title: Excitation mechanism of A1gmode and origin of nonlinear temperature dependence of Raman shift of CVD-grown mono- and few-layer MoS2films.
abstract: MoS2films are grown on SiO2/Si substrates by chemical vapor deposition. The vibrational properties of optical phonons of mono-, bi- and multilayer MoS2are studied by Raman scattering spectroscopy over temperature range from 90 to 540 K with 514.5 nm and 785 nm lasers. The Raman peaks of E2g1 and A1gmodes are observed simultaneously for mono-, bi- and multilayer MoS2with 514.5 nm laser, but only the Raman peak of E2g1 mode is seen for monolayer MoS2as 785 nm laser is used, revealing electron-phonon exchange excitation mechanism of A1gmode for the first time. The Raman shifts of E2g1 and A1gmodes present obvious nonlinear temperature dependence. A semi-quantitative model is used to fit the nonlinear temperature dependence of Raman shifts which matches well to experimental data. Meanwhile, the fitting results reveal that the nonlinear temperature dependence of Raman shifts of E2g1 mode mainly originates from three-phonon anharmonic effect, while one of A1gmode is contributed by stronger three- and weaker four-phonon anharmonic effects cooperatively but two contributions are comparable in intensity.
authors.forename: Tianqi
authors.initials: T
authors.lastname: Yang
authors.forename: Xiaoting
authors.initials: X
authors.lastname: Huang
authors.forename: Hong
authors.initials: H
authors.lastname: Zhou
authors.forename: Guangheng
authors.initials: G
authors.lastname: Wu
authors.forename: Tianshu
authors.initials: T
authors.lastname: Lai