Si-SiO_2 interface passivation by plasma NH_3 and atomic H

Plasma ammonia treatment at 400 ℃ leads to de-passivation of a fully hydrogenated Si-SiO2 interface, and to passivation of a fully de-hydrogenated Si-SiO2 interface. Plasma NH3 exposure causes irreversible Si surface damage and degradation of thermal stability. Atomic hydrogen exposure, although it results in similar effects on the Si-SiO2 interface, does not introduce additional defects or a decrease of the Si surface thermal stability. The difference between plasma NH3 exposure and atomic H exposure is speculated to be due to either the nitridation of Si-SiO2 interface or radiation damage resulting from plasma NH3 exposure. EPR measurements indicate changes of the paramagnetic defect properties and an increase in the paramagnetic defect density generated by plasma NH3 exposure.

对没有接种疫苗儿童的调查

Context.Each year 2.1 million children 19 to 35 months of age are undervaccinated.Among these are children who have received no vaccinations.Unvaccinated children are at increased risk of acquiring and transmitting vaccine-preventable diseases.Objectives.To assess whether the characteristics of children with no vaccinations differ from those of undervaccinated children, tomonitor trends in the numbers of unvaccinated children, and to identify states with high rates and counties with large numbers of unvaccinated children.Design.A nationally representative probability sample of children 19 to 35 months of age was collected annually between 1995 and 2001.Vaccination histories were ascertained from children’s medical providers.Undervaccinated children had received ≥1 dose of diphtheriatetanus-pertussis, polio, measles, Haemophilus influenzae type b, hepatitis B, or varicella vaccine butwere not fully vaccinated.Unvaccinated children were children who were reported as having no medical providers and having received no vaccinations or children whose medical providers reported administering no vaccinations.Participants.A total of 151 720 children sampled between 1995 and 2001, 795 of whom were unvaccinated.Results.Undervaccinated children tended to be black, to have a younger mother who was not married and did not have a college degree, to live in a household near the poverty level, and to live in a central city.Unvaccinated children tended to be white, to have a mother who was married and had a college degree, to live in a household with an annual income exceeding ＄75 000, and to have parents who expressed concerns regarding the safety of vaccines and indicated that medical doctors have little influence over vaccination decisions for their children.Unvaccinated children were more likely to be male than female.Annually, ～17 000 children were unvaccinated.The largest numbers of unvaccinated children lived in counties in California, Illinois, New York, Washington, Pennsylvania, Texas, Oklahoma, Colorado, Utah, and Michigan.States that allowed philosophical exemptions to laws mandating vaccinations for children as they entered school had significantly higher estimated rates of unvaccinated children.Conclusions.Unvaccinated children have characteristics that are distinctly different from those of undervaccinated children.Unvaccinated children are clustered geographically, increasing the risk of transmitting vaccine-preventable diseases to both unvaccinated and undervaccinated children.