RETRACTED: Two-Dimensional Violet Phosphorus P<sub>11</sub>: A Large Band Gap Phosphorus Allotrope
Gary Cicirello, Mengjing Wang, Quynh P. Sam, James L. Hart, Natalie Williams, Huabing Yin, J. Judy, Jian Wang
Abstract
The discovery of novel large band gap two-dimensional (2D) materials with good stability and high carrier mobility will innovate the next generation of electronics and optoelectronics. A new allotrope of 2D violet phosphorus P 11 was synthesized via a salt flux method in the presence of bismuth. Millimeter-sized crystals of violet-P 11 were collected after removing the salt flux with DI water. From single-crystal X-ray diffraction, the crystal structure of violet-P 11 was determined to be in the monoclinic space group C 2/ c (no. 15) with unit cell parameters of a = 9.166(6) Å, b = 9.121(6) Å, c = 21.803(14)Å, β = 97.638(17)°, and a unit cell volume of 1807(2) Å 3 . The structure differences between violet-P 11, violet-P 21, and fibrous-P 21 are discussed. The violet-P 11 crystals can be mechanically exfoliated down to a few layers (∼6 nm). Photoluminescence and Raman measurements reveal the thickness-dependent nature of violet-P 11, and exfoliated violet-P 11 flakes were stable in ambient air for at least 1 h, exhibiting moderate ambient stability. The bulk violet-P 11 crystals exhibit excellent stability, being stable in ambient air for many days. The optical band gap of violet-P 11 bulk crystals is 2.0(1) eV measured by UV–Vis and electron energy-loss spectroscopy measurements, in agreement with density functional theory calculations which predict that violet-P 11 is a direct band gap semiconductor with band gaps of 1.8 and 1.9 eV for bulk and monolayer, respectively, and with a high carrier mobility. This band gap is the largest among the known single-element 2D layered bulk crystals and thus attractive for various optoelectronic devices.