Quasi-isotropic scaling behavior on an anisotropic substrate: $\mathrm{Ni}∕\mathrm{Ni}\left(110\right)$

The homoepitaxial nucleation and growth on Ni(110) at coverages up to 0.1 monolayer (ML) are investigated by variable-temperature scanning tunneling microscopy. At temperatures up to $280\mathrm{K}$ the Ni islands grow as very anisotropic, one-dimensional strings of monatomic width. At higher temperatures two-dimensional islands start to evolve. Due to the strongly elongated island shape, considerable coalescence must occur already at coverages of 0.1 ML. Despite the anisotropy of the Ni(110) substrate, adatom diffusion appears to be only weakly anisotropic, resulting in a quasi-isotropic scaling behavior with an effective diffusion barrier of $0.60\mathrm{eV}$.

Figure 1

STM images $(560\mathrm{\AA }\times 560\mathrm{\AA })$ of 0.09 ML $\mathrm{Ni}∕\mathrm{Ni}\left(110\right)$ prepared at different deposition fluxes $F$ and substrate temperatures $T$. Insets: atomically resolved images, showing that islands are of monatomic width at low temperatures and broaden above $280\mathrm{K}$.

Figure 2

Scaling of island density $n_x$ with deposition flux $F$ at a deposition temperature of $228\mathrm{K}$.

Figure 3

Arrhenius diagram of island density $n_x$ (squares, left axis) and inverse island width $w_{\mathrm{av}}^{-1}$ (triangles, right axis) at a deposition flux of $2.6\times {10}^{-3}\mathrm{ML}∕\mathrm{s}$. Note that $w_{\mathrm{av}}^{-1}\approx n_{1\mathrm{D}}∕\Theta$, where $n_{1\mathrm{D}}$ is the line density of islands along [001].

Figure 4

Autocorrelation plot $(400\mathrm{\AA }\times 400\mathrm{\AA })$ of island positions at $T=218\mathrm{K}$ and $F=1.3\times {10}^{-3}\mathrm{ML}∕\mathrm{s}$ at a coverage of 0.04 ML. The positions of the various pixels specify the various interisland vectors, while the gray tone of a pixel indicates the probability of finding this particular inter-island vector. Black represents a vanishing probability, white the maximum probability. The origin of interisland vectors is chosen at the center of the diagram. For comparison an island of average size is depicted at the origin.

Figure 5

Scaled island-size distribution obtained at $T=228\mathrm{K}$ and $F=2.6\times {10}^{-3}\mathrm{ML}∕\mathrm{s}$. Dashed and dotted lines; theoretical predictions for critical island sizes $i=1$ and $i=2$, respectively (Ref. 22). Solid curve: model calculation, including the effect of coalescence onto the theoretical curve for $i=1$ (see text). Inset: theoretical curve for $i=1$ (dashed line) and effect of coalescence (solid line) on an absolute scale. The dash-dotted line gives the contribution of islands that have undergone a coalescence event.