Figure 4: Mapping of CNT diameter and electronic structure using cavity-enhanced hyperspectral imaging.

Example of cavity-enhanced G-band spectra for a semiconducting (a) and a metallic (b) nanotube, taken at the location of the circles shown in c and d. The solid line is a sum of two Lorentzians fitted to the data and the dashed lines are the underlying individual Lorentzians of the G⁻ and G⁺lines, respectively. (c) Spatial map of the evaluated tube diameter from the G⁺/G⁻ line splitting measured on the same area as shown in Fig. 3a. An average diameter of 1.5 nm is observed, in good agreement with atomic force microscopy. (d) Spatial map of the evaluated G⁻ linewidth (full width at half maximum, FWHM). Broad lines are expected for metallic nanotubes, while semiconducting nanotubes typically show narrow lines. Scale bars, 10 μm.