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Published July 2015 | Supplemental Material
Journal Article Open

Transient Structures and Possible Limits of Data Recording in Phase-Change Materials


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.

Additional Information

© 2015 American Chemical Society. Received for review April 1, 2015 and accepted May 29, 2015. Publication Date (Web): June 2, 2015. This work was supported by the National Science Foundation and the Air Force Office of Scientific Research in the Center for Physical Biology at Caltech funded by the Gordon and Betty Moore Foundation. The authors gratefully acknowledge the assistance of Dr. W. Liang during the initial phase of UEC experiments. We also thank Drs. S. T. Park and J. S. Baskin for helpful discussions. J.H., G.M.V., and A.H.Z. equally contributed to the research outcome and writing of the paper; J.H. and G.M.V. performed the experiments; Z.Y. and X.M. provided the phase-change materials.

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