Further aspects of enhanced ion scattering near 180 degrees.
The role of rainbow scattering in enhanced ion scattering near 180{degree} was explored by comparing calculated enhancements for protons and antiprotons. Since the rainbow effect does not occur for negative particles and since the enhancement was much smaller for them than for positive particles, this comparison demonstrated in a more direct way than previously done the importance of rainbow scattering in producing the enhancement. A procedure for calculating a similarity factor between the ingoing and outgoing portions of a trajectory was developed, and its use showed that trajectories returning near 180{degree} differ in nature from random-return trajectories. A discussion is given of the possible relationship of the enhancement to phenomena such as the correlation effect in self-diffusion by the vacancy mechanism in solids and surface-structure studies by impact-collision ion-scattering spectrometry.
Ion scattering simulations of the Si(100)-SiO2 interface
We carry out ion scattering simulations to investigate the nature of the transition region at the Si(100)-SiO2 interface. Ion scattering experiments performed in the channeling geometry provide us with a genuine interfacial property, the excess Si yield, resulting from distortions in the Si substrate and from Si atoms in intermediate oxidation states. To interpret the ion scattering data, we first generate a series of model structures for the interface by applying sequentially classical molecular dynamics and density-functional relaxation methods. These models reproduce atomic-scale features consistent with a variety of available experimental data. Then, we design a classical scheme to perform ion scattering simulations on these model interfaces. In our study, we separate the excess Si yield obtained from experiments in two distinct contributions. First, Si atoms in intermediate oxidation states account for similar to 25% of the excess Si yield, a contribution that is fully determined by the population of suboxide determined from photoemission data. The remaining similar to 75% of the excess Si yield characterizes the amount of lateral distortion of the substrate Si layers in the vicinity of the Si(100)-SiO2 interface. The comparison between calculated and experimental excess Si yields indicates that the distortions propagating from the interface into the Si substrate are consistent with interfacial transition structures extending over more than two Si layers, eventually including a disordered bonding pattern. Nearly abrupt interfaces induce distortions in the upper layers of the Si substrate which are insufficient for reproducing the experimental excess Si yields.
Influence of electric fields on friction electrification between metals and borosilicate glass
Abstract In a cylindrical geometry, electric fields were applied through the entire contact area between the sliding metal and the glass surface. The maximum electric charges developed on the metal were measured and plotted against the applied voltage producing the field. The metals were high-purity nickel and gold. The borosilicate glass was Pyrex, brand 7740. The experiments with nickel, which has a work function greater than that of the glass, were performed in 10 −7 mm Hg vacuum. The experiments with gold, with a work function smaller than that of glass, were carried out in air at atmospheric pressure. The results show that: 1. 1) There is both asymmetry and a reversed slope portion in the charge vs. voltage plot. 2. 2) For a certain range of reversing fields, the electric charge developed on the nickel is always negative and the charge on gold is always positive.