ChemMatCARS Nuggets - Materials Science

Liquid Gold Silicide, a Nanocircuit Solder, Shows Unexpected Crystalline "Skin"

Accomplishment
In contrast to the previously observed behavior of very dilute liquid alloys and pure liquid metals, a nondilulte liquid eutectic gold-silicon alloy (Au₈₂Si₁₈) developed both a crystallized alloy "skin" and an ordered structure extending several atomic layers into the bulk. The "skin" remained an alloy, rather than segregating to a pure metal as in other liquid alloys. The layering is deeper and qualitatively different than that observed in other alloys. The discovery of the frozen crystalline surface was made by using X-ray reflectivity; the underlying layers were studied with grazing incidence X-ray scattering, a method that can probe atomic-level structure at the surface of liquids.

Impact
Because AuSi eutectic alloy melts at a relatively low temperature, it is used to solder micro- and nanoelectromechanical devices (MEMS and NEMS) and to grow silicon nanowires. The new results are important because properties at the nanoscale are expected to depend heavily on surface effects. New theoretical and experimental approaches are being pursued to explain the unexpected surface crystallization in AuSi.

Principal Investigator: Peter S. Pershan, Harvard University
Published in: O. G. Shpyrko, R. Streitel, V. S. K. Balagurusamy, A. Y. Grigoriev, M. Deutsch, B. M. Ocko, M. Meron, B. Lin, P. S. Pershan, "Surface Crystallization in a Liquid AuSi Alloy," Science 2006, 313, 77-80 (DOI: 10.1126/science.1128314)

September 2007

« Back to top