Crystallization kinetics of amorphous red phosphorus to black phosphorus by chemical vapor transport

Black phosphorus (BP) is an emerging two-dimensional semiconductor material, which has interesting structural features and broad application prospects in the fields of optoelectronic devices, energy storage, and biomedicine. However, a large amount of evidence is still needed to clarify the potential mechanism for the synthesis of high-quality BP crystals in chemical vapor transport (CVT) reactions. In this work, high-purity BP crystals were synthesized by the CVT method in an amorphous red phosphorus (aRP), Sn and I-2 system. We found that the synthesis of BP experienced the three stage structural transformation of aRP-P-4-Hittorf's phosphorus (HP)-BP. First, the phase transition of aRP and P-4 molecules was reversible in the sublimation stage; then, the P-4 molecules were gradually transformed into the HP structure in the transportation and deposition stage; however, the nucleation of BP quickly inhibited the growth of HP and completed the phase transition quickly; finally, the remaining P-4 molecules were transformed into the BP structure, which promoted the growth of BP crystals. Crystallization kinetics explained the nucleation mechanism during the formation of BP, and the competitive nucleation between HP and BP provided the possibility for the bottom-up preparation of BP nanobelts.

Automated summary

High-purity BP crystals were successfully synthesized by the CVT method in an aRP, Sn, and I-2 system. The synthesis of BP involved a three-stage structural transformation of aRP-P-4-Hittorf's P (HP)-BP, with crystallization kinetics explaining the nucleation mechanism and competitive nucleation between HP and BP enabling the bottom-up preparation of BP nanobelts.