Abstract
We demonstrate that shadowing instabilities can dramatically alter the very early stages of growth of amorphous thin films on nominally smooth surfaces. These observations are made by comparing the porosity and morphological evolutions of thin films grown under conditions of normal and glancing incidences of the vapor flux. At conditions of normal incidence, we see evidence of nucleation, followed by coalescence and growth of a continuous film; at glancing incidence, we observe the development of a mounded surface morphology before deposition of the first nanometer, followed by growth of isolated nanopillars.