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Copyright of Aufsichtsrat is the property of Fachmedien Otto Schmidt KG and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A statistical approach to the description of inner-shell ionization is presented in terms of a random walk in energy space of particle-hole excitations on interacting level crossings to unoccupied states. It describes impact-parameter dependent and total cross sections for K and L shell excitations in symmetric and near-symmetric atomic collisions accurately in terms of only one parameter related to the density of levelcrossings.

Mass spectrometric kinetic measurements were performed on a dc plasma during the etching of Si by CF4. The apparatus and procedures used were identical to those developed and used in an earlier study dealing with the Si/SF6 system. The signals representative of CF3+, CF2+, CF+, F+, SiF3+, SiF+, and C2F5+ were studied in some detail. CF3+ and CF2+ transients produced by stepwise changes of the applied voltage were found to be very similar, on a fractional basis. CF+ and C2F5+ signals showed a close correlation, while the F+ signals indicated a small amount of extra fluorine atoms or ions to be present at relatively high applied voltages. The initial transient rates, following plasma ignition, tended to be slower than those obtained at the higher applied voltages, so the sample surface is somehow etched more rapidly after the first few seconds. In contrast to this, slow signal changes of the sort observed in the Si/SF6 system were absent, so the carbonaceous layers which may form on the Si sample surface appear to adjust rapidly to composition changes in the plasma.

Results are reported of extensive calculations on atomic photoabsorption cross sections by the statistical method in various approximations, based on developments presented in previous papers. A closely spaced family of photoabsorption cross sections emerges which, on scaling with regard to atomic numbers, represents in an unified manner the absorption cross sections of all atoms over wide frequency ranges. A limited search into detailed spectral properties of atoms reveals everywhere some, and in certain instances strong evidence for collective effects in the response of atoms to external disturbances.

The reflectance spectra of iridescent hummingbird feathers were measured spectrophotometrically for many species, and the structure of the iridescent parts of such feathers investigated by electron microscopy. In the direction normal to the iridescent feather surfaces the structure is found to be periodic in optical dimensions. It consists of stacks of 7–15 elliptical platelets of a material with refractive index ~2, each containing a structurally reinforced air gap. To interpret the reflectance spectra in terms of the surface structures, a theory is given of reflection coefficients of stratified media with analytic refractive-index variations. The theory is applied to the iridescence of hummingbird feathers and accounts quantitatively for the iridescent colors as interference colors by reflection from the observed feather structures.