Surface-specific Data Research Articles

Atmosphere influence on in-situ ion beam analysis of thin film growth

In-situ non-destructive surface characterization of thin film growth processes in an environment of chemically active gas at pressures of several millitorrs is required both for the understanding of growth processes in multicomponent films and layered heterostructures and for the improvement of process reproducibility and device reliability. We have developed a differentially pumped pulsed ion beam surface analysis system that includes ion scattering spectroscopy (ISS) and direct recoil spectroscopy (DRS), coupled to an automated ion beam sputter deposition system, to study film growth processes in an environment of chemically active gas, such as required for the growth of oxide, nitride or diamond thin films. The influence of gas-phase scattering and gas-surface interactions on the ISS and DRS signal intensity and peak shape has been studied. From the intensity variation as a function of ambient gas pressure, we have calculated the mean free path and the scattering cross-section for several combinations of primary ion species and ambient gas. Depending on the system geometry and the combination of primary beam and background gas, it is shown that surface-specific data can be obtained during thin film growth at pressures ranging up to several millitorrs. Detailed information such as composition, structure and film growth mechanism may be obtained in real time, making ion beam analysis an ideal non-destructive in-situ probe of thin film growth processes.

Modelling dry deposition of SO<sub>2</sub>

The goals of this paper are to briefly describe experimental methods that are used to measure SO 2 dry deposition, and to discuss the physical, biological and chemical processes that control SO 2 deposition fluxes over vegetation and to describe how these fluxes are modelled. The predominant pathway for gaseous SO 2 uptake to dry vegetation is via turbulent transfer through the atmosphere surface boundary layer and molecular diffusion through the leaf laminar boundary layer and the stomata. The soil surface is a significant, but weaker sink for sulphur, especially when frozen or covered with snow. The appreciable solubility of SO 2 causes its uptake to be enhanced greatly in the presence of moisture on leaves and the soil. The aqueous uptake of SO 2 , however, causes the pH of a solution to decrease which in turn produces a reduction in the solubility of SO 2 . Neutralising species (ammonia, inner plant species) may cancel this reduction. A method is proposed to estimate local scale dry deposition fluxes of SO 2 in Europe. The method combines long-range transport modelling results, land use and surface specific data and an inferential approach. DOI: 10.1034/j.1600-0889.1994.t01-2-00001.x

The New Mexico sealant program: a progress report.

In 1979, the dental health program of the New Mexico Health and Environment Department began a school-based sealant activity. Children in the first, second, third, sixth, and seventh grades in selected New Mexico communities were offered sealants through this sealant activity. During the 1984-85 school year, program staff began seeing several hundred sixth-grade students who had received sealants in either the first, second, or third grade. Tooth- and surface-specific data on the current condition of all the previously sealed occlusal surfaces were collected from all these previous recipients of sealants. During the 1985-86 school year, we found that sixth-grade students who received sealants as first, second, or third graders had 5.6 percent of the occlusal surfaces of their first permanent molars either decayed, missing, or filled. Their classmates who had not previously received sealants had 26.85 percent of the same tooth surfaces either decayed, missing, or filled. During the 1985-86 school year, the complete retention rates for sealants were found to be 67.36 percent after six years, 78.53 percent after five years, and 93.47 percent after one year. The partial retention rates were found to be 10.46 percent after six years, 10.63 percent after five years, and 3.04 percent after one year.