Nucleation kinetics during homoepitaxial growth of TiN(001) by reactive magnetron sputtering

We use scanning tunneling microscopy to study the nucleation of homoepitaxial TiN layers grown on TiN(001) by ultrahigh vacuum reactive magnetron sputtering in pure N-2. Nucleation lengths are measured using in situ scanning tunneling microscopy as a function of temperature on two-dimensional islands as well as on large open terraces. At low growth temperatures, 500less than or equal toT(s)less than or equal to865 degreesC, nucleation is diffusion limited and we extract a surface diffusion energy of 1.4+/-0.1 eV. At higher temperatures, 865less than or equal toT(s)less than or equal to1010 degreesC, nucleation is limited by the formation rate of stable clusters for which we obtain an activation energy of 2.6+/-0.2 eV. Ab initio calculations combined with our experimental results suggest that the primary diffusing adspecies are TiNx molecules with x=2 and/or 3.