Raman spectroscopy of atomically thin HfX2 (X=S, Se)

초록

We investigated interlayer modes of few-layer HfX2 (X = S, Se) by using low-frequency micro-Raman spectroscopy with three excitation energies (1.96 eV, 2.33 eV, 2.54 eV) under vacuum condition (similar to 10(-6)Torr). We observed interlayer modes in HfSe2 when the 2.54 eV excitation energy was used. The low-frequency Raman spectra reveal a series of shear and breathing modes (<50 cm(-1)) that are helpful for identifying the number of layers. The in-plane E-g and out-of-plane A(1g) modes of HfSe2 are located at similar to 150 cm(-1) and similar to 200 cm(-1), respectively. In HfS2, in-plane E-g and out-of-plane A(1g) optical phonons are observed at similar to 260 cm(-1) and similar to 337 cm(-1), respectively. The in-plane and out-of-plane force constants of atomically thin HfSe2 are obtained to be 1.87 x 10(19)N m(-3) and 6.55 x 10(19)N m(-3), respectively, by fitting the observed interlayer modes using the linear chain model. These results provide valuable information on materials parameters for device designs using atomically-thin layered HfX2 (X = S, Se).

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