Extended Data Fig. 2: FGT thin-flake device fabrication.

a, A representative optical image of FGT thin flakes exfoliated on top of Al₂O₃ film supported on a sapphire substrate. The image was captured with a CCD camera mounted on an optical microscope operating in transmission mode. b, Cross-sectional profile of optical transmission \({G}_{{\rm{sample}}}^{{\rm{T}}}/{G}_{{\rm{substrate}}}^{{\rm{T}}}\) along the black line in a. Scale bar, 10 μm. c, Layer-dependent optical transmission extracted from the image shown in a. The black line is a fit to the data (blue squares) using the Beer–Lambert law. d, e, Optical images obtained in transmission mode (d) and reflection mode (e) for a typical monolayer sample. f, Device fabricated from the monolayer sample shown in d and e. Electrical contacts to the sample were made with indium microelectrodes. Scale bar, 100 μm. g, h, Optical images obtained in transmission mode (g) and reflection mode (h) for a typical trilayer sample. i, Device fabricated from the trilayer sample shown in g and h. Electrical contacts to the sample were made with thermally evaporated Cr/Au electrodes. Scale bar, 100 μm. The optical transmission of the monolayer and trilayer sample shown in d and g are presented as red dots in c.