title: Phase transitions, melting dynamics, and solid-state diffusion in a nano test tube.
abstract: Confined nanoscale geometry greatly influences physical transformations in materials. The electron microscope enables direct visualization of these changes. We examined the evolution of a germanium (Ge) nanowire attached to a gold (Au) nanocrystal as it was heated to 900 degrees C. The application of a carbon shell prevented changes in volume and interfacial area during the heating cycle. Au/Ge eutectic formation was visualized, occurring 15 degrees C below the bulk eutectic temperature. Capillary pressure pushed the melt into the cylindrical neck of the nanowire, and Ge crystallized in the spherical tip of the carbon shell. Solid-state diffusion down the length of the confined Ge nanowire was observed at temperatures above 700 degrees C; Au diffusion was several orders of magnitude slower than in a bulk Ge crystal.
authors.affiliation: Department of Chemical Engineering, Texas Materials Institute, Center for Nano and Molecular Science and Technology, University of Texas at Austin, Austin, TX 78712, USA.
authors.forename: Vincent C
authors.initials: VC
authors.lastname: Holmberg
authors.forename: Matthew G
authors.initials: MG
authors.lastname: Panthani
authors.forename: Brian A
authors.initials: BA
authors.lastname: Korgel