Yan Cheng

Self-extrusion of Te nanowire from Si–Sb–Te thin films

A crystallized Si2Sb2Te5 thin film was observed to extrude single-crystalline [0001] oriented tellurium nanowires at room temperature. The single crystalline Te nanowires nucleation and extruded outgrowth can be greatly accelerated by electron-beam-illumination (EBI) in a transmission electron microscope by an order as high as four. The EBI-enhanced outgrowth speed of Te nanowires is a function of electron beam flux and can be described as v=ku2009ln(J+m). This Te nanowires self-outflow phenomenon comes from a decomposition process of the Si2Sb2Te5 matrix and provides an interesting model and mechanism of the nanowires’ growth, which is distinctive to the vapor-liquid-solid (VLS) mechanism.

Microstructure evolution of the phase change material TiSbTe

The crystallization process and crystal structure of the phase change material TiSbTe alloy have been successfully established, which is essential for applying this alloy in phase change memory. Specifically, transmission electron microscopy (TEM) analyses of the film annealed in situ were used in combination with selected-area electron diffraction (SAED) and radial distribution function (RDF) analyses to investigate the structural evolution from the amorphous phase to the polycrystalline phase. Moreover, the presence of structures with medium-range order in amorphous TST, which is beneficial to high-speed crystallization, was indicated by the structure factors S(Q)s. The crystallization temperature was determined to be approximately 170°C, and the grain size varied from several to dozens of nanometers. As the temperature increased, particularly above 200°C, the first single peak of the rG(r) curves transformed into double shoulder peaks due to the increasing impact of the Ti–Te bonds. In general, the majority of Ti atoms enter the SbTe lattice, whereas the remainder of the Ti atoms aggregate, leading to the appearance of TiTe2 phase separation, as confirmed by the SAED patterns, high-angle annular dark field scanning transmission electron microscopy (HAADFSTEM) images and the corresponding energy-dispersive X-ray (EDX) mappings.