All-optical trion generation in single walled carbon nanotubes

We present evidence of all optical trion generation and emission in undoped single walled carbon nanotubes (SWCNTs). Luminescence spectra, recorded on individual SWCNTs over a large CW excitation intensity range, show trion emission peaks red-shifted with respect to the bright exciton peak. Clear chirality dependence is observed for 22 separate SWCNT species, allowing for determination of electron-hole exchange interaction and trion binding energy contributions. Luminescence data together with ultrafast pump probe experiments on chirality sorted bulk samples suggest that exciton-exciton annihilation processes generate dissociated carriers that allow for trion creation upon a subsequent photon absorption event.Comment: 13 pages, 4 figure

High-Throughput Fabrication of Resonant Metamaterials with Ultrasmall Coaxial Apertures via Atomic Layer Lithography

We combine atomic layer lithography and glancing-angle ion polishing to create wafer-scale metamaterials composed of dense arrays of ultrasmall coaxial nanocavities in gold films. This new fabrication scheme makes it possible to shrink the diameter and increase the packing density of 2 nm-gap coaxial resonators, an extreme subwavelength structure first manufactured via atomic layer lithography, both by a factor of 100 with respect to previous studies. We demonstrate that the nonpropagating zeroth-order Fabry-Pérot mode, which possesses slow light-like properties at the cutoff resonance, traps infrared light inside 2 nm gaps (gap volume ∼ λ[superscript]3/10[superscript 6]). Notably, the annular gaps cover only 3% or less of the metal surface, while open-area normalized transmission is as high as 1700% at the epsilon-near-zero (ENZ) condition. The resulting energy accumulation alongside extraordinary optical transmission can benefit applications in nonlinear optics, optical trapping, and surface-enhanced spectroscopies. Furthermore, because the resonance wavelength is independent of the cavity length and dramatically red shifts as the gap size is reduced, large-area arrays can be constructed with λresonance ≫ period, making this fabrication method ideal for manufacturing resonant metamaterials.United States. Air Force Office of Scientific Research (Grants FA9550-12-1-0357 and FA9550-11-1-0141

Magneto-photoluminescence of individual semiconducting single-walled carbon nanotubes

International audienc

Multimodal Photodiode and Phototransistor Device Based on Two-Dimensional Materials

With strong light matter interaction in their atomically thin layered structures, two-dimensional (2D) materials have been widely investigated for optoelectronic applications such as photodetectors and photovoltaic devices. Depending on the aim of optoelectronic applications, different device structures have been employed. Lateral phototransistor structures have been employed for high optical gain, while vertical photodiode structures have been employed for fast response and low power operation. Herein, we demonstrate a multimodal photodetector platform based on 2D materials, combining both a phototransistor and a photodiode and taking the corresponding desirable characteristics from each structure within a single device. In this platform, a multilayered transition-metal dichalcogenide flake is transferred on top of metal electrodes, and a transparent gate electrode is employed. The channel region of the flake between electrodes operates as a phototransistor providing a high gain mode, while the electrode region in the same flake operates as a vertical Schottky photodiode providing a fast response mode. These modes can be dynamically selected by controlling the drain voltage and gate voltage

Stilbenoid chemistry from wine and the genus <em>Vitis</em>, a review

Stilbenoids are of great interest on account of their many promising biological activities, especially in regards to prevention and potential treatment of many chronic diseases associated with aging. The simple stilbenoid monomer, E-resveratrol, has received the most attention due to early in vitro and in vivo biological activities in anti-aging assays. Since Vitis vinifera, primarily in the form of wine, is a major dietary source of these compounds, there is a tremendous amount of research on resveratrol in wine and grapes. Relatively few biological studies have been performed on other stilbenoids from Vitis, primarily due to the lack of commercial sources of many of these compounds. The diverse stilbenoids from this economically important genus are an untapped source of health promoting compounds and because of this, numerous efforts for isolation, identification and quantification of additional stilbenoids have been ongoing. Additionally, due to their role as phytoalexins, stilbenoids play an important role in the defense against pathogens. Therefore, the compounds produced by highly resistant strains are of great interest for the development of resistant crops, natural spray reagents, and as new dietary supplements or pharmaceuticals. Since closely related species are likely to have similar metabolic pathways, a more thorough understanding of the chemical diversity of stilbenoids within Vitis is useful in this endeavor. In this review, we focus on stilbenoids found in the Vitis genus with the aim of aiding future stilbenoid chemistry, particularly in V. vinifera and wine. Additionally, we discuss the efforts to quantify stilbenoids in Vitis, with a focus on non-resveratrol stilbenoid compounds

Nanoscale Block Copolymer Ordering Induced by Visible Interferometric Micropatterning: A Route towards Large Scale Block Copolymer 2D Crystals

Milieux magnétiques pour stockage d'information et processus lithographique basés sur les propriétés d'auto assemblage de copolymères séquencé

Multiparametric MRI of Epiphyseal Cartilage Necrosis (Osteochondrosis) with Histological Validation in a Goat Model.

To evaluate multiple MRI parameters in a surgical model of osteochondrosis (OC) in goats.Focal ischemic lesions of two different sizes were induced in the epiphyseal cartilage of the medial femoral condyles of goats at 4 days of age by surgical transection of cartilage canal blood vessels. Goats were euthanized and specimens harvested 3, 4, 5, 6, 9 and 10 weeks post-op. Ex vivo MRI scans were conducted at 9.4 Tesla for mapping the T1, T2, T1ρ, adiabatic T1ρ and TRAFF relaxation times of articular cartilage, unaffected epiphyseal cartilage, and epiphyseal cartilage within the area of the induced lesion. After MRI scans, safranin O staining was conducted to validate areas of ischemic necrosis induced in the medial femoral condyles of six goats, and to allow comparison of MRI findings with the semi-quantitative proteoglycan assessment in corresponding safranin O-stained histological sections.All relaxation time constants differentiated normal epiphyseal cartilage from lesions of ischemic cartilage necrosis, and the histological staining results confirmed the proteoglycan (PG) loss in the areas of ischemia. In the scanned specimens, all of the measured relaxation time constants were higher in the articular than in the normal epiphyseal cartilage, consistently allowing differentiation between these two tissues.Multiparametric MRI provided a sensitive approach to discriminate between necrotic and viable epiphyseal cartilage and between articular and epiphyseal cartilage, which may be useful for diagnosing and monitoring OC lesions and, potentially, for assessing effectiveness of treatment interventions