Paper NS-TuM11
Crystal Structure Engineering of Ge Nanowires

Tuesday, November 1, 2011, 11:20 am, Room 203

Semiconductor nanowire engineering provides a promising route to achieve next generation energy conversion, photonic, and electronic materials. In order to enable the appropriate function for a particular application, control of nanowire crystal structure (e.g. lattice, orientation, faceting) is critical. Unfortunately, this remains a challenging task with bottom-up nanostructure syntheses. To this end, we rationally control Ge nanowire crystal structure for the first time via the addition of bifunctional alkylgermanes, which adjust the interface energetics near the three-phase line. More specifically, Ge nanowires are grown using the vapor-liquid-solid (VLS) technique with germane combined with methyl-, ethyl- or tertbutyl-germane. Scanning electron microscopy (SEM) and high resolution transmission electron microscopy (TEM) reveal that nanowires transition to a new growth direction upon addition of an alkylgermane, but remain single crystalline throughout. For the case of methyl-germane, nanowires transition from the <111> to <110> crystal growth direction. A significant reduction in tapering is also observed in all cases. Infrared spectroscopy (IR) shows that nanowire sidewalls are alkyl terminated and X-ray photoelectron spectroscopy (XPS) indicates this termination reduces the rate of oxidation. The impact of alkylgermane identity and surface coverage on crystal growth direction will be discussed in detail. The control of interface chemistry demonstrated by this work provides an important new handle for controlling nanowire structure and properties. Furthermore, the ability to effectively passivate nanowire sidewalls during growth is expected to enable more robust doping profiles by only permitting precursor incorporation through the catalyst tip.