Mechanically accessible band engineering via indentation-induced phase transition on two-dimensional layered β-InSe

Abstract

Understanding phase transition in two-dimensional (2D) layered materials is essential for controlled manipulation of their electronic properties. We report a mechanically induced phase transition on 2D layered β-InSe from the hexagonal to monoclinic (MC) phase. The critical pressure required for this transition was determined to be ∼4.03 ± 0.16 GPa using a nanoindentation technique. Using confocal Raman spectroscopy, we verified that a new Raman mode at ∼144 cm−1 can be attributed to MC-InSe. Moreover, the bandgap changes from ∼1.26 to ∼1.88 eV. The MC-InSe was in the form of nanocrystals of diameter ranging from 25 to 35 nm embedded in an amorphous InSe matrix at ambient conditions, which was unambiguously confirmed via high-resolution transmission electron microscopy. The obtained results are discussed based on density function theory calculations. We hope that this study paves the way for the development of novel InSe-based optoelectronic devices with mechanically accessible bandgap engineering.