Temperature-dependent high-angle electron scattering from a phase-separated amorphous GeTe thin film

This paper describes the results of experiments and simulations on the thermal diffuse scattering of 200 keV electrons from an amorphous Ge48Te52 thin film using high-angle annular-dark-field (HAADF) imaging in a scanning transmission electron microscope (STEM). This imaging techniques shows that the film is phase separated on a ∼ 10–20 nm length scale into Te-rich and Ge-rich amorphous domains. The average high-angle-scattered intensity increases as the temperature increases from 106 to 300 K. The contrast between the two domains decreases over this same range indicating that, in addition to the atomic-number (Z) effects on contrast for a given temperature, the temperature-dependent vibrational properties and, hence, phonon-scattering behavior are different for the two different elements in this specimen. Simulations of the HAADF intensity based on an Einstein model using a Debye expression for the mean-square vibrational amplitude give qualitative agreement where temperature-dependent contrast variations are due to differences in atomic number, Debye temperature, and atomic-scattering factor.