151 research outputs found
A near-field study on the transition from localized to propagating plasmons on 2D nano-wedges
In this manuscript we report on a near-feld study of two-dimensional
plasmonic gold nano-wedges using electron energy loss spectroscopy in
combination with scanning transmission electron microscopy, as well as
discontinuous Galerkin time-domain computations. With increasing nano-wedge
size, we observe a transition from localized surface plasmons on small
nano-wedges to non-resonant propagating surface plasmon polaritons on large
nano-wedges. Furthermore we demonstrate that nano-wedges with a groove cut can
support localized as well as propagating plasmons in the same energy range
Interferometric near-field characterization of plasmonic slot waveguides in single- and poly-crystalline gold films
Plasmonic waveguides are a promising platform for integrated nanophotonic
circuits and nanoscale quantum optics. Their use is however often hampered by
the limited propagation length of the guided surface plasmon modes. A detailed
understanding of the influence of the material quality and the waveguide
geometry on the complex mode index is therefore crucial. In this letter, we
present interferometric near-field measurements at telecommunication wavelength
on plasmonic slot waveguides fabricated by focused ion beam milling in single-
and poly-crystalline gold films. We observe a significantly better performance
of the slot waveguides in the single-crystalline gold film for slot widths
below . In contrast for larger slot widths, both gold films
give rise to comparable mode propagation lengths. Our experimental observations
indicate that the nature of the dominant loss channel changes with increasing
gap size from Ohmic to leakage radiation. Our experimental findings are
reproduced by three dimensional numerical calculations.Comment: 4 figure
Improved serial sectioning workflow for multi-beam SEM applications â How to produce the ideal section for Volume EM
Cover Article Research Articles, Systems/Circuits
Double cones are the most common photoreceptor cell type in most avian retinas, but their precise functions remain a mystery. Among their suggested functions are luminance detection, polarized light detection, and light-dependent, radical-pair-based magnetoreception. To better understand the function of double cones, it will be crucial to know how they are connected to the neural network in the avian retina. Here we use serial sectioning, multi-beam scanning electron microscopy (ssmSEM) to investigate double cone anatomy and connectivity with a particular focus on their contacts to other photoreceptor and bipolar cells in the chicken retina. We found that double cones are highly connected with neighbouring double cones and with other photoreceptor cells through telodendria-to-terminal and telodendria-to-telodendria contacts. We also identified 15 bipolar cell types based on their axonal stratifications, photoreceptor contact pattern, soma position, and dendritic and axonal field mosaics. Thirteen of these 15 bipolar cell types contacted at least one or both members of the double cone. All bipolar cells were bi- or multistratified. We also identified surprising contacts between other cone types and between rods and cones. Our data indicate a much more complex connectivity network in the outer plexiform layer of the avian retina than originally expected
Freestanding metasurfaces for optical frequencies
We present freestanding metasurfaces operating at optical frequencies with a
total thickness of only 40nm. The metasurfaces are fabricated by focused
ion beam milling of nanovoids in a carbon film followed by thermal evaporation
of gold and plasma ashing of the carbon film. As a first example, we
demonstrate a metasurface lens based on resonant V-shaped nanovoids with a
focal length of 1mm. The second example is a metasurface phase-plate
consisting of appropriately oriented rectangular nanovoids that transforms a
Gaussian input beam into a Laguerre-Gaussian mode
Adult food choices depend on sex and exposure to early-life stress:Underlying brain circuitry, adipose tissue adaptations and metabolic responses
Mosaic structure in the spines of Holopneustes porossisimus
Sea urchin spines of Holopneustes porossisimus are porous singlecrystals, with the pores being filled with a material rich in carbon,silicon, fluorine and sodium. The magnesian calcite constituting thespine is highly strained. Even though the spines appear to be singlecrystalline on a macroscopic scale, the calcitic material exhibits anextended defect network. We find dislocations as well as rotational andother, not yet identified boundaries. We also observe within spinecalcite a patterned distribution of sulphur. Both distributions, that ofthe defect network and that of sulphur resemble in their pattern to eachother and have a similar mesh size of 50 nm. We conclude from theseobservations that they arise from the growth process of the spine andaccount for the mosaicity within the spine single crystals
Retinal horizontal cells use different synaptic sites for global feedforward and local feedback signaling
In the outer plexiform layer (OPL) of the mouse retina, two types of cone photoreceptors (cones) provide input to more than a dozen types of cone bipolar cells (CBCs). This transmission is modulated by a single horizontal cell (HC) type, the only interneuron in the outer retina. Horizontal cells form feedback synapses with cones and feedforward synapses with CBCs. However, the exact computational role of HCs is still debated. Along with performing global signaling within their laterally coupled network, HCs also provide local, cone-specific feedback. Specifically, it has not been clear which synaptic structures HCs use to provide local feedback to cones and global forward signaling to CBCs. Here, we reconstructed in a serial block-face electron microscopy volume the dendritic trees of five HCs as well as cone axon terminals and CBC dendrites to quantitatively analyze their connectivity. In addition to the fine HC dendritic tips invaginating cone axon terminals, we also identified âbulbsâ, short segments of increased dendritic diameter on the primary dendrites of HCs. These bulbs are located well below the cone axon terminal base and make contact to other cells mostly identified as other HCs or CBCs. Using immunolabeling we show that HC bulbs express vesicular gamma-aminobutyric acid transporters and co-localize with GABA receptor Îł2 subunits. Together, this suggests the existence of two synaptic strata in the mouse OPL, spatially separating cone-specific feedback and feedforward signaling to CBCs. A biophysics-based computational model of a HC dendritic branch supports the hypothesis that the spatial arrangement of synaptic contacts allows simultaneous local feedback and global feedforward signaling
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