Figure 4: Microscopic and spectroscopic identification of thin franckeite.
From: Exfoliation of natural van der Waals heterostructures to a single unit cell thickness
(a,b) Bright-field and dark-field optical images of a franckeite crystal exfoliated on an SiO2/Si substrate. (c) AFM image of a selected monolayer area indicated by the magenta rectangle in b. All scale bars denote 2 μm. (d) Step-height profile of a monolayer franckeite flake taken from an area indicated by the transparent magenta rectangle in c. (e) Raman spectra of monolayer, bilayer, trilayer and bulk franckeite using a 532 nm laser excitation wavelength at 19 kW cm−2 power density. Spectrum of the underlying Si substrate is subtracted from the thin layer spectra (≤3). (f) Intensity of the three major peaks as a function of thickness.
