The phenomena accompanied by the low-temperature emission of electrons, positive and negative ions, neutral molecules, and photons show that exoemission is excited either by physico-chemical processes in the surface layers of materials, for example, adsorption, desorption, oxidation, corrosion, and catalytic reaction, or by external influences such as from mechanical or radiation effects. The nature of exoemission from solid surface has been intensely studied. The majority of studies are based on the experimental analogy between the phenomena of exoemission and phosphorescence, and are directed to the investigation of the physical, chemical, and mechanical properties of materials. This review of these studies shows that an elucidation of the detailed mechanisms of exoemission is closely related to the nature of the material surface itself.
The existence of the relationship between surface lattice imperfections and heterogeneous catalysis was proposed by H.S. Taylor in 1925. Since then, much work has been done to support this relationship. Various approaches have been used such as by applying catalytic activity versus annealing temperature curves of cold-worked, electron- or ion- bombarded metals. However, the results are rather qualitative. More recently, techniques such as AES, LEED, and EELS have been used to characterize the electronic, atomic, and defect structures of solid surfaces on an atomic scale. These were successfully applied first by G.A. Somorjai's group and then by other investigators. Many interesting and quantitative relationships were obtained between step or kink concentration and adsorptive or catalytic activities on well-defined surfaces. This article reviews the qualitative and quantitative results.
A new sample preparation technique to profile multilayer films on glass substrates by Auger electron spectroscopy (AES) was examined. The sample surface layer was sputtered by Ar ions to make a slope that was at a slight gradient to the original surface. This ramp-etching caused cross sections of each layer of the multilayer film to appear in consecutive order on this new surface. The depth profile was obtained by scanning the electron beam along the slope, and then converting the lateral magnitude of each section into layer depth. It was found that the ramp-etching technique, which provided a ramp gradient of 1.4×10-5 (tanθ) corresponding to 70 Å of depth resolution in depth-profiling, could be used to determine with improved accuracy the complex constitution of antireflection coatings.
For the last several years, solid super acids and bases have been synthesized. Among these, SbF5-SiO2-Al2O3, TiO2+SO42-, ZrO2+SO42-, Fe2O3+SO42-, ZSM zeolite, supported heteropoly acids, or MgO+Na are being used as efficient catalysts for such processes as isomerization, dehydration, esterification, and acylation. Some of these materials were proven to be useful as catalysts in replacing such environmentally undesirable materials as concentrated sulfuric acid and aluminum chloride. The surface structures of the acidic and bacic sites, as well as the catalytic activity and selecrivity, are described. Acid-base bifunctional catalysis is another recent topic. Properly pretreated ZrO2 and MgO, which possess both acidic and basic properties, have been found to exhibit a pronounced catalytic action for hydrogenation and alkylation, suggesting their potential use as catalysts for industrially important reactions. The surface nature of these bifunctional catalysts is discussed.
The relation between the nature of surfaces and interfaces, and the ceramics fabrication process, is discussed; and a concept, “free energy theory of material transport” is proposed to explain the diffusion process observed during sintering. In the theory, the excess energy stored at the surface and/or interface in the system is considered to stimulate the material transport directly. This contrasts with the traditional “vacancy theory” in which diffusion during sintering is considered to be promoted by the surface and/or interface tension. The background of the free energy theory is explained based on the difference of the nature between the energy and tension. The densification, grain growth, and the diffusional creep of elastic solids are treated to illustrate the theory.