Applications of Surface Science最新文献

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.

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.

An ultrathin iron film deposited on a MgO single crystal in UHV is heated up to 500°C. AES/LEED measurements combined with TEM observations performed on small single crystal platelets show that the film is transformed into small particles below 300°C. Around 380°C, surface diffusion induces a spectacular growth of some particles. Upon further heating, the evolution of the system depends on the shape of the particles. In most cases, the particles become square and orient themselves along the MgO(110) direction (epitaxial configuration); however, they are unstable: they progressively dissolve in the MgO matrix, leading to a substitutional (Mg_xFe_1−x)O solid solution. In other cases, the iron particles remain shapeless and stable, suggesting that dissolution only occurs when the particles grow epitaxially.

Measurements of electrical conductivity and optical constants of thin films of a-SiH : B produced with varying hydrogen concentration (C_H = 0–30 at%) and boron concentration (C_B = 0.1–10 at%) are used to investigate the effects of increasing hydrogenation and doping on the density of states (DOS) of the a-Si network. There exist strong and abnormal dependences of electronic properties on C_H and C_B which correlate with increasing topological disorder of the a-Si network. For undoped films, concentrations of hydrogen up to 15 at% lead to a general decrease in the density of defect and band-tail states, a redistribution of valence band states, and a widening of the optical gap. A hydrogen content > 15 at% leads to increasing density of localized dangling-bond type states and deep-lying valence band states suggesting substantial topological disorder.

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.

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.

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 VEEL spectra of benzene, deuterobenzene, and pyridine adsorbed on Pt(110) at room temperature have been examined in emission planes both coincident with and orthogonal to the plane of incidence. The inelastic peak intensities are found to be almost independent of angle in both directions. This implies that neither of the established mechanisms, nor others presently examined, is an adequate description of the scattering. It also leads to a reassignment of the benzene spectrum.

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.