Acoustic Enhancement of Surface Diffusion

Abstract

The idea of acoustic activation of surface diffusion is explored theoretically and in atomistic simulations. It is found that a substantial diffusion enhancement by surface acoustic waves is possible via (1) transient surface straininduced modification of the diffusion barriers, (2) adiabatic variation in the surface temperature, and (3) dynamic coupling of the acoustic waves with vibrational states of adsorbed species. The approximate scaling laws describing the first two effects are established and verified in kinetic Monte Carlo simulations. The combined contribution of all three effects is studied in molecular dynamics simulations, and the conditions for the diffusion activation through the dynamic coupling are elucidated. The acoustic enhancement of surface diffusion provides an attractive alternative to thermal activation in thin film growth on heat-sensitive substrates.

Femtosecond ultraviolet laser ablation of silver and comparison with nanosecond ablation

“…In both cases the laser pulses are much shorter than the electron-lattice relaxation time, which is $9.4 ps for Ag in the ablation conditions considered here. 30 It should be noted that after the delivery of 500-1000 pulses at the same position the floor of the ablation crater is highly structured, showing 50% modulation of the ablation depth on a typical lateral scale length of 50 lm.…”

Application of a laser heterodyne technique to characterize surface acoustic waves generated via a pulsed laser excitation

“…Techniques for altering the local speed of sound have been published by Kim and Helvajian 10 , which may result in an additional process control parameter. Further experimental study utilizing SAWs for novel thin film growth and chemical catalysis is encouraged by recent modeling studies 11 showing that SAWs can enhance surface mobility of molecular adsorbates via surface strain.…”

Interplay Between Mechanochemistry and Sonochemistry

“…Atomistic explanations remain largely obscure in view of the frequency mismatch between SAWs and the vibrational states of the adsorbed species. The acoustic enhancement of surface diffusion has recently been suggested [38], which might also account for well-known cases of surface catalysis [39,40] and molecular desorption [41,42]. The experimental observation of ultrasonically-induced birefringence is also relevant [43,44].…”