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Abstract Optical phase modulators are critical components in integrated photonics, but conventional designs suffer from a trade-off between modulation efficiency and optical loss. Two-dimensional materials like graphene offer strong electro-optic effects, yet their high optical absorption at telecom wavelengths leads to significant insertion losses. Although monolayer transition metal dichalcogenides (TMDs) provide exceptional telecom-band transparency for low-loss electro-refractive response, their practical implementation in phase modulators requires top electrodes to enable vertical electric field tuning, which typically introduces parasitic absorption. Here, we address this challenge by developing hybrid tungsten oxyselenide/graphene (TOS/Gr) electrodes that minimize optical loss while enabling efficient phase modulation in TMD-based devices. The UV-ozone-converted TOS (from WSe₂) acts as a heavy p-type dopant for graphene, making the graphene transparent in the NIR region while enhancing its conductivity. Our complete device integrates a hybrid TOS/graphene transparent electrode with a hexagonal boron nitride dielectric spacer and monolayer WS₂electro-optic material on a SiN microring platform. This achieves a high modulation efficiency of 0.202 V·cm while maintaining an exceptionally low extinction ratio change of just 0.08 dB, demonstrating superior performance compared to modulators employing conventional electrodes. Our breakthrough in near-lossless phase modulation opens new possibilities for energy-efficient optical communications, photonic computing, and fault-tolerant quantum networks. 

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Abstract Strain modulation is a crucial way in engineering nanoscale materials. It is even more important for single photon emitters in layered materials, where strain can trap a delocalized exciton, leading to quantum emission. Herein, we apply strain by using the piezoelectric relaxor ferroelectric substrate. In addition to the strain-tuning of energy and polarization, we report on new observations, including the enhanced polarizability and tunable diamagnetic shift, from the charged localized excitons. As indicated from the polarization-resolved measurements, we attribute the formation of charged localized excitons to selenium vacancy defects. The shallow defect trap, supported by the value of g-factor, further allows for strain-modulation of the electron-hole overlap, hence resulting in the tunable diamagnetic shift. Our results provide a new perspective in integrating layered materials with functional substrates. The contrasting features observed from the charged localized excitons also signify the prospect of charged localized emitters for quantum science and technology. 

Abstract Shaping low-dimensional crystals into precise geometries with low disorder is an outstanding challenge. Here, we present a method to grow single crystals of arbitrary geometry within van der Waals (vdW) materials. By injecting molten material between atomically flat vdW layers within an SiO₂mold, we produce ultraflat and thin crystals of bismuth, tin, and indium that are shaped as hallbars, rings, and nanowires. The crystals are grown fully encapsulated in hexagonal boron nitride, a vdW material, providing protection from oxidation. Varying the depth of the mold allows us to control the crystal thickness from ten to a hundred nanometers. Structural measurements demonstrate large single crystals encompassing the entire mold geometry, while transport measurements show reduced disorder scattering. This approach offers a means to produce complex single-crystal nanostructures without the disorder introduced by post-growth nanofabrication. 

We report a technique for fabricating suspended structures using tilted electron beam lithography. This technique enables the formation of beveled anchor profiles, which significantly increase structural integrity compared to previous techniques. We demonstrate the technique by fabricating a suspended top gate over a graphene device, achieving a breakdown electric field of up to 1.5 V/nm, and induced carrier densities of ∼ 7 × 1012 cm−2, both representing more than 10-fold increase from previous methods. This technique provides a pathway to robust suspended electronic structures capable of withstanding large electrostatic forces common in two-dimensional material systems and nanoelectromechanical devices. 

We fabricate and measure electrically-gated tunnel junctions in which the insulating barrier is a sliding van der Waals ferroelectric made from parallel-stacked bilayer hexagonal boron nitride and the electrodes are single-layer graphene. Despite the nominally-symmetric tunnel-junction structure, these devices can exhibit substantial electroresistance upon reversing the ferroelectric polarization. The magnitude and sign of tunneling electroresistance are tunable by bias and gate voltage. We show that this behavior can be understood within a simple tunneling model that takes into account the quantum capacitance of the graphene electrodes, so that the tunneling densities of states in the electrodes are separately modified as a function of bias and gate voltage.