Fig. 4
a Image of a CNT/graphene system obtained at 1585 cm−1. Point no. 1 and point no. 2 (the same areas on a, c, and d are circled and numbered) have the same brightness while corresponding spectra (b) at the resonance frequency show “peak” and “dip,” respectively. c Image of a CNT/graphene system obtained at 1610 cm−1. d The difference image of images a and c. After subtraction procedure separation of negative (e) and positive (f) amplitudes reveal graphene and CNTs respectively (see text). Brighter pixels in the pictures (e, f) correspond to a larger amplitude