Title: Characterising Atomic-Scale Surface Disorder on 2D Materials Using Neutral Atoms Show Chinese title

Title: 使用中性原子表征二维材料的原子尺度表面无序性

Abstract: Two-dimensional (2D) transition metal dichalcogenides (TMDs), such as MoS2, have the potential to be widely used in electronic devices and sensors due to their high carrier mobility and tunable band structure. In 2D TMD devices, surface and interface cleanness can critically impact the performance and reproducibility. Even sample surfaces prepared under ultra-high vacuum (UHV) can be contaminated, causing disorder. On such samples, trace levels of submonolayer contamination remain largely overlooked, and conventional surface characterisation techniques have limited capability in detecting such adsorbates. Here, we apply scanning helium microscopy (SHeM), a non-destructive and ultra-sensitive technique, to investigate the surface cleanness of 2D MoS2. Our measurements reveal that even minute amounts of adventitious carbon induce atomic-scale disorder across MoS2 surfaces, leading to the disappearance of helium diffraction. By tracking helium reflectivity over time, we quantify the decay of surface order across different microscopic regions and find that flat areas are more susceptible to contamination than regions near edges. These findings highlight the fragility of surface order in 2D materials, even under UHV, and establish SHeM as a powerful tool for non-damaging microscopic 2D material cleanness characterisation. The approach offers a new route to wafer-scale characterisation of 2D material quality. Show Chinese abstract

Abstract: 二维（2D）过渡金属二硫属化物（TMDs），如MoS2，由于其高载流子迁移率和可调带结构，有望在电子器件和传感器中得到广泛应用。 在二维TMD器件中，表面和界面的清洁度会严重影响性能和可重复性。 即使在超高真空（UHV）下制备的样品表面也可能受到污染，导致无序。 对于这样的样品，亚单层污染的微量水平大多被忽视，传统表面表征技术在检测这些吸附物方面能力有限。 在此，我们应用扫描氦显微镜（SHeM），一种非破坏性和超灵敏的技术，来研究二维MoS2的表面清洁度。 我们的测量结果表明，即使是微量的杂质碳也会在MoS2表面引起原子尺度的无序，导致氦衍射的消失。 通过跟踪氦反射率随时间的变化，我们量化了不同微观区域表面秩序的衰减，并发现平坦区域比靠近边缘的区域更容易受到污染。 这些发现突显了二维材料表面秩序的脆弱性，即使在UHV条件下也是如此，并确立了SHeM作为一种强大的工具，用于无损的二维材料清洁度显微表征。 该方法为二维材料质量的晶圆级表征提供了一条新途径。