Rapid thermal thinning of black phosphorus

Abstract

Mass fabrication of two dimensional materials with a desirable thickness using a highly efficient and low-cost approach is ideal for industry applications. In this article, a two-step thermal annealing method is reported to prepare thickness controlled black phosphorus (BP) flakes under moderate temperature within an ultra-short time, and thus, with ultralow power consumption, which can be potentially applied for mass production. The strategy is to sequentially anneal exfoliated BP flakes in the flow of air and a N₂/H₂ mixture. Due to the rapid oxidation rate of BP in air and the relatively low sublimation temperature of oxidized phosphorus, the thermal thinning can be accomplished under temperatures ranging from 330 °C to 360 °C within several minutes, which is much shorter than the traditional thermal annealing method using the direct sublimation approach. A monolayer BP flake with a highly crystalline structure is successfully attained by two-step thermal thinning of a 7-layer BP flake under 340 °C within 2 minutes. The field effect transistor fabricated from the two-step thermally thinned BP flake also exhibits improved performances, further demonstrating it a promising method to produce high quality BP flakes.