Observed Effects of a Changing Step-Edge Density on Thin-Film Growth Dynamics

We grew ${\mathrm{S}\mathrm{r}\mathrm{T}\mathrm{i}\mathrm{O}}_3$ on ${\mathrm{S}\mathrm{r}\mathrm{T}\mathrm{i}\mathrm{O}}_3(001)$ by pulsed laser deposition, while observing x-ray diffraction at the $(00\frac{1}{2})$ position. The drop $\Delta I$ in the x-ray intensity following a laser pulse contains information about plume-surface interactions. Kinematic theory predicts $\frac{\Delta I}{I}=-4\sigma (1-\sigma )$, so that $\frac{\Delta I}{I}$ depends only on the amount of deposited material $\sigma$. In contrast, we observed experimentally that $|\frac{\Delta I}{I}|<4\sigma (1-\sigma )$ and that $\frac{\Delta I}{I}$ depends on the phase of x-ray growth oscillations. The combined results suggest a fast smoothing mechanism that depends on surface step-edge density.

Figure 1

(a) Anti-Bragg x-ray intensity oscillations during homoepitaxy of $\sim 42\mathrm{M}\mathrm{L}$ of ${\mathrm{S}\mathrm{r}\mathrm{T}\mathrm{i}\mathrm{O}}_3$; $P_{{\mathrm{O}}_2}=10\mathrm{m}\mathrm{T}\mathrm{o}\mathrm{r}\mathrm{r}$, $T=540°\mathrm{C}$, $f=0.03\mathrm{H}\mathrm{z}$. The fit (solid line) to the data (dashed line) is generated using Eq. (1). (b) Evolution of layer coverages ${\theta }_n$, determined by the fit. Each line represents the growth of 1 ML. Inset: surface rms roughness ${\sigma }_{\mathrm{r}\mathrm{m}\mathrm{s}}$ versus film thickness $t$ during growth (both axes in lattice units). The dashed line indicates random growth.

Figure 2

Simulated quasi-2D growth of 1.2 ML, at growth rate $\frac{1}{\sigma }=12\mathrm{\text{pulses}}/\mathrm{M}\mathrm{L}$.

Figure 3

Average of all normalized MCS passes for a sample grown at $P_{{\mathrm{O}}_2}=0.01\mathrm{m}\mathrm{T}\mathrm{o}\mathrm{r}\mathrm{r}$, $T=750°\mathrm{C}$, $f=0.1\mathrm{H}\mathrm{z}$. The solid lines represent linear ($t<5\mathrm{s}$) and exponential ($t>5\mathrm{s}$) fits.

Figure 4

(a) The average of normalized MCS data at three growth oscillation phases $\varphi$. (b) Measured $\frac{\Delta I}{I}$ at all experimental $\varphi$. The dotted lines represent theoretical upper and lower bounds.