Anjan Goswami

Since the initial synthesis of van der Waals 2D indium selenide is first documented in 1957, five distinct polymorphs and their corresponding polytypes are identified. In this study, a unique phase of indium selenide is reported via Scanning Transmission Electron Microscopy (STEM) analysis in the synthesized large‐area films – which is named the phase. The quintuple layers of the phase, characterized by a unique zigzag atomic configuration with unequal indium‐selenium bond lengths from the middle selenium atom, are distinct from any other previously reported phase of indium selenide. Cross‐sectional STEM analysis has revealed that the layers exhibit intralayer shifting. It is found that indium selenide films with layers display electric‐field‐induced switchable polarization characteristic of ferroelectric materials, suggesting the breaking of the inversion symmetry. Experimental observations of nonlinear optical phenomena – Second Harmonic Generation (SHG) responses further support this conclusion. This study reports a phase of indium selenide showing ferroelectricity over large areas at room temperature in a low‐dimensional limit.

Physical processes involving hot electrons, including their generation, transport, injection, and relaxation, have been an extensive area of research. The most widely utilized method for actuating the creation of hot electrons involves the excitation of plasmonic modes followed by their non-radiative decay, channeling the energy into these energetic carriers. Since plasmonics has already evolved into a mature field of scientific exploration, active plasmonic devices serve as an ideal platform to study hot-electron physics. In this Perspective article, we will provide the reader with a comprehensive outline of the physics underlying hot-electron dynamics. Emphasis will be placed on the characteristic timescales involved with the lifecycle of hot electrons, the generation and decay mechanisms of surface plasmon-induced hot electrons, and the material platforms suitable for such a study. Then, we will move on to discuss different temperature models used to explain the evolution of hot electrons and the changes in the optical properties of the materials they are generated in or injected into. Finally, we will focus on some of the interesting optical phenomena occurring at ultrafast timescales mediated by hot-carrier dynamics. Such a discussion is expected to incorporate valuable insights into our understanding of the synergistic relationship between hot-electron dynamics and active plasmonics, thereby paving the way for novel applications involving optoelectronics and energy conversion.