97 research outputs found
Epitaxial growth of aligned semiconductor nanowire metamaterials for photonic applications
A novel class of optical metamaterials is presented consisting of high densities of aligned gallium phosphide (GaP) nanowires fabricated using metal-organic vapor phase-epitaxy. Starting from a gold island film as a catalyst for nanowire growth, a sequential combination of vapor-liquid-solid and lateral growth modes is employed to obtain a continuous tunability of the nanowire volume fraction from 7% to over 35%. By choosing different crystallographic orientations of the GaP substrate, metamaterials are designed with different nanowire orientations. The anisotropy of the nanowire building blocks results in strong optical birefringence. Polarization interferometry demonstrates a very large polarization extinction contrast of 4 × 103 combined with a sharp angular resonance which holds promise for optical sensing. Nanowire metamaterials may find applications in photonics, optoelectronics, non-linear and quantum optics, microfluidics, bio-, and gas sensing
Imaging of X-Ray-Excited Emissions from Quantum Dots and Biological Tissue in Whole Mouse
© The Author(s) 2019. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.Optical imaging in clinical and preclinical settings can provide a wealth of biological information, particularly when coupled with targetted nanoparticles, but optical scattering and absorption limit the depth and resolution in both animal and human subjects. Two new hybrid approaches are presented, using the penetrating power of X-rays to increase the depth of optical imaging. Foremost, we demonstrate the excitation by X-rays of quantum-dots (QD) emitting in the near-infrared (NIR), using a clinical X-ray system to map the distribution of QDs at depth in whole mouse. We elicit a clear, spatially-resolved NIR signal from deep organs (brain, liver and kidney) with short (1 second) exposures and tolerable radiation doses that will permit future in vivo applications. Furthermore, X-ray-excited endogenous emission is also detected from whole mouse. The use of keV X-rays to excite emission from QDs and tissue represent novel biomedical imaging technologies, and exploit emerging QDs as optical probes for spatial-temporal molecular imaging at greater depth than previously possible.Peer reviewe
Selective Response of Mesoporous Silicon to Adsorbants with Nitro Groups
We demonstrate that the electronic structure of mesoporous silicon is
affected by adsorption of nitro-based explosive molecules in a
compound-selective manner. This selective response is demonstrated by probing
the adsorption of two nitro-based molecular explosives (trinitrotoluene and
cyclotrimethylenetrinitramine) and a nonexplosive nitro-based arematic molecule
(nitrotoluene) on mesoporous silicon using soft X-ray spec- troscopy. The Si
atoms strongly interact with adsorbed molecules to form Si-O and Si-N bonds, as
evident from the large shifts in emission energy present in the Si L2,3 X-ray
emission spectroscopy (XES) measurements. Furthermore, we find that the energy
gap of mesoporous silicon changes depending on the adsorbant, as estimated from
the Si L2,3 XES and 2p X-ray absorption spectroscopy (XAS) measurements. Our ab
initio molecular dynamics calculations of model compounds suggest that these
changes are due to spontaneous breaking of the nitro groups upon contacting
surface Si atoms. This compound-selective change in electronic structure may
provide a powerful tool for the detection and identification of trace
quantities of airborne explosive molecules.Comment: 27 pages, 9 figure
Chromogenic detection of nerve agent mimics
A new chromogenic protocol for the selective detection of nerve agent mimics is reported.Costero Nieto, Ana Maria, [email protected] ; Gil Grau, Salvador, [email protected] ; Parra Alvarez, Margarita, [email protected]
Controlling interferometric properties of nanoporous anodic aluminium oxide
A study of reflective interference spectroscopy [RIfS] properties of nanoporous anodic aluminium oxide [AAO] with the aim to develop a reliable substrate for label-free optical biosensing is presented. The influence of structural parameters of AAO including pore diameters, inter-pore distance, pore length, and surface modification by deposition of Au, Ag, Cr, Pt, Ni, and TiO2 on the RIfS signal (Fabry-Perot fringe) was explored. AAO with controlled pore dimensions was prepared by electrochemical anodization of aluminium using 0.3 M oxalic acid at different voltages (30 to 70 V) and anodization times (10 to 60 min). Results show the strong influence of pore structures and surface modifications on the interference signal and indicate the importance of optimisation of AAO pore structures for RIfS sensing. The pore length/pore diameter aspect ratio of AAO was identified as a suitable parameter to tune interferometric properties of AAO. Finally, the application of AAO with optimised pore structures for sensing of a surface binding reaction of alkanethiols (mercaptoundecanoic acid) on gold surface is demonstrated
Noise Properties of Rectifying Nanopores
Ion currents through three types of rectifying nanoporous structures are studied and compared for the first time: conically shaped polymer nanopores, glass nanopipettes, and silicon nitride nanopores. Time signals of ion currents are analyzed by power spectrum. We focus on the low-frequency range where the power spectrum magnitude scales with frequency, f, as 1/f. Glass nanopipettes and polymer nanopores exhibit non-equilibrium 1/f noise, thus the normalized power spectrum depends on the voltage polarity and magnitude. In contrast, 1/f noise in rectifying silicon nitride nanopores is of equilibrium character. Various mechanisms underlying the voltage-dependent 1/f noise are explored and discussed, including intrinsic pore wall dynamics, and formation of vortices and non-linear flow patterns in the pore. Experimental data are supported by modeling of ion currents based on the coupled Poisson-Nernst-Planck and Navier Stokes equations. We conclude that the voltage-dependent 1/f noise observed in polymer and glass asymmetric nanopores might result from high and asymmetric electric fields inducing secondary effects in the pore such as enhanced water dissociation
Microcavity effect on dye impregnated porous silicon samples
The properties of porous silicon microcavities impregnated with a laser dye are investigated
by photoluminescence and reflection measurements. The spontaneous emission spectrum of
the optically excited rhodamine 800 is drastically modified by microcavity effects: the peak
emission intensity is increased, the linewidth is narrowed. These results demonstrate that
using all porous silicon or dye-filled microcavities provides new possibilities to improve the
properties of photonic devices
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