Physical self-assembly and the nucleation of three-dimensional nanostructures by oblique angle deposition

Growth front morphology of a thin film formed by physical vapor deposition is controlled by many factors including surface diffusion and shadowing effects. Instabilities can occur if shadowing is more dominant compared to other surface effects and can lead to many diverse physically self-assembled three-dimensional nano-size structures. In this article, we explore the fundamental nucleation and growth mechanisms of the nanostructures during oblique angle deposition. Monte Carlo simulations were carried out to predict the island density, island size distribution, and island–island correlation during the initial stages of growth. The results were compared to that obtained by the oblique angle sputter deposited tungsten films imaged by atomic force microscopy and scanning electron microscopy. Isolated islands with quasiperiodic distribution were formed as a natural consequence of the shadowing effect. Isolated columnar structures are shown to grow on these islands and the width W of the columns is predicted to grow as a function of column length d in a power law form, $W∼dp,$ where the exponent p is between 0.3 and 0.5. The predicted p is consistent with the experimentally determined exponent values for growth of column widths from a variety of materials such as W, Co, Cu, and Si. The exponent values calculated from a derived continuum equation were also consistent with the experimental results.