Low-energy electron microscopy studies of interlayer mass transport kinetics on TiN(1 1 1)

In situ low-energy electron microscopy was used to study interlayer mass transport kinetics during annealing of three-dimensional (3D) TiN(1 1 1) mounds, consisting of stacked 2D islands, at temperatures T between 1550 and 1700 K. At each T, the islands decay at a constant rate, irrespective of their initial position in the mounds, indicating that mass is not conserved locally. From temperature-dependent island decay rates, we obtain an activation energy of 2.8 ± 0.3 eV. This is consistent with the detachment-limited decay of 2D TiN islands on atomically flat TiN(1 1 1) terraces [Phys. Rev. Lett. 89 (2002) 176102], but significantly smaller than the value, 4.5 ± 0.2 eV, obtained for bulk-diffusion-limited spiral step growth [Nature 429 (2004) 49]. We model the process based upon step flow, while accounting for step–step interactions, step permeability, and bulk mass transport. The results show that TiN(1 1 1) steps are highly permeable and exhibit strong repulsive temperature-dependent step–step interactions that vary between 0.03 and 0.76 eV · Å. The rate-limiting process controlling TiN(1 1 1) mound decay is surface, rather than bulk, diffusion in the detachment-limited regime.