Fabrication of core-shell Ge-GeO2 nanoneedles

Core-shell Ge-GeO2 nanoneedles were prepared by a hydrothermal deposition using Ge and GeO2 as starting materials. The samples were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy and high-resolution transmission electron microscopy. The results demonstrate that the length of the samples with typical needle structure is higher than 10 žm. The obtained nanoneedles are composed of single crystalline Ge with diamond cubic structure and amorphous oxide outer layers. An explanation of the formation and growth of Ge nanoneedles is proposed, and is based on the metallic-catalyst vapour-liquid-solid and oxide-assisted growth mechanisms.