Identification of soft phonon modes in Ge-Sb-Te using electron diffraction

The atomistic structure of crystalline Ge-Sb-Te thin film for phase-change optical recording was investigated using transmission electron microscopy and nanobeam electron diffraction. Nonradial diffuse streaks were observed in electron diffraction patterns obtained from laser-induced crystalline phases of Ge-Sb-Te thin films. The intensities of the diffuse streaks were pronounced in particular directions in this alloy. The diffuse streaks were due to low-frequency transverse lattice waves that occur along directions perpendicular to the near neighbor zigzag atomic chains.