Fig. 1

Morphological and structural characterization of the black phosphorus flakes. a Transmission electron microscopy (TEM) image of black phosphorus (BP) that was centrifuged at 4000 rpm (BP-4 K), b TEM image of BP centrifuged at 8000 rpm (BP-8K), c high-resolution TEM (HRTEM) image and corresponding selected area electron diffraction (SAED) pattern (inset) of BP-8K, d–f TEM and HRTEM images of black phosphorus quantum dots (BPQDs) with monodispersion and high crystallinity, g Raman spectra of bulk BP (red) and BPQD (blue) on a silicon (Si) substrate. Scale bars, 200 nm (a, b); 5 nm (c); 10 nm⁻¹ inset (c); 100 nm (d); 2 nm (e, f)