Direct visualization of out-of-equilibrium structural transformations in atomically thin chalcogenides
Direct visualization of out-of-equilibrium structural transformations in atomically thin chalcogenides
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DOI：
10.1038/s41699-020-0150-2
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发表时间：
2020-02
影响因子：
9.7
通讯作者：
Pawan Kumar;James P. Horwath;Alexandre C. Foucher;Christopher C. Price;Natalia Acero;V. Shenoy;E. Stach;D. Jariwala
中科院分区：
文献类型：
--
作者：
Pawan Kumar;James P. Horwath;Alexandre C. Foucher;Christopher C. Price;Natalia Acero;V. Shenoy;E. Stach;D. Jariwala
二维（2D）过渡金属二硫属化合物（TMDCs）由于其特殊的电子和光学性质一直是人们研究的热点。它们还表现出广泛的结构相，因为原子在单层内可以具有不同的取向，或者由于不同层可以堆叠的方式。在这里，我们报告了一个独特的研究，涉及直接可视化的结构转换在原子薄层高度非平衡热力学条件下。我们探测这些转换在原子尺度上使用实时，像差校正的扫描透射电子显微镜和观察强烈的依赖性所产生的结构和阶段的加热速率和温度。快速加热速率（25 °C/秒）产生高度有序的结晶六方岛，其尺寸小于20 nm，由2 H和3R相的混合物组成。然而，缓慢的加热速率（25 °C/min）产生纳米晶和亚化学计量的非晶区域。这些差异是由不同的硫蒸发和再沉积速率解释的。使用非平衡加热速率从2D原子层实现高度结晶和量子限制的功能，提出了一种新的途径来合成原子薄的，横向受限的纳米结构，并开辟了新的途径，用于调查在受限的尺寸基本的电子现象。
Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been the subject of sustained research interest due to their extraordinary electronic and optical properties. They also exhibit a wide range of structural phases because of the different orientations that the atoms can have within a single layer, or due to the ways that different layers can stack. Here we report a unique study involving direct visualization of structural transformations in atomically thin layers under highly non-equilibrium thermodynamic conditions. We probe these transformations at the atomic scale using real-time, aberration-corrected scanning transmission electron microscopy and observe strong dependence of the resulting structures and phases on both heating rate and temperature. A fast heating rate (25 °C/sec) yields highly ordered crystalline hexagonal islands of sizes of less than 20 nm which are composed of a mixture of 2H and 3R phases. However, a slow heating rate (25 °C/min) yields nanocrystalline and sub-stoichiometric amorphous regions. These differences are explained by different rates of sulfur evaporation and redeposition. The use of non-equilibrium heating rates to achieve highly crystalline and quantum-confined features from 2D atomic layers present a new route to synthesize atomically thin, laterally confined nanostructures and opens new avenues for investigating fundamental electronic phenomena in confined dimensions.