Fig. 2

Single-layer h-BN characterization. a Raman spectroscopy is used to determine the single-layer nature of the suspended material. As reported in ref. 9, we find a peak at 1370 cm⁻¹ that corresponds to a monolayer h-BN. Inset Vibrational mode of a h-BN ring for that Raman frequency. b AFM height image of a h-BN material edge before cleaning. The obtained thickness (5 nm) is larger than that expected for single-layer (0.44 nm). The material is covered with polymer contamination that can be removed by oven annealing at 450 °C in air and ozone as seen in c, where areas of 0.5 nm thick are found