Observations of self-assembled microscale triangular-shaped spikes in copper and silver thin films

Abstract

We present observations on the formation of previously unreported self-assembled triangular-shaped morphological features in copper and silver thin films deposited at oblique and glancing vapor incidence angles by electron-beam evaporation in ultrahigh vacuum, and characterized them by using scanning electron microscopy (SEM). This systematic study investigates the morphology of 500nm thick copper and silver films, fabricated at vapor incidence angles between 0 and 85 degrees, from the substrate normal. Films fabricated at 50 degrees vapor incidence and greater exhibit triangular-shaped “microspikes” scattered seemingly randomly across the surface with areal densities on the order of 50 spikes per 10×10micrometer area. SEM analysis reveals that the microspikes increase in size with increasing vapor incidence angle. Films deposited at glancing vapor incidence angles (80 degrees and greater), are composed of inclined nanoscale columnar structures, with a high degree of interconnectivity between adjacent columns; where microspikes grow randomly from these tilted columns, and the spikes range in size from 100 to 2000nm in length.