Real-time x-ray scattering study of surface morphology evolution during ion erosion and epitaxial growth of Au(111)

Abstract

We describe a detailed real-time x-ray scattering study of the evolution of the surface morphology of Au(111) both during ion erosion with 500-eV ${\mathrm{Ar}}^{+}$ ions, and during homoepitaxial growth. We monitor the erosion and growth morphologies as a function of substrate temperature. We also monitor the surface reconstruction, since it is known to play an important role in determining growth regimes on Pt(111). Ion irradiation of Au(111) leads to surface morphology evolution by step retraction above 270 \ifmmode^\circ\else\textdegree\fi{}C and quasi-layer-by-layer removal at 90--220 \ifmmode^\circ\else\textdegree\fi{}C. The extent of the surface reconstruction on Au(111) during ion irradiation gradually decreases with decreasing temperature. While the herringbone reconstruction remains during ion irradiation at 270 \ifmmode^\circ\else\textdegree\fi{}C, the long range order is lost and only the (22\ifmmode\times\else\texttimes\fi{}$\sqrt{3}$) reconstruction is present at 170 \ifmmode^\circ\else\textdegree\fi{}C. We also observe layer-by-layer growth in the Au/Au(111) system at 55--145 \ifmmode^\circ\else\textdegree\fi{}C, a result that differs from the usual behavior of homoepitaxy on fcc(111) surfaces. As in the layer-by-layer erosion regime, only the (22\ifmmode\times\else\texttimes\fi{}$\sqrt{3}$) reconstruction is present during layer-by-layer growth. Room temperature ion irradiation leads to a (1\ifmmode\times\else\texttimes\fi{}1) surface structure and a three-dimensional rough morphology exhibiting pattern formation with a characteristic lateral length scale. Line-shape analysis of the diffuse scattering in transverse x-ray scans taken during low temperature ion irradiation, indicates that the characteristic lateral length scale increases with time consistent with a power law $l\ensuremath{\sim}{t}^{0.28}.$ This agrees with a simple analysis of the position of the satellite peak in the diffuse scattering in these transverse x-ray scans.