Berlin 2015 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 19: Frontiers of Electronic Structure Theory: Many-Body Effects on the Nano-Scale I

O 19.11: Vortrag

Dienstag, 17. März 2015, 13:15–13:30, MA 004

Ti and N adatom diffusion on, and N₂ desorption from TiN(001) surfaces via ab initio and classical molecular dynamics — •Davide G. Sangiovanni¹, Daniel Edström¹, Lars Hultman¹, Ivan Petrov^1,2, Valeriu Chirita¹, and Joe E. Greene^1,2 — ¹Thin Film Physics, IFM, Linköping University, Sweden — ²University of Illinois, Urbana-Champaign, Illinois, USA

We use classical and ab initio molecular dynamics to investigate fundamental atomistic processes and surface properties responsible for TiN surface evolution during thin film growth. The rate of adatom migration and N₂ desorption events are determined as a function of temperature to extract activation energies, attempt frequencies, and diffusion coefficients. Ti adatoms (Ti_ad), highly mobile on TiN(001) terraces, diffuse among fourfold hollow sites, primarily along <100> channels via single and long jumps. Ti_ad jumps on TiN(001) are highly correlated; an effect which leads to smaller diffusion coefficients than those determined via adatom random walks. Due to strong bonds formed with underlying N surface (N_surf) atoms, N adatoms (N_ad) are considerably less mobile on TiN(001) than Ti adatoms. After several N_ad/N_surf-pair exchange reactions, with very few N_ad jumps among neighboring stable surface sites, the N_ad/N_surf pair desorbs, leaving an anion surface vacancy which acts, in turn, as a catalyst for N₂ dissociative chemisorption. This pathway for N₂ desorption from TiN(001) is considerably more probable than N adatom recombination, which is kinetically hindered due to short-range N_ad/N_ad repulsive interactions.