Research On The Growth Of Black Phosphorus Single Crystals And The Electrical Properties Of Its Few Layered Microribbon

Compared with zero-gap of graphene and wide-gap of transition metal sulfides,black phosphorus has a naturally direct and tunable band gap between 0.3eV(bulk)and 2.0eV(monolayer), which depends on its number of layers. In addition, it has unique in-plane anisotropy properties in electrical, optical and thermal field. This advantage makes it be seriously concerned by more and more people. It is also a promising candidate in future semiconductor optoelectronic devices. The application and wide spread of high performance device relies on the controllable synthesis of high quality black phosphorus single crystalline samples. Much disadvantages have been found in the earlier synthetic methods of black phosphorus,such as high cost,low yield, time-consuming and not environmentally friendly of source materials. In addition, the growth mechanism of black phosphorus is still unknown. Given these issues, we designed a series of experiments to investigate the growth mechanism of black phosphorus microribbons via chemical vapor transport(CVT) method in detail,and received some innovative research results as follows,(1 ) A method has been developed to controllably grow black phosphorus with or without temperature gradient. By using this method, we successfully grow high purity black phosphorus mircoribbons with a convert ratio as high as 97%. The overall cost has been dramatically decreased and the growth efficiency has been improved remarkably.(2) The growth mechanism of black phosphorus ribbons has been explained by studying its growth process in detail. The bottom-up growth behaviour of black phosphorus microribbons has been found. Further study by recording the different growth stage of black phosphorus microribbons show that the liquid nucleation sites containing P/Sn/I elements were first formed during cooling stage, through which BP microribbons were formed and crystallographic. The metal Sn and Pb(or their alloys)play an important role in BP's growth. BP's convert ratio depends on the solubility of phosphorus in liquid metals.(3) The exfoliated few layered BP has been made as FETs and their electrical properties have been tested. Due to the natural smooth surface of black phosphorus microribbons oriented along (0k0) cleavage plane, it is easier to be exfoliated compared with the ones grown during a temperature gradient.As a whole, we systematically investigate the growth of black phosphorus and fabrication of few layered BP devices. Also, the direct growth of BP film has been tried. We hope it lay the foundation of investigating BP's rich physical properties in the future.