Fig. 1: Mechanical exfoliation and electrical contacting of multilayer BP.

Exemplary optical micrographs of a BP flakes transferred onto the SiO₂-coated silicon substrate. Inset: single BP flake (scale bar 10 μm). b A flake after electrical contact with Ti/Au electrodes in a 4-point configuration. Large electrodes are current-carrying leads, side electrodes are 4-point voltage probes (cf. “Methods”). c Raman spectrum of two flakes of different thicknesses after device processing. Only the common BP signature lines A_g¹, B_2g and A_g² and the intrinsic BP second-order Raman response (ca. 790–920 nm⁻¹ range) are observed (Si line from the substrate as expected at 520 cm⁻¹). No trace of other lines associated with oxidation or degradation is present. The expected positions of theoretically predicted prominent oxidation lines are indicated by the arrows^28,29. d Flake height profile extracted from an atomic force micrograph (inset) after electrical characterisation. The extracted flake height is (15.1 ± 1.8) nm corresponding to (29 ± 3) phosphorene layers.