title: Metastability of Au-Ge liquid nanocatalysts: Ge vapor-liquid-solid nanowire growth far below the bulk eutectic temperature.
abstract: The vapor-liquid-solid mechanism of nanowire (NW) growth requires the presence of a liquid at one end of the wire; however, Au-catalyzed Ge nanowire growth by chemical vapor deposition can occur at approximately 100 degrees C below the bulk Au-Ge eutectic. In this paper, we investigate deep sub-eutectic stability of liquid Au-Ge catalysts on Ge NWs quantitatively, both theoretically and experimentally. We construct a binary Au-Ge phase diagram that is valid at the nanoscale and show that equilibrium arguments, based on capillarity, are inconsistent with stabilization of Au-Ge liquid at deep sub-eutectic temperatures, similar to those used in Ge NW growth. Hot-stage electron microscopy and X-ray diffraction are used to test the predictions of nanoscale phase equilibria. In addition to Ge supersaturation of the Au-Ge liquid droplet, which has recently been invoked as an explanation for deep sub-eutectic Ge NW growth, we find evidence of a substantial kinetic barrier to Au solidification during cooling below the nanoscale Au-Ge eutectic temperature.
authors.affiliation: Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA. h.adhikari@gmail.com
authors.forename: Hemant
authors.initials: H
authors.lastname: Adhikari
authors.forename: Ann F
authors.initials: AF
authors.lastname: Marshall
authors.forename: Irene A
authors.initials: IA
authors.lastname: Goldthorpe
authors.forename: Christopher E D
authors.initials: CE
authors.lastname: Chidsey
authors.forename: Paul C
authors.initials: PC
authors.lastname: McIntyre