Formation and stabilization of single-crystalline metastable AuGe phases in Genanowires

Abstract

We use in situ observations by variable temperature transmission electron microscopy onAuGe alloy drops at the tips of Ge nanowires (NWs) with systematically varyingcomposition to demonstrate the controlled formation of metastable solid phases integratedin NWs. The process, which operates in the regime of vapor–liquid–solid growth, involves asize-dependent depression of the alloy liquidus at the nanoscale that leads to extremely Ge-richAuGe melts at low temperatures. During slow cooling, these liquid AuGe alloy drops showpronounced departures from equilibrium, i.e., a frustrated phase separation of Ge into theadjacent solid NW, and ultimately crystallize as single-crystalline segments of metastableγ-AuGe. Our findings demonstrate a general avenue for synthesizing NW heterostructurescontaining stable and metastable solid phases, applicable to a wide range of materials ofwhich NWs form by the vapor–liquid–solid method.