Self-assembly of periodic nanoclusters of Si and Ge along atomically straight steps of a vicinal Si(111)

摘要

The very initial stage of the molecular beam epitaxy of Si and Ge on Si(111)-7x7 substrates with atomically straight steps has been studied by scanning tunneling microscopy and spectroscopy. The atomically straight steps have been prepared on a miscut Si(111) substrate by annealing at 830 degrees C with kink-up direct current. The length of the steps can be maximized by selecting a proper annealing time. The steps have a well-defined U(2, 0) step-edge structure. The growth of both Si and Ge at temperatures between 250 and 400 degrees C starts with formation of a single-adatom-row nanowire (0.67 nm in width) along the lower edge of each U(2, 0) step. Subsequent growth of Si and Ge at temperatures between 250 and 300 degrees C results in formation of one-dimensional arrays of nanoclusters (less than 2.0 nm in width) in the unfaulted halves of the 7x7 structure along the upper step edges. Scanning tunneling spectroscopy reveals localized electronic states of the nanoclusters. Differences between the growth of Si and Ge nanoclusters are discussed.