Confined in-fiber solidification and structural control of silicon and silicon-germanium microparticles

TitleConfined in-fiber solidification and structural control of silicon and silicon-germanium microparticles
Publication TypeJournal Article
Year of Publication2017
AuthorsGumennik, A, Levy, EC, Grena, B, Hou, C, Rein, M, Abouraddy, AF, Joannopoulos, JD, Fink, Y
JournalProceedings of the National Academy of Sciences of the United States of America
Volume114
Issue28
Pagination7240 - 7245
Date Published2017/07/11/
ISBN Number0027-8424
Keywordsalloy, confined solidification, crystals, czochralski growth, ge-si, hydrostatic-pressure, interface, janus particles, microparticles, multimaterial fibers, Nanoparticles, optical-fiber, silicon-germanium spheres, stability, stressed silicon
Abstract

Crystallization of microdroplets of molten alloys could, in principle, present a number of possible morphological outcomes, depending on the symmetry of the propagating solidification front and its velocity, such as axial or spherically symmetric species segregation. However, because of thermal or constitutional supercooling, resulting droplets often only display dendritic morphologies. Here we report on the crystallization of alloyed droplets of controlled micrometer dimensions comprising silicon and germanium, leading to a number of surprising outcomes. We first produce an array of silicon-germanium particles embedded in silica, through capillary breakup of an alloy-core silica-cladding fiber. Heating and subsequent controlled cooling of individual particles with a two-wavelength laser setup allows us to realize two different morphologies, the first being a silicon-germanium compositionally segregated Janus particle oriented with respect to the illumination axis and the second being a sphere made of dendrites of germanium in silicon. Gigapascal-level compressive stresses are measured within pure silicon solidified in silica as a direct consequence of volume-constrained solidification of a material undergoing anomalous expansion. The ability to generate microspheres with controlled morphology and unusual stresses could pave the way toward advanced integrated in-fiber electronic or optoelectronic devices.

Short TitleProc. Natl. Acad. Sci. U. S. A.