Two-step heating synthesis of sub-3 millimeter-sized orthorhombic black phosphorus single crystal by chemical vapor transport reaction method

A facile and green strategy to synthesize orthorhombic black phosphorus (o-BP) single crystals with high yield (~90%) and large size (sub-3 millimeter) is presented. The strategy was based on a two-step heating chemical vapor transport (CVT) reaction method, in which tin and iodine (Sn/I2) was used as mineralization additives and red phosphorus as precursor. Tin phosphide was the only by-product captured at the end of reaction, which greatly simplified the subsequent separation and purification processes of o-BP single crystals. The full width at half maximum (FWHM) of X-ray rocking curve of the as-grown o-BP was 21.65 arc sec, indicating its respectable crystalline quality. A bottom electrode structure field-effect transistor (FET) based on the multilayer phosphorene mechanically exfoliated from the as-grown o-BP single crystal was successfully fabricated through an all-dry transfer technique. Impressively, the FET based on a 6 nm thick multilayer (approximate 12 layers) phosphorene exhibited a record high hole mobility (µ p) of 1744 cm2 V-1 s-1 and an admirable on/off current switching ratio (I on/I off) of ~104, which further proved the high-quality of the o-BP single crystals synthesized by the twostep heating CVT reaction method using the simple Sn/I2/red phosphorus system.