Applications of Surface Science最新文献

Quantitative three-dimensional studies of morphology together with analysis of validity of quasistatic effective medium theories show the need for a diffraction treatment of the optical properties of solar selective black chrome. The spectral absorptance A(λ) is calculated for a doubly periodic modulation of chrome overcoated with Cr₂O₃ or a cermet of Cr₂O₃ and Cr metal. Various profiles, depths and coating thicknesses are used. Diffraction caused by the surface morphology explains the major features of A(λ) for black chrome. Internal structure is of secondary importance.

When photoillumination is interrupted, the exoelectron emission from scratched metal samples decays quickly. When the illumination is resumed, however, the recovered exoelectron emission shoots up to a value significantly higher than before and then decreases gradually - a fact overlooked by previous researchers. To explain this “storage effect” in PSEE (photo- stimulated exoelectron emission), the authors have proposed a model, according to which there are two excitation processes competing during PSEE; one is the photoexcitation of the electrons at energy levels within the band gap of surface oxide layers, and the other is the tunneling transition of electrons in bulk metals to occupy the vacant levels of the oxide layers. From the rate equations based on this model and also from the PSEE data obtained for scratched aluminum and zinc, three kinds of quantities, i.e., the number of exo-active sites, the emission rate from the sites and the rate of activating exo-inactive sites, are successfully estimated. Other PSEE phenomena such as the peculiar emission intensity versus time profiles can also be elucidated in view of this model.

Energy distributions of sputtered Ni ions and neutrals were measured at non-normal incidence of Ne and Ar ions. Only the Ni particles sputtered in a binary collision can be used for the determination of the charge state fractions. Monte Carlo simulations (TRIM SP) were used for the absolute calibration of the total intensity in the binary recoil peak. The charged fractions are found to be less than 10% for energies below 5 keV. The positive fraction is about one order of magnitude larger than the negative and the doubly charged fractions.

The growth mode of Cu deposits on clean Pd(100) has been studied by means of LEED. AES and angular resolved ultraviolet photoemission spectroscopy. Auger signal versus deposition time curves showed that the growth follows a layer-by-layer mode for two monolayers after which it involves formation of islands as in the Stranski-Krastanov model. Despite the large lattice mismatch between Cu and Pd (7.7%) the substrate p(1×1) LEED pattern persisted with clear distinct spots at least up to the equivalent coverage of 4 ML indicating that Cu starts to grow epitaxially with the Pd lattice constant (pseudomorphic growth). Photoemission results show that the spectrum of the Cu/Pd(100) system does not converge to that of bulk Cu(100) until about 65 ML equivalent coverage. The spectrum below that coverage is composed of separate contributions from the thick regions and from the pseudomorphic basic slab.

The adhesion enhancement of evaporated metal films on silicon and silicon dioxide substrates following electron and photon irradiation has been investigated. It is shown that an electric field applied across the metal-oxide-semiconductor interface during electron irradiation has a dramatic influence on adhesion enhancement. For photon irradiation, comparative adhesion measurements were undertaken as a function of increasing metal film thickness and different irradiation doses, for photon energies <4, <6 and 10.2 eV. Metal-oxide-semiconductor structures were also biased during photon irradiation to indicate the role of secondary processes such as charge flow to the interface from the oxide. Results indicate that adhesion enhancement can be significant even if the metal film thickness exceeds the photon penetration depth, supporting the view that low-energy secondary excitations are responsible for the stronger bonding configurations. It was also concluded that both electron and photon irradiation give rise not only to increased adhesion but also to increased cohesion within the metal film.

This paper reports on the degradation characteristics of moisture-sensitive Ta₂O₅/TiO₂ ceramic films, whose electrical capacitances change with relative humidity. The fabrication process and the capacitance characteristics of the tested samples are described. The durability tests against the temperature and humidity cycle and against 10 ppm CO or SO₂ gas in the atmosphere have been carried out. In order to examine the interaction between water molecules and toxic gases on the ceramic surface, the electrical capacitance and resistance changes are investigated using the samples placed in a vacuum containing traces of CO or SO₂ gas to which pure water is subsequently added. Finally, possible physicochemical effects on the electrical characteristics of the ceramic films are proposed.

Hydrogenated amorphous silicon (a-Si:H) films were deposited on the surface of quartz substrates using the tetrode RF sputtering technique. The conditions for film deposition were controlled by changing the pressure ratio of hydrogen to argon gas, ξ, in the atmospheric gas. We studied the dependence of the optical and electrical properties of deposited films on ξ, and discuss the complex changes of optical absorption coefficient, α, and electrical conductivity, σ, at $\text{ξ ≧ 20\%}$ in terms of the silicon-hydrogen configuration from the results of infra-red absorption and SEM measurements.

While the chemical analysis of a surface has become commonplace using a variety of techniques including Auger Electron Spectroscopy (AES) and Electron Spectroscopy for Chemical Analysis (ESCA), it is often advantageous to differentiate between the chemistry of the surface and the near surface. The method used to make this distinction depends on the thickness of the layers to be differentiated. If the combined thickness of the layers is greater than 100 Å, then the surface must be physically removed by ion bombardment before the subsurface components can be identified. An example of the chemistry revealed by this method is given in a sputter profile of an eight layer, 3000 Å, metal magnetic tape. The internal interfaces show more oxidation than the bulk of the metal layers. If the combined thickness of the layers is less than 100 Å, then the surface and subsurface components can be identified by non-destructive techniques. This is accomplished by using high energy excitation or by angle resolved studies. Examples will be shown of the change in the surface and near surface chemistry of polystyrene as it is treated in H₂ and H₂O plasmas. The degree of oxidation of the polymer surface can be monitored as a function of reaction depth using angle resolved ESCA. Extending the range of angle resolved studies by using Au Mα X-rays is shown for a native oxide on silicon.

This paper summarizes a six-year research program aimed at preparation and characterization of thin films of the chalcopyrite semiconductor CuInSe₂ suitable for photovoltaic solar cells and other semiconductors devices. The thin film deposition methods used were evaporation, flash evaporation, RF-sputtering and chemical spray pyrolysis. Problems with producing films of reproducible properties by these methods are discussed. Gaps in our knowledge of the dependence of the opto-electronic properties of CuInSe₂ crystals and films on structural defects and other imperfections are pointed out.

A new method is developed to determine the tunneling transmission probability through a thin oxide layer by making use of the switching characteristic of a metal-tunnel oxide-semiconductor thyristor. It is found that the tunneling transmission probability is very sensitive to oxide thickness and is dependent on the voltage drop across the oxide layer.