Formation of Ge nanoclusters on Si(1 1 1)-7 × 7 surface at high temperature

We report on Ge nanocluster formation on Si(111)-7×7 surface at elevated substrate temperatures during deposition. The shape and size of the Ge clusters are more uniform than those obtained at room temperature due to an increase in the average mobility of the additional atoms. The Ge clusters have a preferential adsorption site in the faulted halves. Some clusters in the faulted and the unfaulted halves exhibit two different features, which indicate the different adsorption energy and chemical activity of the two half-cells. We also observe some clusters forming in a characteristic star shape at a particular positive bias voltage. The formation mechanism and possible structures are discussed.