Running Droplets of Gallium from Evaporation of Gallium Arsenide
J. Tersoff,1*
D. E. Jesson,2*
W. X. Tang2
High-temperature annealing of gallium arsenide in vacuum causes
excess evaporation of arsenic, with accumulation of gallium
as liquid droplets on the surface. Using real-time in situ surface
electron microscopy, we found that these droplets spontaneously
run across the crystal surface. Running droplets have been seen
in many systems, but they typically require special surface
preparation or gradient forces. In contrast, we show that noncongruent
evaporation automatically provides a driving force for running
droplets. The motion is predicted and observed to slow and stop
near a characteristic temperature, with the speed increasing
both below and above this temperature. The same behavior is
expected to occur during the evaporation of similar III-V semiconductors
such as indium arsenide.
2 School of Physics, Monash University, Victoria 3800, Australia.
* To whom correspondence should be addressed. E-mail: tersoff{at}us.ibm.com (J.T.); david.jesson{at}sci.monash.edu.au (D.E.J.)
