(color online) Effect of laser power on Raman spectra. (a) Raman spectra of monolayer MoS₂ for different values of laser power. Both the E 2g 1 and A_1g modes redshift as the laser power increases. Reproduced with permission from Ref. [64]. Copyright 2014, American Chemical Society. (b) The A_1g mode of WS₂ redshifts with the increasing laser power. Reproduced with permission from Ref. [67]. Copyright 2013, Springer International Publishing. (c) Raman spectra of armchair-edged BP with polarized laser excitation under different temperatures of 24°C, 42°C, 57°C, and 72°C, respectively. The vibrational modes A g 2 , B_2g, and A g 1 are redshifted with the increase of the laser power. (d) Raman shift of the A g 2 mode as a function of temperature for both armchair- and zigzag-edged BP under polarized laser excitation. Open circles and rectangles indicate armchair- and zigzag-edged BP under polarized laser excitation, respectively. Reproduced with permission from Ref. [68]. Copyright 2015, Nature Publishing Group.