AVS 52nd International Symposium
    Electronic Materials and Processing Thursday Sessions
       Session EM2-ThM

Paper EM2-ThM10
Formation of Epitaxial Ge Nanorings on Si by Self-assembled SiO@sub 2@ Particles and Touchdown of Ge Through a Thin Layer of SiO@sub 2@

Thursday, November 3, 2005, 11:20 am, Room 310

Session: Heteroepitaxy and Low-Dimensional Structures
Presenter: Q. Li, University of New Mexico
Authors: Q. Li, University of New Mexico
S.M. Han, University of New Mexico
Correspondent: Click to Email
We demonstrate that hexagonally packed single-crystalline Ge rings can be grown around the contact region between self-assembled SiO@sub 2@ spheres and 1.2-nm-thick chemical SiO@sub 2@ on Si. When the oxide-covered Si substrate is pulled from a colloidal suspension of SiO@sub 2@ spheres, the SiO@sub 2@ spheres self-assemble into a hexagonally packed monolayer on the substrate. These SiO@sub 2@ 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 SiO@sub 2@ 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 SiO@sub 2@ spheres. With a flux of Ge impinging at 45° from the surface normal, the Ge beam cannot directly impinge on the underlying substrate through the openings between SiO@sub 2@ spheres. The Ge adspecies diffuse around the SiO@sub 2@ spheres and "touchdown"[Li et al., APL, 85(11), 1928 (2004)] through the chemical SiO@sub 2@, 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 SiO@sub 2@ sphere self-assembly; the weak interaction between Ge adspecies and SiO@sub 2@; and the touchdown where Ge densely nucleate on Si surface through the 1.2-nm-thick chemical oxide. We will also demonstrate that ring dimension and geometrical arrangement can be precisely controlled by the size of the SiO@sub 2@ spheres and by the artificially introduced surface corrugation, respectively.