Due to the two-dimensional character of graphene, the plasmons sustained by this material have been invariably studied in supported samples so far. The substrate provides stability for graphene but ...often causes undesired interactions (such as dielectric losses, phonon hybridization, and impurity scattering) that compromise the quality and limit the intrinsic flexibility of graphene plasmons. Here, we demonstrate the visualization of plasmons in suspended graphene at room temperature, exhibiting high-quality factor Q~33 and long propagation length > 3 μm. We introduce the graphene suspension height as an effective plasmonic tuning knob that enables in situ change of the dielectric environment and substantially modulates the plasmon wavelength, propagation length, and group velocity. Such active control of micrometer plasmon propagation facilitates near-unity-order modulation of nanoscale energy flow that serves as a plasmonic switch with an on-off ratio above 14. The suspended graphene plasmons possess long propagation length, high tunability, and controllable energy transmission simultaneously, opening up broad horizons for application in nano-photonic devices.
Polaritons are well-established carriers of light, electrical signals, and even heat at the nanoscale in the setting of on-chip devices. However, the goal of achieving practical polaritonic ...manipulation over small distances deeply below the light diffraction limit remains elusive. Here, we implement nanoscale polaritonic in-plane steering and cloaking in a low-loss atomically layered van der Waals (vdW) insulator, α-MoO
, comprising building blocks of customizable stacked and assembled structures. Each block contributes specific characteristics that allow us to steer polaritons along the desired trajectories. Our results introduce a natural materials-based approach for the comprehensive manipulation of nanoscale optical fields, advancing research in the vdW polaritonics domain and on-chip nanophotonic circuits.
The nanocone-shaped carbon nanotubes field-emitter array (NCNA) is a near-ideal field-emitter array that combines the advantages of geometry and material. In contrast to previous methods of ...field-emitter array, laser ablation is a low-cost and clean method that does not require any photolithography or wet chemistry. However, nanocone shapes are hard to achieve through laser ablation due to the micrometer-scale focusing spot. Here, we develop an ultraviolet (UV) laser beam patterning technique that is capable of reliably realizing NCNA with a cone-tip radius of ≈300 nm, utilizing optimized beam focusing and unique carbon nanotube-light interaction properties. The patterned array provided smaller turn-on fields (reduced from 2.6 to 1.6 V/μm) in emitters and supported a higher (increased from 10 to 140 mA/cm
) and more stable emission than their unpatterned counterparts. The present technique may be widely applied in the fabrication of high-performance CNTs field-emitter arrays.
Manipulation of the propagation and energy‐transport characteristics of subwavelength infrared (IR) light fields is critical for the application of nanophotonic devices in photocatalysis, biosensing, ...and thermal management. In this context, metamaterials are useful composite materials, although traditional metal‐based structures are constrained by their weak mid‐IR response, while their associated capabilities for optical propagation and focusing are limited by the size of attainable artificial optical structures and the poor performance of the available active means of control. Herein, a tunable planar focusing device operating in the mid‐IR region is reported by exploiting highly oriented in‐plane hyperbolic phonon polaritons in α‐MoO3. Specifically, an unprecedented change of effective focal length of polariton waves from 0.7 to 7.4 μm is demonstrated by the following three different means of control: the dimension of the device, the employed light frequency, and engineering of phonon–plasmon hybridization. The high confinement characteristics of phonon polaritons in α‐MoO3 permit the focal length and focal spot size to be reduced to 1/15 and 1/33 of the incident wavelength, respectively. In particular, the anisotropic phonon polaritons supported in α‐MoO3 are combined with tunable surface‐plasmon polaritons in graphene to realize in situ and dynamical control of the focusing performance, thus paving the way for phonon‐polariton‐based planar nanophotonic applications.
A planar polariton focusing device based on the natural in‐plane hyperbolic van der Waals material α‐MoO3 is developed, which achieves ultrahigh field compression and wide‐range tunable performance. Moreover, a graphene/α‐MoO3 heterostructure is constructed, which supports hybrid modes consisting of α‐MoO3 phonon polaritons and graphene plasmons to achieve in situ dynamical control of the focal length.
Manipulation of the propagation and energy-transport characteristics of subwavelength infrared (IR) light fields is critical for the application of nanophotonic devices in photocatalysis, biosensing, ...and thermal management. In this context, metamaterials are useful composite materials, although traditional metal-based structures are constrained by their weak mid-IR response, while their associated capabilities for optical propagation and focusing are limited by the size of attainable artificial optical structures and the poor performance of the available active means of control. Herein, a tunable planar focusing device operating in the mid-IR region is reported by exploiting highly oriented in-plane hyperbolic phonon polaritons in α-MoO
. Specifically, an unprecedented change of effective focal length of polariton waves from 0.7 to 7.4 μm is demonstrated by the following three different means of control: the dimension of the device, the employed light frequency, and engineering of phonon-plasmon hybridization. The high confinement characteristics of phonon polaritons in α-MoO
permit the focal length and focal spot size to be reduced to 1/15 and 1/33 of the incident wavelength, respectively. In particular, the anisotropic phonon polaritons supported in α-MoO
are combined with tunable surface-plasmon polaritons in graphene to realize in situ and dynamical control of the focusing performance, thus paving the way for phonon-polariton-based planar nanophotonic applications.
Negative refraction provides an attractive platform to manipulate mid-infrared and terahertz radiation for molecular sensing and thermal radiation applications. However, its implementation based on ...available metamaterials and plasmonic media presents challenges associated with optical losses, limited spatial confinement, and lack of active tunability in this spectral range. Here, we demonstrate gate-tunable negative refraction at mid-infrared frequencies using hybrid topological polaritons in van der Waals heterostructures with high spatial confinement. We experimentally visualize wide-angle negatively-refracted surface polaritons on {\alpha}-MoO3 films partially decorated with graphene, undergoing planar nanoscale focusing down to 1.6% of the free-space wavelength. Our atomically thick heterostructures outperform conventional bulk materials by avoiding scattering losses at the refracting interface while enabling active tunability through electrical gating. We propose polaritonic negative refraction as a promising platform for infrared applications such as electrically tunable super-resolution imaging, nanoscale thermal manipulation, and molecular sensing.
Controlling the charge carrier density provides an efficient way to trigger phase transitions and modulate the optoelectronic properties in natural materials. This approach could be used to induce ...topological transitions in the optical response of photonic systems. Here, we predict a topological transition in the isofrequency dispersion contours of hybrid polaritons supported by a two-dimensional heterostructure consisting of graphene and \(\alpha\)-phase molybdenum trioxide (\(\alpha\)-MoO3). By chemically changing the doping level of graphene, we experimentally demonstrate that the contour topology of polariton isofrequency surfaces transforms from open to closed shapes as a result of doping-dependent polariton hybridization. Moreover, by changing the substrate medium for the heterostructure, the dispersion contour can be further engineered into a rather flattened shape at the topological transition, thus supporting tunable polariton canalization and providing the means to locally control the topology. We demonstrate this idea to achieve extremely subwavelength focusing by using a 1.2-\(\mu\)m-wide silica substrate as a negative refraction lens. Our findings open a disruptive approach toward promising on-chip applications in nanoimaging, optical sensing, and manipulation of nanoscale energy transfer.
•Opposite crab-plant relationships are found between similar saltmarsh ecosystems.•Facilitation on plants may depend on crab burrowing mediated by soil compactness.•Coastal restoration needs to ...consider context-dependent plant-animal interactions.•Plant performance cannot be solely used as indicators of plant-crab interactions.•Inference of plant-crab interactions needs to combine biotic and abiotic indicators.
Increasing effort has been devoted to restoring coastal ecosystems to counteract their degradation globally. Restoration success of coastal ecosystems often relies on harnessing biotic interactions that shape the performance of foundation plant species. Crabs acting as essential ecosystem engineers and consumers are commonly present in coastal saltmarshes. Previous work has focused on the grazing effect of crabs on plants. In line with the idea of top-down control, plant performance (in terms of biomass or height) is often used as indicators of plant-animal interactions. However, crabs could also produce facilitative effects through non-consumptive behavior. It remains unclear if and to what extent the net effect of crabs on coastal plants is dependent on environmental context. Therefore, systematic assessments are needed to test if the reliability of plant performance as an indicator of plant-crab interactions is context-dependent. Here, we conducted field survey in two similar intertidal saltmarsh ecosystems along the Yellow Sea coast, eastern China, and examined the effects of crab burrowing, soil properties, and nutrient availability on plant (Suaeda salsa) performance using multiple regression and structural equation models. We found that crab burrow density was significantly correlated with plant height, which signals strong plant-crab interactions. Surprisingly, we observed opposite signs (positive vs. negative) of plant-crab relationships between the two study sites that have highly similar composition and structure of plant communities. A possible explanation is that soil compactness can mediate crab burrowing behavior, resulting in differential facilitative effects on the plants. Thus, the usefulness of plant height serving as an indicator of plant-crab interactions depends on environmental context to a substantial degree. More comprehensive indicators taking into account soil compactness may facilitate robust inference of plant-crab interactions. Our results highlight landscape-scale spatial heterogeneity and context-dependency of plant-animal interactions in coastal saltmarshes, and provide a useful implication to inferring nuanced biotic interactions using compressive biotic and abiotic indicators in coastal ecosystems.
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