Effects Of Surface Vibrations On Interlayer Mass Transport: Ab Initio Molecular Dynamics Investigation Of Ti Adatom Descent Pathways And Rates From Tin/Tin(001) Islands

We carried out density-functional ab initio molecular dynamics (AIMD) simulations of Ti adatom (Ti-ad ) migration on, and descent from, square TiN(100) epitaxial islands on TiN(001) at temperatures (T) ranging from 1200 to 2400 K. Adatom-descent energy barriers determined via ab initio nudged-elastic-band calculations at 0 Kelvin suggest that Ti interlayer transport on TiN(001) occurs essentially exclusively via direct hopping onto a lower layer. However, AIMD simulations reveal comparable rates for Ti-ad descent via direct hopping vs push-out/exchange with a Ti island-edge atom for T >= 1500 K. We demonstrate that this effect is due to surface vibrations, which yield considerably lower activation energies at finite temperatures by significantly modifying the adatom push-out/exchange reaction pathway.