Formation of nanoscale clusters during the initial stages of CaF2 growth on miscut Si(111)

The initial stages of high temperature CaF2 growth by molecular beam epitaxy on Si(111) substrates with a 3° miscut were characterized using atomic force microscopy and low energy electron diffraction. At a growth temperature of 750 °C, electron diffraction measurements showed that the surface retained the (3×1) surface reconstruction up to a deposition thickness of at least 1.2 nm. The overall topography of the surface was defined by atomically flat terraces decorated with a large number of clusters. These clusters were confined to step edges and were typically 10–20 nm tall. The clusters appear to nucleate at the top of step edges and then grow in size until they extend across the step onto the neighboring terrace below. These results indicate that in this growth regime, the CaF2 molecules diffuse across terraces to aggregate into relatively large nanostructures after the formation of a thin wetting layer. The unusually rounded features and large heights seen in these clusters appear to arise from the t...