X. He, F. Ran, Y. Cheng, H. Li, X. Zhang
King Abdullah University of Science & Technology,
Keywords: WS2, thickness, Raman
Summary:A rapid and undamaged technique to identify the thickness of 2D materials is of great importance, because their physical properties are governed the thickness or the number of layers. Here, we report how to use the optical contrast and Raman spectra in both the low- and high-frequency range to identify the number of layers of the WS2 samples with different thicknesses. With careful chosen substrate and exposure time, the layer number of WS2 can be determined accurately by regular optical microscope. In the high frequency range of Raman spectra, the E12g and A1g modes of WS2 are found to have different dependencies with the sample thickness. In the low frequency range, the shear and breathing modes shows contrary trends, that is, sheer mode stiffens and breathing mode softens with increase layer number. Moreover, the interlayer force constant per unit area of WS2 is obtained from the peak positions of the shear mode using linear-chain model.