Growth Mechanism and Surface Structure of Ge Nanocrystals Prepared by Thermal Annealing of Cosputtered GeSiO Ternary Precursor

• Published in: Journal of nanomaterials 2014-01, Vol.2014 (2014), p.1-7
• Main Authors: Green, Martin, Shrestha, Santosh, Xiang, Yong, Zhang, Bo, Conibeer, Gavin
• Format: Article
• Language: English
• Subjects: Annealing; Atomic structure; Colleges & universities; Core-shell structure; Crystallites; Fourier transforms; Germanium; Growth models; Lasers; Multilayered thin films; Nanocrystals; Nanomaterials; Silicon dioxide; Spectrum analysis; Surface layer
• ISSN: 1687-4110; 1687-4129
• DOI: 10.1155/2014/161637

Ge nanocrystals (Ge-ncs) embedded in a SiO2 superlattice structure were prepared by magnetron cosputtering and postdeposition annealing. The formation of spherical nanocrystals was confirmed by transmission electron microscopy and their growth process was studied by a combination of spectroscopic techniques. The crystallinity volume fraction of Ge component was found to increase with crystallite size, but its overall low values indicated a coexistence of crystalline and noncrystalline phases. A reduction of Ge-O species was observed in the superlattice during thermal annealing, accompanied by a transition from oxygen-deficient silicon oxide to silicon dioxide. A growth mechanism involving phase separation of Ge suboxides (GeO x) was then proposed to explain these findings and supplement the existing growth models for Ge-ncs in SiO2 films. Further analysis of the bonding structure of Ge atoms suggested that Ge-ncs are likely to have a core-shell structure with an amorphous-like surface layer, which is composed of GeSiO ternary complex. The surface layer thickness was extracted to be a few angstroms and equivalent to several atomic layer thicknesses.