(512b) Formation of Epitaxial Ge Nanorings on Si by Self-Assembled Sio2 Particles and Touchdown of Ge through a Thin Layer of Sio2

Authors: 
Li, Q., University of New Mexico
Han, S. M., University of New Mexico


We demonstrate that hexagonally packed single-crystalline Ge rings can be grown around the contact region between self-assembled SiO2 spheres and 1.2-nm-thick chemical SiO2 on Si. When the oxide-covered Si substrate is pulled from a colloidal suspension of SiO2 spheres, the SiO2 spheres self-assemble into a hexagonally packed monolayer on the substrate. These SiO2 spheres provide a surface diffusion path to guide the Ge adspecies to reach the substrate. We have previously determined that the Ge adspecies readily desorb from the bulk SiO2 surface with a desorption activation energy of 42±3 kJ/mol. This low desorption activation energy gives rise to a low surface diffusion barrier, which in turn leads to a high diffusion length on the order of several micrometers, exceeding the dimension of the SiO2 spheres. With a flux of Ge impinging at 45º from the surface normal, the Ge beam cannot directly impinge on the underlying substrate through the openings between SiO2 spheres. The Ge adspecies diffuse around the SiO2 spheres and ?touchdown?[Li et al., APL, 85(11), 1928 (2004)] through the chemical SiO2, forming epitaxial ring structures. The touchdown process anchors nanoscale Ge seed pads to the underlying Si substrate. The ring formation uniquely takes advantage of the SiO2 sphere self-assembly; the weak interaction between Ge adspecies and SiO2; and the touchdown where Ge densely nucleate on Si surface through the 1.2-nm-thick chemical oxide.