| I use scanning tunneling microscopy to study the nucleation of homoepitaxial stoichiometric TiN layers grown on TiN(001) by ultrahigh vacuum reactive magnetron sputtering in pure N2. Nucleation lengths are measured using in-situ scanning tunneling microscopy as a function of temperature and nitrogen gas fraction fN2 in an Ar/N2 gas mixture on two-dimensional islands as well as on large open terraces. The characteristic island size Rc necessary to nucleate a new layer decreases continuously with fN2 , varying from 18.0 nm at Ts = 740°C with fN2 = 0.10 to 11.2 nm with fN2 = 1.00. At low growth temperatures, 500 ≤ Ts ≤ 865°C, nucleation is diffusion limited independent of fN2 and I extract a surface diffusion energy of 1.1 +/- 0.1 eV for TiN(001) growth with fN2 = 0.10 and 1.4 +/- 0.1 eV in pure N2. At higher temperatures, 865 < Ts ≤ 1010°C, nucleation is limited by the formation rate of stable clusters for which I obtain an activation energy of 2.4 +/- 0.2 eV with fN2 = 0.10 and 2.6 +/- 0.2 eV with fN2 = 1.00. Ab-initio calculations combined with my experimental results suggest that the primary diffusing adspecies during growth of TiN(001) in pure nitrogen are TiNx molecules with x = 2 and/or 3. I attribute the decrease in Es for growth at fN2 = 0.10 to a lower steady-state N coverage resulting in a decrease in x. |
