Photoemission studies of passivation of germanium nanowires

The surface of single crystal germanium nanowires grown by cold-wall chemical vapor deposition was studied by synchrotron radiation photoemission spectroscopy and also by conventional x-ray photoelectron spectroscopy. The surfaces of the nanowires are not oxidized from which we infer that they are hydrogen passivated as-grown. Exposure to laboratory atmosphere leads to germanium oxide growth with oxidation states of Ge1+, Ge2+, Ge3+, while exposure to UV light leads to a predominance of the Ge4+ oxidation state. Most of the surface oxide could be removed readily by aqueous HF treatment which presumably leaves the nanowire surface hydrogen terminated. The HF-treated surface has more limited stability in air. Alternatively, chlorine termination could be achieved by aqueous HCl treatment of the oxide-coated nanowires. This chlorine termination was found to be more stable in air than the putative hydrogen termination achieved by aqueous HF treatment. (c) 2005 American Institute of Physics.