Center of Excellence for Green Nanotechnologies, Joint Centers of Excellence Program , King Abdulaziz City for Science and Technology , Riyadh 11442 , Saudi Arabia.
Materials Measurement Science Division, Material Measurement Laboratory , National Institute of Standards and Technology , Gaithersburg , Maryland 20899 , United States.
ACS Appl Mater Interfaces. 2018 May 30;10(21):18104-18112. doi: 10.1021/acsami.8b04717. Epub 2018 May 17.
Transition metal dichalcogenide two-dimensional materials have attracted significant attention due to their unique optical, mechanical, and electronic properties. For example, molybdenum disulfide (MoS) exhibits a tunable band gap that strongly depends on the numbers of layers, which makes it an attractive material for optoelectronic applications. In addition, recent reports have shown that laser thinning can be used to engineer an MoS monolayer with specific shapes and dimensions. Here, we study laser-thinned MoS in both ambient and vacuum conditions via confocal μ-Raman spectroscopy, imaging X-ray photoelectron spectroscopy (i-XPS), and atomic force microscopy (AFM). For low laser powers in ambient environments, there is insufficient energy to oxidize MoS, which leads to etching and redeposition of amorphous MoS on the nanosheet as confirmed by AFM. At high powers in ambient, the laser energy and oxygen environment enable both MoS nanoparticle formation and nanosheet oxidation as revealed in AFM and i-XPS. At comparable laser power densities in vacuum, MoS oxidation is suppressed and the particle density is reduced as compared to ambient. The extent of nanoparticle formation and nanosheet oxidation in each of these regimes is found to be dependent on the number of layers and laser treatment time. Our results can shed some light on the underlying mechanism of which atomically thin MoS nanosheets exhibit under high incident laser power for future optoelectronic applications.
过渡金属二卤化物二维材料由于其独特的光学、机械和电子特性而引起了广泛关注。例如，二硫化钼 (MoS) 具有可调谐带隙，强烈依赖于层数，这使其成为光电器件应用的有吸引力的材料。此外，最近的报告表明，激光减薄可用于工程设计具有特定形状和尺寸的 MoS 单层。在这里，我们通过共焦 μ-Raman 光谱、成像 X 射线光电子能谱 (i-XPS) 和原子力显微镜 (AFM) 在环境和真空条件下研究了激光减薄的 MoS。在环境中的低激光功率下，没有足够的能量来氧化 MoS，这导致在 AFM 中证实的非晶态 MoS 的蚀刻和再沉积。在环境中的高功率下，激光能量和氧气环境使 MoS 纳米颗粒的形成和纳米片的氧化都得以实现，这在 AFM 和 i-XPS 中得到了揭示。在真空环境中可比的激光功率密度下，与环境相比，MoS 的氧化受到抑制，颗粒密度降低。在这些情况下，纳米颗粒的形成和纳米片的氧化程度都取决于层数和激光处理时间。我们的结果可以为原子薄 MoS 纳米片在未来光电器件应用中在高入射激光功率下的潜在机制提供一些启示。
