Phonon Scattering in Monolayer Molybdenum Disulfide under Different Defect Concentrations Based on Temperature-Dependent Raman Spectra

Abstract

Monolayer molybdenum disulfide (MoS2), among other two-dimensional transition-metal dichalcogenides materials, is widely used in a broad range of industries due to its extraordinarily different material properties compared to its bulk counterpart. However, such unique behavior may be greatly affected by its capacity of energy dissipation or heat conduction, largely attributed to its inherent phonon scattering properties. In addition, the phonon properties of MoS2 may be greatly affected by parameters such as temperature, defect concentration, etc., reflected by the Raman spectra evolution of A1g or E2g peaks. In this light, we analyze the combined influences of temperature and defect concentration on phonon scattering for the first time. We specifically elaborate experiments based on the temperature-dependent Raman spectroscopy in order to characterize the effect of defects on phonon scattering properties of MoS2. On this basis, a predictive model is developed for the estimation of phonon lifetime under different defect concentrations that may be served as a brief yet accurate and efficient designer tool in the early stage of defect/phonon engineering. In addition, our study may provide more physical insights toward a comprehensive understanding of the phonon behavior of MoS2, thus paving a way for more practical application potentials enabled by low-dimensional materials.

Excitonic Rydberg States in a Trilayer to Monolayer H2-Aided CVD-Grown Large-Area MoS2 Film with Excellent UV to Visible Broad Band Photodetection Applications

“…For an in-depth understanding of electron–phonon interaction, the temperature dependence of Raman spectra has been investigated for MAr and MArH10 from the 93–303 K temperature range for MAr, MArH5, and MArH10 (Figure a–c). A clear symmetric red shift is evident for both the E 2g 1 and A 1g modes as we move toward higher temperature, revealing a linear dependency of the peak position (ω) of E 2g 1 and A 1g with temperature T, which is perfectly fitted with a solid green line (as shown in Figure d–f) using the common equation where ω 0 is the frequency of vibration at absolute zero temperature and χ is the first-order temperature coefficient of E 2g 1 and A 1g peaks. Other higher order coefficients of temperature are not considered here, as they are significant only at higher temperatures.…”

“…For an in-depth understanding of electron−phonon interaction, the temperature dependence of Raman spectra has been investigated for MAr and MArH10 from the 93−303 K temperature range for MAr, MArH5, and MArH10 (Figure 5a−c). A clear symmetric red shift is evident for both the E 2g 1 and A 1g modes as we move toward higher temperature, revealing a linear dependency of the peak position (ω) of E 2g 1 and A 1g with temperature T, which is perfectly fitted with a solid green line (as shown in Figure 5d−f) using the common equation 50 T T ( )…”

“…Change in FWHM values of E 2g 1 and A 1g modes with temperature has been presented in Figure g–i for MAr, MArH5, and MArH10, respectively. The shift of the FWHM value is associated with higher order anharmonic electron–phonon coupling as expressed by the following equation normalΓ ( T ) = Γ 0 + B ( 1 + 2 normale x − 1 ) where Γ 0 is the inherent FWHM brought on by inhomogeneous strain and phonon confinement and B is the anharmonic constant for three-phonon scattering. The extracted values of B are presented in Table .…”

Explaining Mysterious “Shoulder” Raman Band in TiS2 by Temperature-dependent Anharmonicity and Defects

“…Similarly, we observe a good agreement between all data sets of the full widths at half-maximum (fwhm), provided that temperature-independent constants (of 13 cm –1 for A 1g and 22 cm –1 for E g ) are added to the simulation results (Figure d,e). The necessity for those corrections suggests the presence of other scattering processes, apart from the anharmonicity-induced phonon–phonon interactions: e.g., phonon–defect and polycrystallinity-induced phonon–boundary scattering . The observed discrepancies between the simulated and measured A 1g band parameters at temperatures above 300 K can be attributed primarily to an asymmetric non-Lorentzian shape of the band caused by the high-anharmonicity effects.…”

“…More precise results would be obtained with nonperturbative methods such as a self-consistent approach�as has been recently demonstrated for TiO 2 characterized with partial anharmonicity-induced shifts (due to three-or four-phonon interaction processes) reaching individually ∼100 cm −1 (much larger than in TiS 2 ). 60 To analyze the parameters of the calculated bands quantitively, we fitted the Lorentzian curves to Raman spectra in the vicinities of the E g and the primary A 1g bands (in the case of the A 1g band, the curves were fitted using only the points to the left from the band's maximum)�see gray lines in Figure 4a. The obtained centers of the fitted Lorentzian functions (Figure 4b,c) are consistent with available Raman measurements 15−17 except for the A 1g band's position at temperatures above 300 K.…”