Solid-state thinning of violet phosphorus by femtosecond laser and facile recognition of its thickness

Violet Phosphorus (VP), as a burgeoning layered material, has numerous remarkable merits, which strongly depend on its thicknesses. It is significant to control and recognize the thickness in a facile way for widely applications. This paper employed 515 nm femtosecond (fs) laser to control VP thickness in solid state precisely. The VP nanosheets were exfoliated from 500 nm to 80 nm at a span of dozens of nanometers. The mechanism of VP exfoliation was the interaction of laser and VP. The laser decreased the interlayer Van der Waals force and increases the lattice vibration, leading to the decomposition of VP. Various approaches were conducted to characterize the thickness of VP quantitatively and qualitatively. The strict correspondence was established between RGB in optical images and layer number of VP. It can easily obtain the thickness information only by optical images rather than expensive and time-consuming atomic force microscopy (AFM). This work develops a novel approach to exfoliate VP in solid state for high-end applications, and provides a facile thought to quantitative characterize the VP thicknesses in an efficient and low-cost mean.