Using in situ electron diffraction techniques, we demonstrate that femtosecond optical excitation above a threshold fluence of the amorphous, as-deposited, phase change material Ge₂Sb₂Te₅ creates large, 100 μm scale single crystals. This is 2 orders of magnitude larger than previously reported grains synthesized via photoexcitation. Transmission electron microscopy shows that these large crystals are dewetted regions with a face-centered cubic structure. Energy-dispersive X-ray spectroscopy indicates that the crystals have the same composition as the initial amorphous phase. We present a theoretical model which shows that this arises from a crossover from a nucleation-dominated crystallization regime to a growth-dominated crystallization regime, and we show that the measured grain size is consistent with Johnson–Mehl–Avrami–Kolmogorov (JMAK) crystallization theory for temperatures near the melting temperature. The ability to grow macroscopic single crystals from an amorphous material, and on arbitrary amorphous substrates, opens up a large area of potential applications, as well as new opportunities for tuning the nucleation, growth, and switching characteristics of phase-change materials.

中文翻译：

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单次飞秒光激发法合成Ge ₂ Sb ₂ Te ₅宏观单晶

使用原位电子衍射技术，我们证明了飞秒光学激发在非晶态，沉积态相变材料Ge ₂ Sb ₂ Te ₅的阈值通量之上产生100μm的大型单晶。这比先前报道的通过光激发合成的晶粒大2个数量级。透射电子显微镜显示，这些大晶体是具有面心立方结构的润湿区域。能量色散X射线光谱法表明该晶体具有与初始非晶相相同的组成。我们提出了一个理论模型，该模型表明这是从成核为主的结晶方式过渡到生长为主的结晶方式的结果，并且我们显示测得的晶粒尺寸与Johnson-Mehl-Avrami-Kolmogorov（JMAK）结晶相一致接近熔化温度的温度理论。从非晶态材料以及在任意非晶态衬底上生长宏观单晶的能力，