Using narrow nuclear reaction resonance profiling, aluminum profiles are obtained in ϳ3.5 nm Al 2 O 3 films deposited by low temperature ͑Ͻ400°C͒ chemical vapor deposition on Si͑100͒. Narrow nuclear resonance and Auger depth profiles show similar Al profiles for thicker ͑ϳ18 nm͒ films. The Al profile obtained on the thin film is consistent with a thin aluminum silicate layer, consisting of Al-O-Si bond units, between the silicon and Al 2 O 3 layer. Transmission electron microscopy shows evidence for a two-layer structure in Si/Al 2 O 3 /Al stacks, and x-ray photoelectron spectroscopy shows a peak in the Si 2p region near 102 eV, consistent with Al-O-Si units. The silicate layer is speculated to result from reactions between silicon and hydroxyl groups formed on the surface during oxidation of the adsorbed precursor.
In Part I of this series of papers, structures and geometries of the four-step preforms were studied and analysed. In this part, an account is given of similar work conducted on the two-step preforms. Theoretical models for both regular and tubular two-step preforms are established with a few assumptions. Structu.ral geometries of the preforms are analysed aud discussed according to the theoretical models developed. Mathematical relations between the structural parameters, such as the fibre orientation, yam-volume ft-action, and prefoirm contour sizes, as well as their dependence on operating conditions, are derived. It is found that the preform structures are determined hy the constitucint yams, the braiding arrangements, and the process operating conditions. The extreme values ofthe parameters in the jamming conditions are also discussed. To verify the validity of the analytical models, experimental investigatic>ns were also carried out. The experimental results strongly support the theoretical predictions.
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