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Three series of SiC/AlN samples were prepared by pyrolysis of “poly(aluminosilazane)”, the product of the reaction between hexamethylcyclotrisilazane and triethylaluminum. The Si/Al ratio was varied for one series (with constant pyrolysis temperature) and the pyrolysis temperature was varied for the other two series, with Si/Al = 1 and 3. 27Al and 29Si magic angle spinning NMR were used to analyze these samples in terms of coordination number, nearest neighbor atoms, and crystallinity. NMR results indicate that higher crystallinity and phase separation into discrete SiC and AlN crystallites accompany an increase in pyrolysis temperature. Disorder and increased heterogeneity in connectivity are observed with increasing Si/Al ratio of the initial reactants.

Background: Community concerns about a potential excess of multiple sclerosis (MS) prompted this study. Objective: To determine the period prevalence of MS in a community bordering a closed oil refinery and a control community. Methods: Cases seen by a neurologist during 1998 to 2001 were obtained from area neurologists and hospital discharge data. Population data were obtained from the year 2000 US Census. Patient data were abstracted by a trained abstractor onto a standardized report form. A consulting neurologist reviewed the form and made a final diagnosis using the Poser criteria plus the category of presumed. Age-adjusted prevalence rates and rates of agreement were calculated. Results: The direct age-adjusted period prevalence for both sexes and all races for the entire study area was 113 per 100,000 (95% CI = 93 to 136). For white subjects only, the prevalence was 123 per 100,000 (95% CI = 102 to 147). With use of an indirect method of age adjustment, the number of observed cases in the community bordering the refinery was similar to the number of cases expected (standardized morbidity ratio = 130.8, 95% CI = 62.3 to 199.3), based on rates from the comparison area. The agreement between the treating neurologist (for definite plus probable cases) and the consulting neurologist (for definite plus probable plus presumed cases) was good (κ = 0.5733). Conclusions: The prevalence of multiple sclerosis (MS) for this area was generally consistent with prevalence estimates calculated in previous studies in other areas. No significant excess was seen in the exposed area. MS was more prevalent in females than in males. The overall agreement between the consulting and treating neurologist was good.

Microstructural analysis was performed on several crystalline SiC samples previously prepared by three separate processing methods and subsequently sintered under high pressure and high temperature conditions using the cubic anvil cell MAX80 at Hasylab. Microcrystalline SiC was prepared using SHS conditions, while nanocrystalline SiC was prepared using both combustion synthesis methods and polymer precursors. High purity, highly disordered nanocrystalline SiC powders, with average particle diameters below 100 nm, were synthesized via combustion methods from precise mixtures of silane and acetylene. The properties of the silicon carbide powders prepared in this manner were dependent on the initial stoichiometry and pressure of the combustion mixture. Pyrolysis of polymer precursors to SiC was also used to fabricate ceramic powders containing uniformly-sized, highly disordered nanocrystalline SiC grains. The grain sizes ranged from approximately 3 nm to greater than 50 nm, and depended on the initial composition of the polymer, the pyrolysis conditions, as well as the annealing atmosphere, temperature and time. This paper describes the preparation methods for each of the SiC powders, the densification procedure, and preliminary results obtained primarily from transmission electron microscopy and X-ray diffraction analysis.

The preparation of clean Si and SiO2 substrates for basic semiconductor processing has become a more important technical problem as device geometries are reduced in order to increase the active element densities of VLSI‐ and VHSIC‐integrated circuits. The traditional surface analysis techniques such as Auger spectrometry and ESCA analysis no longer have sufficient sensitivity to detect and quantitate the surface impurity levels. Therefore, a program to apply secondary ion mass spectrometry (SIMS) analysis to the first several nanometers at the surface of wafers undergoing cleaning processing has been undertaken. After determining the SIMS instrumental parameters needed to perform reproducible analyses, wafers cleaned by FSI‐A, aqua regia, fuming nitric acid and Piranha plus HF cleaning procedures were analyzed. Each cleaning procedure removed some of the alkali elements (Na, K) but the difference between the best and worst performance gave greater than a factor of 10 variation in surface alkali content. T...