Abstract
The growth of high density germanium (Ge) nanostructures (nanowires and nanotowers) and influence of chromium (Cr) doping on its morphology have been investigated. It is observed that in the absence of Cr, Ge nanowires (NWs) are formed whereas the presence of Cr leads to the growth of Ge nanotowers (NTrs), wherein all other experimental parameters were kept constant. Independent of the Cr concentration, the crystal structures of both nanostructures, that is, NWs and NTrs, are identical. Traditional vapor-liquid-solid (VLS) process was used to explain the growth mechanism of the top of the Ge NTr, consisting of a thin nanowire with a gold tip. The bottom of the NTr consists of lateral (111) and (001) planes of polygonal structure; VLS process along with vapor-solid (VS) process accounts for its further growth. The mechanism for the dopant-dependent morphological changes in Ge nanostructures is clarified. The magnetic properties of the NTrs were probed using a superconducting quantum interference device (SQUID). Room-temperature ferromagnetism in Cr-doped Ge nanotowers was discovered. These findings can thus be exploited for controlling the morphology and generating the magnetic ordering in nonmagnetic semiconductors to develop stabilized novel spintronics devices. c 2011 American Chemical Society.