Abstract. The uptake of gas phase nitric acid by half-microndiameter ice crystals has been studied at 230 K by measuring the nitrate content of ice particles which have been exposed to 5x10 '6 torr of nitric acid in a low temperature flow tube. A cold NaOH-coated denuder is used to distinguish gas-phase nitric acid from adsorbed nitric acid. Ice particle diameters were determined by fitting measured aerosol infrared extinction spectra to spectra calculated via Mie theory, and their number density is measured directly with a CN counter.Under conditions in which the surface is saturated and not all the gas-phase nitric acid adsorbs, the measured uptakes are 14 21.2x10 molecules/cm where the surface area is the geometric area of the particles. Within experimental uncertainties, this surface coverage is the same as that measured on thin films of ice formed by freezing liquid water. These results are the first quantitative study of the nitric acid uptake capacity of ice particles, and they provide additional support to the suggestion that ice and snow provide a route for the efficient scavenging of nitric acid from the atmosphere.

For making porous silicon devices, it is important to study the overall effect of important processing steps on this material. This paper deals with the most important steps required for fabricating discrete devices and also for integration with silicon integrated circuits. A p-n junction has been formed in porous silicon by diffusion at high temperatures and it has reduced the resistance of the material. A new technique has been developed, which is known as waxolithography, for making small structures in this material. The metallic structure has also been optimized for good ohmic contact. Optical propetties of porous silicon are also discussed.

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Specimens of high purity aluminum with a high temperature oxide film, or certain others, were compared in 16% HCl with polished and etched specimens. Pitting attack was initiated only at sites where the film had suffered mechanical damage during cooling. The structure-related distribution of these sites, associated with vacancy condensation voids or grain boundary shearing, could determine the distribution of attack overshadowing the intrinsic effects of substrate structure. The pitting parameters were correlated with corrosion kinetics. Previous work in this system was reviewed with regard to possible influences of initial surface condition on the results.

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