Figure 1

(a) The atomic force microscopy (AFM) image of the exfoliated BP flake, in which the few-layer (FL) and bulk BP layer are marked. (b) The film thickness was directly measured by AFM in a non-contact mode. The measured thickness is 4.50 and 41.78 nm, for FL and bulk BP film, respectively. (c) Raman spectra at 300 K of FL and bulk BP layer. Three active-Raman modes, , B2g, and
are clearly observed.