An important factor that determines the possible lateral resolution in sputter depth profiling experiments is ion induced lateral displacement of substrate atoms. Molecular dynamics (MD) simulations are performed to model the successive bombardment of Si with 20 keV C 60 at normal incidence. A statistical analysis of the lateral displacement of atoms that originate from the topmost layer is presented and discussed. From these results, it is determined that the motion is isotropic and can be described mathematically by a simple diffusion equation. A "diffusion coefficient" for lateral displacement is determined to be 3.5 2/impact. This value can be used to calculate the average lateral distance moved as a function of the number of impacts. The maximum distance an atom may move is limited by the time that it remains on the surface before it is sputtered. After 800 impacts, 99% of atoms from the topmost layer have been removed, and the average distance moved by these atoms is predicted to be 100 . Although the behavior can be described mathematically by the diffusion equation, the behavior of the atoms is different than what is thought of as normal diffusion. Atoms are displaced a large distance due to infrequent large hops.
|Original language||English (US)|
|Number of pages||4|
|Journal||Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms|
|State||Published - Jul 15 2011|
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics