The hexagonal shapes of Si(0.13)Ge(0.87) quantum dots (QDs) and rings on Si(110) reflect the lattice symmetry of the top two Si layers on Si, which is different from that on Si(100). The formation time of nanorings on Si(110) is much longer than that on Si(100). This is probably due to the slow diffusion of Ge and Si on Si(110) substrate. Based on both transmission electron microscopy and Raman spectroscopy, the formation of SiGe nanorings can be attributed to Ge outdiffusion from the top of the central SiGe QDs during in situ annealing. Moreover, the Si cap layer is essential for nanorings formation. The uncapped QDs cannot transform into rings even after a long time annealing. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3309773]
