Temperature Dependent Phonon Shifts in Single-Layer WS₂

Abstract

Atomically thin two-dimensional tungsten disulfide (WS2) sheets have attracted much attention due to their potential for future nanoelectronic device applications. We report first experimental investigation on temperature dependent Raman spectra of single-layer WS2 prepared using micromechanical exfoliation. Our temperature dependent Raman spectroscopy results shows that the E(1)2g and A1g modes of single-layer WS2 soften as temperature increases from 77 to 623 K. The calculated temperature coefficients of the frequencies of 2LA(M), E(1)2g, A1g, and A1g(M) + LA(M) modes of single-layer WS2 were observed to be -0.008, -0.006, -0.006, and -0.01 cm(-1) K(-1), respectively. The results were explained in terms of a double resonance process which is active in atomically thin nanosheet. This process can also be largely applicable in other emerging single-layer materials.

Highly Anisotropic GeSe Nanosheets for Phototransistors with Ultrahigh Photoresponsivity

“…Notably, the calculated first‐order temperature coefficients of GeSe are larger than those of MoS 2 (A 1g mode: −0.011 cm −1 K −1 )34 and SnSe 2 (A 1g mode: −0.0129 cm −1 K −1 ),30 while comparable to those of BP (A 2g mode: −0.0283 cm −1 K −1 )35 and SnS flake (A g mode: −0.023 cm −1 K −1 ) 36. It has been proposed that the first‐order temperature coefficients of 2D materials are related to the van der Waals interaction between the adjacent layers 29. For SnSe 2 and MoS 2 , the weak interaction between adjacent layers may induce the smaller first‐order temperature coefficients.…”

“…Figure 1d illustrates the temperature‐dependent Raman spectra measured at the temperature range from 80 to 500 K, which is a practical way for uncovering the atomic bonds, thermal expansion, and phonon vibration properties of 2D materials 21, 29, 30, 31, 32. The peak positions around 82.5, 149.2, and 185.9 are corresponding to the A 1 g , B 3g , and A 3 g modes, respectively, in good agreement with the previous reports 13, 33.…”

“…The variation of phonon frequency with temperature may result from the anharmonicity between different atoms at constant pressure including the contraction of the crystal and the thermal expansion. The variation of phonon frequency can be determined by29 $\begin{array}{c}left\\ \hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\begin{array}{c}\mathrm{\Delta }\omega =({\chi }_T+{\chi }_{\mathrm{normalV}})\mathrm{\Delta }T={\left(\frac{\mathrm{normald}\omega }{\mathrm{normald}T}\right)}_V\mathrm{\Delta }T+{\left(\frac{\mathrm{normald}\omega }{\mathrm{normald}V}\right)}_T\mathrm{\Delta }V\\ \begin{array}{c}left\hspace{0.17em}={\left(\frac{\mathrm{d}\omega }{\mathrm{d}T}\right)}_V\mathrm{\Delta }T+{\left(\frac{\mathrm{d}\omega }{\mathrm{d}V}\right)}_T{\left(\frac{\mathrm{d}\omega }{\mathrm{d}T}\right)}_P\mathrm{\Delta }T\\ \end{array}\end{array}\end{array}$where χ = χ T + χ V , in which χ T is the shift of self‐energy induced by the phonon modes coupling and χ V is the shift resulting from volume change caused by thermal expansion 29, 30. Notably, the calculated first‐order temperature coefficients of GeSe are larger than those of MoS 2 (A 1g mode: −0.011 cm −1 K −1 )34 and SnSe 2 (A 1g mode: −0.0129 cm −1 K −1 ),30 while comparable to those of BP (A 2g mode: −0.0283 cm −1 K −1 )35 and SnS flake (A g mode: −0.023 cm −1 K −1 ) 36.…”

Temperature-dependent thermal properties of single-walled carbon nanotube thin films

“…28 ) We chose the Raman technique because it is a simple and reliable method for the characterization of thermal properties of nanomaterials. Thus far, this method has been applied to study the thermal properties of CNTs (individual and films), 10,29 graphene, 27 WS 2 , 30 and MoS 2 . 31,32 The mentioned approach enables calculation of the thermal conductivity (j) and the interfacial thermal conductance per unit area (g) using the local temperatures (depending on the heat transport ability of the material) provided by Raman studies with different heating powers.…”

Enhanced field emission properties of doped graphene nanosheets with layered SnS2

“…0003-6951/2014/105(4)/043109/5/$30.00 V C 2014 AIP Publishing LLC 105, 043109-1 nucleation process for the formation of SnS 2 /RGO hybrids. [28][29][30] The sulfur generated from the dissociated thioacetamide is promoted to form pristine SnS 2 and SnS 2 /RGO during the hydrothermal process. Field emission scanning electron microscopy (FESEM) images (Figs.…”