Two-component nanopillar arrays grown by Glancing Angle Deposition

Periodic arrays of 160- to 500-nm-wide Si and Cr nanostructures were grown on patterned Si(001) substrates by Glancing Angle Deposition (GLAD). Initial patterning was achieved by colloidal self-assembly of 500-nm-diameter polystyrene and 160-nm-diameter silica microspheres which form, during drying from suspension, close-packed hexagonal arrays. Si deposition onto a monolayer of 500-nm-diameter spheres from an angle α, with respect to the surface normal, of 72°, yields a regular array of 2-μm-tall and 450-nm-wide nanopillars. Regular arrays of 300-nm-wide Cr nano-half-moon structures are obtained with α = 86°. Cr–Si two-component multi-stack nanopillars were grown on 160-nm-diameter nanospheres by successive Cr and Si deposition sequences with continuous rotation of the substrate about the polar axis. The resulting 300-nm-tall pillars have a large distribution in width, ranging from 120 to 170 nm, show height variations, and some randomness in arrangement. This is in strong contrast to nanostructures on 500-nm spheres which perfectly replicate the underlying microsphere array. The transition to a less ordered morphology is attributed to a competitive growth mode which becomes dominant when the pattern period is smaller than the length scales of surface diffusion and column self-shadowing. That is, in the case of 160-nm patterns, competition between neighboring columns causes exacerbated growth of some columns at the cost of others which die out. This competition is delayed for growth on 500-nm-diameter spheres, yielding regular nanostructure arrays.