Nucleation kinetics versus nitrogen partial pressure during homoepitaxial growth of stoichiometric TiN(0Â 0Â 1): A scanning tunneling microscopy study

We grow homoepitaxial stoichiometric TiN(0 0 1) layers by ultra-high vacuum reactive magnetron sputtering in Ar/N2 mixtures and use scanning tunneling microscopy to study nucleation as a function of the N2 gas fraction fN2 and growth temperature Ts. 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. Over the temperature range 600 ⩽ Ts ⩽ 860 °C, nucleation is diffusion limited with an activation energy Es of 1.1 ± 0.1 eV for TiN(0 0 1) growth with fN2=0.10 and 1.4 ± 0.1 eV in pure N2. We attribute the increase in Es to a higher steady-state N coverage resulting in an increase in the average x-value of the primary surface-diffusing species, TiNx admolecules.