Fig. 1

Crystal structures of 2HMoSe₂ and schematics of MoSe₂ film samples a before and b after He⁺ irradiation. The black dashed boxes indicate unit cells of MoSe₂. c Raman spectra of the unirradiated MoSe₂ film (black curve) and MoSe₂ films irradiated with different He⁺ doses: 10¹⁴ (red), 10¹⁵ (green), and 10¹⁶ cm⁻²(blue). Peaks attributed to the mica substrate are labeled “S.” The inset shows that the normalized E¹_2g peaks did not shift. d Normalized A_1g peaks showing gradual red shift with the variation of the ion dose. The inset shows the position and FWHM of the A_1g peaks as a function of the ion dose