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(a) An optical image of the free standing graphene sample; (b) Raman spectra of the free standing graphene and the graphene on SiO2/Si substrate (excitation energy is 2.33 eV); (c) Lorentzian fitting of G′ band of the free standing graphene; and (d) energy dispersion of the G′ subbands of the free standing graphene.
The outer (a) and inner (b) scattering processes of G′ band. The influence of trigonal warping effect on the outer and inner processes is illustrated in (c) for low energy level and (d) for high energy level. The outer scattering process is in black lines, and the inner scattering process is in red lines.
Polarized G′ band Raman spectra of the free standing graphene. The incident laser beam is in a fixed polarization and the polarization angles of the analyzer respect to incident polarization are 0° and 90°. The excitation energies are 1.58 eV for (a) and (b), and 3.49 eV for (c) and (d), respectively.
Polarized Raman spectra of the free standing graphene under excitation of 1.96 eV.
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