Unveiling the origin of anomalous low-frequency Raman mode in CVD-grown monolayer WS2

• Published in: Nano research 2021-11, Vol.14 (11), p.4314-4320
• Main Authors: Xiang, Qian, Yue, Xiaofei, Wang, Yanlong, Du, Bin, Chen, Jiajun, Zhang, Shaoqian, Li, Gang, Cong, Chunxiao, Yu, Ting, Li, Qingwei, Jin, Yuqi
• Format: Article
• Language: English
• Subjects: Atomic/Molecular Structure and Spectra; Biomedicine; Biotechnology; Chemical vapor deposition; Chemistry and Materials Science; Condensed Matter Physics; Coupling; Materials Science; Monolayers; Nanotechnology; Raman spectroscopy; Research Article; Spectroscopy; Spectrum analysis; Substrates; Tensile strain; Transition metal compounds; Tungsten; Tungsten disulfide; Wavelengths
• ISSN: 1998-0124; 1998-0000
• DOI: 10.1007/s12274-021-3769-1

Substrates provide the necessary support for scientific explorations of numerous promising features and exciting potential applications in two-dimensional (2D) transition metal dichalcogenides (TMDs). To utilize substrate engineering to alter the properties of 2D TMDs and avoid introducing unwanted adverse effects, various experimental techniques, such as high-frequency Raman spectroscopy, have been used to understand the interactions between 2D TMDs and substrates. However, sample-substrate interaction in 2D TMDs is not yet fully understood due to the lack of systematic studies by techniques that are sensitive to 2D TMD-substrate interaction. This work systematically investigates the interaction between tungsten disulfide (WS 2 ) monolayers and substrates by low-frequency Raman spectroscopy, which is very sensitive to WS 2 -substrate interaction. Strong coupling with substrates is clearly revealed in chemical vapor deposition (CVD)-grown monolayer WS 2 by its low-wavenumber interface mode. It is demonstrated that the enhanced sample-substrate interaction leads to tensile strain on monolayer WS 2 , which is induced during the cooling process of CVD growth and could be released for monolayer WS 2 sample after transfer or fabricated by an annealing-free method such as mechanical exfoliation. These results not only suggest the effectiveness of low-frequency Raman spectroscopy for probing sample-substrate interactions in 2D TMDs, but also provide guidance for the design of high-performance devices with the desired sample-substrate coupling strength based on 2D TMDs.