Thin Film Compressive Stresses due to Adatom Insertion into Grain Boundaries

Atomic simulations of the growth of polycrystalline Ni demonstrate that deposited atoms incorporate into the film at boundaries, resulting in compressive stress generation. Incorporated atoms can also leave the boundaries and thus relieve compressive stress. This leads to a complex interplay between growth stress, adatom incorporation, and surface structure. A simple, theoretical model that accounts for grain size effects is proposed and is in good agreement with simulation results.

Figure 1

Simulation snapshots during deposition on the $L=5\mathrm{nm}$ system (system $A$). Light gray atoms highlight GBs and free surface. (a) $t_f=0.14\mathrm{ML}$; (b) $t_f=0.36\mathrm{ML}$; (c) $t_f=0.49\mathrm{ML}$. Only part of the system is shown in $z$.

Figure 2

Stress evolution during deposition for (a) system $A$, (b) system $B$, and (c) system $C$.

Figure 3

(a) Number of atoms in the film bulk $N_L$ vs depth from the surface $D$ for system B at $t_f=0$, 0.64, and 0.89 ML. (b) The number of extra atoms $N_X$ incorporated into the grain boundaries vs film thickness $t_f$.

Figure 4

The film stress-thickness product $\Delta {\sigma }_{xx}h$ vs the density of incorporated extra atoms ${\rho }_X$ for three deposition simulations.