Direct Visualization of the Earliest Stages of Crystallization
Direct Visualization of the Earliest Stages of Crystallization
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DOI：
10.1017/s1431927621000441
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发表时间：
2021-05
影响因子：
2.8
通讯作者：
M. Singh;C. Ghosh;B. Miller;C. B. Carter
中科院分区：
文献类型：
--
作者：
M. Singh;C. Ghosh;B. Miller;C. B. Carter
研究结晶的早期阶段需要使用透射电子显微镜（TEM），对于受电子束影响的材料尤其具有挑战性。通常，当以足够高的放大率成像以观察局部结晶度时，电子束的电流密度必须很高才能产生足够的图像对比度。然而，最小化电子剂量是必要的，以减少由光束引起的变化。随着一种灵敏的、高速的、用于TEM的直接探测相机的出现，这种相机可以校正球差，从而有可能在原子尺度上探测结晶的早期阶段。现在可以使用新的计算方法分析低对比度的高质量图像。在本文中，说明了这种方法在Ge2Sb2Te5 （GST-225）相变材料中的结晶，该材料可以经历特别快速的相变并且对电子束敏感。在TEM中直接成像GST-225薄膜（20 nm），并使用Python脚本处理低剂量图像以提取纳米级核的细节。对视频序列中处理过的图像进行定量分析也可以跟踪这些细胞核的生长。
Abstract Investigating the earliest stages of crystallization requires the transmission electron microscope (TEM) and is particularly challenging for materials which can be affected by the electron beam. Typically, when imaging at magnifications high enough to observe local crystallinity, the electron beam's current density must be high to produce adequate image contrast. Yet, minimizing the electron dose is necessary to reduce the changes caused by the beam. With the advent of a sensitive, high-speed, direct-detection camera for a TEM that is corrected for spherical aberration, it is possible to probe the early stages of crystallization at the atomic scale. High-quality images with low contrast can now be analyzed using new computing methods. In the present paper, this approach is illustrated for crystallization in a Ge2Sb2Te5 (GST-225) phase-change material which can undergo particularly rapid phase transformations and is sensitive to the electron beam. A thin (20 nm) film of GST-225 has been directly imaged in the TEM and the low-dose images processed using Python scripting to extract details of the nanoscale nuclei. Quantitative analysis of the processed images in a video sequence also allows the growth of such nuclei to be followed.