Absolute apparent cross sections for electron-impact excitation of helium to the 43D level measured as a function of target-gas pressure (3 x Torr) have been analysed by means of the 'F-cascade model'. proposed by St John and Fowler, in order to study the process of collisional transfer in helium. Because resonance states play an important role, special attention is paid to imprisonment of resonance radiation. Furthermore it is found that scaling of the collisional transfer cross sections with a power of the principal quantum number n leads to results which are inconsistent with the experimental findings. By extrapolation of the apparent 43D cross section to zero pressure we are able to estimate electron-impact excitation cross sections for the 4 l F level.

The structural inhomogeneities of hydrogenated amorphous silicon (a-Si:H) prepared at high-deposition rates (20–27 Å/s) have been studied by the small angle X-ray scattering (SAXS) technique by changing the rf-electrode (cathode) bias voltages for controlling the ion flux impinging on the growing film surface. The total bonded hydrogen contents of the deposited films are independent of dc-bias, while light-induced degradation is significantly suppressed at the cathode bias V c=+25 V. It is found that structural fluctuation in the range of 10–400 Å as evaluated by SAXS is reduced to about one half at V c=+25 V in comparison with that of conventional deposition conditions at a rate of ∼1 Å/s.