Shape-controlled growth of single-crystalline Ge nanostructures

We report the shape-controlled growth of single-crystalline germanium nanostructures by Au catalyst-assisted chemical-vapor syntheses using GeH4 as a precursor. By independently controlling the axial- and the radial-growth kinetics near the eutectic temperature of Au and Ge, we reproducibly direct the shape of Ge nanostructures from nanowires to nanocones with various aspect ratios. Based on our observation of the shape variation we discuss a phenomenological model of the growth of Ge nanostructures that goes beyond the conventional vapor-liquid-solid growth mechanism. The precise control of the shape in semiconductor nanostructures in our study suggests the implication of various applications into electronic and optical devices.