Secondary ion mass spectrometry (SIMS) has been used to study the formation of surface double layer on the cleaved (100) surface of a NaCl single crystal at ambient temperature. According to the theory of Kliewer and Koehler on the surface double layer of the alkali halide crystal surface, an excess amount of doubly ionized impurity ions should exist beneath the crystal surface in contrast with the deficiency of positive ion vacancy there at room temperature. The theory also predicts that the concentrations of these two species of point defects are equivalent in the interior of the crystal, thus assuring the electrical neutrality. Cleaving of well-annealed crystal creates diffusional fluxes of point defects toward the surface. Experimental results show that the acculumation of impurity ions onto the crystal surface is indeed in progress after cleaving, thusk substantiating the Kliewer and Koehler theory. Numerical calculations to solve the diffusional equations on impurity ions suggest that new potential of the type A exp[-Bx2] must be introduced to its chemical potential. Here x is the depth from the surface, A and B being constants.
This paper describes a mechanism of the growth mode transition from layer-by-layer to three dimensional island formation due to the large lattice mismatch. The island formation and strain relaxation of GaAs heteroepitaxial growth onto GaP (001) by molecular beam epitaxy is studied by means of an analysis of the reflection high-energy electron diffraction (RHEED) pattern. The anisotropic strain relaxation of formed islands is in agreement with the prediction of the model which considers an elastic strain relaxation within coherent islands. The model is also supported by the oscillation of the lattice parameter of the growing film during the layer-by-layer growth. The change of the RHEED intensity profile reveals the transformation of the film structure from layer to islands and the relaxation of the misfit strain even after the growth has stopped. This finding shows the kinetically limited pseudomorphic structure of the GaAs film and suggests the presence of kinetically controlled critical thickness of the growth mode transition.
Coadsorption-induced recombination of surface hydroxyl species (OD(a)) on Ni (110) was verified by infrared reflection absorption spectroscopy (IRAS) and temperature programmed desorption (TPD). The O-D stretching mode of the surface hydroxyl species appeared at 2650 cm-1 at 173 K on D2O/ONi (110) surface. The hydroxyl species were thermally recombined and desorbed as D2O from the Ni (110) surface at 350 K. The recombination of the OD species to water (2731 and 2567 cm-1), was also observed at a lower temperature (117 K) when CO was coadsorbed. This OD recombination induced by CO adsorption is considered to result from a strong effect of coadsorbed CO, which lowers the reaction temperature from 350 to 117 K.
The composition of a ZnO (0001) polar surface irradiated with hydrogen ions has been investigated with the measuring temperature range from 22°C to 800°C. The surface has been analyzed by Auger electron spectroscopy for surface composition, X-ray photoelectron spectroscopy for chemical binding states, and reflection high energy electron diffraction for surface crystal structures and morphology. The surface oxygen concentration is found to increase at temperatures above 400°C. Reactions of oxygen with the hydrogen in the surface region are discussed with the results of the temperature programmed desorption. A model explaning the combined effects of oxygen segregation onto the surface, H2 desorption, H2O desorption and zinc atom evaporation is presented, by which the experimental results are well understood.
The structure and photoluminescent properties of the ZnF2: Mn thin films deposited by electron beam evaporation relating to the preparation conditions has been investigated. It was found that when the pressure is of the order of 10-6Torr, a fraction of the film is oxidized to ZnO if the substrate temperature is higher than 400°C. This oxidation process could not be observed even at 500°C if the pressure lies in the order of 10-8Torr. The crystallinity of the film was improved with increasing the substrate temperature and decreasing the pressure. Fluoride thin-film EL devices consisted of ZnF2: Mn as an emission layer and CaF2 as an insulating layer were also prepared and their EL properties were measured. EL intensity is observed to increase with the increase of substrate temperature. However, the breakdown voltage of the EL device is decreased at higher substrate temperatures. The mutual diffusion might take place in between CaF2 and ITO and causing breakdown of the device. This could be suppressed by an experiment in which SiO2 is inserted between the those two layers.
For the first step toward sharing the Auger spectra obtained by using different types of instruments, the round robin on the energy dependence of sensitivity of Auger electron spectrometer has been made. Participants, who use many different types of commercially available instruments, obtained a wide range of spectra of copper. Each spectrum was transferred to the Common Data Processing System. The energy dependence of each instrument was evaluated by the comparison of the spectrum with the 'standard' spectrum registered in the System. It became clear that the energy dependence of the sensitivity of the instruments which use CMA as an energy analyzer is explained mainly as the reflection of the energy dependence of electron multiplier. As a result, it is concluded that the energy dependence of sensitivity of the instruments is well explained by simulating the process of the cascade of secondary electron emission.
The surface structure of a Si (100) substrate exposed to an As ionized cluster beam (ICB) was investigated by means of coaxial impact collision ion scattering spectroscopy (CAICISS). As a result of the measurements, first, it was proven that the Si surface is not damaged by As ICB exposure, although implanted As atoms of several percent were detected in the surface region. Second, both As and Si atoms from double domains of 2×1 and 1×2, and the predominant domain seems to be 2×1. Furthermore, 1×2 domain of As contributes to a lateral contraction of the surface.
Molecular arrangement of smectic B liquid crystal, 1-(4'-cyanocyclohexyl)-trans-4(1-penten-5-yl)-cyclohexane, on a highly oriented pyrolytic graphite (HOPG) substrate was first observed by using a scanning tunneling microscope (STM). The end-on oriented molecules of hexagonal-like packing were observed. The observed structure is discussed in terms of the balance of molecule-molecule and molecule-substrate interactions.
In situ XPS measurements of Ar+-sputtered γ-bismuth molybdate surfaces during heating under ultra high vacuum (UHV) and/or on exposure to oxygen stream (O2-Jet) at 5×10-6 Pa were dynamically performed. By Ar+-sputtering, Bi3+ or Mo6+ was reduced partially to Bi0 or Mo5+, respectively, and Mo6+ was reduced in preference to Bi3+. When the reduced surfaces were heated under UHV, Bi0 and Mo5+ began to be converted to the original states, and at 423 K they were completely oxidized. The reoxidation of Bi0 to Bi3+ proceeded smoothly for a long time. The reoxidation rate of Mo5+ decreased rapidly with time, although it was larger than that of Bi0 in the initial stage. Exposure of the reduced species to O2-Jet prompted the reoxidation. The initial reoxidation rate for Bi0 or Mo5+ was 1.4 or 2.4 times that obtained during heating under UHV, respectively. Apparent activation energies for the reoxidation of Bi0 and Mo5+, which were calculated from the Arrhenius plots of the initial rates, were 24 and 30 kJ mol-1 under UHV, whereas during the exposure to O2-Jet they were 20 and 33 kJ mol-1, respectively. These results were able to be explained in terms of the diffusible migration of lattice oxygen anions to anion vacancies.
We previously disscussed the influence of Mn addition on the positive temperature coefficient (PTC) effect of BaTiO3 ceramics using Jonker's model. Jonker derived his model from a “jump” of the resistance at the Curie temperature ; however, a “jump” was not observed by us. The distribution of the Curie temperature, Tc of each grain was estimated by experiment and simulation. The permittivity peak was observed at 6 K-above the pyroelectric current peak. Such a peak shift was simulated only when the Tc distribution was assumed. The disappearance of a “jump” can be attributed to the Tc-distribution of our specimens.