The acoustic vibrations of metal–dielectric core–shell nanoparticles (Ag@SiO2 and Au@SiO2) are investigated using ultrafast pump–probe spectroscopy. The experimental results are in good agreement with calculations of the period of the breathing vibration of the core–shell particles. The transition from one overtone of the breathing mode to the next one as the size of the silica shell increases is observed for slightly thinner SiO2 shells than previously reported. Our results confirm that this optical technique permits the determination of the quality of the mechanical contact at the metal dielectric interface. This is of major importance for many applications, in particular because it modifies significantly the thermal conductivity at the nanoscale. Moreover, we observed that for two different synthesis routes, poor contact core–shell samples could sneak in among good sample series based on the same metallic core particles. This confirms the suitability of this all optical and noninvasive technique to obt...

The aim of this paper is to determine how microgels adsorb at a model oil-water interface and how they adapt their conformation to compression, which gives rise to surface elasticity depending on the microgel packing. The structure of the film is determined by the Langmuir films approach (forced compression) and compared to spontaneous adsorption using the pendant drop method. The behaviour of microgels differs significantly from that of non-deformable particles but resembles that of linear polymers or proteins. We also correlate the properties of microgels spontaneously adsorbed at model interfaces to their forced adsorption during emulsification. Finally we propose a route to easily control a posteriori the microgel packing at the surface of droplets and the flow properties of emulsions stabilised by the microgels.

The importance of electrostatics on microgel adsorption at a liquid interface is studied, as well as its consequence on emulsion stabilization. In this work, poly(N-isopropylacrylamide) (pNIPAM) microgels bearing different numbers of charges and various distribution profiles are studied, both in solution and at the oil-water interface of emulsion drops. Charged microgels are compared to neutral ones, and electrostatic interactions are screened by adding salt to the aqueous solution. In solution, electrostatics has a significant impact on microgel swelling, as induced by the osmotic pressure exerted by mobile counterions in the gel network. At the interface of drops, microgels pack in a hexagonal array, whose lattice parameter is independent of the number of charges and range of electrostatic interactions. Microgel morphology and packing are ruled only by the adsorption of the pNIPAM chain at the interface. Conversely, decreasing the charge density of microgels by the protonation of the carboxylic groups leads to unstable emulsions, possibly as a result of the impact of hydrogen bonding on microgel deformability.

Self-assembled plasmonic metamaterials are fabricated from silver nanoparticles covered with a silica shell. These metamaterials demonstrate topological darkness or selective suppression of reflection connected to global properties of the Fresnel coefficients. The optical properties of the studied structures are in good agreement with effective medium theory. The results suggest a practical way of achieving high phase sensitivity in plasmonic metamaterials.

This article reports a one-step approach for the fabrication of highly uniform, spherical Ag particles with tailored dimensions ranging from 10 to 30 nm. Coated with silica shell, the high uniformity of the particles allows their spontaneous assembly into millimeter-long extended 3-D arrays with transverse dimensions of tens of micrometers, using a microfluidic evaporation-based process.

In an attempt to fabricate low index metamaterials by a bottom-up approach, meta-atoms constituted of silica-coated silver nanoparticles are assembled by a Langmuir-Schaefer technique into thin films of large area and well-controlled thickness. The silica shells ensure a constant distance between the silver cores, hence providing a constant coupling of the localized surface plasmon resonance (LSPR) of the nanoparticles in the assembled composite material. The optical response is studied by normal angle spectral reflectance measurements and by variable angle spectroscopic ellipsometry. The normal incidence data are described well in the framework of a single effective Lorentz oscillator model. The resonance of the assembled material is blue-shifted and shows no significant broadening with respect to the absorption band of the individual nanoparticles. The observation of these two effects is enabled by the core-shell structure of the meta-atoms that prevents aggregation of the metallic cores. The ellipsometry study confirms the general behavior and reveals the natural birefringence of the few-layer materials. The amplitude of the observed resonance is weaker than expected from the Maxwell-Garnett mixing rule. This well-characterized system may constitute a good model for numerical simulations.

In this paper we present the fabrication of nanostructured metal-dielectric composite materials that are designed to exhibit dielectric resonances at visible light frequencies. The resonators are constituted of silver and gold nanoparticles coated with a dielectric silica shell that enables a fine tuning of the distance between the plasmonic cores. These core-shell nanoresonators are self-assembled in close-packed monolayers and transferred onto a solid substrate by a Langmuir-Schaefer method. Three dimensional materials of controlled thickness are then obtained over large areas. The electromagnetic behaviour is investigated by reflectance experiments at normal incidence. The presence of strong dielectric resonances is demonstrated and the variations of the effective refractive index vs. wavelength are inferred.

Novel silsesquioxane thin films were conveniently synthesized by the sol-gel route under mild conditions. Thus, a sol was prepared from 4,4'-bis(triethoxysilyl)-1,1'-biphenyl (4,4'-BTEBp) under a hydroalcoholic medium without a surfactant, deposited by spin-coating on silica supports, and dried at 280 degrees C. The resulting biphenylene-bridged films exhibited very smooth surfaces, excellent mechanical behavior and no cracks. Moreover, SEM and TEM studies showed flawless, homogeneous interfaces with silica substrates. The acoustic waveguide properties of these films on piezoelectric quartz microsensors were investigated at high frequency through a network analyzer. For an optimal thickness close to 1 mu m, a marked frequency shift of the main broad lobe and a decrease of the insertion loss were observed. These results show a strong effect of the waveguide for trapping the acoustic energy, promising an unprecedented ability to provide a new generation of sensors. The capability of this device in the detection of mass is also demonstrated through the immobilization of Bovine Serum Albumin (BSA). This novel approach appears very promising in view of the development of surface acoustic wave sensors and biosensors.

We have fabricated several heterostructures made of two opal slabs separated by a defect. The optical properties of the resulting materials have been characterized by recording their near-infrared (NIR) transmission spectra and by simulating them using the finite-difference time-domain method, The presence of the extrinsic defect led to an impurity mode within the photonic stop band, which was observed as a pass band in the NIR spectra. We show that the amplitude of the pass band is maximal when the two opals confining a defect monolayer made of smaller colloids have the same number of layers. On the other hand, this middle position of the defect layer does not correspond to an optimal cavity when the guest particles are larger than the host ones, as the presence of the defect induces a deterioration of the crystalline organization of the upper opal slab. To minimize the presence of unintentional defects in the heterostructures, we incorporated a planar defect made of particles of a different nature but of the same size than those forming the host opal. A pass band within the band gap was also observed in the NIR transmission spectra of the samples due to the difference between the refractive indexes of the guest and host colloids.

We have fabricated three-dimensional (3D) colloidal crystals containing a two-dimensional (2D) defect made of particles of different nature and of different size. The presence of the extrinsic defect led to an impurity mode within the photonic stop band, which was observed as a pass band in the near-infrared (NIR) spectra. We also built a heterostructure containing a planar defect made of particles of different nature but of the same size than those forming the host opal. A pass band was also observed, due to the difference between the refractive indexes of the guest and host colloids.

We describe the elaboration of organized macroporous electrode surfaces with a complex composition using the hard sphere template procedure. In a first approach, different metals are subsequently generated in the template leading finally to a multicomponent porous material showing interesting electrochemical features combining the redox properties of the different metals. In a complementary second approach, alternating porous and compact metal layers are formed, with the compact layer being introduced on purpose as a defect layer allowing the controlled destruction of the sandwich-type architecture using a chemical or electrochemical trigger.

Colloidal photonic crystals containing one to four periodically embedded planar defect layers are fabricated (see figure). It appears that the fabrication of such periodic superlattices leads to a redistribution of the photonic density of states, resulting in the opening of new bands and gaps in the photonic band structure, in comparison with defect-free opals.

Composite vanadium oxide/PVA/latex macroscopic fibers have been generated by using an extrusion process. Specifically, inorganic vanadium oxide fibers enable the detection of 0.1 ppm of ethanol within 3-5 s at 42 degrees C, which is certainly one of the highest sensitivities to date concerning alcohol sensors. More importantly, by varying the starting latex inclusion contents, the shear rates applied during the extrusion process, and the final appliance of a thermal treatment, we were able to segregate each parameter involved within the mechanical and sensing properties associated with these as-synthesized fibers, i.e., the amount of the organic insulator counterpart, the degree of vanadium oxide ribbons alignment, and the induced porosity reached upon latex removal. Overall, we found out that all the parameters described above and involved within the as-synthesized fibers' mechanical and sensing properties are acting within a partitive action mode rather than a cooperative one.

The synthesis of novel meso-/macroporous SiO2 monoliths by combining a nano-building-blocks-based approach with the confined geometry of a tailored air-liquid foam structure is described. The resulting macrostructure in which ordered close-packed colloidal silica nanoparticles constitute the monolith's scaffolds very closely resembles the tailored periodic air-liquid foam template. The void spaces between adjacent particles create textural mesoporosity; therefore, the as-prepared silica networks are characterized by hierarchical porosity at the macroscopic and mesoscopic length scales. The fine-tuning of both the liquid foam's fraction and the bubble size allows a rational design over the macroscopic cell morphologies ( shape, Plateau border's length, and width). Striking results of this approach are the weak shrinkage of the as-synthesized opal-like scaffolds during the thermally induced sintering process and, in contrast with previous studies, the formation of closed-cell structures. Particle organization and the foam film surface roughness are investigated by atomic force microscopy (AFM), showing the influence of the liquid flow, within the foams' Plateau borders and films, on the final assemblies.

This paper describes the elaboration of photonic crystal heterostructures with a perfectly defined architecture. The transfer of a Langmuir film of functionalized silica particles onto a solid substrate gave us the ability to build three-dimensional (3D) colloidal crystals. The influence of the withdrawing speed of the substrate on the crystalline quality of the 3D photonic materials has been studied. Photonic crystal heterostructures have been fabricated by the successive depositions of layers of silica spheres with different diameters. The composite materials have been characterized by scanning electron microscopy (SEM) and near infrared (NIR) spectroscopy. Our results establish that the optical properties of these multilayer systems can be tailored by adjusting either the thickness or the stacking order of each component crystal

We have fabricated three-dimensional (3D) colloidal crystals containing a two-dimensional (2D) defect as the middle layer by the Langmuir-Blodgett (LB) technique. Either a homogeneous sheet made of hundreds layers of behenic acid or a single monolayer of silica colloidal particles of various sizes was inserted between two opal films of silica spheres. The presence of the extrinsic defect led to an impurity mode within the photonic stop band, which was observed as a pass band in the near-infrared (NIR) spectra. The position of this defect mode was found to vary periodically with the value of the ratio of the thickness of the defect layer to the diameter of the colloids of the upper and lower opals.