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.

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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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With the use of Escherichia coli O157:H7 as a model, a procedure for the quantitative detection of viable Shiga toxin-producing E. coli (STEC) in broth and cooked ground beef enrichments with multiple-time point quantitative competitive polymerase chain reaction (QC-PCR) was developed. The A subunit (a 401-bp fragment) of the stx2 gene was chosen as a target sequence. Immunomagnetic separation (IMS) was used to isolate and concentrate cells from ground beef enrichments. Cell viability was confirmed on the basis of the quantitative increase in the signal of target bands from QC-PCR across multiple time points. The application of IMS increased detection limits relative to those for QC-PCR without IMS. E. coli O157:H7 inoculated at 0.20 CFU/g of cooked ground beef (25 g of ground beef plus 225 ml of Bacto modified EC medium plus novobiocin) was detected and confirmed to be viable in <15 h. A DNA-based molecular approach can be used to determine cell viability.

The continued reduction in the size of critical features in integrated circuits has resulted in the need to develop rapid, site-specific, sectioning techniques to enable efficient physical characterization of the structures of interest. We have implemented a mechanical polishing approach to achieve this objective with the additional goals of maximizing the number of targeted sites in a sample that can be analyzed, and minimizing physically destructive procedures, such as ion beam exposure. Precision sample preparation approaches have been under investigation for both transmission electron microscopy and scanning electron microscopy.The mechanical specimen preparation approach used in this work is a variant of the well-known wedge polishing technique. Here we use a polishing tool that does not contact the grinding surface, thus allowing precise control of the wedge angle. Prior to sample preparation, the polishing tool head was precision aligned parallel to the platen.