A negative electron affinity (NEA) state is formed on the surfaces of Si and some III-V compound semiconductors, on which are adsorbed a Cs and/or Cs-0 monolayer. Since NEA surfaces exhibit a high rate of electron emission, many studies, on both the fundamental and practical levels, have been carried out. This paper reviews the the results of surface studies related to NEA. First, the physical principles of NEA operation and the preparation of clean surfaces for NEA ane explained. Included are the main results of studies on NEA surfaces of Si and GaAs, obtained by LEED, AES and photoemission spectroscopy. Finally, the states of Cs and Cs-O adsorbed on GaP surfaces as determined by the thermal desorption method are discussed and the optimum Cs vapor pressures for preparation of NEA GaP surfaces are presented.
The dehydration of isopropanol has been studied at 180-220°C with zeolite Y catalysts which were ion-exchanged (CaKY, LaKY), decationized (HKY, HNaY) or de-aluminated (d-HNaY) up to various levels. The solid acidity of each catalyst was determined as the acidity function H0 from absorption spectra of an acid-base indicator absorbed on the catalyst in decaline. The acidity of catalysts and their catalytic activity were generally enhanced with increasing exchange or pretreatment. But excessive decationation or de-alumination caused deactivation due to partial destruction of the crystalline lattice. As seen in Figs. 10 and 11, experimental data shows good linear relations between log k0, the zero order rate constant, and H0. This linearity is theoretically supported by assuming a surface reaction mechanisms analogus to homogenous acid catalysis. The line slopes were less than unity in absolute value and varied somewhat with the respective catalyst as seen in Table 1, suggesting a proton mobility characteristic for zeolite. The application of H0 to solid acid catalysis was considered to be available by supposing a correction of pKa of indicators suitable to the surface or intracrystalline state.
Small jumping of a slider under various sliding conditions has been observed. The results of measurments of the contact resistance during sliding contacts indicated that many small jumps occurred during ordinary sliding contact. The mean duration of the jumps was about 3 milliseconds, their mean frequency increased with increasing sliding velocity. The number of jumps was roughly proportional to the real sliding distance, about 103 jumps per 1 meter of sliding. The ratio of non-contact vs. contact time increases with increasing sliding velocity and easily exceeds 75% under ordinary sliding conditions. The mean duration of real contacts decreases from 4 milliseconds to 1.6 milliseconds with the increase of the non-contact ratio. The wear sustained by the specimens (sintered-metal pins and copper rings) were also measured, in the from of the difference in weight before and after sliding. The results indicated that the noncontact ratio has little influence on the specific wear rate, Despite the short mean contact time, Holm's law of adhesive wear is found to be appropriate for such sliding conditions as teese, in which the jump frequency is high.
Alloying reactions of metal films deposited on chemically etched GaAs and InP surfaces, (Ni/Au-Ge and Ni films for GaAs, Au and Au-Zn films for InP), were studied using micro-probe Auger electron spectroscopy, X-ray photoelectron spectroscopy, reflection and transmission electron diffraction, and X-ray diffraction. The chemically etched surfaces are covered with thin native oxide layers (5-10 Å thick). Metallization without interfacial native oxide layers is realized by depositing metals, (Ni for GaAs and Au for InP), which have a capability to produce compounds with both III and V group elements.
Recent developments and applications of functional thin films on metals, in some cases on semiconductors or glasses, are reviewed. Functional thin films can roughly be classified into three categories: 1) functional plating, 2) functional anodized alumina films, 3) modified electrodes. Functional plating encompasses dispersion or composite plating, alloy plating, and the other special type of plating. The aim of these plating methods is to improve the hardness, optical, electrical, thermal, adhesive, or the magnetic properties. Anodized alumina films have many micropores on their surfaces, and various substances, acting as functional material, can be impregnated into the micropores. Metals and semiconductors can be coverd with a thin adsorbed layer of organic or inorganic functional groups, which give the substrate metal a special character, such as catalytic activity, ECD, selective reactivity, or photoelectrochemical activity.
The present status of the study of adsorption of metal atoms on clean Si (111) surfaces is reviewed. In particular we give an outline of the growth processes of the adsorbed layers, and the structures and phase transitions of two dimensional phases on the silicon surfaces. Electronic structures of these surfaces are also discussed.