High pressure lattice dynamics study of few layer α-In2Se3

Few-layer α-In2Se3 has been studied under pressure using 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 the one of the bulk powder-like form of α-In2Se3 ( α → β′ → IV ), an abrupt (with respect to the narrow pressure range ofthe coexistence of the two phases) β ′→ IV phase transition (at ≈ 45 GPa) was observed, in contrast with the case of the bulk specimen where the two phases coexist over a wide pressure range. This is attributed to the difference in specimens morphology, i.e. single crystal and powder in the case of few-layer and bulkα-In2Se3, respectively. This study documents the significance of specimens 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.