In situ high resolution electron microscopy observation of amorphous phase formation in isolated nanometer-sized alloy particles

The size dependence of the glass transition temperature in alloys has been studied using particles in the Au-Sn and Sn-Bi systems by transmission electron microscopy. A solid amorphous phase was produced in approximately 5.5- and 4- nanometer-sized alloy particles in the Au-Sn system at room temperature. Upon heating, the amorphous phase directly changed into a liquid phase, and upon cooling, the liquid phase directly solidified into the amorphous phase. The temperature range in which the granular contrast in the particles starts to fluctuate and eventually disappear were almost the same for the two different-sized particles. In the Sn-Bi system, a fluid and solid amorphous structure is obtained at room temperature in 9-nm-sized and 6-nm-sized alloy particles, respectively. These two sets of observations indicate that the dependence of the glass transition temperature on the size of a system (i.e., of a particle) is rather weak, if any.