AI 中文总结
该研究针对GaAs衬底上外延2H-MoTe2薄膜，探究金属覆盖层的保护效果，明确其厚度依赖的降解特性与光学可及性，为空气敏感的MoTe2等范德华材料的相关表征与处理提供实用指南。
AI 中文摘要
我们研究了在GaAs(111)B衬底上通过分子束外延生长的外延2H-MoTe2薄膜的降解途径与表面保护策略。利用X射线光电子能谱、扫描隧道显微镜、原子力显微镜（AFM）、开尔文探针显微镜（KPM）、拉曼光谱以及密度泛函理论（DFT）计算，我们分析了由Co和Ni覆盖层保护的MoTe2薄膜的结构、化学与电子演化。X射线光电子能谱显示，金属覆盖层可有效抑制短期空气转移过程中的氧化，同时薄膜呈现出明显的富Te近表面组成。然而，随着暴露时间增加，覆盖层的去除难度逐渐增大，这表明界面键合在逐步形成，该过程可能由过量碲和富含缺陷的MoTe2界面促进。原子力显微镜与开尔文探针显微镜揭示了随时间（老化）产生的强烈厚度依赖变化，超薄区域的接触电势演化与较厚薄膜存在显著差异。针对原始和氧化MoTe2基结构的密度泛函理论计算定性支持功函数与态密度对厚度和表面化学的敏感性。通过约20nm厚金属覆盖层进行的拉曼测量表明，此类层可为被保护材料提供部分光学可及性。额外的原子力显微镜与拉曼观测显示，富Te纳米结构可能在激光照射下或样品边缘、机械形成的碎片附近局部形成。这些结果为空气敏感的MoTe2及相关范德华材料的短期保护、转移、剥离与光学表征建立了实用指南。
英文摘要
We investigate degradation and surface protection of epitaxial 2H-MoTe2 films grown by molecular beam epitaxy on GaAs(111)B substrates. Using X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy, atomic force microscopy (AFM), Kelvin probe microscopy (KPM), Raman spectroscopy, and density functional theory (DFT), we examine the structural, chemical, and electronic evolution of MoTe2 protected by Co and Ni capping layers. XPS shows that the metallic caps effectively suppress oxidation during short-term air transfer, while revealing a pronounced Te-rich near-surface composition. With time, the caps become increasingly difficult to remove, suggesting gradual interfacial bonding promoted by excess tellurium and defect-rich MoTe2 interfaces. AFM and KPM reveal pronounced thickness-dependent ageing, with ultrathin regions showing markedly different contact-potential evolution from thicker films. DFT calculations support the sensitivity of work function and density of states to thickness and surface chemistry. Raman measurements through approximately 20 nm thick metallic caps demonstrate partial optical access to the protected material. Additional AFM and Raman observations suggest local formation of Te-rich nanostructures under laser illumination or near mechanically damaged regions. These results provide practical guidelines for protecting, transferring, delaminating, and optically characterizing air-sensitive MoTe2 and related van der Waals materials.
CommentsMain text: 29 pages, 5 figures; supporting information: 4 pages, 3 figures, 2 tables
