SiO_x/GeO_x nanowires grown via the active oxidation of Si/Ge substrates

Silica nanowires have recently been grown via the vapor-liquid-solid growth mechanism where the vapor precursor is obtained directly from the substrate via active oxidation processes. In this study, we extend this technique to the Ge-O system and show that Au coated Ge substrates can be used as a volatile GeO source, resulting in germania nanowire formation above 550°C. The process is highly dependent on Au and native oxide thickness', the partial pressure of O₂ and annealing temperature. If the oxide layer is too thick, the bare wafer is protected from the active oxidation process. However, if the oxide layer is too thin, it will be readily decomposed leaving no stable surface for nanowires to grow and only an etched surface is observed. In this study we show that a native Ge oxide is unstable and that a thicker oxide is required as a buffer layer, separating active oxidation and nanowire nucleation processes. We also show that nanowires can be grown on stable oxide particles present on the Ge wafer surface.