Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, United Kingdom.
ACS Nano. 2015 Apr 28;9(4):3695-703. doi: 10.1021/acsnano.5b00852. Epub 2015 Apr 14.
Synthetic 2D crystal films grown by chemical vapor deposition are typically polycrystalline, and determining grain size within domains and continuous films is crucial for determining their structure. Here we show that grain boundaries in the 2D transition metal dichalcogenide WS2, grown by CVD, can be preferentially oxidized by controlled heating in air. Under our developed conditions, preferential degradation at the grain boundaries causes an increase in their physical size due to oxidation. This increase in size enables their clear and rapid identification using a standard optical microscope. We demonstrate that similar treatments in an Ar environment do no show this effect, confirming that oxidation is the main role in the structural change. Statistical analysis of grain boundary (GB) angles shows dominant mirror formation. Electrical biasing across the GB is shown to lead to changes at the GB and their observation under an optical microscope. Our approach enables high-throughput screening of as-synthesized WS2 domains and continuous films to determine their crystallinity and should enable improvements in future CVD growth of these materials.
通过化学气相沉积生长的合成二维晶体膜通常是多晶的，确定域和连续膜内的晶粒尺寸对于确定其结构至关重要。在这里，我们表明，通过在空气中控制加热，可优先氧化 CVD 生长的二维过渡金属二硫属化物 WS2 中的晶界。在我们开发的条件下，由于氧化，晶界处的优先降解会导致其物理尺寸增加。这种尺寸的增加使得可以使用标准的光学显微镜清晰快速地识别它们。我们证明，在 Ar 环境中的类似处理不会显示出这种效果，这证实了氧化是结构变化的主要作用。晶界（GB）角度的统计分析显示出主导的镜像形成。在 GB 上施加电偏置会导致 GB 发生变化，并在光学显微镜下观察到这些变化。我们的方法可用于对合成的 WS2 域和连续膜进行高通量筛选，以确定其结晶度，并且应该能够改进这些材料的未来 CVD 生长。
