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Abstract Low‐symmetry van der Waals materials are promising candidates for the next generation of polarization‐sensitive on‐chip photonics since they do not require lattice matching for growth and integration. Due to their low‐symmetry crystal behavior, such materials exhibit anisotropic and polarization‐dependent optical properties for a wide range of optical frequencies. Here, depolarization characteristics of orthorhombic α‐MoO₃is studied in the visible range. Using polarizers and analyzers, it is demonstrated that α‐MoO₃has negligible loss and that birefringence values as high as 0.15 and 0.12 at 532 nm and 633 nm, respectively, are achievable. With such a high birefringence, quarter‐ and half‐wave plate actions are demonstrated for a 1400 nm α‐MoO₃flake at green (532 nm) and red (633 nm) wavelengths, and polarizability as high as 90% is reported. Furthermore, a system of double α‐MoO₃heterostructure layer is investigated that provides the possibility of tuning polarization as a function of rotation angle between the α‐MoO₃layers. These findings pave the way to the promising future of on‐chip photonic heterostructures and twist‐optics that can dictate the polarization state of light. 

Abstract Exploiting polaritons in natural vdW materials has been successful in achieving extreme light confinement and low-loss optical devices and enabling simplified device integration. Recently, α-MoO₃has been reported as a semiconducting biaxial vdW material capable of sustaining naturally orthogonal in-plane phonon polariton modes in IR. In this study, we investigate the polarization-dependent optical characteristics of cavities formed using α-MoO₃to extend the degrees of freedom in the design of IR photonic components exploiting the in-plane anisotropy of this material. Polarization-dependent absorption over 80% in a multilayer Fabry-Perot structure with α-MoO₃is reported without the need for nanoscale fabrication on the α-MoO₃. We observe coupling between the α-MoO₃optical phonons and the Fabry-Perot cavity resonances. Using cross-polarized reflectance spectroscopy we show that the strong birefringence results in 15% of the total power converted into the orthogonal polarization with respect to incident wave. These findings can open new avenues in the quest for polarization filters and low-loss, integrated planar IR photonics and in dictating polarization control. 

The growth of layered 2D compounds is a key ingredient in finding new phenomena in quantum materials, optoelectronics, and energy conversion. Here, we report SnP₂Se₆, a van der Waals chiral (R3 space group) semiconductor with an indirect bandgap of 1.36 to 1.41 electron volts. Exfoliated SnP₂Se₆flakes are integrated into high-performance field-effect transistors with electron mobilities >100 cm²/Vs and on/off ratios >10⁶at room temperature. Upon excitation at a wavelength of 515.6 nanometer, SnP₂Se₆phototransistors show high gain (>4 × 10⁴) at low intensity (≈10⁻⁶W/cm²) and fast photoresponse (< 5 microsecond) with concurrent gain of ≈52.9 at high intensity (≈56.6 mW/cm²) at a gate voltage of 60 V across 300-nm-thick SiO₂dielectric layer. The combination of high carrier mobility and the non-centrosymmetric crystal structure results in a strong intrinsic bulk photovoltaic effect; under local excitation at normal incidence at 532 nm, short circuit currents exceed 8 mA/cm²at 20.6 W/cm². 

The presence of heavy metals in our water supply poses an immense global public health burden. Heavy metal consumption is tied to increased mortality and a wide range of insidious health outcomes. In recent years, great strides have been made toward nanotechnological approaches for environmental problems, specifically the design of adsorbents to detoxify water, as well as for a related challenge of recovering valuable metals at low concentrations. However, applying nanomaterials at scale and differentiating which nanomaterials are best suited for particular applications can be challenging. Here, we report a methodology for loading nanomaterial coatings onto adsorbent membranes, testing different coatings against one another, and leveraging these materials under a variety of conditions. Our tailored coating for lead remediation, made from manganese-doped goethite nanoparticles, can filter lead from contaminated water to below detectable levels when coated onto a cellulose membrane, and the coated membrane can be recovered and reused for multiple cycles through mild tuning of pH. The Nano-SCHeMe methodology demonstrates a platform approach for effectively deploying nanomaterials for environmental applications and for direct and fair comparisons among these nanomaterials. Moreover, this approach is flexible and expansive in that our coatings have the potential to be applied to a range of sorbents. 

Abstract Material properties strongly depend on the nature and concentration of defects. Characterizing these features may require nano- to atomic-scale resolution to establish structure–property relationships. 4D-STEM, a technique where diffraction patterns are acquired at a grid of points on the sample, provides a versatile method for highlighting defects. Computational analysis of the diffraction patterns with virtual detectors produces images that can map material properties. Here, using multislice simulations, we explore different virtual detectors that can be applied to the diffraction patterns that go beyond the binary response functions that are possible using ordinary STEM detectors. Using graphene and lead titanate as model systems, we investigate the application of virtual detectors to study local order and in particular defects. We find that using a small convergence angle with a rotationally varying detector most efficiently highlights defect signals. With experimental graphene data, we demonstrate the effectiveness of these detectors in characterizing atomic features, including vacancies, as suggested in simulations. Phase and amplitude modification of the electron beam provides another process handle to change image contrast in a 4D-STEM experiment. We demonstrate how tailored electron beams can enhance signals from short-range order and how a vortex beam can be used to characterize local symmetry.