Probing the Strain Direction-Dependent Nonmonotonic Optical Bandgap Modulation of Layered Violet Phosphorus.

Recent theoretical investigations have well predicted strain-induced nonmonotonic optical band gap variations in low-dimensional materials. However, few 2D materials have been experimentally confirmed to exhibit nonmonotonic optical band gap variation under the varying strain. Here, we observe a strain-induced nonmonotonic optical bandgap variation in violet phosphorus nanosheets, as evidenced by photoluminescence spectroscopy, which has been reported in few other 2D materials in our knowledge. The optical bandgap variations are characterized to show the modulation rates of 41 meV/% and -24 meV/% with compression and tensile strains, respectively. Remarkably, first-principle calculations predict and clarify the nonmonotonic modulation accurately, highlighting its relationship with the strain direction-dependent asymmetric distribution of conduction band minimum wavefunctions, demonstrating that this unique nonmonotonic optical bandgap modulation is determined by the distinctive crystal structure of VP. This work provides a deep insight into the design of 2D materials towards optoelectronic and photoelectrochemical applications via strain engineering. This article is protected by copyright. All rights reserved.