Nanostaircases: An atomic shadowing instability during epitaxial CrN(001) layer growth

Abstract

Epitaxial CrN(001) layers, 57 and 230 nm thick, were grown on MgO(001) at 700 °C by ultrahigh-vacuum magnetron sputter deposition in pure N2 discharges. An oblique deposition angle α=80° was utilized to purposely increase the effect of atomic shadowing on surface morphological and microstructural evolution. The layers are single crystals with a surface morphology that is characterized by dendritic ridge patterns extending along orthogonal ⟨110⟩ directions superposed by square-shaped supermounds with ⟨100⟩ edges. The ridge patterns are due to a two-dimensional growth instability related to a gradient in the adatom density while the supermounds form due to atomic shadowing. The supermounds protrude out of the surface and capture a larger deposition flux than the surrounding layer. This leads to both vertical and lateral growth and the formation of inverted pyramids that are epitaxially embedded in a single crystalline matrix. The inverted pyramids are terminated by 1–3-nm-wide tilted voids that form nanostaircases due to kinetic faceting along orthogonal {100} planes.