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

TL;DR

This study uses ab initio molecular dynamics to investigate how surface vibrations influence the descent pathways and rates of titanium adatoms on TiN surfaces, revealing temperature-dependent mechanisms.

Contribution

It uncovers the significant role of surface vibrations in lowering activation energies and altering descent pathways of Ti adatoms on TiN surfaces at finite temperatures.

Findings

Surface vibrations significantly lower activation energies for adatom descent.

Descent rates via different pathways become comparable at T >= 1500 K.

Vibrations modify the reaction pathway, enabling alternative descent mechanisms.

Abstract

We carry out density-functional ab initio molecular dynamics (AIMD) simulations of Ti adatom (Tiad) migration on, and descent from, TiN <100>-faceted 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 Tiad descent via direct-hopping vs. push-out/exchange with a Ti island edge atom for T >= 1500 K. We demonstrate that the 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.