductivity relaxation measurements. The LSCO thin films were deposited on LaAlO3 (LAO) single crystal substrates by pulsed laser deposition (PLD). The electrical conductivity relaxation behavior of the film was measured at high temperature on switching the oxygen partial pressure between 0.01, 0.05, 0.10, 0.30, 0.50 and 1.00 atm. The kchem values were obtained by fitting the conductivity relaxation curves using a surface-limited kinetics model. The results show that kchem increases with temperature and with the oxygen partial pressure after the switch, but is not sensitive to the initial partial pressure. After prolonged heating at 900 °C, kchem increased substantially. The increase is associated with a change in the thin film surface morphology on prolonged heating.

LEED study of the Pt(110)-(1 × 2) surface

Abstract The results of a quantitative LEED study of the clean, reconstructed Pt(110)-(1 × 2) surface are described, in which experimental intensity-energy spectra for ten diffracted beams have been compared, by an γ-factor analysis, to intensity spectra calculated using a dynamic theory for various structural models. Despite considerable effort in ensuring the reliability of the experimental and calculated intensities, a satisfactory level of agreement has not been achieved for any of the model structures considered although a “missing-row” model leads to the closest agreement between experimental and calculated intensities.

Spatially extended nature of resistive switching in perovskite oxide thin films

The authors report the direct observation of the electric pulse induced resistance-change effect at the nanoscale on La1−xSrxMnO3 thin films by the current measurement of the atomic force microscopy (AFM) technique. After a switching voltage of one polarity is applied across the sample by the AFM tip, the conductivity in a local nanometer region around the AFM tip is increased, and after a switching voltage of the opposite polarity is applied, the local conductivity is reduced. This reversible resistance switching effect is observed under both continuous and short-pulse-voltage switching conditions. It is important for future nanoscale nonvolatile memory device applications.

Refinement of solar absorbing black chrome microstructure and its relationship to optical degradation mechanisms

An in depth characterization of the electrodeposited solar absorber black chrome resulting in refinement of the microstructural model of the coating is presented in light of current studies in valence band Auger electron spectroscopy, x‐ray photoelectron spectroscopy, thermal desorption spectroscopy, secondary ion mass spectroscopy, and the chromium electrodeposition mechanism. Through the presented model, the structural and chemical parameters of the coating are linked to its optical response with the degradation of the optical response at elevated temperatures related to changes in these parameters. The degradation process is divided into two distinct phases. First, upon heating to low temperatures (≲300 °C) the chromium hydroxide localized on the surface and within the microstructure of the film decomposes producing H2O and chromium oxide leaving an expected microvoid‐metallic particle structure. Heating to temperatures in excess of 300 °C leads to the second degradation phase. The fine chromium crysta...

Concentration depth profiles by XPS; A new approach

A new technique is proposed to extract quantitative depth information from a single XPS spectrum. The technique has the advantages over existing methods of being non-destructive, simple and extremely fast. Depending on the system studied alternative methods may, however, give more detailed information. A quantity is defined, which for homogeneous samples is independent of the rate of generation of photoelectrons as well as of the peak shape, but which for inhomogeneous samples, due to elastic and inelastic electron scattering, is a strong function of the depth composition. This quantity D, which is essentially the ratio of the XPS peak area to the increase in background signal associated with the peak, is studied experimentally and theoretically. Through an analysis of eighteen XPS peaks from seven homogeneous polycrystalline metals, D is found to be a weak function of both the XPS peak energy and the metal. The experimental points scatter less than 25% around the mean value D0 = 23 eV. Thus, for homogeneous solids, D is to first order matrix, concentration, and energy independent, i.e. it is a “universal” constant. As a consequence, by measuring this ratio for a given XPS peak, quantitative information on the depth location of the corresponding element can be obtained. The technique is demonstrated for a system where the depth composition is known in advance. This system consists of a submonolayer of Ag situated at varying depth underneath the surface of an Al sample.