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Stability and dynamics of Pt-Si liquid microdroplets on Si,,001... W.-C. Yang, H. Ade, and R. J. Nemanich*

Summary: Stability and dynamics of Pt-Si liquid microdroplets on Si,,001...
W.-C. Yang, H. Ade, and R. J. Nemanich*
Department of Physics, North Carolina State University, Raleigh, North Carolina 27695-8202, USA
Received 7 May 2003; revised manuscript received 10 September 2003; published 29 January 2004
The formation and dynamics of Pt-Si liquid droplets on Si 001 surfaces are explored with real-time
ultraviolet photoelectron emission microscopy. PtSi islands of micrometer lateral diameter begin to melt and
are transformed into molten Pt-Si alloy islands below the melting point of bulk PtSi. In particular, at 1100 C
surface migration of the liquid microdroplets is observed, where the droplets move directionally from the cold
to the hot regions of the surface following the temperature gradient across the substrate. It is proposed that the
droplet surface migration is due to dissolution-diffusion-deposition flow of Si through the droplet driven by the
Si concentration difference in the droplet. In addition, the migration rate of the droplet is measured as a
function of temperature and droplet diameter. Above a minimum diameter, the migration velocity is indepen-
dent of the droplet size, which indicates that Si diffusivity through the droplet is the primary factor determining
the rate of migration. The activation energy for the Si diffusion in the droplet is found to be 0.57 eV. We
conclude that the thermal and chemical stability of the droplet-substrate interface significantly affects the
evolution and dynamics of the liquid island on the surface.
DOI: 10.1103/PhysRevB.69.045421 PACS number s : 68.08. p, 68.37.Nq
It is well known that thin metal films on Si react to form
an equilibrium silicide-Si interface and higher-temperature


Source: Ade, Harald W.- Department of Physics, North Carolina State University


Collections: Physics