Fan Xuge, Siris Rita, Hartwig Oliver, Duesberg Georg S, Niklaus Frank
Division of Micro and Nanosystems, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden.
Faculty of Electrical Engineering and Information Technology, EIT2 Universität der Bundeswehr München, 85577 Neubiberg, Germany.
ACS Appl Mater Interfaces. 2020 Jul 29;12(30):34049-34057. doi: 10.1021/acsami.0c06910. Epub 2020 Jul 16.
Grain boundaries in two-dimensional (2D) material layers have an impact on their electrical, optoelectronic, and mechanical properties. Therefore, the availability of simple large-area characterization approaches that can directly visualize grains and grain boundaries in 2D materials such as molybdenum disulfide (MoS) is critical. Previous approaches for visualizing grains and grain boundaries in MoS are typically based on atomic resolution microscopy or optical imaging techniques (i.e., Raman spectroscopy or photoluminescence), which are complex or limited to the characterization of small, micrometer-sized areas. Here, we show a simple approach for an efficient large-area visualization of the grain boundaries in continuous chemical vapor-deposited films and domains of MoS that are grown on a silicon dioxide (SiO) substrate. In our approach, the MoS layer on a SiO/Si substrate is exposed to vapor hydrofluoric acid (VHF), resulting in the differential etching of SiO at the MoS grain boundaries and SiO underneath the MoS grains as a result of VHF diffusing through the defects in the MoS layer at the grain boundaries. The location of the grain boundaries can be seen by the resulting SiO pattern using optical microscopy, scanning electron microscopy, or Raman spectroscopy. This method allows for a simple and rapid evaluation of grain sizes in 2D material films over large areas, thereby potentially facilitating the optimization of synthesis processes and advancing applications of 2D materials in science and technology.
二维（2D）材料层中的晶界会对其电学、光电和机械性能产生影响。因此，能够直接可视化二维材料（如二硫化钼（MoS））中的晶粒和晶界的简单大面积表征方法至关重要。此前用于可视化MoS中晶粒和晶界的方法通常基于原子分辨率显微镜或光学成像技术（即拉曼光谱或光致发光），这些方法复杂或仅限于对小尺寸（微米级）区域的表征。在此，我们展示了一种简单的方法，可对在二氧化硅（SiO）衬底上生长的连续化学气相沉积MoS薄膜和畴中的晶界进行高效大面积可视化。在我们的方法中，SiO/Si衬底上的MoS层暴露于蒸汽氢氟酸（VHF）中，由于VHF通过晶界处MoS层中的缺陷扩散，导致MoS晶界处的SiO和MoS晶粒下方的SiO发生差异蚀刻。通过光学显微镜、扫描电子显微镜或拉曼光谱观察所得的SiO图案，即可看到晶界的位置。该方法能够对二维材料薄膜中的晶粒尺寸进行大面积的简单快速评估，从而有可能促进合成工艺的优化，并推动二维材料在科学技术中的应用。
