Liquid-Solid phase transition of Ge-Sb-Te alloy observed by in-situ transmission electron microscopy

Figure 1: (a) TEM image series taken at 600°C showing the melting of a crystalline [cry] GST nanoparticle surrounded by GST melt. The video of this sequence is available on the left side. (b) Graph of nanoparticle diameter [d] versus time. The reduction of the diameter increases significantly after reaching a size of approximately 50 nm. (c) Close-up view of GST nanoparticle visualizing the super-lattice structure and the broad and diffuse interface (marked by black arrows).

Melting and crystallization dynamics of the multi-component Ge-Sb-Te alloy have been investigated by in-situ transmission electron microscopy (TEM). Starting point of the phase transition study is an ordered hexagonal Ge1Sb2Te4 thin film on Si(111) where the crystal structure and the chemical composition are verified by scanning TEM and quantitative electron energy-loss spectroscopy, respectively. The in-situ observation of the liquid phase at 600°C including the liquid-solid and liquid-vacuum interfaces and their movements was made possible due to an encapsulation of the TEM thin foil sample. The solid-liquid interface during melting displays a broad and diffuse transition zone (cf. Fig.1 (c)) characterized by a vacancy induced disordered state. Although the velocities of interface movements are measured to be in the nanometer per second scale, both, for crystallization and solidification, the underlying dynamic processes are considerably different. Melting reveals linear dependence on time, (Fig.1(b)) whereas crystallization exhibits a non-linear time-dependency featuring a superimposed start-stop motion. Our results may provide valuable insight into the atomic mechanisms at interfaces during the liquid-solid phase transition of Ge-Sb-Te alloys. 

1 Author K. Berlin , A. Trampert

Liquid-solid phase transition of Ge-Sb-Te alloy observed by in-situ transmission electron microscopy

Source Ultramicroscopy , 178 , 27 ( 2017 )
DOI : 10.1016/j.ultramic.2016.10.010 | 2883 Cite : Bibtex RIS
K. Berlin, and A. Trampert