In situ high-temperature scanning tunneling microscopy studies of two-dimensional TiN island coarsening kinetics on TiN(0 0 1)

In situ high-temperature (1023–1223 K) scanning tunneling microscopy was used to study the coarsening/decay kinetics of two-dimensional (2D) TiN adatom islands on TiN(0 0 1) terraces and in single-atom-deep vacancy pits. Island coarsening/decay behavior was found to be non-linear with time and to depend on the local environment (i.e., on adatom concentration gradients on the terrace), the signature of surface-diffusion-limited kinetics. Two simple island geometries––a single 2D adatom island on an atomically smooth terrace and a single 2D adatom island within a vacancy island––were used to extract adatom surface transport parameters. We model diffusion-limited island decay kinetics for these configurations based upon steady-state diffusion equations solved by adaptive finite-element methods with a form of the Gibbs–Thomson equation describing anisotropic islands serving as the boundary condition. Calculated decay rates were compared with the experimental results to obtain an activation energy Ea for adatom formation and diffusion on TiN(0 0 1). Ea was found to be 2.6±0.6 and 3.1±0.5 eV for adatom islands in vacancy pits and on terraces, respectively. The difference in the two Ea values corresponds to the step edge Ehrlich barrier, which for TiN(0 0 1) is less than the experimental uncertainties in the measurements.