Growth of epitaxial CrN on MgO(001): Role of deposition angle on surface morphological evolution

CrN layers, 6 to 500 nm thick, were grown on MgO(001) at 600 degrees C by ultra-high-vacuum magnetron sputter deposition in pure N-2 discharges at 2.6 Pa. The deposition angle a with respect to the surface normal was varied from 0 degrees to 80 degrees in order to directly probe the effect of atomic shadowing on the surface morphological evolution. Layers grown with alpha = 0 degrees are single crystals which develop a regular surface mound structure. At low layer thicknesses, t less than or similar to 25 nm, the surface mounds grow primarily vertically, due to kinetic roughening, and form square-shapes with edges along low-energy (100), directions. Continued growth at t greater than or similar to 25 nm is dominated by mound-competition and coalescence which leads to a self-similar growth mode with increases in both mound height and width. Layers deposited from oblique angles alpha = 80 degrees also nucleate as single crystals with a cube-on-cube epitaxial relationship with the substrate. However, rough surfaces with cauliflower-type morphologies cause the nucleation of misoriented CrN grains that develop into cone-shaped grains that protrude out of the epitaxial matrix to form triangular faceted surface mounds. Atomic shadowing exacerbates the growth rate of these misoriented grains, causing a dramatic increase in the root-mean-square surface roughness, which is similar to 16 x higher for layers grown at alpha = 80 degrees than at alpha = 0 degrees. The roughening follows a power-law with a roughening exponent beta that increases from 0.37 +/- 0.04 to 0.57 +/- 0.15 as a is increased from 0 degrees to 80 degrees. This increase is attributed to a transition from kinetic roughening to roughening caused by atomic shadowing effects. (c) 2005 Elsevier B.V. All rights reserved.