期刊
ACS NANO
卷 9, 期 7, 页码 6728-6737出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.5b01965
关键词
phase-change materials; ultrafast electron diffraction; phase transitions; structural dynamics; germanium telluride; Ge-Sb-Te alloy
类别
资金
- National Science Foundation
- Air Force Office of Scientific Research in the Center for Physical Biology at Caltech - Gordon and Betty Moore Foundation
Phase-change materials (PCMs) represent the leading candidates for universal data storage devices, which exploit the large difference in the physical properties of their transitional lattice structures. On a nanoscale, it is fundamental to determine their performance, which is ultimately controlled by the speed limit of transformation among the different structures involved. Here, we report observation with atomic-scale resolution of transient structures of nanofilms of crystalline germanium telluride, a prototypical PCM, using ultrafast electron crystallography. A nonthermal transformation from the initial rhombohedral phase to the cubic structure was found to occur in 12 ps. On a much longer time scale, hundreds of picoseconds, equilibrium heating of the nanofilm is reached, driving the system toward amorphization, provided that high excitation energy is invoked. These results elucidate the elementary steps defining the structural pathway in the transformation of crystalline-to-amorphous phase transitions and describe the essential atomic motions involved when driven by an ultrafast excitation. The establishment of the time scales of the different transient structures, as reported here, permits determination of the possible limit of performance, which is crucial for high-speed recording applications of PCMs.
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