Effect of Surface Roughness on Laser-driven InstabilityDewetting of Ultrathin Co Films

摘要

Previous studies on dewetting of ultrathin Co films by nanosecond pulsed laser melting have shown that thefilms dewet due to a thin film hydrodynamic instability and form a system of ordered nanoparticles with uniformaverage size and nearest neighbor particle spacing. For Co films less than 8 nm thick, the nanoparticle spacing,E_(NN)was dependent on the initial film thickness,h,and varied ash~2.For Co films thicker than 8 nm, thenanoparticle spacing decreased with increasing film thickness, due to a thermocapillary effect generated by thens laser heating. Here we show the results from investigations on dewetting of Co films that had initially muchrougher surfaces with root mean square roughness values, 0.9 < R_(rms) < 2.8 nm as compared to smoother filmsexamined in prior investigations, for which R_(rms)iu0.2 nm . Laser induced dewetting of Co films with much largeR_(ms) values generated nanoparticles that were qualitatively similar to those created from smoother Co films. Thesize distribution of the nanoparticles was monodispersed and there was short range spatial order present in thesystem from the average nearest neighbor nanoparticle spacing; however, a drastic reduction in the characteristiclength scales was observed in the nanoparticulate arrays created from the rougher Co films. This result suggeststhat knowledge of film thickness and roughness are important towards predicting characteristic length scalesfrom metal film dewetting.