Effects of heat and electron irradiation on the melting behavior of Al-Si alloy particles and motion of the Al nanosphere within.
In situ heating and electron-beam irradiation in the transmission electron microscope were performed to study melting of Al-11.6 at.% Si alloy submicron particles supported on an amorphous-C thin film. It was found that electron irradiation could be used to melt the particles, even when the hot-stage specimen holder was kept at a much lower temperature than the bulk melting point (i.e. the eutectic temperature) of the particles. The critical current densities required to achieve partial melting increased linearly with the incident electron-beam energy for a given temperature. Comparison between this behavior and analytical calculations indicates that melting under electron-beam irradiation is caused by a temperature rise due to electron thermal spikes in the particles and poor thermal conduction away from the particles. The motion of the crystalline Al nanosphere inside the partially molten particles was also investigated, using the electron beam to both stimulate and observe the motion of the nanosphere. The irregular motion observed was quantified as antipersistent fractional Brownian motion. Analysis of possible phenomena contributing to the motion demonstrates that the incident electrons provide the fractional force that moves the Al nanosphere, and that gravity and the oxide shell on the partially molten particle cause the antipersistent behavior. Another interesting phenomenon observed in this study was that the crystalline Al nanosphere inside the partially molten Al-Si alloy particle followed a focused electron beam as it was moved about on the partially molten particle. This observation suggests that it may be possible to manipulate metallic nanospheres inside opaque liquids using an electron beam.
Howe
James M
JM
Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22904-4745, USA. jh9s@virginia.edu
Yokota
Takeshi
T
Murayama
Mitsuhiro
M
Jesser
William A
WA