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Polaritons in layered materials—including van der Waals materials—exhibit hyperbolic dispersion and strong field confinement, which makes them highly attractive for applications including optical nanofocusing, sensing and control of spontaneous emission. Here we report a near-field study of polaritonic Fabry–Perot resonances in linear antennas made of a hyperbolic material. Specifically, we study hyperbolic phonon–polaritons in rectangular waveguide antennas made of hexagonal boron nitride (h-BN, a prototypical van der Waals crystal). Infrared nanospectroscopy and nanoimaging experiments reveal sharp resonances with large quality factors around 100, exhibiting atypical modal near-field patterns that have no analogue in conventional linear antennas. By performing a detailed mode analysis, we can assign the antenna resonances to a single waveguide mode originating from the hybridization of hyperbolic surface phonon–polaritons (Dyakonov polaritons) that propagate along the edges of the h-BN waveguide. Our work establishes the basis for the understanding and design of linear waveguides, resonators, sensors and metasurface elements based on hyperbolic materials and metamaterials. Here, the authors report a near-field study of hyperbolic phonon polaritons in linear antennas made of hexagonal boron nitride. Infrared nanospectroscopy and nanoimaging experiments reveal sharp Fabry-Perot resonances with large quality factors, exhibiting atypical modal behaviour.

Launching and manipulation of polaritons in van der Waals materials offers novel opportunities for field-enhanced molecular spectroscopy and photodetection, among other applications. Particularly, the highly confined hyperbolic phonon polaritons (HPhPs) in h-BN slabs attract growing interest for their capability of guiding light at the nanoscale. An efficient coupling between free space photons and HPhPs is, however, hampered by their large momentum mismatch. Here, we show —by far-field infrared spectroscopy, infrared nanoimaging and numerical simulations— that resonant metallic antennas can efficiently launch HPhPs in thin h-BN slabs. Despite the strong hybridization of HPhPs in the h-BN slab and Fabry-Pérot plasmonic resonances in the metal antenna, the efficiency of launching propagating HPhPs in h-BN by resonant antennas exceeds significantly that of the non-resonant ones. Our results provide fundamental insights into the launching of HPhPs in thin polar slabs by resonant plasmonic antennas, which will be crucial for phonon-polariton based nanophotonic devices. Momentum mismatch prevents efficient coupling between free space photons and hyperbolic phonon polaritons. The authors show, using far-field infrared spectroscopy, infrared nanoimaging and numerical simulations, that resonant metallic antennas can efficiently launch hyperbolic phonon polaritons in thin h-BN slabs.

Photonic crystals (PCs) are periodically patterned dielectrics providing opportunities to shape and slow down the light for processing of optical signals, lasing and spontaneous emission control. Unit cells of conventional PCs are comparable to the wavelength of light and are not suitable for subwavelength scale applications. We engineer a nanoscale hole array in a van der Waals material (h-BN) supporting ultra-confined phonon polaritons (PhPs)—atomic lattice vibrations coupled to electromagnetic fields. Such a hole array represents a polaritonic crystal for mid-infrared frequencies having a unit cell volume of 10 -5 λ 0 3  (with λ 0 being the free-space wavelength), where PhPs form ultra-confined Bloch modes with a remarkably flat dispersion band. The latter leads to both angle- and polarization-independent sharp Bragg resonances, as verified by far-field spectroscopy and near-field optical microscopy. Our findings could lead to novel miniaturized angle- and polarization-independent infrared narrow-band couplers, absorbers and thermal emitters based on van der Waals materials and other thin polar materials. Photonic crystals can steer, shape, and sculpture the flow of photons. Here, the author fabricate a deep-subwavelength photonic crystal slab that supports ultra-confined phonon polaritons, by patterning a nanoscale hole array in h-BN.

Defect engineering has developed over the last decade to become an inimitable tool with which to shape Metal-Organic Framework (MOF) chemistry; part of an evolution in the perception of MOFs from perfect, rigid matrices to dynamic materials whose chemistry is shaped as much by imperfections as it is by their molecular components. However, challenges in defect characterisation and reproducibility persist and, coupled with an as-yet opaque role for synthetic parameters in defect formation, deny chemists the full potential of reticular synthesis. Herein we map the broad implications defects have on MOF properties, highlight key challenges and explore the remarkable ways imperfection enriches MOF chemistry.Engineering defects into metal-organic frameworks is a strategy to grant additional properties but there are still challenges with their reproducibility. Here, this Perspective presents the benefits of defects in metal-organic framework properties and key challenges in the field.

Plasma-activated water (PAW) is a sustainable and innovative alternative for agriculture, especially in controlled environments like greenhouses. Tomato and pepper are key horticultural crops worldwide, with a considerable part of their production in greenhouses. This study examined the effects of PAW irrigation on seed germination, plant growth, and oxidative stress in tomato and bell pepper plants. PAW was activated for up to 15 min using a 1 L capacity plasma reactor based on a glow-type discharge in air with water-cathode. The concentration of nitrogen compounds and the energy efficiency of synthesis obtained with the reactor were moderately high (5.4 mM and 60 nmol/J, respectively). The most notable effects of PAW were observed in bell pepper. The germination percentage in bell pepper increased by up to 26%, while no significant effects were found in tomato seeds. PAW irrigation significantly promoted plant growth, with dry weight increasing by up to 61% in bell pepper and 42% in tomato. Lipid peroxidation results showed no oxidative damage in either crop. The biochemical analysis of antioxidant enzymes (catalase, superoxide dismutase, and guaiacol peroxidase) confirmed that plant defense systems responded adequately to PAW irrigation. These results highlight PAW’s potential as an innovative and eco-friendly alternative in agriculture.

Researchers demonstrate graphene plasmon edge modes at infrared wavelengths. Such modes may offer additional electromagnetic field confinement compared with conventional sheet modes. Plasmons in graphene nanoresonators have many potential applications in photonics and optoelectronics, including room-temperature infrared and terahertz photodetectors, sensors, reflect arrays or modulators 1 , 2 , 3 , 4 , 5 , 6 , 7 . The development of efficient devices will critically depend on precise knowledge and control of the plasmonic modes. Here, we use near-field microscopy 8 , 9 , 10 , 11 between λ 0  = 10–12 μm to excite and image plasmons in tailored disk and rectangular graphene nanoresonators, and observe a rich variety of coexisting Fabry–Perot modes. Disentangling them by a theoretical analysis allows the identification of sheet and edge plasmons, the latter exhibiting mode volumes as small as 10 −8 λ 0 3 . By measuring the dispersion of the edge plasmons we corroborate their superior confinement compared with sheet plasmons, which among others could be applied for efficient 1D coupling of quantum emitters 12 . Our understanding of graphene plasmon images is a key to unprecedented in-depth analysis and verification of plasmonic functionalities in future flatland technologies.

Graphene plasmons promise unique possibilities for controlling light in nanoscale devices and for merging optics with electronics. We developed a versatile platform technology based on resonant optical antennas and conductivity patterns for launching and control of propagating graphene plasmons, an essential step for the development of graphene plasmonic circuits. We launched and focused infrared graphene plasmons with geometrically tailored antennas and observed how they refracted when passing through a two-dimensional conductivity pattern, here a prism-shaped bilayer. To that end, we directly mapped the graphene plasmon wavefronts by means of an imaging method that will be useful in testing future design concepts for nanoscale graphene plasmonic circuits and devices.

We report measurements on magnetization reversal in the Fe8 molecular magnet using fast pulsed magnetic fields of 1.5 kT s−1 and in the temperature range of 0.6-4.1 K. We observe and analyze the temperature dependence of the reversal process, which involves in some cases several resonances. Our experiments allow observation of resonant quantum tunneling of magnetization up to a temperature of ∼4 K. We also observe shifts in the maxima of the relaxation within each resonance field with temperature that suggest the emergence of a thermal instability-a combination of spin reversal and self-heating that may result in a magnetic deflagration process. The results are mainly understood in the framework of thermally-activated quantum tunneling transitions in combination with emergence of a thermal instability.

Background For the first time, almost half a century after its discovery and description, the poorly known endemic gobiid fish Chriolepis lepidota was seen alive at Malpelo Island. Methods During a 12-day expedition on March 2017, 18 specimens of this species were observed and photographed at different depths by means of SCUBA diving. Results Species maximum size and habitat preference are herein documented. Conclusions This sighting represents the first record of the species in the wild. Also, this report increases our knowledge on the ecology and biology of an unknown species.