Dewetting of Ultrathin Solid Films

Ultrathin crytalline solid films are found to dewet with a faceted rim. In the case of heterogeneous dewetting initiated from a linear trench or from periodically arranged holes, the dewetted area expands either with a faceted multilayer rim or in a layer-by-layer fashion. In the case of homogeneous dewetting, holes are accompanied with multilayer rims and the uncoverage increases as a power law of time. Results of kinetic Monte Carlo simulations are elucidated within the frame of nucleation theory and surface diffusion limited dynamics.

Figure 1

KMC simulations with $T=0.4$ and $h=3$. Black lines indicate atomic steps. (a) Detail of the initial stages of a $600\times 1000$ simulation with $E_s=0.5$. A faceted rim forms. (b),(c) Dewetting from one hole in a $400\times 400$ system. (b) A rim forms at $E_S=0.4$. (c) Layer-by-layer dewetting at $E_S=0.25$.

Figure 2

(a) Position $x_1$ and rim height $h_1$ for a straight front. Symbols: KMC with $L=1000$, $T=0.4$, $E_S=0.5$, $h=3$. Solid lines: model Eqs. (4, 5). $h_1$ saturates, whereas $x_1\sim t^{1/2}$ asymptotically. (b) A similar behavior is found for the rim height $h_1$ and radius $R_1$ of a hole. Symbols: KMC with $L_H=800$, $A_0=225$, $T=0.4$, $E_S=0.5$, and $h=3$. Solid lines: numerical solution of Eqs. (10, 11, 14). (c) Area $A_1$ of a hole in the presence of a monolayer rim. KMC with $L_H=400$, $T=0.4$, and various ($E_S$, $h$, $A_0$): ○ (0.2, 2, 144); □ (0.17, 2, 144); ◇ (0.25, 3, 576); △ (0.3, 3, 576). Solid line: Eq. (16) with $A_1=\pi R_1^2\sim t$ and a prefactor between 0.88 and 1.15.

Figure 3

(a) Snapshots of a $1000\times 1000$ KMC simulation, with $h=3$, $T=0.5$, and $E_s=0.7$, at $t=1.6\times {10}^6$, and $4.1\times {10}^6$. (b) Uncoverage in KMC during homogeneous dewetting. Solid lines are guides to the eye $\sim t^2$. Symbols represent KMC simulation with $h=2$ and ($T$, $E_S$): ○ (0.4, 0.5); □ (0.5, 0.7); ◇ (0.4, 0.7); △ (0.5, 0.3); System sizes are $600\times 600$ or $400\times 400$. ◁ correspond to the parameters of (a).