High-pressure lattice dynamics study of few-layer α -In2Se3

Few-layer α-In2Se3 has been studied under pressure by Raman spectroscopy in a diamond anvil cell up to 60 GPa (at room temperature). A combination of AFM and Raman was used to estimate the thickness of the specimens. While few-layer α-In2Se3 shows identical structural evolution with one of the bulk powder-like forms of α-In2Se3 (α→β′→ IV), an abrupt (with respect to the narrow pressure range of the coexistence of the two phases) β′→ IV phase transition (at ≈45 GPa) was observed, in contrast to the case of the bulk specimen where the two phases coexist over a wide pressure range. This is attributed to the difference in the specimen morphology, i.e., single crystal and powder in the case of few-layer and bulk α-In2Se3, respectively. This study documents the significance of the specimen morphology on the observed pressure-induced phase transitions. The methodology developed in this study for performing high-pressure Raman measurements can be applied to other nanodimensional layered materials.