It has been found that the oxidation process in heat treatment of Fe-Co double-layer films is different depending upon whether the film is Fe/Co or Co/Fe type. The relations between the magnetic properties and microscopic structures of the oxides of the films have been studied by X-ray diffraction, AES and VSM. Both types of films had perpendicular magnetic anisotropy. When the Fe/Co film was heat treated the upper Fe layer was oxidized, and the oxide grains grown perpendicularly to the substrate are considered to cause the anisotropy. In the case of the Co/Fe film, the Fe layer which had a greater affinity for oxygen than Co, diffused to the surface and was preferentially oxidized. The anisotropy can be attributed to weakening of magnetic interaction between grains by the oxides formed at the Co grain boundaries.
Interface states between an insulating layer and a transparent electrode were investigated, being concerned with the stability and the luminescent properties of CaS thin film electroluminescent (EL) devices. It was found that Y2O3 and CaS thin films deposited on an ITO transparent electrode at 500°C were peeled off when these films were heat-treated at 500°C for one hour. The peeling-off is thoroughly prevented by inserting a SiO2 thin film as a buffer layer between the Y2O3 and ITO films. It was shown that the luminescent properties of the EL device was also improved by using the SiO2 buffer layer. The roles of the buffer layer are discussed from the results of the elemental depth profile measured by Auger electron spectroscopy.
A surface derivatization technique was applied to the XPS analysis of inorganic carbons. Radiofrequency (13. 56 MHz) plasma with CF4 gas has been used for the surface derivatization. Various kinds of graphites and diamonds that had been analysed by XRD and EELS were studied. The XPS data were analyzed with regard to the difference of binding energy between C1s-F1s (ΔEF-C), and the ratio of fluorine and carbon (F/C). It was found that diamond, graphite and amorphous-carbon could be discriminated with ΔEF-C, and that crystallinity could be estimated with F/C.
Since RHEED provides different reconstructed patterns for different surface stoichiometry, the pattern can be used to evaluate the surface stoichiometry of the growing layer in MBE process. However, this technique gives only qualitative information. We have extensively investigated the dependence of RHEED intensity on growth conditions. We have revealed that the surface stoichiometry can be evaluated quantitatively by the RHEED intensity variation.
Theoretical calculations using the DV-Xα-MO method have been performed for various clurters (3-10 atoms) to investigate the electronic structure of Ag (111) surface. The total density of states (TDOS) curves for the clusters are not in agreement with the experimental ARPE spectra because of the large contribution of edge atoms. To minimize the edge effects we have calculated the local DOS (LDOS) for a surface central atom surrounded by all of their nearest-neighbour atoms and have found that the LDOS curves are in good agreement with experimental spectra. Moreover it was found that the LDOS curve composed of the orbitals with total symmetry is in very good agreement with normal emission APRE spectra, indicating that the LOOS method is compatible with the symmetry selection rules.
Photoluminescence (PL) and X-ray diffraction measurements have been performed to investigate the effects et thermal annealing and ion irradiation on the interface properties of low-pressure MOCVD-grown ZnSe-ZhS strained-layer superlattices (SLSs). It is shown from the evaluation of PL linewidth that a fluctuation of the heterointerface between the ZnSe well and the ZnS barrier layers can be completely controlled, within one monolayer. In the present SLS, the interface characteristics are retained against annealing in H2 atmosphere up to 580°C and no additional strain was observed. On the other hand, N+-ion irradiation and the subsequent annealing studies reveal that irradiation-induced defects quench the photoluminescence bands and consequently the fluctuation at the interface takes place. The results of Ar+-ion irradiation also suggest that such defects generation causes an additional fluctuation of the interface from about one monolayer to two monolayer.
The intensity oscillations of reflection high energy electron diffraction (RHEED) patterns during molecular beam epitaxial (MBE) growth of Zn chalcogenides have been investigated with regard to its dependence on the growth conditions. The stable oscillations in a wide range of substrate temperatures of 200-465°C for ZnSe and 190-420°C for ZnTe and of beam pressure ratios (VI/II) of 0.2-9.2 for ZnSe and 0.2-30.0 for ZnTe, respectively, have been observed. This is the first paper that reports the stable oscillation with more than 150 periods in MBE growth of ZnTe. Furthermore, the oscillation during the sublimation process of ZnTe at higher substrate temperatures above 420°C has been observed, which indicates that layer-by-layer sublimation occurs at this temperature range.