Uniform silica coating of isoprene-passivated germanium nanowires via Stöber method

Abstract

Encapsulation of an amorphous silica shell can significantly enhance the thermal and chemical stability of core materials. Traditional silica coating methods on semiconductors such as silicon (Si) and germanium (Ge) mostly involve various high-temperature oxidation processes. This paper describes a solution-based Stöber method for the coating of Ge nanowires (NWs) with a uniform shell of amorphous silica. Ge–silica core–shell NWs were prepared by mixing isoprene-protected Ge NWs with tetraethyl orthosilicate (TEOS) and ammonia solution. The SiO₂ species migrated around the surface of the Ge NWs and were incorporated onto the nanowire through hydrolysis and condensation of TEOS in ammonia solution. Without isoprene passivation, Ge NWs easily oxidize upon exposure to ambient conditions to form a GeO_2−x shell, which renders them water-soluble and makes the NWs inapplicable. We also show that the thickness of the silica shell can be tuned with different reaction times. Finally, fluorescein isothiocyanate (FITC) incorporated on the Ge–silica core–shell structure was demonstrated.