Controlled synthesis of germanium nanowires and nanotubes with variable morphologies and sizes.

TLDR: The synthesis of structurally uniform and morphologically versatile Ge nanostructures may open up new opportunities for integrated Ge-nanostructure-based nanocircuits, nanodevices, and nanosystems.

Abstract: We report on the controlled growth of germanium (Ge) nanostructures in the form of both nanowire (NW) and nanotube (NT) with ultrahigh aspect ratios and variable diameters The nanostructures are grown inside a porous anodic aluminum oxide (AAO) template by low-temperature chemical vapor deposition (CVD) assisted by an electrodeposited metal nanorod catalyst Depending on the choice of catalytic metals (Au, Ni, Cu, Co) and germane (GeH4) concentration during CVD, either Ge NWs or NTs can be synthesized at low growth temperatures (310−370 °C) Furthermore, Ge NWs and NTs with two or more branches can be grown from the same stem while using AAO with branched channels as templates Transmission electron microscopy studies show that NWs are single crystalline and that branches grow epitaxially from the stem of NWs with a crystalline direction independent of diameter As-grown NTs are amorphous but can crystallize via postannealing at 400 °C in Ar/H2 atmosphere, with a wall thickness controllable between 6 and