Characteristic Plasmon Energies for 2D In₂Se₃ Phase Identification at Nanoscale

Two-dimensional (2D) materials with competing polymorphs offer remarkable potential to switch the associated 2D functionalities for novel device applications. Probing their phase transition and competition mechanisms requires nanoscale characterization techniques that can sensitively detect the nucleation of secondary phases down to single-layer thickness. Here we demonstrate nanoscale phase identification on 2D In2Se3 polymorphs, utilizing their distinct plasmon energies that can be distinguished by electron energy-loss spectroscopy (EELS). The characteristic plasmon energies of In2Se3 polymorphs have been validated by first-principles calculations, and also been successfully applied to reveal phase transitions using in situ EELS. Correlating with in situ X-ray diffraction, we further derive a subtle difference in the valence electron density of In2Se3 polymorphs, consistent with their disparate electronic properties. The nanometer resolution and independence of orientation make plasmon-energy mapping a versatile technique for nanoscale phase identification on 2D materials

A Giant Tunable Piezoelectric Performance in Two‐dimensional In2Se3 via Interface Engineering

Abstract Two‐dimensional (2D) layered piezoelectric materials have attracted enormous interest, which leads to wide applications in stretchable electronic, energy and biomedicine. The piezoelectric properties of 2D materials are mainly modulated by strain, thickness, defect engineering and stacked structure. However, the tunability of piezoelectric properties is typically limited by the small variation within one order of magnitude. It is challenging to obtain high tunable piezoelectric properties of 2D materials. Here, this study reports that the out‐of‐plane piezoelectric properties of 2D van der Waals In2Se3 are significantly manipulated using interface engineering. The variation value of piezoelectric properties is above two orders of magnitude, giving rise to the highest variation value in the 2D piezoelectric materials system. In particular, the 2D materials In2Se3 can be directly fabricated onto silicon substrate, which suggests its compatibility with the state‐of‐the‐art silicon semiconductor technology. Combining the experimental and computational results, this study reveals that the ultrahigh tunable piezoelectric properties result from the interface charge transfer effect. The work opens the door to design and modulate the unprecedented applications of atomic‐scale smart and multifunctional devices