Ab initio theoretical computations have been performed to reveal the mechanism of the etching reaction of silicon oxide (SiO2) by HF molecules. The probable reaction paths, in which the etching reaction proceeds through four sequential steps to remove a single fragment of SiO2, are presented with their potential energy curves. In every step, the insertion of an HF molecule into an Si-O bond leads to the dissociation of the Si-O connection. The potential energy barriers evaluated along the reaction paths suggest that the HF molecule has an ability to etch the SiO2 surface. The strong interaction among HF molecules, however, likely causes HF polymer formation, which is expected to reduce the reaction rate of SiO2 etching.

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(Ba0.5Sr0.5)TiO3 thin films (200-300 nm) were deposited on Pt-coated Si substrates by laser ablation at 500 and 650°C. The leakage currents of crystalline films grown at 650°C were found to be higher than those of amorphous films grown at 500°C. The crystalline thin films showed higher surface roughness than the amorphous films as measured by atomic force microscopy (AFM). A columnar grain structure was observed for crystalline films with a grain size of 20-30 nm by transmission electron microscope (TEM) analysis. These factors may be responsible for high leakage currents of crystalline films. Constant current injection measurements for Au/(Ba0.5Sr0.5)TiO3/Pt capacitors showed that electron trapping states near the top electrode interface were higher in number than at bottom electrode interface. This may be due to the presence of reactive sites on the surface of deposited films as observed by X-ray photoelectron spectroscopy (XPS) measurements.

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Interface states in almost the entire SiC band gap are observable by means of x-ray photoelectron spectroscopy ͑XPS͒ measurements under bias, although SiC is a wide-gap semiconductor having 2.9 eV band-gap energy. When a SiO 2 layer is formed by wet oxidation at 1000°C on 6H-SiC(0001) Si-faced surfaces, only a broad interface state peak is observed at ϳ2 eV above the SiC valence-band maximum ͑VBM͒, while for dry oxidation at the same temperature, an additional sharp interface state peak is caused at 1.8 eV above the VBM. When the wet-oxidation temperature is increased to 1150°C, this 1.8-eV interface-state peak also appears. The concentration of graphitic carbon at the SiO 2 /SiC interface is found to increase with the heat treatment temperature. The 1.8-eV interface-state peak is tentatively attributed to graphitic carbon with a special structure near the interface. On the other hand, the broad 2-eV interface-state peak is attributed to Si dangling bonds at the interface. Without the 1.8-eV interface-state peak, current-voltage (I-V) curves measured under x-ray irradiation deviate only slightly from the ideal I-V curve ͑ϳ0.4 V͒, while with this peak, the deviation becomes much larger ͑ϳ0.8 V͒. XPS measurements under bias show that the I-V curves under x-ray irradiation are determined by the magnitude of band bending in SiC. Therefore, the deviation from the ideal I-V curve is attributed to the accumulation of holes ͑i.e., minority carriers͒, generated by x-ray irradiation, at interface states with energies between the SiC and metal Fermi levels, causing a downward SiC band-edge shift and thus resulting in a decrease in the magnitude of band bending in SiC. This result demonstrates that the interface states affect I-V characteristics by a static effect ͑i.e., interface state charges͒, not by a dynamical effect ͑i.e., electron-hole recombination at the interface states͒.