Hada Masaki, Oba Wataru, Kuwahara Masashi, Katayama Ikufumi, Saiki Toshiharu, Takeda Jun, Nakamura Kazutaka G
Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan.
PRESTO, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan.
Sci Rep. 2015 Aug 28;5:13530. doi: 10.1038/srep13530.
Because of their robust switching capability, chalcogenide glass materials have been used for a wide range of applications, including optical storages devices. These phase transitions are achieved by laser irradiation via thermal processes. Recent studies have suggested the potential of nonthermal phase transitions in the chalcogenide glass material Ge2Sb2Te5 triggered by ultrashort optical pulses; however, a detailed understanding of the amorphization and damage mechanisms governed by nonthermal processes is still lacking. Here we performed ultrafast time-resolved electron diffraction and single-shot optical pump-probe measurements followed by femtosecond near-ultraviolet pulse irradiation to study the structural dynamics of polycrystalline Ge2Sb2Te5. The experimental results present a nonthermal crystal-to-amorphous phase transition of Ge2Sb2Te5 initiated by the displacements of Ge atoms. Above the fluence threshold, we found that the permanent amorphization caused by multi-displacement effects is accompanied by a partial hexagonal crystallization.
由于其强大的开关能力，硫族化物玻璃材料已被广泛应用于包括光存储设备在内的各种领域。这些相变是通过热过程的激光照射实现的。最近的研究表明，超短光脉冲可引发硫族化物玻璃材料Ge2Sb2Te5中的非热相变；然而，对非热过程所控制的非晶化和损伤机制仍缺乏详细了解。在这里，我们进行了超快时间分辨电子衍射和单次光泵浦-探测测量，随后进行飞秒近紫外脉冲照射，以研究多晶Ge2Sb2Te5的结构动力学。实验结果表明，由Ge原子位移引发的Ge2Sb2Te5发生了非热晶态到非晶态的相变。在能量密度阈值以上，我们发现多位移效应导致的永久非晶化伴随着部分六方晶化。
