Beyond quantum confinement: excitonic nonlocality in halide perovskite nanoparticles with Mie resonances.

Halide perovskite nanoparticles have demonstrated pronounced quantum confinement properties for nanometer-scale sizes and strong Mie resonances for 102 nm sizes. Here we studied the intermediate sizes where the nonlocal response of the exciton affects the spectral properties of Mie modes. The mechanism of this effect is associated with the fact that excitons in nanoparticles have an additional kinetic energy that is proportional to k2, where k is the wavenumber. Therefore, they possess higher energy than in the case of static excitons. The obtained experimental and theoretical results for MAPbBr3 nanoparticles of various sizes (2-200 nm) show that for particle radii comparable with the Bohr radius of the exciton (a few nanometers in perovskites), the blue-shift of the photoluminescence, scattering, and absorption cross-section peaks related to quantum confinement should be dominating due to the weakness of Mie resonances for such small sizes. On the other hand, for larger sizes (more than 50-100 nm), the influence of Mie modes increases, and the blue shift remains despite the fact that the effect of quantum confinement becomes much weaker.

Light-Emitting Halide Perovskite Nanoantennas.

Nanoantennas made of high-index dielectrics with low losses in visible and infrared frequency ranges have emerged as a novel platform for advanced nanophotonic devices. On the other hand, halide perovskites are known to possess high refractive index, and they support excitons at room temperature with high binding energies and quantum yield of luminescence that makes them very attractive for all-dielectric resonant nanophotonics. Here we employ halide perovskites to create light-emitting nanoantennas with enhanced photoluminescence due to the coupling of their excitons to dipolar and multipolar Mie resonances. We demonstrate that the halide perovskite nanoantennas can emit light in the range of 530-770 nm depending on their composition. We employ a simple technique based on laser ablation of thin films prepared by wet-chemistry methods as a novel cost-effective approach for the fabrication of resonant perovskite nanostructures.

Resonant silicon nanoparticles for enhancement of light absorption and photoluminescence from hybrid perovskite films and metasurfaces.

Recently, hybrid halide perovskites have emerged as one of the most promising types of materials for thin-film photovoltaic and light-emitting devices because of their low-cost and potential for high efficiency. Further boosting their performance without detrimentally increasing the complexity of the architecture is critically important for commercialization. Despite a number of plasmonic nanoparticle based designs having been proposed for solar cell improvement, inherent optical losses of the nanoparticles reduce photoluminescence from perovskites. Here we use low-loss high-refractive-index dielectric (silicon) nanoparticles for improving the optical properties of organo-metallic perovskite (MAPbI3) films and metasurfaces to achieve strong enhancement of photoluminescence as well as useful light absorption. As a result, we observed experimentally a 50% enhancement of photoluminescence intensity from a perovskite layer with silicon nanoparticles and 200% enhancement for a nanoimprinted metasurface with silicon nanoparticles on top. Strong increase in light absorption is also demonstrated and described by theoretical calculations. Since both silicon nanoparticle fabrication/deposition and metasurface nanoimprinting techniques are low-cost, we believe that the developed all-dielectric approach paves the way to novel scalable and highly effective designs of perovskite based metadevices.

Extended carrier lifetimes and diffusion in hybrid perovskites revealed by Hall effect and photoconductivity measurements.

Impressive performance of hybrid perovskite solar cells reported in recent years still awaits a comprehensive understanding of its microscopic origins. In this work, the intrinsic Hall mobility and photocarrier recombination coefficient are directly measured in these materials in steady-state transport studies. The results show that electron-hole recombination and carrier trapping rates in hybrid perovskites are very low. The bimolecular recombination coefficient (10(-11) to 10(-10) cm(3) s(-1)) is found to be on par with that in the best direct-band inorganic semiconductors, even though the intrinsic Hall mobility in hybrid perovskites is considerably lower (up to 60 cm(2) V(-1) s(-1)). Measured here, steady-state carrier lifetimes (of up to 3 ms) and diffusion lengths (as long as 650 µm) are significantly longer than those in high-purity crystalline inorganic semiconductors. We suggest that these experimental findings are consistent with the polaronic nature of charge carriers, resulting from an interaction of charges with methylammonium dipoles.

Nanoimprint of dehydrated PEDOT:PSS for organic photovoltaics.

We demonstrate the fabrication of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) nanogratings by a dehydration-assisted nanoimprint lithographic technique. Dehydration of PEDOT:PSS increases its cohesion to protect the nanostructures formed by nanoimprinting during demolding, resulting in the formation of high quality nanogratings of 60 nm in height, 70 nm in width and 70 nm in spacing (aspect ratio of 0.86). PEDOT:PSS nanogratings are used as hole transport and an electron blocking layer in blended poly(3-hexylthiophene-2,5-diyl) (P3HT):[6,6]-penyl-C61-butyric-acid-methyl-ester (PCBM) organic photovoltaic devices (OPV), showing enhancement of photocurrent and power efficiency in comparison to OPV devices with non-patterned PEDOT:PSS films.

Nonlinear surface waves at the interfaces of left-handed electromagnetic media.

We report the existence of families of nonlinear TE-polarized surface waves propagating along the interface between different conventional and left-handed electromagnetic media as well as between two left-handed media. Both nonlinear/nonlinear and linear/nonlinear interfaces are considered. The constraints for the mode existence are identified and the energy flow associated with the surface modes is calculated.

[An experience of intra-arterial thrombolytic therapy of ischemic stroke in Uzbek republic center of emergency care].

Acute period of stroke is a crucial stage of the disease. The differential therapy in the first 3-6 h from the onset of acute ischemic stroke, so-called "therapeutic window", is of special importance. Obviously, favorable clinical outcome in such patients is largely depends on the early recanalization during "therapeutic window". Presented, are the results of intra-arterial thrombolysis in patients with ischemic stroke, which reveal its high therapeutic effectiveness. Though there was limited clinical evidence for a high effect of recanalization of intra-arterial thrombolysis, this approach opens new perspectives for large scale clinical investigations using endovascular methods in thrombolytic therapy of patients with ischemic stroke.

Charge-induced anisotropic distortions of semiconducting and metallic carbon nanotubes.

To accommodate extra electrons or holes injected into a single-wall carbon nanotube, carbon-carbon bonds adjust their lengths. Resulting changes in carbon-nanotube length as a function of charge injection provide the basis for electromechanical actuators. We show that a key mechanism at low injection levels, modulation of electron kinetic energy, provides nanotube deformations that are both anisotropic and strongly dependent on nanotube structure. Nanotubes can exhibit both expansion and contraction, as well as nonmonotonic size changes. The magnitude of the actuation response of semiconducting carbon nanotubes may be substantially larger than that of graphite.

Anomalous coherent backscattering of light from opal photonic crystals.

We studied coherent backscattering (CBS) of light from opal photonic crystals with incomplete band gaps. We observed a dramatic broadening of the CBS cone for incident angles close to the Bragg condition in the crystals. We modify the conventional CBS theory to incorporate Bragg attenuation resulting from the photonic band structure. By fitting the CBS data with the modified theory, we extract both the disorder-induced light mean-free path and the Bragg attenuation length of the inherent opal photonic crystal.

Electro-optic behavior of liquid-crystal-filled silica opal photonic crystals: effect of liquid-crystal alignment.

Photonic crystals made of nematic liquid crystal intercalated into the void space of close-packed silica spheres (synthetic porous opal) exhibit significant electric-field-induced shift of the optical Bragg reflection peak when the liquid crystal has the long molecular axis oriented parallel to the sphere surfaces. No such effect is observed for comparable fields when the long-axis orientation is normal to the sphere surfaces.

[Somatosensory evoked potentials and the spinal cord conduction velocity in multiple sclerosis]. / Somatosensornye vyzvannye potentsialy i skorost' provedeniia po spinnomu mozgu pri rasseiannom skleroze.

Somatosensory evoked potentials (SSEP) on n. medianus and n. tibialis stimulation were studied in 25 patients with multiple sclerosis (MS) and 30 normals (N). Sensory conduction velocity (SVC) calculated by indirect method using formula of Eisen and Nudelman (1979) in which instead of time parameters of F- and M-responses latencies of the N13 and N21 for hand and leg, respectively, of spinal SSEP was used. Normal spinal cord SCV was 60.8 +/- 1.3 m/s, SCV in MS was 51.9 +/- 10.7 m/s. Extreme dispersion of data in MS is caused by false "normal and paradoxically "increased" SCV values in patients. The causes of false results are analysed. In difference of Eisen and Nudelman methods, the proposed approach allows proper clinical interpretation of the false values and excludes possibility of diagnostic mistakes, as in each case the whole set of the data from cerebral and spinal SSEP is interpreted systematically.

[A case of familial congenital analgesia with autosome-dominant type of inheritance]. / Semeinyi sluchai vrozhdennoi anal'gezii s autosomno-dominantnym tipom nasledovaniia.

Inborn analgesia (IA) is described in 3 members of a family: a 14 month-old girl, hel father and grandfather on the paternal line. Generalized indifference to pain and visceral analgesia with other senses intact was noted in all patients since birth. Profound reflexes, intellectual development, karyotype, motor and sensory nervous excitation propagation velocities, somatosensory evoked potentials were all normal. Notedly, the IA inheritance was found to be autosome-dominant in this family.