Dynamics of Ti, N, and TiNx(x=1–3) admolecule transport on TiN(001) surfaces

Abstract

We use classical molecular dynamics and the modified embedded atom method formalism to investigate the dynamics of atomic-scale transport on a low-index model compound surface, TiN(001). Our simulations, totaling 0.25 \ensuremath{\mu}s for each case study, follow the pathways and migration kinetics of Ti and N adatoms, as well as TiN${}_{x}$ complexes with $x=1--3$, which are known to contribute to the growth of TiN thin films by reactive deposition from Ti, N${}_{2}$, and N precursors. The simulations are carried out at 1000 K, within the optimal range for TiN(001) epitaxial growth. We find Ti adatoms to be the highest-mobility species on TiN(001), with the primary migration path involving jumps of one nearest-neighbor distance ${d}_{\mathrm{NN}}$ between adjacent fourfold hollow sites along in-plane $\ensuremath{\langle}100\ensuremath{\rangle}$ channels. Long jumps, 2${d}_{\mathrm{NN}}$, are also observed, but at much lower frequency. N adatoms, which exhibit significantly lower migration rates than Ti, diffuse along in-plane $\ensuremath{\langle}110\ensuremath{\rangle}$ directions and, when they intersect other N atoms, associatively form N${}_{2}$ molecules, which desorb at kinetic rates. As expected, TiN and TiN${}_{3}$ complexes migrate at even lower rates with complex diffusion pathways involving rotations, translations, and rototranslations. TiN${}_{2}$ trimers, however, are shown to have surprisingly high diffusion rates, above that of N adatoms and almost half that of Ti adatoms. TiN${}_{3}$ motion is dominated by in-place rotation with negligible diffusion.