Results are reported from a pilot study under the Consultative Committee for Amount of Substance (CCQM) to compare measurements of and resolve any relevant measurement issues in the amount of thermal oxide on (100) and (111) orientation silicon wafer substrates in the thickness range 1.5-8 nm. As a result of the invitation to participate in this activity, 45 sets of measurements have been made in different laboratories using 10 analytical methods: medium -energy ion scattering spectrometry (MEIS), nuclear reaction analysis (NRA), RBS, elastic backscattering spectrometry (EBS), XPS, SIMS, ellipsometry, grazing -incidence x-ray reflectometry (GIXRR), neutron reflectometry and transmission electron microscopy (TEM). The measurements are made on separate sets of 10 carefully prepared samples, all of which have been characterized by a combination of ellipsometry and XPS using carefully established reference conditions and reference parameters.The results have been assessed against the National Physical Laboratory (NPL) data and all show excellent linearity. The data sets correlate with the NPL data with average root-mean-square scatters of 0.15 nm, half being better than 0.1 nm and a few at or better than 0.05 nm. Each set of data allows a relative scaling constant and a zero thickness offset to be determined. Each method has an inherent zero thickness offset between 0 nm and 1 nm and it is these offsets, measured here for the first time, that have caused many problems in the past. There are three basic classes of offset: water and carbonaceous contamination equivalent to ∼1 nm as seen by ellipsometry; adsorbed oxygen mainly from water at an equivalent thickness of 0.5 nm as seen by MEIS, NRA, RBS and possibly GIXRR; and no offset as seen by XPS using the Si 2p peaks. Each technique has a different uncertainty for the scaling constant and consistent results have been achieved. X-ray photoelectron spectroscopy has large uncertainties for the scaling constant but a high precision and critically, if used correctly, has zero offset. Thus, a combination of XPS and the other methods allows the XPS scaling constant to be determined with low uncertainty, traceable via the other methods. The XPS laboratories returning results early were invited to test a new reference procedure. All showed very significant improvements. The reference attenuation lengths thus need scaling by 0.986 ± 0.009 (at an expansion factor of 2), deduced from the data for the other methods. Several other methods have small offsets and, to the extent that these can be shown to be constant or measurable, these methods will also show low uncertainty. Recommendations are provided for parameters for XPS, MEIS, RBS and NRA to improve their accuracy.  Crown

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Barrier-type anodic films 3-15 nm thick have been formed on electropolished 99.999% aluminium. Variable-angle XPS has been used to identify a significant proportion of hydroxyl ions at the surface of the relatively compact alumina films. The location of an oxygen-rich region at the outer surface of the oxide has been confirmed by medium-energy ion scattering (MEIS). Combining the information from these two techniques leads to the conclusion that a hydroxyl-containing surface region is responsible for this oxygen-rich surface layer, MEIS revealing an approximately linear relationship between the total oxide thickness and the thickness of the hydroxyl-rich surface region. From consideration of the mechanisms of amorphous alumina formation by ionic transport, with incorporation of electrolyte-derived species into the thickening film, the generation of the hydroxyl-rich outermost region is considered to result from the formation of gel-like material at the film/electrolyte interface.

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A quantitative structure-activity relationship (QSAR) system for estimating skin sensitization potency has been developed that incorporates skin metabolism and considers the potential of parent chemicals and/or their activated metabolites to react with skin proteins. A training set of diverse chemicals was compiled and their skin sensitization potency assigned to one of three classes. These three classes were, significant, weak, or nonsensitizing. Because skin sensitization potential depends upon the ability of chemicals to react with skin proteins either directly or after appropriate metabolism, a metabolic simulator was constructed to mimic the enzyme activation of chemicals in the skin. This simulator contains 203 hierarchically ordered spontaneous and enzyme controlled reactions. Phase I and phase II metabolism were simulated by using 102 and 9 principal transformations, respectively. The covalent interactions of chemicals and their metabolites with skin proteins were described by 83 reactions that fall within 39 alerting groups. The SAR/QSAR system developed was able to correctly classify about 80% of the chemicals with significant sensitizing effect and 72% of nonsensitizing chemicals. For some alerting groups, three-dimensional (3D)-QSARs were developed to describe the multiplicity of physicochemical, steric, and electronic parameters. These 3D-QSARs, so-called pattern recognition-type models, were applied each time a latent alerting group was identified in a parent chemical or its generated metabolite(s). The concept of the mutual influence amongst atoms in a molecule was used to define the structural domain of the skin sensitization model. The utility of the structural model domain and the predictability of the model were evaluated using sensitization potency data for 96 chemicals not used in the model building. The TIssue MEtabolism Simulator (TIMES) software was used to integrate a skin metabolism simulator and 3D-QSARs to evaluate the reactivity of chemicals thus predicting their likely skin sensitization potency.