Correlations between In Situ Conductivity and Uniform-Height Epitaxial Morphology in $\mathrm{Pb}/\mathrm{Si}(\mathbf{1}\mathbf{1}\mathbf{1})\text{−}(\mathbf{7}\times \mathbf{7})$

The growth of Pb on $\mathrm{Si}(111)\text{−}(7\times 7)$ at temperatures from 72 to 201 K has been investigated using in situ electrical resistivity measurements and scanning tunneling microscopy. For temperatures $T>140\mathrm{K}$ the specific resistivity $\rho (\theta )$ versus coverage $\theta$ shows an unusual “hump,” instead of the expected monotonic decrease with $\theta$. This novel result correlates well with the formation of uniform height eight-layer Pb islands and the superdiffusive motion of the wetting layer, despite the low temperatures. A model of the film resistivity as two resistors in series, the amorphous wetting layer and the crystalline islands, explains quantitatively the resistivity dependence on $\theta$.

Figure 1

(a) $500\times 500{\mathrm{nm}}^2$ STM image. (b) The corresponding island-height histogram. The experiment was carried out at 190 K with 4.2 ML deposited. The tunneling bias was $+3.5\mathrm{V}$ and the tunneling current was 0.28 nA.

Figure 2

Specific resistivity during the growth of Pb on $\mathrm{Si}(111)\text{−}(7\times 7)$ substrate as a function of Pb deposited amount with the substrate temperature ranging from 72 K $-201\mathrm{K}$. The curves are shifted vertically with the origin of each curve shown to the right as a straight segment.

Figure 3

Experimental specific resistivity (continuous line) measured at 180 K, and calculated (open dots) according to Eq. (3) with $H=7$ (left) and $H=8$ (right). The parameters $\rho (H=8)=40.6\mu \mathrm{\Omega }\mathrm{cm}$ and for $\rho (H=7)=43.6\mu \mathrm{\Omega }\mathrm{cm}$ are from Eq. (4) and ${\rho }_{\text{WL}}=170\mu \mathrm{\Omega }\mathrm{cm}$ at ${\theta }_{\text{WL}}$. The sharp coverage transition at ${\theta }_{\text{WL}}=1.4\text{ML}$ where the wetting layer converts to crystalline islands is in agreement with the result of other experiments.