Numerical Experiments on Scattering of Noble Gases from Single-Crystal Silver

Abstract

Three-dimensional numerical experiments on the scattering of noble-gas atoms from single-crystal surfaces of silver are described. This numerical method can be very useful in determining the relative importance of different variables in the interactions although it cannot be expected to give quantitative agreement with individual cases until a better knowledge of the interatomic binding energies and the surface state is available. Most of the cases are for neon on the fcc (111) surface, but isolated cases of helium and argon on (111) and neon on (100) are included. The energies include those of effusive molecular beams from 300° to 45 000°K equivalent source temperatures (0.06 to 7.8 eV). Several interaction parameters describing mean energy and momentum exchanges and traces of the spatially resolved flux in the incident plane are given for most of the cases. Sample out-of-plane flux data and some typical data on spatially resolved energy are also given, and general trends for the rest of the data are described. The results give trapping probabilities that are much greater than those inferred from laboratory experience, and flux patterns that are significantly broader than those encountered in the experiments for the few cases that can be compared directly. The neon trends with increasing energy are quite similar to those of the Saltsburg and Smith experiments for xenon, with new effects appearing in the present results for energies higher than those of the laboratory experiments. These new effects include multiple peaks, one above and one below specular, and a broadening of the patterns with increasing incident energy. They are attributed to increased resolution of the surface atomic configuration due to deeper penetration of the potential field above the surface. The trends of the Logan, Keck, and Stickney hard-cube theory are shown in the present results at low incident energy, and the expected hard-sphere limit behavior is observed at very high incident energy, in agreement with the recent calculations of Goodman.

Angular and velocity distributions characteristic of the transition between the thermal and structure regimes of gas-surface scattering

“…4, which displays the angular widths (FWHM) as a function of £, for 0, =30°, 45°, and 60°. The results are consistent with previous scattering studies [6,7,[9][10][11][12], and calculations [5], and can be said to cover the transition from the so-called "thermal scattering" regime at low energies to the "structure scattering" regime at high energies.…”

Atomic scale simulation of physical sputtering of silicon oxide and silicon nitride thin films

“…For the case of He + ion bombardment, the reflected ions were widely distributed in their reflection angles and they have relatively higher energies compared to other ions, since He + ions did not efficiently transfer their kinetic energy to the substrate during collisional process. This high-energy broad distribution is attributed to the so-called ''structure scattering'', which occurs when the incoming atom senses the structure of the individual surface atoms [30]. Considering this scattering characteristics of He + ions, it is expected that the use of light ions may produce unwanted undercutting of the mask and sidewall etching in plasma sputtering process for patterning a vertical feature.…”

Scattering of xenon from Ni(111): Collision-induced corrugation and energy transfer dynamics

“…Such behavior has been described as a transition from structure scattering to thermal scattering. 21 At high incident energies, the impinging atoms penetrate more deeply into the repulsive part of the gas-surface potential, so the structure of the surface is the dominant factor in determining the scattering behavior. At low incident energies, the thermal motion of the surface atoms becomes important, so that the surface appears flat except for the relatively small displacements of the surface atoms about their equilibrium positions.…”