The morphology and optical response of Au and Ag nanoparticles capped with dielectric amorphous Si3N4, BN, and Al2O3 layers are studied. Quantitative analysis of high-angle annular dark-field images obtained in a scanning transmission electron microscope and simulations of optical transmittance spectra are used to investigate the dependence of the morphology of the nanoparticles on the particle size and on the capping material. It is demonstrated that capping-layer effects induce a size-dependent and cap-dependent reshaping of the nanoparticles.

Nanodots forming dense assembly on a substrate are difficult to characterize in terms of size, density, morphology and cristallinity. The present study shows how valuable information can be obtained by a combination of electron microscopy techniques. A silicon nanodots deposit has been studied by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) to estimate essentially the dot size and density, quantities emphasized because of their high interest for application. High resolution SEM indicates a density of 1.6 × 1012 dots/cm2 for a 5 nm to 10 nm dot size. TEM imaging using a phase retrieval treatment of a focus series gives a higher dot density (2 × 1012 dots/cm2) for a 5 nm dot size. High Resolution Transmission Electron Microscopy (HRTEM) indicates that the dots are crystalline which is confirmed by electron diffraction. According to HRTEM and electron diffraction, the dot size is about 3 nm which is significantly smaller than the SEM and TEM results. These differences are not contradictory but attributed to the fact that each technique is probing a different phenomenon. A core-shell structure for the dot is proposed which reconcile all the results. All along the study, Fourier transforms have been widely used under many aspects.

Confocal microscopy has been used to study the crystallization of two colloidal model systems that are geometrically frustrated in a completely different way: (I) hard colloidal polyhedrals, where crystallization is frustrated due to the incommensurate particle shape and (II) large spherical impurities in a sea of monodisperse colloidal hard spheres, where crystallization is frustrated by the introduction of impurities. As a reference system, we analyzed the crystallization of pure monodisperse colloidal hard spheres. We show that although the crystal structures of both systems are highly dissimilar on the individual particle level, both sources of geometrical frustration have a similar effect on the structure on the grain level. We quantitatively characterize the polycrystalline structures and study the crystallization process in time. Whereas grain boundaries persist in the frustrated systems due to structural arrest, the majority of grain boundaries anneals out quite rapidly in the reference system. Therefore, we argue that both sources of geometrical frustration cause a polycrystalline structure.

We report a tomographic diffractive microscope, which permits imaging non-labelled transparent or semi-transparent samples. Based on a combination of microholography with a tomographic illumination, our set-up creates 3-D images of the index of refraction distribution within the sample. One acquires successively interferograms, rotating the illumination (the specimen being static) and using phase-shifting holography. Within the first Born approximation, each interferogram is interpreted as a subset of the Fourier transform of the specimen index of refraction distribution. The reconstruction is therefore similar to synthetic aperture imaging: one recombines the information in the Fourier space, and a final Fourier transform gives a 3-D image of the specimen. First recalling the theoretical foundations, we then describe our experiment, and show initial results obtained on biological samples.

Wavelength dispersive and energy dispersive spectrometers were fitted on a scanning electron microscope (SEM) in order to perform combined analysis and to use the advantages of the two spectrometers. The combined system is simple, adaptable to a lot of SEM and cheaper than Electron Probe Micro Analyzer (EPMA). Its originality is to combine two spectrometers: a parallel beam WDS with a silicon drift EDS spectrometer. This makes analysis easier (easy to find the optimum parameters to set up, as beam current) and saves time. With this system, quantitative analysis is more accurate than with EDS alone, better resolution can be achieved, less overlap of lines and better spatial resolution can be obtained. A sample recently studied by a microanalyst association was analysed with the present system in order to test its efficiency. In a second series of analyses, a sample showing difficulties (peak overlaps, small phases, low mass fraction) was analysed and good results were achieved.

Photodiodes with a p-ZnO/oxide/n-Si substrate structure were fabricated. The N-In codoped p-type ZnO films were deposited by ultrasonic spray pyrolysis on a (111)-oriented silicon substrate with a thin oxide layer. A photocurrent of ~ 4.99 × 10-5 A was measured at a reverse bias of 1 V, and a photocurrent to dark current contrast ratio of almost five orders of magnitude was found. The photodiode responses exhibited three regions of behaviour: around 400 nm, between 400 nm–700 nm, and between 700 nm–1000 nm, denoted as regions A, B, and C, respectively. Region A corresponds to band-to-band absorption in the ZnO film, region B to band-to-deep level absorption in the ZnO film, and region C to band edge absorption in the Si substrate.

Molecular dynamics simulations with Tersoff potentials were used to study the tensile and compressive mechanical behavior of SiC nanowires with torsion strain. The simulation results show that small torsion strain does not affect the mechanical behavior of SiC nanowires. However, large torsion strain induces the decrease of the critical stress. With large torsion strain, the collapse occurs in the nanowires before tensile failure and compressive buckling, and deformation zone occurs in the collapsed part.

The formation of crystalline silicon nanoparticles was investigated by means of Raman spectroscopy. SiOx (x = 1 and x = 1.5) films deposited by electron-gun evaporation onto silica substrates were submitted to post-deposition thermal treatments at 1000 and 1100 °C for various times. From lineshape analysis of the Raman band, it appeared that the crystalline volume fraction never excessed 30% for annealing at 1000 °C, while the mean diameter remained almost constant. Complete crystallisation was achieved after annealing at 1100 °C, accompanied by an increase of the nanoparticle size. Mean diameters of the nanoparticles obtained from Raman spectra analysis along the two main confinement models, Richter et al., Campbell, Fauchet model and bond-polarizability model, were discussed and compared to values deduced from transmission electron microscopy measurements.

The effect of thickness and heat treatment on the structural and optical properties of Sb2Te3 thin films fabricated by using flash evaporation technique were investigated. The as-deposited films were found to be stoichiometric. For the as-deposited and annealed samples of thickness in the range of 20.7–120.5 nm, large variations in transmittance and reflectance were observed for wavelength below 2000 nm due to strong absorption, while slight variations were observed above 2000 nm. The optical constants, n and k, measured in the range of 500–4000 nm, increased slightly by annealing the samples at 573 K for 2 h in air and a red shift was observed. Allowed indirect transitions were observed for the as-deposited and the annealed samples. The results showed two energy gaps for these transitions varied from 0.28 to 0.31 eV for the as-deposited samples and from 0.56 to 0.54 eV for the annealed films. The spectral distribution of the real part of the dielectric constant ε′ showed a maximum at 0.73 eV for the as-deposited films decreased to 0.65 eV by annealing.

A dispersion compensating fiber exhibiting low losses is used to study the phase to amplitude noise and amplitude to phase noise conversion mechanisms with a very good signal-to-noise ratio over a 20 GHz bandwidth. It is shown that the large frequency noise of semiconductor lasers and the losses in the fiber restrain this technique from efficiently reducing the relative intensity noise to improve the dynamic range of opto-microwave links. However, these properties are proved to be useful to precisely characterize the laser phase noise over a large bandwidth.

High-k (Zr,Sn)TiO4 films were grown on glass substrate by DC magnetron sputtering at ambient temperature using elemental, all metallic targets. Films were polycrystalline irrespective of the oxygen partial pressure. The refractive index and optical bandgap of the films were in the range 1.79–1.59 at 600 nm and 3.27–3.39 eV, respectively. Highest value of microwave dielectric constant exhibited was 33 and lowest loss tangent was 0.001 at 10 GHz. Films prepared at 40% oxygen mixing percentage (OMP) gave minimum strain and the same film gave minimum dielectric loss with highest dielectric constant. A correlation between strain values and dielectric loss was observed. The grain sizes as observed from atomic force microscope images are found to be triangular in nature.

In this paper, we describe the design of a permanent magnet actuator that can make linear and rotary movements independently or simultaneously. Special attention has been placed on the simplicity of the structure and its dynamic behavior. First, we compare the different approaches to perform a linked movement and a structure is chosen. Then, we detail the magnetic conversion used through a rotary machine and a linear actuator. In a last part, the actuator designed is presented and studied using the 3D finite element approach. Results concerning the flux linkages and forces are given and discussed.

To cool down the stack system in polymer electrolyte fuel cells (PEFCs), a coolant is needed that must be electrically nonconductive. In the specialized coolant that is modeled by us, charged nanoparticles are added into the flow to neutralize the ion contamination that otherwise gradually degrades the coolant until shunt currents become significant. A computational fluid dynamics (CFD) physicochemical model of the multiphase coolant flow with charged nanoparticles has been formulated and coded using COMSOL Multiphysics and MEMS. Electrochemistry, fluid mechanics, steric stabilization, and heat transfer are coupled in this model. For nanoparticles in the fluid, electrokinetic force, electrical double layer (EDL) force, hydrodynamic force, and buoyancy force have been taken into account for the prediction of the electrodeposition rate onto channel walls. The overall goal of the model is to provide a fundamental first principles-based design tool for a specialized coolant to enable operations in a fuel cell stack for 2−3 years without the need for frequent replacement or filtering of the coolant.

Wall slip and wall divergence are known to have large and opposing effects on the stability of flow in a two-dimensional channel. While divergence hugely destabilises, slip dramatically stabilizes the linear mode. In a non-parallel stability analysis, we study a combination of these two effects, since both will coexist in small-scale flows with wall roughness. Our main results are (i) that the stabilising effect of slip is reversed at higher angles of divergence, (ii) transient growth of disturbances is unaffected by either wall-divergence, or by slip at any divergence. Moreover, at the Reynolds numbers relevant here, transient growth is too low to be a significant player in transition to turbulence, which is more likely to be driven by linear instability. The results would have implications for the onset of unsteadiness and mixing in small scale flows.