Low-temperature synthesis of single-crystal germanium nanowires by chemical vapor deposition.

Chemically derived nanowire materials have attracted much attention because of their interesting geometries, properties, and potential applications.[1±3] Various methods have been developed for synthesizing semiconducting nanowires including laser ablation,[2,3] physical vapor deposition under high temperatures,[3±7] and solvothermal growth under high pressures and moderate temperatures.[3,8±10] Chemical vapor deposition (CVD) has been extensively used for carbon nanotube growth,[11±13] but is much less explored for the synthesis of semiconductor nanowires, with the exception for silicon.[14,15] Herein, we present the first synthesis of single-crystal germanium nanowires, prepared by the CVD of germane (GeH4) at 275 8C with Au nanocrystals as seed particles. Germanium is an important semiconducting electronic material with high carrier mobility and a band gap of approximately 0.6 eV. Nanowires of germanium were first reported by the group of Heath about ten years ago, synthesized by using a solvothermal approach.[8] Recently, laser ablation (820 8C),[2] vapor transport (900±1100 8C),[4,7,16] and solvothermal methods (300±400 8C, 100 atm)[9] were used for growth. We show here that high-quality Ge nanowires are synthesized by a simple CVD process at 275 8C under atmospheric pressure. This represents the mildest growth conditions for single-crystal nanowire synthesis. An efficient Ge feedstock from GeH4 and the low eutectic temperature of Ge±Au nanoclusters are the key factors that afford vapor-liquid-solid (VLS) growth of Ge nanowires at low temperatures. Further, we show that the CVD approach allows for patterned growth of Ge nanowires, which yields nanowires from well-defined patterned sites on surfaces. We carried out CVD growth at 275 8C under a 10 sccm (standard cubic centimeter) flow of GeH4 (10% in He) in tandem with a 100 sccm flow of H2 in a 2.5 cm furnace reactor (total gas pressure 1 atm) for 15 min. The SiO2 substrate used in this work contained preformed Au nanocrystals (approximately 20 nm in diameter) deposited uniformly on the surface from a colloidal solution. The inset of Figure 1a shows an atomic force microscopy (AFM) image of the Au particles on a substrate, recorded before CVD. After the COMMUNICATIONS