Mechanisms of Pulsed Laser-Induced Dewetting of Thin Platinum Films on Tantalum Substrates-A Quantitative Study

The mechanism of pulsed laser-induced dewetting (PLiD) of Pt thin films in the thickness range from 3.2 to 8.9 nm was investigated on smooth chemically polished Ta (PT) and patterned dimpled Ta (DT) substrates, both of which have a thin Ta2O5 layer on the surface. Complete dewetting was achieved for a film thickness of 3.2-4.6 nm. Beyond that, a distinct morphological evolution in the intermediate stages from bicontinuous to polygonal structures was observed with the change in thin-film thickness, enabling the determination of the transition thickness for Pt on Ta2O5/DT substrates to be between 5.9 and 7.7 nm. Furthermore, by examining the dependence of Pt nanoparticle (NP) size (D), nearest neighbor interparticle distance (L), and NP surface density (N) on the Pt film thickness (h), quantitative evidence was provided to demonstrate that PLiD of Pt thin films on Ta2O5/Ta substrates occurred via the spinodal dewetting mechanism. In particular, a power-law fit to the data obtained from Pt NPs on the Ta2O5/PT substrate showed that L has a quadratic dependence on h, that is, L = 5.13 h(2.04). Also, the thickness dependence of D and N on Ta2O5/PT showed a power-law relationship of D = 3.74 h(1.76) and N = 2.93 x 10(12) h(-4.03), respectively. These results are in excellent agreement with predictions from the spinodal dewetting theory. It has also been shown that the patterned DT surface underneath the Pt films exerted extra control on the NP morphology, causing a deviation from the power law as predicted by the spinodal dewetting mechanism. From the thickness dependence of L, D, and N, the Hamaker constant (A) of Pt, the proportional constant (a) correlating the characteristic spinodal length scale (Lambda) and L, and the geometric factor ( f (theta)) were determined.