Two kinds of surface phonons, macroscopic and microscopic, are excited at solid surfaces. Macroscopic surface phonons, such as Rayleigh waves and Fuchs-Kliewer waves, have been long known experimentally and theoretically, and have been applied to electric devices. On the other hand, microscopic surface phonons, whose vibrational amplitude is localized to a few atomic layers near the surface, have been measured only during the last few years. Large progress has recently been made in this field, and is reviewed.
Semiconductor-semiconductor heterojunctions are attracting much interest in relation to thin-film growth technology, device applications and electcon physics. To obtain fundamental physical understanding about these heterojunctions, we review the nature of extended eletronic states near the interface. Regarding energy-band discontinuities at the interface, the basic parameters, Harrison's LCAO prediction, and Cohen's self-consistent pseudopotential method are discussed. Also, empirical approaches are surveyed. Among them, a recent C-V experiment seems the most reliable. When the effective-mass theory is applied to heterojunctions, the boundary condition for envelope functions at the interface becomes a specific problem. Ando-Mori's determination by the tight-binding method is detailed. Self-consistent calculation for AlGaAs/GaAs heterojunctions was carried out by Ando and by Stern. The results of the subband structure and the carrier mobility are in good agreement with observed light-scattering spectra and the Hall experiment, respectively.
Some problems are pointed out in the derivation process of the Thomson-Freundlich equation and in extended applications of the equation for the estimation of solubility and vapour pressure at the curved surface or interface. A serious misunderstanding in the derivation process is in the evaluation of the contribution of free energy of the surface or interface on the solubility or the vapour pressure. New ideas are proposed to solve these problems and using these results, the rate process for treating the deformation of a surface pattern is discussed theoretically.
A uniform and adherent deposit of V2O5 thin film onto electroconductive glasses (ITO) has been obtained by electrolyzing colloidal V2O5 solution. A V2O5 sol was prepared from dilute solution of ammonium metavandate by passing the solution through an ion-exchange column (filled with Dowex 50 WX2 resin). The sol was then allowed to stand in a 40°C thermostat for 80 hrs. The viscosity of this sol increased with time, The measurement of the zeta potential of this sol indicated that the sol was negatively charged. Cathodic deposition of V2O5 is not a simple electrophoretic nature, since actually the V2O5 deposition occurred at the negative pole. We propose a following mechanism; the reduction of polyvanadic acid sol yielded a kind of vanadium bronze which coagulated onto the cathode (ITO) to form a solid film. On cathodic reduction the color of V2O5 film changes to green and on anodic oxidation it changes to light orange. The intermediate color tone has been also obtainable, therefore this system can be used as a multicolor device. The reversibility and durability for the electrochromic uses was almost comparable to a vacuum evaporated film.
In developing electrodes to detect biological substances, such as antigens, antibodies and enzymes, several modifications of the surface structure and texture of electrode substrates were carried out by the treatments of rolling, annealing and ion bombardment. With these electrodes, the relation between electric responses and surface properties was investigated in a system of trypsin-trypsin inhibitor. The potential shift detected with each electrode was expressed by the following equation : V=V0 (1-exp (-kt)), where V0 is the terminal potential, t is the response time and k is the rate constant. Results showed that the value of k in the equation depended on the concentration of biological substances as well as the characteristics of the electrode surface developed by the above treatments. Ion bombardment in an argon atmosphere was found to be the most effective for modifying the electrode substrate of a bio-sensor, because it resulted in a rapid response and high potential shift.
SiO2 film consisting of a heat-treated mixture of silicone polymer and silica gel was prepared. Alkali metal carbonates (Li2CO3, Na2CO3 and K2CO3) were respectively doped into the film by a surface treatment. The humidity-sensing property was examined. The effects of heat treatment and exposure to high humidity air were studied after doping. By doping with different carbonates, the impedance of SiO2 films became low at various humidities. The impedance value of the doped films with dopant showed the order of Li2CO3>Na2CO3>K2CO3. After a final heat treatment and aging in high humidity air after doping, the humidity-sensing characteristics of the films scarecely change with exposure to indoor atmosphere. This effect of aging could be caused by the stable formation of hydration water to alkali metal carbonate.
A newly built focusing-type time-of-flight atom-probe is capable of (1) achieving 100% detection efficiency and (2) performing mass analyses under truly ultra-high vacuum conditions (10-11 Torr). The details of the instrumentation and its performance are presented. As for its applications into materials science, we discuss the following topics : (1) surface and grain boundary segregation of binary alloys, (2) metal-semiconductor interfaces and (3) metastable phases of Al-Ag alloys.