Electron spectroscopic comparison of the C-rich SiC(0001̄) and Si-rich SiC(0001) surfaces after cleaning and disordering by Ar+ ion sputtering and subsequent annealing is reported. The chemical behavior of the two disordered surfaces differs significantly. Three distinct temperature regions with different carbon surface segregation kinetics are discernible on SiC(0001̄). On SiC(0001) only one temperature region for C-segregation is observed. Below 900 K, no spectroscopic differences between the two crystal surfaces are observed. Between 900 and 1300 K, both faces are terminated by a surface graphite layer and the C-rich face shows an additional carbon surface segregation process. Above 1300 K, the C-terminated surface graphitizes at a higher rate than the Si-terminated surface. Massive graphitization on both surfaces above 1300 K is attributed to Si(g) sublimation from the SiC surfaces. The results demonstrate that extensive surface disordering of polar SiC faces does not destroy the memory for the polarity of the original crystal insofar as high-temperature surface chemistry is concerned.

A comparison of the kinetics of oxidation at 995 and 1345 K of the SiC(0001̄) and SiC(0001) crystal faces is made. The oxidation rate on the SiC(0001̄) (C-rich face) is higher at both temperatures. SiO2 is formed. At 1345 K, the initial oxidation process is retarded by excess surface carbon. When the excess carbon is volatilized by either CO or CO2 formation, the oxidation rate is higher at 1345 K than at 995 K.

Wetting of transition-metal boride and arsenide liquid metal alloys (Ni5sB,5, Pd72B28, Pt72B28, Pd2As) is strongly influenced by surface segregation of low-level bulk impurities in the alloys. At melting, the impurities segregate to the liquid surface and inhibit wetting, resulting in a poorly wetted drop of alloy. Good wetting is achieved by introducing materials into the contact system with high chemical affinity to the major segregants. The materials suppress the impurity segregation by tying up the impurities as solid phases during liquefaction.

No abstract

A source of thermal, ground-state atomic oxygen has been used to expose thin copper films at a flux of 1.4×1017 atoms/cm2 s for times up to 50 min for each of five temperatures between 140 and 200 °C. Rutherford backscattering spectroscopy was used to characterize the oxide formed during exposure. The observations are consistent with the oxide phase Cu2O. The time dependence and the temperature dependence of the oxide layer thickness can be described using oxide film growth theory based on rate limitation by diffusion. Within the time and temperature ranges of this study, the growth of the oxide layers is well described by the equation L(T,t)=3.6×108 exp(−1.1/2kBT)t12, where L, T, and t are measured in angstroms, degrees Kelvin, and minutes, respectively. The deduced activation energy is 1.10±0.15 eV, with the attendant oxidation rate being greater than that for the corresponding reaction in molecular oxygen.