Effect of Surface Roughness on Laser-driven Instability Dewetting of Ultrathin Co Films

摘要

Previous studies on dewetting of ultrathin Co films by nanosecond pulsed laser melting have shown that the films dewet due to a thin film hydrodynamic instability and form a system of ordered nanoparticles with uniform average size and nearest neighbor particle spacing. For Co films less than 8 nm thick, the nanoparticle spacing, λ_(NN) was dependent on the initial film thickness, h, and varied as h~2. For Co films thicker than 8nm, the nanoparticle spacing decreased with increasing film thickness, due to a thermocapillary effect generated by the ns laser heating. Here we show the results from investigations on dewetting of Co films that had initially much rougher surfaces with root mean square roughness values, 0.9 < R_(rms)< 2.8 nm as compared to smoother films examined in prior investigations, for which R_(rms) ≤ 0.2 nm . Laser induced dewetting of Co films with much large R_(ms) values generated nanoparticles that were qualitatively similar to those created from smoother Co films. The size distribution of the nanoparticles was monodispersed and there was short range spatial order present in the system from the average nearest neighbor nanoparticle spacing; however, a drastic reduction in the characteristic length scales was observed in the nanoparticulate arrays created from the rougher Co films. This result suggests that knowledge of film thickness and roughness are important towards predicting characteristic length scales from metal film dewetting.