Abstract
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 (MoS2) is critical. Previous approaches for visualizing grains and grain boundaries in MoS2 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 MoS2 that are grown on a silicon dioxide (SiO2) substrate. In our approach, the MoS2 layer on a SiO2/Si substrate is exposed to vapor hydrofluoric acid (VHF), resulting in the differential etching of SiO2 at the MoS2 grain boundaries and SiO2 underneath the MoS2 grains as a result of VHF diffusing through the defects in the MoS2 layer at the grain boundaries. The location of the grain boundaries can be seen by the resulting SiO2 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.
Highlights
Two-dimensional (2D) materials such as molybdenum adpispullificadteion(sM1−o3S2s)uchhavaes been studied for transistors,[4] light use in potential emitters,[5] photodetectors,[6] modulators,[7] pressure sensors,[8] resonators,[9] biosensors,[10] gas sensing,[11] photocatalysis,[12] and electrochemical applications.[13]
Grown MoS2 was composed of domains with continuous MoS2 films without visible grain boundaries (Figure S1a), as well as domains in which there were presumed visible grain boundaries between the adjacent MoS2 grains that were incompletely stitched to each other (Figure S1b)
The typical cEm21g−b1)anddeppicotsitthioensin(3gl8e5-l.a4yecrmM−1o)Sa2n(dFigAu1rgebSa2ned).pFousrittihoenrm(o40re[6], we used Raman spectroscopy to indicate the presence of grain boundaries between the adjacent MoS2 grains that were incompletely stitched to each other (Figure S2b−d)
Summary
Two-dimensional (2D) materials such as molybdenum adpispullificadteion(sM1−o3S2s)uchhavaes been studied for transistors,[4] light use in potential emitters,[5] photodetectors,[6] modulators,[7] pressure sensors,[8] resonators,[9] biosensors,[10] gas sensing,[11] photocatalysis,[12] and electrochemical applications.[13]. The MoS2 grain boundaries can be identified using atomic force microscopy (AFM) by decorating a self-assembled octadecylphosphonic acid monolayer on the MoS2 surface.[34] these techniques are time-consuming, require complex sample preparation procedures, and/or are limited to the characterization of very small areas. Another approach to Received: April 15, 2020 Accepted: July 3, 2020 Published: July 3, 2020. SiO2 is one of the most commonly used growth substrates for large-area CVD-grown MoS2, and our method will be useful in the development, characterization, and optimization of large-area MoS2 synthesis processes
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