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Plasmonic sensors leverage the enhanced near-fields associated with the constituent optical nanoantennas to achieve better sensing performance. The design and fabrication of these optical nanoantennas, especially metallic ones, are thus becoming critical steps to advance this thriving and important field. Low-cost and high-throughput nanofabrication techniques are greatly desirable. In this work, we demonstrate a cost-effective nanofabrication method derived from conventional colloidal lithography. With polystyrene nanospheres and subsequently formed copper (Cu) nanoholes as consecutive deposition masks, disk nanoantennas can be produced in a large-scale fashion with no dry etching required. Furthermore, the nanodisks can be readily tuned via thermal heating of the sacrificial Cu nanohole layers. Finally, we combined the fabricated Au nanodisks with the metal-organic framework material zeolitic imidazolate framework-8 and demonstrated highly sensitive detection of volatile organic compounds. We believe that this nanofabrication method could be readily implemented in a variety of plasmonic sensors.

Since the discovery of Dirac semimetal graphene, two-dimensional (2D) Weyl semimetals (WSMs) have been widely used in low-energy photon detection, polarization imaging, and other systems due to their rich physical characteristics, such as unique nonlinear optical structure, topological nontrivial electronic structure, thickness-tunable bandgap, high electric conductivity, and so on. However, it is difficult to detect the photocurrent signal at room temperature because of its large intrinsic background current. Fortunately, the fabrication of a van der Waals (vdW) heterojunction based on WSM can effectively suppress the background current, greatly extend the detection range, improve the light absorption efficiency, and increase the response speed. Herein, the 2D type-II WSM 1T′-WTe2/bulk GaAs vdW vertical Schottky diode is investigated. Benefiting from the lateral built-in electric field of 260 meV and zero-bandgap structure of 52 nm 1T′-WTe2, it delivers a rectifying ratio over 103 and can respond to the wavelength range of 400–1100 nm. Particularly, when the light power density is 0.02 mW/cm2, the maximum photoresponsivity (R) and specific detectivity (D*) under 808 nm are 298 mA/W and 1.70 × 1012 Jones, respectively. Meanwhile, the Ilight/Idark ratio and response time are 103 and 520/540 μs, respectively. Moreover, an abnormal negative response behavior can be observed with thin WTe2 (11 nm) under 1064 nm illumination because of the open surface bandgap. It is suggested that such 2D WTe2/GaAs mixed-dimensional vdW structure can be extended to other WSM/3D semiconductor junctions and used in fast response and wide broadband spectrum photodetectors' arrays.

A van der Waals heterojunction photodetector has been constructed by vertically stacking a TaIrTe4 flake, a 2D type-II Weyl semimetal, and a WSe2 flake, a typical isotropic 2D semiconductor. Interestingly, the device exhibits a switchable operating mode depending on the direction of the voltage bias. Specifically, under a source-drain bias of −1 V, the device operates in a photovoltaic mode, featuring rapid response rate. Its response/recovery time is down to 22.5/25.1 ms, which is approximately one order of magnitude shorter than that of a pristine WSe2 photodetector (320/360 ms). In contrast, under a source-drain bias of +1 V, the device operates in a photoconductive mode with high photogain. The optimized responsivity reaches 9.1 A/W, and the corresponding external quantum efficiency and detectivity reach 2776% and 3.09 × 1012 Jones, respectively. Furthermore, the effective wavelength range of the TaIrTe4–WSe2 device has been extended to the long-wavelength region as compared to a WSe2 device. Beyond these, by virtue of the highly anisotropic crystal structure of TaIrTe4, the hybrid device exhibits polarized photosensitivity. Its anisotropy ratio reaches 1.72 (1.75) under a voltage bias of +1 (−1 V). On the whole, this research work provides a paradigm for the design and implementation of 2D materials based multifunctional optoelectronic devices.

Rhenium disulfide (ReS2) has drawn much scientific interest as it possesses many distinctive features due to its unusual structure. However, the synthesis of large-area continuous ReS2 films with high crystalline quality is still a challenge to date. Here, chemical vapor deposition (CVD) of the substrate-scale continuous ReS2 film with an atomic thickness and spatial uniformity, as well as its thickness-dependent optoelectronic properties, was reported. By using a space-confined CVD configuration, the ReS2 film on mica with the thickness varying from the monolayer to few layers can be accurately tuned via changing the position of the substrate. HRTEM and AFM images revealed that the grain size of the ReS2 film is on the scale of tens of nanometers. Field effect transistors based on the ReS2 thin film exhibited a high photoresponsivity of 278 mA/W under 405 nm illumination. A decrease in bandgap energy from 1.59 eV in the monolayer to 1.50 eV in bulk and the absorption coefficient as large as 105 × cm−1 in the visible range were found for the ReS2 thin film, suggesting great potential of using ReS2 as an absorber material for photovoltaic application.