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.
Enhanced Backscattering near 180° for Energetic Ions in Solids
A new ion scattering effect which enhances backscattering yields near 180° has been recently reported. A computer program which simulates this scattering effect is discussed and the results compared with measurements. Both the angular distribution and depth profiles of the backscattered yield enhancements are compared. These comparisons verify the proposed explanation for the new scattering phenomena and a tentative explanation is offered for the small discrepancies which exist.