Applications of Surface Science最新文献

The treatment, appearance, and corrosion resistance of metallic coatings are largely governed by the chemical composition of the surface. Auger electron spectroscopy shows that the surfaces of hot-dipped metallic coatings differ markedly from the bulk compositions of the coatings. For example, the surfaces of terne coatings, lead-tin alloys, contain little lead. The conventional galvanized coating, which is more than 99% zinc, has a predominantly aluminium oxide surface. Typical surface compositions of a range of hot-dipped metallic coatings are provided. A qualitative prediction of the dominant metallic species present on the surface of each of these coatings is presented in terms of the relative oxygen affinities of the metals. Theoretical equations for various mechanisms, such as atomic size mismatch, solubility, and oxidation, which could lead to surface segregation are considered, in order to place the experimental observations on a more quantitative basis.

We have used a variety of novel approaches in characterizing metal-semiconductor interfaces — soft X-ray photoemission spectroscopy with interlayers or markers, surface photovoltage spectroscopy, and cathodoluminescence spectroscopy, coupled with pulsed laser annealing — to reveal systematics between interface chemical and electronic structure. The chemical basis for these interfacial properties suggest new avenues for controlling electronic structure on a microscopic scale.

The process is intended to grow polycrystalline or epitaxial thin films of water-insoluble ionic or ionocovalent compounds of the C_mA_n type by heterogeneous chemical reaction at the solid-solution interface between adsorbed Cⁿ⁺ cations and A^m− anions. The process involves an alternate immersion of the substrate in a solution containing a soluble salt of the cation of the compound to be grown and then in a solution containing a soluble salt of the anion. The substrate supporting the growing film is rinsed in high-purity deionized water after each immersion. Polycrystalline and epitaxial thin films of ZnS and CdS have been deposited following this process at room temperature on different substrates.

The existence of several surface phases formed by the adsorption of iodine on Ni{100} has been established using qualitative LEED, thermal desorption and Auger electron spectroscopy, and models have been proposed for these structures on the basis of data from these techniques. In particular, two different phases can be found at room temperature, a c(2 × 2) chemisorbed phase and an incommensurate structure identified as a slightly distorted single sandwich layer of NiI₂. Heating of either of these phases leads to some desorption and the formation of a variable-sized centred rectangular mesh chemisorbed phase characterized by varying iodine- iodine repulsive energies. More recent data obtained using surface EXAFS and angle-resolved core and valence level photoemission confirm the structural assignment for the surface iodide and show its electronic structure to be essentially that expected of bulk NiI₂. Studies of core level binding energy changes as seen in photoemission in the range of chemisorbed structures are discussed, and are interpreted as indicating that the Ni-I bond in this system is essentially covalent with the I-I repulsion resulting from roughly equal contributions from through metal and through space interactions.

The nature of the chemisorptive CO bond on Ni(001) and Fe(110) is considered in terms of coordination and charge transfer in analogous metal carbonyl molecular clusters, and of new data on valence level shifts in photoemission based on the bond stretching model of Brodén et al. A preliminary theoretical analysis of photoemission dispersion based on recent ab initio self-consistent calculation results using Kasowski's original self-consistent field extended muffin- tin orbital (SCF-EMTO) slab calculational approach is presented for CO bonding on single atom slab nickel and iron. The roles of charge transfer, backbonding and bond stretching are discussed.

Much of what is known about the metal-solution interface has been discovered using electrochemical techniques from which information about reaction rates, extents of reaction, concentrations, etc., can be readily obtained. The value of electrochemical measurements to the study of metal-solution reactions is illustrated by considering examples of adsorption, metal oxidation and catalysis at an electrode surface. A comparison of metal-solution and metal-gas reactions indicates that the former are more complex and that the associated experimental difficulties are greater. The problems of cleaning a metal surface and maintaining it is in a clean state over the time scale of an experiment are considerable but important in obtaining reproducible results.

The columnar physical structures commonly found in vapor-deposited thin films have been classified by several variations of what have been termed structure zone models. Perhaps the most interesting feature of these various models is their universal application to apparently all film materials and deposition processes. A structural self-similarity over a wide range of film thicknesses, preparation conditions, and materials types appear to be pointing toward a common origin. Reasons will be presented as to why thin films may be fractals and the consequence of this suggestion to understanding the origin and evolution of thin film physical structure. In particular, recent ballistic aggregation computer models provide a promising avenue of research.

We review here work which demonstrates that silicon dangling bonds, Si₃, are the predominant, electrically active deep states associated with the clean crystalline silicon/amorphous SiO₂ interface. Si₃ exists in three charge states in the silicon band gap with and $\text{E}{}_{\mathrm{0,-}}\text{⋍ E}{}_{\mathrm{<mtext>v</mtext>}}\text{+ 0.9}\text{eV}$, where E represents a demarcation level between charge states. We discuss the structural and electronic characteristics of Si₃ at the Si/SiO₂ interface, including degree of charge localization, effective correlation energies, role of hydrogen passivation, etc. We argue, from the strongly analogous behavior in amorphous silicon, that the electronic density of states in the gap is dominated by the characteristic effects of disorder in covalently bonded semiconductors. The states consist of two topologically distinct entities: distorted, fully-bonded network configurations giving rise to shallow silicon band tails, and three-fold coordinated, amphoteric silicon defects.

Powdered chlorinated copper phthalocyanine (ClCuPc) was sublimated to a thickness of 400 Å onto KCl cleavage faces, and the films were examined with electron microscopy and diffraction. The ClCuPc crystals grew with S-orientation in which the molecules stand on the substrate, and with P-orientation in which the molecules lie parallel to the substrate. At the substrate temperature of 250°C, the S-orientation became dominant with increasing deposition rates. The growth mechanism of the crystals with these orientations is discussed on the basis of the adsorption energy of ClCuPc on a KCl surface.

The migration of implanted nitrogen during wear has been investigated. Nitrogen depth profiles measured by Auger Electron Spectroscopy (AES) and argon sputter milling within wear tracks made in mild steel are reported. These in-track AES profiles are compared with profiles for as-implanted nitrogen and wear-track roughness. Evidence in favour of nitrogen migration beyond the implant depth is qualified by the effect of surface roughness on the AES data. Some preliminary data and thoughts on the role of oxygen in the wear process are presented.