Développement d’un comparateur cryogénique de courant (CCC) pour la métrologie des faibles courants

Un nouveau comparateur cryogénique de courant (CCC) a été développé au LNE. Avec un gain maximum de 30 000, il sera utilisé pour amplifier et mesurer les faibles courants générés par des pompes à électron actuellement à l’étude pour servir comme étalon quantique de courant. Cet article présente la conception et la réalisation du comparateur et les performances atteintes. Une résolution record très proche de 1 fA/Hz1/2 en régime de bruit blanc a été obtenue. Grâce à une géométrie inédite adoptée pour les enroulements, les phénomènes de résonance émanant des circuits LC par couplage de leur inductance aux capacités parasites existantes sont observes à des fréquences au delà de 1 kHz, n’affectant pas ainsi la bande passante du système. Un modèle èlectrique représentatif du comportement fréquentiel du CCC est en cours de développement

A femto ampere current amplifier based on a 30 000∶1 cryogenic current comparator

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Evaluation of the size distribution of a multimodal dispersion of polymer nanoparticles by microscopy after different methods of deposition

International audienceParticle size distribution (PSD) is an important factor determining the efficiency of industrial manufacturing processes for nanomaterials, assuring the reproducibility and safety of the final product. Among the instruments that have been developed to determine size and PSD of nanoparticle dispersions, the easiest to handle are based on indirect measurements; therefore, it is recommended to use at least two approaches to evaluate the PSD. This work evaluates the possibility of using direct size measurement methods based on the analysis of images of multimodal dispersion of nanomaterials by electron microscopy. Samples for measurement of the PSD were prepared by different deposition methods from a multimodal dispersion of poly(isobutylcyanoacrylate) nanoparticles. Grids prepared by flotation showed particle agglomeration and segregation between large and small particles and was found unsuitable for obtaining relevant measurement of the PSD. In contrast, spin-coating produced a homogenous and random deposition of well isolated particles on the substrate used to prepare the samples for electron microscopy. This deposition method was suitable for evaluating the PSD of this highly heterogenous dispersion. Deposition strategies are therefore essential to provide a statistically representative sample for PSD measurement of nanomaterial-based products using a direct measurement method

Développement d’un comparateur cryogénique de courant (CCC) pour la métrologie des faibles courants

International audienc

A new method for measuring nanoparticle diameter from a set of SEM images using a remarkable point

International audienceScanning Electron Microscopy (SEM) is considered as a reference technique for the determination of nanoparticle (NP) dimensional properties. Nevertheless, the image analysis is a critical step of SEM measuring process and the initial segmentation phase consisting in determining the contour of each nano-object to be measured must be correctly carried out in order to identify all pixels belonging to it. Several techniques can be applied to extract NP from SEM images and evaluate their diameter like thresholding or watershed. However, due to the lack of reference nanomaterials, few papers deals with the uncertainty associated with these segmentation methods. This article proposes a novel approach to extract the NP boundaries from SEM images using a remarkable point. The method is based on the observation that, by varying the electron beam size, the secondary electron profiles crosses each other at this point. First, a theoretical study has been performed using Monte Carlo simulation on silica NP to evaluate the robustness of the method compared with more conventional segmentation techniques (Active Contour or binarization at Full Width at Half-Maximum, FWHM). The simulation results show especially a systematic discrepancy between the NP real size and the measurements performed with both conventional methods. Moreover, generated errors are NP size-dependent. By contrast, it has been demonstrated that a very good agreement between measured and simulated diameters has been obtained with this new technique. As an example, this method of the remarkable point has been applied on SEM images of silica particles. The quality of the segmentation has been shown on silica reference nanoparticles by measuring the modal equivalent projected area diameter and comparing with calibration certificate. The results show that the NP contour can be very accurately delimited with using this point. The measurement uncertainty has been also reduced from 4.3 nm (k = 2) with conventional methods to 2.6 nm (k = 2) using the remarkable point