Sublimation of GeTe Nanowires and Evidence of Its Size Effect Studied by in Situ TEM

We report sublimation of crystalline GeTe nanowires at elevated temperatures in vacuum imaged by in situ transmission electron microscopy. The GeTe nanowires exhibit significant melting point suppression in the presence of Au contamination. A nanosized effusion cell is formed by coating the GeTe core with a SiO(2) shell, where the core can be evaporated or sublimated from the open end of the shell at high temperatures. By measuring the speed of the moving interface between the condensed and vapor phases, we determined the vaporization coefficient of these nanowires to be greater than or equal to approximately 10(-3) over a wide range of temperatures. At the final stage of the nanowire vaporization, the material loss occurs at a higher rate, which is evidence of a higher vaporization coefficient for nanosized GeTe. This in situ technique offers a quantitative method of investigating phase transition dynamics and kinetics of nanomaterials, an important topic for designing nanoscale devices to be operated at high temperatures such as phase change memory.