Direct observations of recording marks in the phase-change disk

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Atomistic structures of the Ge_2Sb_2Te_5 thin film in the real phase-change disk have been investigated using transmission electron microscopy (TEM). As-deposited amorphous Ge_2Sb_2Te_5 films were laser-irradiated for initialization (crystallization) and recording. Cross-sectional TEM observations revealed that the recording mark was fully amorphized by laser irradiation. A slight difference between the as-deposited and the laser-irradiation-induced amorphous Ge_2Sb_2Te_5 was observed in the intensity profile of nano-beam electron diffraction patterns and atomic pair distribution functions. This difference was attributed to structural relaxation of amorphous Ge_2Sb_2Te_5, which gives rise to the alteration of chemical order.