Fluorescent oxide nanoparticles adapted to active tips for near-field optics

We present a new kind of fluorescent oxide nanoparticles with properties well suited to active-tip based near-field optics. These particles with an average diameter in the range 5-10 nm are produced by Low Energy Cluster Beam Deposition (LECBD) from a YAG:Ce3+ target. They are studied by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), classical photoluminescence, cathodoluminescence and near-field scanning optical microscopy (NSOM). Particles of extreme photo-stability as small as 10 nm in size are observed. These emitters are validated as building blocks of active NSOM tips by coating a standard optical tip with a 10 nm thick layer of YAG:Ce3+ particles directly in the LECBD reactor and by subsequently performing NSOM imaging of test surfaces.Comment: Changes made following Referee's comments; added references; one added figure. See story on this article at: http://nanotechweb.org/cws/article/tech/3606

YAG nano-light sources with high Ce concentration

We investigate the luminescence properties of 10 nm YAG nanoparticles doped with Ce ions at 0.2%, 4% and 13% that are designed as active probes for Scanning Near field Optical Microscopy. They are produced by a physical method without any subsequent treatment, which is imposed by the desired application. The structural analysis reveals the amorphous nature of the particles, which we relate to some compositional defect as indicated by the elemental analysis. The optimum emission is obtained with a doping level of 4%. The emission of the YAG nanoparticles doped at 0.2% is strongly perturbed by the crystalline disorder whereas the 13% doped particles hardly exhibit any luminescence. In the latter case, the presence of Ce4+ ions is confirmed, indicating that the Ce concentration is too high to be incorporated efficiently in YAG nanoparticles in the trivalent state. By a unique procedure combining cathodoluminescence and Rutherford backscattering spectrometry, we demonstrate that the enhancement of the particles luminescence yield is not proportional to the doping concentration, the emission enhancement being larger than the Ce concentration increase. Time-resolved photoluminescence reveals the presence of quenching centres likely related to the crystalline disorder as well as the presence of two distinct Ce ions populations. Eventually, nano-cathodoluminescence indicates that the emission and therefore the distribution of the doping Ce ions and of the defects are homogeneous

Image analysis characterization of multi-walled carbon nanotubes

An original image analysis method is presented to characterize multi-walled carbon nanotubes from transmission electron microscopy images. The analysis is performed in three steps: (i) image preprocessing in order to isolate the nanotubes from the background, (ii) image segmentation, aiming at keeping only the measurable sections of nanotubes, and finally (iii) tube characteristics measurement. The measurement is based on a Lambert-like electron absorption law and is performed on the original gray level image itself. Two geometrical and one physical characteristics are determined for each tube, namely, its outer and inner radius and a linear electron absorption coefficient. The method is illustrated by comparing a pristine and an annealed carbon nanotube samples. The compaction of the tube walls during annealing is shown to result from a lowering of the external radius while the inner radius is left unchanged. (C) 2003 Elsevier Ltd. All rights reserved

Tunable mid IR plasmon in GZO nanocrystals

International audienceDegenerate metal oxide nanoparticles are promising systems to expand the significant achievements of plasmonics into the infrared (IR) range. Among the possible candidates, Ga-doped ZnO nanocrystals are particularly suited for mid IR, considering their wide range of possible doping level and thus of plasmon tuning. In the present work, we report on the tunable mid IR plasmon induced in degenerate Ga-doped ZnO nanocrystals. The nanocrystals are produced by a plasma expansion and exhibit unprotected surfaces. Tuning the Ga concentration allows tuning the localized surface plasmon resonance. Moreover, the plasmon resonance is characterized by a large damping. By comparing the plasmon of nanocrystals assemblies to that of nanoparticles dispersed in an alumina matrix, we investigate the possible origins of such damping. We demonstrate that it partially results from the self-organization of the naked particles but also from intrinsic inhomogeneity of dopants

Visible luminescence improvement of ZnO/PAA nano-hybrids by silica coating

International audienceThe effect of a silica coating on the improvement of the visible light emission properties of ZnO/polyacrylic acid (PAA) nanohybrids is reported. The synthesized material consists of ZnO nanocrystals incorporated into the PAA mesospheres and then coated with silica. The silica amount can be controlled by the concentration of ammonia used in the sol-gel process as catalyst. The interaction between PAA and ammonia is crucial, the presence of the former tending to inhibit the catalytic action of the latter. We show that there is an optimum in the silica amount around the mesospheres, which leads to a drastic increase in the defect-related visible photoluminescence quantum yield of ZnO nanocrystals. A six-fold increase of the quantum yield can thus be achieved, reaching competitive values higher than 60%. This optimum is a compromise between a complete protective silica layer around the mesospheres and too thick a layer inducing inefficient absorption of excitation light by the coating

Fabrication and characterization of organic semiconductor-based microcavities

International audienc

Numerical model for injection and transport in multilayers OLEDs

International audienceWe present a recently developed numerical code for OLED simulation. This code contains a detailed description of contacts, charge transport and recombination. Its efficiency is briefly shown through examples of single- and bilayer devices and discussed in more detail through the investigation of the action of a LiF thin film on injection. In particular, we show how the code can help to discriminate between several possible explanations for this phenomeno