Origin of Second Harmonic Generation from individual Silicon Nanowires

We investigate Second Harmonic Generation from individual silicon nanowires and study the influence of resonant optical modes on the far-field nonlinear emission. We find that the polarization of the Second Harmonic has a size-dependent behavior and explain this phenomenon by a combination of different surface and bulk nonlinear susceptibility contributions. We show that the Second Harmonic Generation has an entirely different origin, depending on whether the incident illumination is polarized parallel or perpendicularly to the nanowire axis. The results open perspectives for further geometry-based studies on the origin of Second Harmonic Generation in nanostructures of high-index centrosymmetric semiconductors.Comment: 7 Pages, 4 Figures + 3 Pages, 6 Figures in Appendi

Engineered Near and Far Field Optical Response of Dielectric Nanostuctures using Focused Cylindrical Vector Beams

Near- and far-field optical properties of silicon nanostructures under linear polarization (Gaussian beam), and azimuthally or radially focused cylindrical vector beams are investigated by finite-difference time-domain method (FDTD) in Meep open-source software. A python toolkit allowing FDTD simulations in Meep for using those excitation sources is provided. In addition to the preferential excitation of specific electric or magnetic resonance modes as function of the excitation beam polarization, it is shown in the case of spheroids that shape anisotropy affects the resonance wavelength and the dipole orientation of the magnetic or electric dipole mode. For radial or linear polarization, the electric dipole resonance is split by an anapole mode depending on the spheroid symmetry axis with respect to the electric field orientation. Finally, the optical properties in both far-field (scattering pattern) and near-field (electric and magnetic field hot spots) can be tuned by changing the excitation polarization at a fixed wavelength and selecting properly the spheroid shape and dimensions. These numerical simulations can be extended to more complex shapes, or fabrication-friendly nanostructures such as nanocylinders with circular or elliptic sections

Ultraviolet photon absorption in single- and double-wall carbon nanotubes and peapods: Heating-induced phonon line broadening, wall coupling, and transformation

Ultraviolet photon absorption has been used to heat single- and double-wall carbon nanotubes and peapods in vacuum. By increasing the laser intensity up to 500 mW, a downshift and a broadening of the optical phonons are observed corresponding to a temperature of 1000°C. The UV Raman measurements are free of blackbody radiation. We find that the linewidth changes for the G+ and G− bands differ considerably in single-wall carbon nanotubes. This gives evidence that the phonon decay process is different in axial and radial tube directions. We observe the same intrinsic linewidths of graphite (highly oriented pyrolytic graphite) for the G band in single- and double-wall carbon nanotubes. With increasing temperature, the interaction between the walls is modified for double-wall carbon nanotubes. Ultraviolet photon induced transformations of peapods are found to be different on silica and diamond substrates

Analysis of splicing patterns by pyrosequencing

Several different mRNAs can be produced from a given pre-mRNA by regulated alternative splicing, or as the result of deregulations that may lead to pathological states. Analysing splicing patterns is therefore of importance to describe and understand developmental programs, cellular responses to internal or external cues, or human diseases. We describe here a method, Pyrosequencing Analysis of Splicing Patterns (PASP), that combines RT–PCR and pyrosequencing of PCR products. We demonstrated that: (i) Ratios of two pure RNAs mixed in various proportions were accurately measured by PASP; (ii) PASP can be adapted to virtually any splicing event, including mutually exclusive exons, complex patterns of exon skipping or inclusion, and alternative 3′ terminal exons; (iii) In extracts from different organs, the proportions of RNA isoforms measured by PASP reflected those measured by other methods. The PASP method is therefore reliable for analysing splicing patterns. All steps are done in 96-wells microplates, without gel electrophoresis, opening the way to high-throughput comparisons of RNA from several sources

Postural Performance and Strategy in the Unipedal Stance of Soccer Players at Different Levels of Competition

International audienceContext: Sport training enhances the ability to use somato-sensory and otolithic information, which improves postural capabilities. Postural changes are different according to the sport practiced, but few authors have analyzed subjects' postural performances to discriminate the expertise level among highly skilled athletes within a specific discipline. Objective: To compare the postural performance and the postural strategy between soccer players at different levels of competition (national and regional). Design: Repeated measures with 1 between-groups factor (lev-el of competition: national or regional) and 1 within-groups factor (vision: eyes open or eyes closed). Dependent variables were center of pressure surface area and velocity; total spectral energy; and percentage of low-, medium-, and high-frequency band. Setting: Sports performance laboratory. Patients or Other Participants: Fifteen national male soccer players (age ϭ 24 Ϯ 3 years, height ϭ 179 Ϯ 5 cm, mass ϭ 72 Ϯ 3 kg) and 15 regional male soccer players (age ϭ 23 Ϯ 3 years, height ϭ 174 Ϯ 4 cm, mass ϭ 68 Ϯ 5 kg) participated in the study. Intervention(s): The subjects performed posturographic tests with eyes open and closed. Main Outcome Measure(s): While subjects performed static and dynamic posturographic tests, we measured the center of foot pressure on a force platform. Spatiotemporal center-of-pressure measurements were used to evaluate the postural performance, and a frequency analysis of the center-of-pressure excursions (fast Fourier transform) was conducted to estimate the postural strategy. Results: Within a laboratory task, national soccer players produced better postural performances than regional players and had a different postural strategy. The national players were more stable than the regional players and used proprioception and vision information differently. Conclusions: In the test conditions specific to playing soccer , level of playing experience influenced postural control performance measures and strategies. P ostural regulation is organized in hierarchic and stereotypic patterns 1 and requires the integration of afferent information from the visual, vestibular, and proprioceptive systems. 2 Sport training enhances the ability to use somatosensory and otolithic information, which improves postural capabilities. 3 Postural changes are different according to the sport practiced. 4 For example, judo training leads to greater importance being placed on somatosensory information, whereas dance training results in more attention to visual information. 5 Each sport develops specific postural adaptations that are not transferable to the usual upright postures. 6,7 Indeed, Asseman et al 6 evaluated elite gymnasts in 3 postural conditions: bipedal, unipedal, and hand-stands. The gymnasts who were best in the specific unipedal or handstand conditions were not the same as those who were best in the nonspecific bipedal task. Even though nonspecific tasks such as bipedal stance are typically used in activities of daily living, in athletes, it is more relevant to evaluate postural abilities in specific conditions relative to the particular sport. Soccer requires a unipedal posture to perform different technical movements (eg, shooting, passing). The stability of the supporting foot turns out to be critical to shoot as accurately as possible. Therefore, soccer players' postural control should be evaluated in a unipedal stance to respect the specific conditions of soccer. Previous authors have studied soccer players' postural control in a unipedal stance to reduce the risk of traumatic injuries to the lower extremities 8 or to evaluate the effects of rehabilitative training of the ankle joint. 9,10 However, as far as we know, no study has yet been carried out comparing postural performance and strategy in soccer players of different levels of expertise. The postural performance can be characterized by the ability to minimize postural sway, and the postural strategy corresponds to the preferential involvement of short or long neuronal loops in balance regulation. Our aim was to compare postural performance and strategy in unipedal stance between players at different levels of soccer competition

Structured ZnO-based contacts deposited by non-reactive rf magnetron sputtering on ultra-thin SiO2/Si through a stencil mask

In this paper, we study the localized deposition of ZnO micro and nanostructures deposited by non-reactive rf-magnetron sputtering through a stencil mask on ultra-thin (10 nm) SiO2 layers containing a single plane of silicon nanocrystals (NCs), synthetized by ultra-low energy ion implantation followed by thermal annealing. The localized ZnO-deposited areas are reproducing the exact stencil mask patterns. A resistivity of around 5×10−3 Ω cm is measured on ZnO layer. The as-deposited ZnO material is 97% transparent above the wavelength at 400 nm. ZnO nanostructures can thus be used as transparent electrodes for Si NCs embedded in the gate-oxide of MOS devices

Directional silicon nano-antennas for quantum emitter control designed by evolutionary optimization

We optimize silicon nano-antennas to enhance and steer the emission of local quantum sources. We combine global evolutionary optimization (EO) with frequency domain electrodynamical simulations, and compare design strategies based on resonant and non-resonant building blocks. Specifically, we investigate the performance of models with different degrees of freedom but comparable amount of available material. We find that simpler geometric models allow significantly faster convergence of the optimizer, which, expectedly, comes at the cost of a reduced optical performance. We finally analyze the physical mechanisms underlying the directional emission that also comes with an emission rate enhancement, and find a surprising robustness against perturbations of the source emitter location. This makes the structures highly interesting for actual nano-fabrication. We believe that optimized, all-dielectric silicon nano-antennas have high potential for genuine breakthroughs in a multitude of applications in nanophotonics and quantum technologies.Comment: 8 pages, 6 figure

Kapitza-resistance-like exciton dynamics in atomically flat MoSe2_{2}-WSe2_{2} lateral heterojunction

Being able to control the neutral excitonic flux is a mandatory step for the development of future room-temperature two-dimensional excitonic devices. Semiconducting Monolayer Transition Metal Dichalcogenides (TMD-ML) with extremely robust and mobile excitons are highly attractive in this regard. However, generating an efficient and controlled exciton transport over long distances is a very challenging task. Here we demonstrate that an atomically sharp TMD-ML lateral heterostructure (MoSe$_{2}$-WSe$_{2}$) transforms the isotropic exciton diffusion into a unidirectional excitonic flow through the junction. Using tip-enhanced photoluminescence spectroscopy (TEPL) and a modified exciton transfer model, we show a discontinuity of the exciton density distribution on each side of the interface. We introduce the concept of exciton Kapitza resistance, by analogy with the interfacial thermal resistance referred to as Kapitza resistance. By comparing different heterostructures with or without top hexagonal boron nitride (hBN) layer, we deduce that the transport properties can be controlled, over distances far greater than the junction width, by the exciton density through near-field engineering and/or laser power density. This work provides a new approach for controlling the neutral exciton flow, which is key toward the conception of excitonic devices