Papers by Author: Se Ahn Song

Abstract: Phase transformation and crystal growth behavior of Ge2Sb2Te5 were investigated systematically by means of in situ heating (from room temperature to 500 oC) of amorphous Ge2Sb2Te5 alloy in a high voltage electron microscope with real-time monitoring. Large-scale crystallization occurred to amorphous Ge2Sb2Te5 around 200 oC. Large crystal growth developed on heating from 200 oC to 400 oC, and single crystalline grains grew up to 150 nm. Eventually the onset of partial melting of thin Ge2Sb2Te5 foil was at 500 oC and liquid Ge2Sb2Te5 was observed for the first time by high-resolution transmission electron microscopy. Hexagonal Ge2Sb2Te5 phase remains after a subsequent cooling.

Abstract: Transformation of uniformly strained GexSi1-x layers into GeSi dots of 3 ~ 7 nm which are compositionally ordered by one or concurrently two sets of {111} planes was carried out for the first time under non-equilibrium conditions induced by 1.25 MeV electron irradiation at Tc ≥ 200 oC in the high voltage electron microscope (JEM-ARM1300S). This microscope installed in the KBSI is characterized by an excellent point-to-point resolution of 0.12 nm allowing obtaining detailed information on chemical ordering at specific parameters of defocus (-800 Å) and crystal thickness (200~250 Å) determined by extensive HRTEM image simulation for the ordered dots.

Abstract: Characteristic 60° dislocations occurred in hexagonal phase of Ge2Sb2Te5 thin foil cooled from 500°C to room temperature in a high voltage transmission electron microscope. The Burgers vector of dislocation was identified as 1/ 24 < 9902 > which is the edge component of 1 3 < 2110 > projected on the (1120) lattice plane. The dislocation resulted from the cooling-induced stress/strain in the Ge2Sb2Te5 alloy.