Germanium Nanowires and Core−Shell Nanostructures by Chemical Vapor Deposition of [Ge(C₅H₅)₂]

High-yield synthesis of germanium nanowires (NWs) and core−shell structures is achieved by the chemical vapor deposition (CVD) of dicyclopentadienyl germanium ([Ge(C 5 H 5 ) 2 ]). The one-dimensional (1D) nanostructures are formed on an iron substrate following a base-growth model in which an Fe−Ge epilayer functions as a catalytic bed. The wire growth is selective and no catalyst particles are observed at the tip of the NWs, which is contrary to the characteristic feature of a 1D growth based on the vapor−liquid−solid (VLS) mechanism. The diameter and length of the NWs were in the ranges 15−20 nm and 25−40 μm, respectively, as found by high-resolution electron microscopy. Both axial and radial dimensions of the NWs can be controlled by adjusting the precursor feedstock, deposition temperature, and size of alloy nuclei in the Fe−Ge epilayer. High precursor flux produced coaxial heterostructures where single-crystalline Ge cores are covered with an overlayer of nanocrystalline Ge. Single-crystal Ge nanowires exhibit a preferred growth direction [112̄] confirmed by X-ray and electron diffraction patterns. When compared to bulk Ge, the micro-Raman spectra of Ge NWs show a low field shift, probably due to the dimensional confinement. Patterned growth of Ge NWs was achieved by shadow-masking the Fe substrate with a carbon film, which prevents the formation of Fe−Ge nuclei, thereby inhibiting the nanowire growth.