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Defining autism : a guide to brain, biology, and behavior
\"Drawing on the most up-to-date research on autism, this incisive book argues that while there are different causes and variations of autism, there is in fact one biological autism. By examining developmental and genetic factors and investigating lesser known autism-related syndromes, it clears away misconceptions surrounding this complex condition\"-- Back cover.
BOOK
Real-space mapping of tailored sheet and edge plasmons in graphene nanoresonators
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
,
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,
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
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,
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,
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,
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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.
Journal Article
Nanoimaging of resonating hyperbolic polaritons in linear boron nitride antennas
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.
Journal Article
Launching of hyperbolic phonon-polaritons in h-BN slabs by resonant metal plasmonic antennas
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.
Journal Article
Deeply subwavelength phonon-polaritonic crystal made of a van der Waals material
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.
Journal Article
Resolving the electromagnetic mechanism of surface-enhanced light scattering at single hot spots
Light scattering at nanoparticles and molecules can be dramatically enhanced in the 'hot spots' of optical antennas, where the incident light is highly concentrated. Although this effect is widely applied in surface-enhanced optical sensing, spectroscopy and microscopy, the underlying electromagnetic mechanism of the signal enhancement is challenging to trace experimentally. Here we study elastically scattered light from an individual object located in the well-defined hot spot of single antennas, as a new approach to resolve the role of the antenna in the scattering process. We provide experimental evidence that the intensity elastically scattered off the object scales with the fourth power of the local field enhancement provided by the antenna, and that the underlying electromagnetic mechanism is identical to the one commonly accepted in surface-enhanced Raman scattering. We also measure the phase shift of the scattered light, which provides a novel and unambiguous fingerprint of surface-enhanced light scattering.
Light scattering from nanoscale objects can be dramatically enhanced in the proximity of optical antennas. Here, by studying the amplitude and phase of the light scattered from a tip located at the hot spot of an antenna, the underlying electromagnetic mechanism of this enhancement is resolved.
Journal Article
Controlling graphene plasmons with resonant metal antennas and spatial conductivity patterns
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.
Journal Article
Tuning the charge flow between Marcus regimes in an organic thin-film device
Marcus’s theory of electron transfer, initially formulated six decades ago for redox reactions in solution, is now of great importance for very diverse scientific communities. The molecular scale tunability of electronic properties renders organic semiconductor materials in principle an ideal platform to test this theory. However, the demonstration of charge transfer in different Marcus regions requires a precise control over the driving force acting on the charge carriers. Here, we make use of a three-terminal hot-electron molecular transistor, which lets us access unconventional transport regimes. Thanks to the control of the injection energy of hot carriers in the molecular thin film we induce an effective negative differential resistance state that is a direct consequence of the Marcus Inverted Region.
To demonstrate charge transfer in different Marcus regimes in an organic semiconductor, precise tuning of the material’s electronic properties is required. Here, the authors use a three-terminal hot-electron technique to access the Marcus regimes for electronic transport in organic thin films.
Journal Article
The Relationship between Autism and Ehlers-Danlos Syndromes/Hypermobility Spectrum Disorders
Considerable interest has arisen concerning the relationship between hereditary connective tissue disorders such as the Ehlers-Danlos syndromes (EDS)/hypermobility spectrum disorders (HSD) and autism, both in terms of their comorbidity as well as co-occurrence within the same families. This paper reviews our current state of knowledge, as well as highlighting unanswered questions concerning this remarkable patient group, which we hope will attract further scientific interest in coming years. In particular, patients themselves are demanding more research into this growing area of interest, although science has been slow to answer that call. Here, we address the overlap between these two spectrum conditions, including neurobehavioral, psychiatric, and neurological commonalities, shared peripheral neuropathies and neuropathologies, and similar autonomic and immune dysregulation. Together, these data highlight the potential relatedness of these two conditions and suggest that EDS/HSD may represent a subtype of autism.
Journal Article
Ringing Decay of Gamma Oscillations and Transcranial Magnetic Stimulation Therapy in Autism Spectrum Disorder
Research suggest that in autism spectrum disorder (ASD) a disturbance in the coordinated interactions of neurons within local networks gives rise to abnormal patterns of brainwave activity in the gamma bandwidth. Low frequency transcranial magnetic stimulation (TMS) over the dorsolateral prefrontal cortex (DLPFC) has been proven to normalize gamma oscillation abnormalities, executive functions, and repetitive behaviors in high functioning ASD individuals. In this study, gamma frequency oscillations in response to a visual classification task (Kanizsa figures) were analyzed and compared in 19 ASD (ADI-R diagnosed, 14.2 ± 3.61 years old, 5 girls) and 19 (14.8 ± 3.67 years old, 5 girls) age/gender matched neurotypical individuals. The ASD group was treated with low frequency TMS (1.0 Hz, 90% motor threshold, 18 weekly sessions) targeting the DLPFC. In autistic subjects, as compared to neurotypicals, significant differences in event-related gamma oscillations were evident in amplitude (higher) pre-TMS. In addition, recordings after TMS treatment in our autistic subjects revealed a significant reduction in the time period to reach peak amplitude and an increase in the decay phase (settling time). The use of a novel metric for gamma oscillations. i.e., envelope analysis, and measurements of its ringing decay allowed us to characterize the impedance of the originating neuronal circuit. The ringing decay or dampening of gamma oscillations is dependent on the inhibitory tone generated by networks of interneurons. The results suggest that the ringing decay of gamma oscillations may provide a biomarker reflective of the excitatory/inhibitory balance of the cortex and a putative outcome measure for interventions in autism.
Journal Article