Fig. 2: Diverse structure of TMDs and phase transition between them.

a TMDs crystal structure of 2H, 1T, 1T′, \({\mathrm{1T}}^{\prime}_{{\mathrm{or}}}\), and \(1{\mathrm{T}}^{\prime}_{{\mathrm{mo}}}\) phases. b Representative Raman spectra before, during and after transition from the 2H to the 1T′ phase of MoTe₂, as the bias changes from 0 to 4.4 V. The characteristic Raman modes, \({{A}}^{\prime}_1\) and E′ of 2H phase, and A_g mode of 1T′ phase are shown by red, green, and blue dashed lines, respectively. c Gate-dependent Raman intensity ratios, \(F = 1{\mathrm{T}}^{\prime}\left( {A_{\mathrm{g}}} \right)/\left[ {2{\mathrm{H}}\left( A^{\prime}_{1} \right) + 1{\mathrm{T}}^{\prime}\left( {A_{\mathrm{g}}} \right)} \right]\) (y-axis). The black and red curves show increasing and decreasing gate voltage, respectively. b, c Used with permission from Springer Nature⁴⁵. d Raman spectra of pristine 2H-MoS₂ and plasma-treated MoS₂, and new peaks induced by plasma treatment indicate a mixture of 1T and 2H phase MoS₂. The insert shows enlarged Raman spectra of 1T-MoS₂. Image d adapted with permission from Zhu et al.⁴⁶ copyright [2017] American Chemical Society⁴⁷. e The Raman spectra of T′-MoTe₂ at 78 and 296 K obtained with θ = 45° and 0° and vertically polarized scattering photons, where θ is the angle between the polarization of the incident laser light and the crystal a-axis. The yellow bands highlight appearance of new Raman peaks in \({\mathrm{T}}^{\prime}_{{\mathrm{or}}}\) phase, comparing with \({\mathrm{T}}^{\prime}_{{\mathrm{mo}}}\) phase. f Temperature-dependent intensity of the \(m_{{\mathrm{or}}}^{12.6}\) mode during cooling (dark blue) and warming (red) process. Images e, f adapted with permission from Chen et al.⁴¹.