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.

二维（2D）过渡金属二硫化碳（TMDC）由于其非凡的电子和光学特性而受到了持续的研究兴趣。由于原子在单层中可能具有不同的方向，或者由于不同层的堆叠方式，它们还显示出广泛的结构相。在这里，我们报告了一项独特的研究，涉及在高度非平衡热力学条件下直接观察原子薄层中结构转变的情况。我们使用像差校正的实时扫描透射电子显微镜，在原子尺度上探测这些转变，并观察到所得结构和相对加热速率和温度的强烈依赖性。快速加热速率（25°C / sec）产生大小小于20 nm的高度有序的晶体六角岛，由2H和3R相的混合物组成。但是，缓慢的加热速率（25°C / min）会产生纳米晶和亚化学计量的非晶区。这些差异可以通过硫蒸发和再沉积的速率不同来解释。利用非平衡加热速率从2D原子层中获得高度结晶和量子受限的特征，为合成原子上薄的，侧向受限的纳米结构提供了一条新途径，并为研究有限尺寸的基本电子现象开辟了新途径。这些差异可以通过硫蒸发和再沉积的速率不同来解释。利用非平衡加热速率从2D原子层中获得高度结晶和量子受限的特征，为合成原子上薄的，侧向受限的纳米结构提供了一条新途径，并为研究有限尺寸的基本电子现象开辟了新途径。这些差异可以通过硫蒸发和再沉积的速率不同来解释。利用非平衡加热速率从2D原子层中获得高度结晶和量子受限的特征，为合成原子上薄的，侧向受限的纳米结构提供了一条新途径，并为研究有限尺寸的基本电子现象开辟了新途径。