In situ high-temperature scanning tunneling microscopy studies of two-dimensional TiN island coarsening kinetics on TiN [formula omitted

Abstract

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 E a for adatom formation and diffusion on TiN(0 0 1). E a 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 E a values corresponds to the step edge Ehrlich barrier, which for TiN(0 0 1) is less than the experimental uncertainties in the measurements.