Solid-state dewetting mechanisms of ultrathin Ni films revealed by combining in situ time resolved differential reflectometry monitoring and atomic force microscopy

In this study we report on the solid-state dewetting of ultrathin Ni films on amorphous SiO2. The dewetting process is monitored in situ using time resolved differential reflectometry (TRDR). The time resolved differential reflectivity signal during dewetting is found to exhibit a rich behavior, which is intimately connected the changes in morphology. Finite-difference time-domain simulation is used to explain the observed reflectivity data, where experimentally acquired atomic force microscope heightmaps are used as simulation inputs. From ex situ atomic force microscope heightmaps, the sequential processes of grain growth, grain boundary grooving, hole growth, and particle coarsening are observed. Grain growth of ultrathin films prior to dewetting is critically important in determining the particle density, which has been largely unexplored in previous dewetting studies. Kinetic analysis of the TRDR data revealed two rate-limiting processes, with activation energies of 0.31 +/- 0.04 and 0.59 +/- 0.06 eV. We hypothesize that these kinetic pathways correspond to Ni grain growth and surface mass self-diffusion on the Ni(111) planes, respectively.