Beijing Engineering Research Center of Applied Laser Technology, Beijing University of Technology, 100124, Beijing, People's Republic of China.
Nanotechnology. 2020 Mar 13;31(11):115706. doi: 10.1088/1361-6528/ab5a1a. Epub 2019 Nov 21.
Studies have shown that the crystallization phase state of GeSbTe (GST) can be reversibly modulated by femtosecond (fs) laser multiple pulses, which have excellent applications in reconfigurable multi-level operation fields. In this study, the temporal-spatial crystalline evolution dynamics of amorphous GST film is investigated during two fs laser pulses excitation through a pump-probe shadowgraph imaging technique. A quasi-amorphous phase state, which is different from that in the initial as-deposited amorphous GST, is emerged through the first fs laser pulse excitation with a pulse energy lower than crystallization threshold. The experimental results reveal that a crystallization enhancement effect can be induced through the second pulse excitation based on this quasi-amorphous surface structure. The stimulative cluster generated in the quasi-amorphous reduces the amorphous-to-crystalline phase transition threshold for the second fs laser pulse irradiation. The spatially-resolved phase-transition threshold extension effect in a horizontal direction is proposed with the increasing pulse number to summarize the mechanism of the crystallization enhancement effect. The specific-grain-appearance (coarse grains and fine grains representing different phase transition approach) distributed area induced by single and double fs laser pulses irradiation are experimentally demonstrated corresponding to threshold extension theory.
研究表明，飞秒（fs）激光多脉冲可以可逆地调制锗锑碲（GST）的结晶相态，在可重构多级操作领域具有优异的应用。在这项研究中，通过泵浦-探测阴影成像技术研究了非晶态 GST 薄膜在两个飞秒激光脉冲激发下的时空结晶演化动力学。通过低于结晶阈值的第一 fs 激光脉冲激发，出现了一种与初始沉积非晶态 GST 不同的准非晶相态。实验结果表明，基于这种准非晶表面结构，可以通过第二脉冲激发诱导出结晶增强效应。在准非晶中产生的刺激团降低了第二 fs 激光脉冲辐照时非晶到结晶的相变阈值。提出了随着脉冲数的增加，在水平方向上的空间分辨相变阈值扩展效应，以总结结晶增强效应的机制。实验证明了单脉冲和双 fs 激光脉冲辐照诱导的特定晶粒出现（粗晶粒和细晶粒代表不同的相变方法）与阈值扩展理论相对应的分布区域。
