Yichao Zou

Developing photodetectors simultaneously exhibiting low energy consumption, suppressed noise, high sensitivity, and broad spectral range has been a long-standing challenge in the optoelectronics field. In this work, high-quality monocrystalline SnS (m-SnS) flakes have been produced via a modified atmospheric pressure vapor deposition method with SnS2 as the precursor. By coupling with silicon, an ultrabroadband photodetector has been achieved, exhibiting photoresponse across 365–2200 nm. The long-wave photosensitivity beyond the intrinsic limits of both Si and SnS has been associated with the interlayer transition, where electrons are excited from the valence band of SnS to the conduction band of Si. Under a self-powered working mode, the m-SnS/Si photodetector achieves the optimal on/off ratio exceeding 104, responsivity of 0.70 A W–1, and detectivity of 2.84 × 1010 Jones. In addition, by virtue of the intrinsic anisotropic crystal structure of SnS, the device manifests pronounced polarization-resolved photoresponse. To consolidate the practical applicability, panchromatic imaging, mixed liquid identification, optical communications, and intelligent agriculture applications have been achieved by exploiting the m-SnS/Si photodetector as a signal receiver. On the whole, this study depicts a new paradigm for the realization of advanced multifunctional optoelectronic systems.

Ion transport across angstrom-scale graphene nanopores is governed by hydration-shell dynamics, yet the kinetic origin of the associated translocation energy barrier remains unresolved. Here, we bridge hydration-shell exchange kinetics and ion translocation energy barriers by resolving water residence events during pore crossing. Ionic conductance measurements establish the angstrom-scale confinement regime of graphene nanopores, within which molecular dynamics simulations are employed to analyze hydration-shell dynamics. We implement a residence-time analysis that decomposes hydration-shell water behavior into confinement-induced dehydration, regular water exchange, and thermal fluctuations. This analysis enables a quantitative determination of the number of hydration waters irreversibly removed during translocation. For both K⁺ and Mg²⁺, the extent of irreversible dehydration increases monotonically with the translocation energy barrier. These results identify hydration-shell exchange kinetics as the molecular-level determinant of ion transport barriers, providing a dynamically grounded and physically transparent picture of ionic transport under extreme nanoconfinement.

Magnetic two‐dimensional materials are a promising platform for novel nano‐electronic device architectures. One such layered crystal is the ferromagnetic semiconductor chromium germanium telluride (Cr ₂ Ge ₂ Te ₆ ) which recently attracted interest due to its potential for spintronics and memory applications. Here we investigate its properties from the structural standpoint using atomic resolution Scanning Transmission Electron Microscopy (STEM) and present the first atomic resolution images down to its monolayer limit. We develop a novel technique that allows one to map the local tilt with unprecedented spatial resolution using only high‐resolution images, enabling mapping of the topography and morphological variation of atomically thin crystals. Using it, we show that the Cr ₂ Ge ₂ Te ₆ monolayer has an unusually large out‐of‐plane rippling, with local tilt variation reaching 20° over few nm length scales. We hypothesize that such a strongly buckled structure originates from both point and extended lattice defects which are more prevalent in monolayer crystals. In addition, we correlate the structural observations with the band structure measurements using Angle‐Resolved Photoemission Spectroscopy (ARPES). We believe that both the atomic scale insights we have gained on Cr ₂ Ge ₂ Te ₆ and our novel approach to nanoscale topography mapping will benefit the development of van der Waals heterostructures in both fundamental and applied research.

Standardisation of data collection and analysis is essential to enable commercialisation of 2D materials in a wide range of technologies. Selected area electron diffraction (SAED) in the transmission electron microscope (TEM) is one of the key methods for distinguishing monolayer from bilayer and few-layer graphene by comparing the 1st and 2nd order diffraction spot intensities. Yet there are many factors that can affect the reliability of data collection and interpretation, causing the measurement of monolayer samples to deviate from the literature boundary condition of I{-2110}/I{1-100}<1 for monolayer graphene. Here we present the results of a large interlaboratory SAED comparison study, where 15 international laboratories measured and analysed nominally identical samples of chemical vapour deposited (CVD) graphene. Large variations were observed in the measured ratios of diffraction spot intensities, with the largest variance associated with poor quality SAED data resulting from poor specimen handling and storage. To inform the reliable determination of monolayer thickness from SAED patterns we provide a description of best practice for specimen handling, TEM operation, data collection and analysis. This work was undertaken within VAMAS Technical Working Area (TWA) 41: Graphene and related 2D materials - Project 9, the results of which have been directly incorporated into ISO/TS 21356-2 for the characterisation of graphene sheets. We find that when this methodology is followed, monolayer graphene can be distinguished from bilayer or thicker material with high confidence where analysis of a single SAED pattern gives I{-2110}/I{1-100}<1.2, even in the absence of precise specimen tilting.

Membranes selective to ions of the same charge are increasingly sought for water waste processing and valuable element recovery. However, while narrow channels are known to be essential, other membrane parameters remain difficult to identify and control. Here we show that Zr⁴⁺, Sn⁴⁺, Ir⁴⁺, and La³⁺ ions intercalated into vermiculite laminate membranes become effectively unexchangeable, creating stable channels, one to two water layers wide, that exhibit robust and tuneable ion selectivity. Ion permeability in these membranes spans five orders of magnitude, following a trend dictated by the ions’ Gibbs free energy of hydration. Unexpectedly, different intercalated ions lead to two distinct monovalent ion selectivity sequences, despite producing channels of identical width. The selectivity instead correlates with the membranes’ stiffness and the entropy of hydration of the intercalated ions. These results introduce an ion selectivity mechanism driven by entropic and mechanical effects, beyond classical size and charge exclusion.

Liquid crystals based on dispersions of two-dimensional (2D) materials have recently been developed for light modulation, exhibiting superior performances compared to conventional organic liquid crystals in a variety of prototypical applications, including coloration, solar-blind communications and blue-light fluoresce. Among the diverse family of 2D liquid crystals, vermiculite-based liquid crystals stand out with advantages in low cost, ease of mass production and environmental sustainability, owing to the high natural abundance of the material. Here, we demonstrated magnetic-field tunable optics with 2D vermiculite dispersions prepared through a facile ‘exchange and redispersion’ method. By exploiting the intrinsic ion-exchange capability of clay minerals, we observed a significantly enhanced magneto-birefringence of the vermiculite dispersion upon replacing the native cations with magnetic ions, manifesting in a doubled Cotton–Mouton coefficient, representing the highest value among previous reports. Magnetization measurements reveal that there is a remarkable magnetic anisotropy in Fe ion-exchanged vermiculite samples in contrast to the isotropic magnetism of pristine vermiculite, which accounts for the observed enhancement of magneto-birefringence. Our findings demonstrate that ion exchange can serve as a simple and effective strategy to modulate the physical and chemical properties of 2D materials’ dispersions, thereby opening avenues for broader and more diverse applications.

This review involves advances in the mechanics of 2D materials, including measurement methods, sample transfer, materials design, and mechanisms covering the impact of defects and thickness for highly-bendable 2D materials.

Unconventional superconductivity, where electron pairing does not involve electron-phonon interactions, is often attributed to magnetic correlations in a material. Well known examples include high-T_c cuprates and uranium-based heavy fermion superconductors. Less explored are unconventional superconductors with strong spin-orbit coupling, where interactions between spin-polarised electrons and external magnetic field can result in multiple superconducting phases and field-induced transitions between them, a rare phenomenon in the superconducting state. Here we report a magnetic-field driven phase transition in β-PdBi₂, a layered non-magnetic superconductor. Our tunnelling spectroscopy on thin PdBi₂ monocrystals incorporated in planar superconductor-insulator-normal metal junctions reveals a marked discontinuity in the superconducting properties with increasing in-plane field, which is consistent with a transition from conventional (s-wave) to nodal pairing. Our theoretical analysis suggests that this phase transition may arise from spin polarisation and spin-momentum locking caused by locally broken inversion symmetry, with p-wave pairing becoming energetically favourable in high fields. Our findings also reconcile earlier predictions of unconventional multigap superconductivity in β-PdBi₂ with previous experiments where only a single s-wave gap could be detected.