Applications of Surface Science最新文献

Extensive study of the vapour deposition of noble metals onto UHV cleaved alkali halide crystal surfaces has made an important contribution to the development of time-dependent nucleation theory. There nevertheless remain significant inconsistencies between results obtained from different studies of identical systems. The role which the time-dependent kinetic approach to nucleation theory has played in the past and that which it might take in the future are discussed.

A scanned electron beam from a commercial SEM is used for the localized alloying of vacuum evaporated AuGeNi contacts on n-type GaAs. The contact quality is studied for metallization thickness, 450–1350 Å, for furnace and electron beam alloyed contacts. For the electron beam alloyed method, the contact resistivity decreases with increasing metallization thickness and remains constant for thicknesses above 750 Å. Scanning electron microscopy and electron microprobe analysis shows that electron beam alloyed contacts undergo less redistribution of contact constituents than furnace alloyed contacts. The stability of the contacts is determined by high temperature ageing.

Negative ion resputtering leads to a nonuniform erosion of material which can result in a wide range of morphological features. These various surface structures are a consequence of focused bombardment processes which are highly sensitive to sputtering system geometry and preparation parameters. The continuous manner in which the features are connected leads to a clearer understanding of each.

The production of amorphous silicon solar cells using deposition from a DC magnetron glow discharge is described. The cells have the p-i-n structure with indium tin oxide front contacts. Fill factors of 40% and overall solar efficiencies of around 1.2% were obtained. Investigations were carried out to determine the reasons for deficiencies in the carrier collection efficiency. The cell efficiency was increased by increasing the μτ product of the i-layer. The spectral dependences of carrier collection efficiency, open circuit voltage and fill factors were determined. Comparison with published theoretical models of similar cells showed that for the best cells, surface recombination effects limited the efficiency. Argon used in the p-layer deposition was the most likely cause of these effects.

The surface compositions of the α/β and γ/γ' phases of different metallographic preparations of Ni-15Cr-24Al and Ni-15Cr-24Al-0.3Zr (at%) alloys are presented. Surfaces investigated include a mechanically polished surface for both alloys, a mechanically polished acid etched surface of the Ni-Cr-Al-Zr both before heating and after heating to 600°C for several hours, and the underlying surface of this latter sample exposed by ball cratering. Both phases of all surfaces considered show depletion of Al. It is concluded that the Al depletion is not an artefact of the sample metallographic preparation or the analytical procedure. This is supported by analysis of the composition of a sample scratched in situ under UHV. It is further concluded that the Al depletion is due to oxidation during bakeout. Cr-rich features in both the α/β and γ/γ' phases are reported. An optimal two dimensionally smoothed Cr Auger image is presented showing these features which are considered to be due to the αCr solid solution particles or clustering of these particles in the α/β phase and the Ni solid solution component in the γ/γ' phase.

Low-temperature experimental results on Ge(111) and Si(111) surfaces prepared by crystal cleavage in ultra-high vacuum (∼ 10^-10 Torr), liquid N₂, and liquid He are presented and briefly discussed. Some of these results are reanalyzed and new interpretations are suggested.

The general applicability of power law forms of the background in electron spectra is pointed out and exploited for background removal from under Auger peaks. This form of B(E) is found to be extremely sensitive to instrumental alignment and to fault-free construction - an observation which can be used to set up analyser configurations in an accurate way. Also, differences between N(E) and B(E) can be used to derive a spectrometer transmission function T(E). The questions of information density in an energy-analysing spatially-resolving instrument are addressed after reliable instrumental characterization has been established. Strategies involving ratio histograms, showing the population distribution of the ratio of a pair of Auger peak heights, composition scatter diagrams and windowed imaging are discussed and illustrated.

The crystalline structure, electrical conductivity, and pyroelectricity of freshly prepared Hg_0.7Cd_0.30Te thin films have been investigated in detail. It was found that these properties hold good with one another. The roles of Hg migration, non-stoichiometry and degree of crystallinity are clearly indicated. Finally, the optimum conditions were evaluated and recommended for mercury telluride thin films for application in electronic industries and engineering.

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.

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.