Search

Accurate shape description is a challenge in materials science. Small-angle X-ray scattering (SAXS) can provide the shape, size and polydispersity of nanoparticles by form factor modelling. However, simple geometric models such as the ellipsoid may not be enough to describe objects with complex shapes. This work shows that the form factor of gold nanobipyramids is accurately described by a truncated bicone model, which is validated by comparison with transmission electron microscopy (TEM) data for nine different synthesis batches; the average shape parameters (width, height and truncation) and the sample polydispersity are obtained. In contrast, the ellipsoid model yields worse fits of the SAXS data and exhibits systematic discrepancies with the TEM results. more...

Mechanical properties of hydrophobically coated gold nanoparticle supercrystals have been studied by small angle X-ray scattering under quasi hydrostatic pressure for various nanoparticle core sizes, ligand length and supercrystal structure. more...

Imogolite nanotubes present a unique spatial separation of conduction and valence bands but the large bandgap inhibits potential application as a photocatalyst. The first step toward using these well-defined nanotubes in photocatalysis and exploiting their natural polarization-promoting charge separation across the nanotubes wall, is to tune their bandgap energy. Here, titanium modified double walled aluminogermanate imogolite nanotubes are prepared to overcome this limitation. Structural and optical properties are determined at different scales and the photocatalytic performance is evaluated for H2 production under UV-visible light irradiation. Although the incorporation of Ti atoms into the structure remains limited, the resulting nanotubes reveal a remarkable hydrogen evolution rate of ~1500 µmol g-1 h-1, corresponding to a 65-fold increase relative to a reference TiO2P25 photocatalyst. These results confirm the theoretical predictions regarding the untapped potential of modified imogolite nanotubes as promising 1D photoactive polarized nanoreactors. more...

We report the two-dimensional self-assembly at the liquid-air interface of spherical gold nanoparticles (NPs) with diameters between 2 and 14 nm. By exploring the self-assembly conditions, such as the dispersing solvent and the coating ligand (thiols with different lengths, oleylamine, polystyrene), we identify suitable conditions for long range close-packed monolayers obtention. We show that though NPs with diameters below 3 nm yield glassy films or fuse during self-assembly depending on the ligand length, NPs with larger sizes dispersed in toluene yield well-ordered monolayers over distances that can span tens of micrometers. Adding free ligand in solution before the self-assembly triggers long range ordering into close-packed structures of otherwise amorphous films. The equilibrium distance between the NPs within the monolayers are compared to predictions by the OPM and OCM geometrical models. We also observed a CaCu5 phase in few-layers assemblies which results from the size segregation of a single monodisperse population of NPs into two populations of different mean sizes occupying the two different sites of this complex lattice. In some instances, Moiré patterns consisting of two close-packed hexagonal monolayers superimposed with a twist angle are evidenced. By comparing the experimental structures with numerically simulated patterns, we show that a twist angle of 30° yields a quasicrystalline order with a 12-fold rotational symmetry. Our work provides insights into fundamental processes behind the self-assembly of colloidal nanocrystals into ordered mono- and few-layers as well as more complex assemblies such as quasicrystalline or Frank-Kasper phases. These structures are of great significance for bottom-up fabrication of functional devices that advantage of (collective) plasmonics properties or surface enhanced raman scattering. more...

Marangoni flow is among the most intriguing effects in complex fluids and interfacial science. We report here on a fluorescent surfactant that enables to monitor Marangoni flows under quasi-steady conditions, without the need of invasive tracers. The Marangoni zone is clearly visible, and its dynamics can be quantitatively probed both at the air-water interface and within the bulk. In particular, we show that the Marangoni zone exhibits unexpected dependencies with the container size and water depth with the pyrene-tailed surfactant. Additionally, recirculation flows are evidenced by fluorescence near the bottom of the container. This fluorescent probe may find other useful applications in deciphering the complexity of the ubiquitous Marangoni effect. more...

International audience; Seeding-growth method for gold nanoparticles with a high level of size predictivity and a very low polydispersity.We report a seed-mediated synthesis strategy to control the size of gold nanoparticles at the atomic scale in the 2-5 nm size range. Starting from 2 nm seeds, a regrowth in organic solvent with a designed amount of precursor can achieve in a predictive fashion a precise mean size with a 0.3 nm resolution. We show that these monodisperse nanoparticles assemble into a 2D hexagonal lattice over a distance that can span tens of micrometers. more...

International audience; In this article, we revisit the colloidal stability of clay imogolite nanotubes by studying the effect of electrostatic interactions on geo-inspired synthetic nanotubes in aqueous dispersions. The nanotubes in question are double-walled aluminogermanate imogolite nanotubes (Ge-DWINTs) with a well-defined diameter (4.3 nm) and with an aspect ratio around 4. Surface charge properties are assessed by electrophoretic measurements, revealing that the outer surfaces of Ge-DWINT are positively charged up to high pH values. Series of Ge-DWINT dispersions have been prepared by osmotic stress to control both ionic strength of the dispersion and the volume fraction in nanotubes. Optical observations coupled to Small and Wide-Angle X-ray Scattering (SAXS/WAXS) experiments allow us to unravel different nanotube organizations. At low ionic strength (IS < 10−2 mol.L−1), Ge-DWINTs are fully dispersed in water while they form an arrested gel phase above a given concentration threshold, which shifts towards higher volume fraction with increasing ionic strength. The swelling law, derived from the evolution of the mean intertube distance as a function of the nanotube concentration, evidences a transition from isotropic swelling at low volume fractions to one-dimensional swelling at higher volume fractions. These results show that the colloidal stability of Ge-DWINT is driven by repulsive interactions for ionic strengths lower than 10-2 mol.L-1. By contrast, higher salt concentrations lead to attractive interactions that destabilize the colloid suspension, inducing nanotube coagulation into larger structures that settle over time or form opaque gels. Detailed simulations of the WAXS diagram reveal that aggregates are mainly formed by an isotropic distribution of small bundles (less than 4 nanotubes) in which the nanotubes organized themselves in parallel orientation. Altogether, these measurements allow us to give the first overview of the phase diagram of colloidal dispersions based on geo-inspired imogolite-like nanotubes. more...

International audience; Engineering symmetry breaking in seed-mediated growth is a fundamental challenge to produce colloidal nanocrystals with controlled morphologies and properties. In this work, we show a simple, aqueous approach to breaking the inversion symmetry of silver nanorods by restricting growth to one end of the pentatwinned gold bipyramid seed. Controlled addition of dimethyl sulfoxide (DMSO) allows us to tune both the symmetry and the length and width of the objects. Simulations and experiments demonstrate the adsorption of DMSO, which displaces interfacial water, reduces binding of surfactant and chloride ions at the gold surface, and slows down the deposition kinetics of silver. Besides showing the potential of DMSO for controlling the synthesis of complex nanostructures, this work opens new perspectives for the study of the physical properties of non-centrosymmetric nanoparticles, e.g. by controlling their plasmon modes and their second-harmonic generation efficiency. more...

International audience; Aqueous suspensions of nanosheets are readily obtained by exfoliating low-dimensional mineral compounds like H3Sb3P2O14. The nanosheets self-organize, at low concentration, into a periodic stack of membranes, i.e. a lamellar liquid-crystalline phase. Due to the dilution, this stack has a large period of a few hundred nanometres, it behaves as a 1-dimensional photonic material and displays structural colours. We experimentally investigated the dependence of the period on the nanosheet concentration. We theoretically showed that it cannot be explained by the usual DLVO interaction between uniform lamellae but that the particulate nature of nanosheet-laden membranes must be considered. Moreover, we observed that adding small amounts of 100 kDa poly(ethylene oxide) (PEO) decreases the period and allows tuning the colour throughout the visible range. PEO adsorbs on the nanosheets, inducing a strong reduction of the nanosheet charge. This is probably due to the Lewis-base character of the EO units of PEO that become protonated at the low pH of the system, an interpretation supported by theoretical modeling. Oddly enough, adding small amounts of 1 MDa PEO has the opposite effect of increasing the period, suggesting the presence of an additional intermembrane repulsion not yet identified. From an applied perspective, our work shows how the colours of these 1-dimensional photonic materials can easily be tuned not only by varying the nanosheet concentration (which might entail a phase transition) but also by adding PEO. From a theoretical perspective, our approach represents a necessary step towards establishing the phase diagram of aqueous suspensions of charged nanosheets. more...

Zinc-blende CdSe semiconducting nanoplatelets (NPL) show outstanding quantum confinement properties thanks to their small, atomically-controlled, thickness. For example, they display extremely sharp absorption peaks and ultra-fast recombination rates that make them very interesting objects for optoelectronic applications. However, the presence of a ground-state electric dipole for these nanoparticles has not yet been investigated. We therefore used transient electric birefringence (TEB) to probe the electric dipole of 5-monolayer thick zinc blende CdSe NPL with a parallelepipedic shape. We studied a dilute dispersion of isolated NPL coated with branched ligands and we measured, as a function of time, the birefringence induced by DC and AC field pulses. The electro-optic behavior proves the presence of a large dipolar moment (>245 D) oriented along the length of the platelets. We then induced the slow face-to-face stacking of the NPL by adding oleic acid. In these stacks, the in-plane dipole components of consecutive NPL cancel whereas their normal components add. Moreover, interestingly, the excess polarizability tensor of the NPL stacks gives rise to an electro-optic contribution opposite to that of the electric dipole. By monitoring the TEB signal of the slowly-growing stacks over up to a year, we extracted the evolution of their average length with time and we showed that their electro-optic response can be explained by the presence of a 80 D dipolar component parallel to their normal. In spite of the 4[combining macron]3m space group of bulk zinc blende CdSe, these NPL thus bear an important ground-state dipole whose magnitude per unit volume is twice that found for wurtzite CdSe nanorods. We discuss the possible origin of this electric dipole, its consequences for the optical properties of these nanoparticles, and how it could explain their strong stacking propensity that severely hampers their colloidal stability. more...

Rational nanoparticle design is one of the main goals of materials science, but it can only be achieved via a thorough understanding of the growth process and of the respective roles of the molecular species involved. We demonstrate that a combination of complementary techniques can yield novel information with respect to their individual contributions. We monitored the growth of long aspect ratio silver rods from gold pentatwinned seeds by three more...

International audience; Engineering plasmonic hot-spots is essential for applications of plasmonic nanoparticles. A particularly appealing route is to weld plasmonic nanoparticles together to form more complex structures sustaining plasmons with symmetries targeted to given applications. However, thecontrol of the welding and subsequent hotspot characteristic is still challenging. Herein, we demonstrate an original method that connects gold particles to their neighbors by another metal of choice. We first assemble gold bipyramids in a tip-to-tip configuration, yielding short chainsof variable length and grow metallic junctions in a second step. We follow the chain formation and the deposition of the second metal (i.e. silver or palladium) via UV/Vis spectroscopy and we map the plasmonic properties using electron energy loss spectroscopy. The formation ofsilver bridges leads to a huge redshift of the longitudinal plasmon modes into the mid-infrared region, while the addition of palladium results in a redshift accompanied by significant plasmon damping. more...

Rational nanoparticle design is one of the main goals of materials science, but it can only be achieved via a thorough understanding of the growth process and of the respective roles of the molecular species involved. We demonstrate that a combination of complementary techniques can yield novel information with respect to their individual contributions. We monitored the growth of long aspect ratio silver rods from gold pentatwinned seeds by three in situ techniques (small-angle x-ray scattering, optical absorbance spectroscopy and liquid-cell transmission electron microscopy). Exploiting the difference in reaction speed between the bulk synthesis and the nanoparticle formation in the TEM cell, we show that the anisotropic growth is thermodynamically controlled (rather than kinetically) and that ascorbic acid, widely used for its mild reductive properties plays a shape-directing role, by stabilizing the {100} facets of the silver cubic lattice, in synergy with the halide ions. This approach can easily be applied to a wide variety of synthesis strategies. more...

International audience; Viral capsid proteins have the remarkable ability to self-assemble around a cargo core, whether their genome, a polyelectrolyte or an inorganic nanoparticle. Although the equilibrium properties of such composite objects have been broadly investigated, little is known about the kinetic pathways leading to their assembly. By exploiting the plasmon resonance effect of gold nanoparticles, we show that the adsorption of viral proteins can be monitored through the redshift of the resonance wavelength. Kinetic measurements reveal that the process occurs in less than a second. The spatial arrangement of nanoparticles is probed by time-resolved small-angle X-ray scattering, and we observe the formation of transient aggregates with a lifetime in the hour range. The biocompatibility of gold nanoparticles induced by adsorbed proteins is of great importance for their use in biomedicine and the reported results should help better understand the processes of formation. more...

Tailoring the crystal structure of plasmonic nanoparticle superlattices is a crucial step in controlling the collective physical response of these nanostructured materials. Various strategies can achieve this goal for isotropic nanoparticles, but few of them have been successful with anisotropic building blocks. In this work we use hybrid particles, consisting of gold nanorods encased in silver shells with a thickness that can be controlled from a few atomic layers to tens of nanometers. The particles were synthesized, characterized by a combination of techniques and assembled into supercrystals with a smectic B configuration, i.e. a 2D in-plane periodic order without interplane lateral correlations. We showed that, by tuning the silver shell thickness, the in-plane order can be changed from hexagonal to square and the lattice parameters can be adjusted. The spatial distribution of the supercrystal was systematically studied by optical and electron microscopy and by small-angle X-ray scattering. Through optimized surface chemistry, we obtain homogeneous, millimeter-size films of standing nanoparticles, which hold promise for all applications using plasmon-enhanced technologies. more...

Under pulsed or a.c. electric fields, colloidal suspensions of nanorods can show strong electro-optic effects, such as the Kerr effect, with fast response times (a few ms), which makes them good candidates for some commercial applications. For this purpose, suspensions of Pigment red 176 nanorods in dodecane were recently developed and their physical properties have been studied. We report here on the investigation of the orientational order induced by electric fields in isotropic suspensions of pigment nanorods by three different techniques: transient electric birefringence, transient electric dichroism, and in-situ small-angle X-ray scattering under electric field (“Electro-SAXS”). We show that, in spite of the apolar character of the solvent, the Maxwell-Wagner-O'Konski mechanism (i.e. the polarization of the counter-ion cloud around each particle) is responsible for the field-induced alignment of the nanorods. Although the particles are only weakly charged and the dielectric constant of dodecane is low, the pigment nanorods effectively behave as metallic particles in an insulating matrix and reach strong values (S ~0.5) of the induced nematic order parameter at moderate field amplitudes (~1 V/μm). This study confirms the feasibility of using suspensions of Pigment red 176 nanorods in dodecane for electro-optic applications. more...

International audience; Periodic DFT-D calculations are used to decipher the role of intermolecular forces on the stability of mixed linear thiol self-assembled monolayers (SAMs) on Au(111) and compared with experiment. The interaction energy is rationalized by quantifying its different contributions. The inter-chain interaction energy is shown to be in direct relation with the surface reconstruction and the formation of adatoms. The stability of the mixed SAM systems is predicted by calculations and validated with experiments. In order to describe predictively the segregation of binary thiol mixtures adsorption on Au surfaces a segregation descriptor is defined. This procedure is a promising step forward in the prediction of segregated SAMs leading to future functional nanomaterials, including Janus or patchy nanoparticles for optics, formulation and self-assembled patterns. more...

International audience; Nanophase segregation of a bi-component thiol self-assembled monolayer is predicted using atomistic molecular dynamics simulations and experimentally confirmed. The simulations suggest the formation of domains rich in acid-terminated chains, on one hand, and of domains rich in amide-functionalized ethylene glycol oligomers, on the other hand. In particular, within the amide-ethylene glycol oligomers region, a key role is played by the formation of inter-chain hydrogen bonds. The predicted phase segregation is experimentally confirmed by the synthesis of 35 and 15 nm gold nanoparticles functionalized with several binary mixtures of ligands. An extensive study by transmission electron microscopy and electron tomography, using silica selective heterogeneous nucleation on acid-rich domains to provide electron contrast, supports simulations and highlights patchy nanoparticles with a trend towards Janus nano-objects depending on the nature of the ligands and the particle size. These results validate our computational platform as an effective tool to predict nanophase separation in organic mixtures on a surface and drive further exploration of advanced nanoparticle functionalization. more...

International audience; Although gold nanoparticles stabilized by organic thiols are the building blocks in a wide range of applications, the role of the ligands on the plasmon resonance of the metal core has been mostly ignored until now. Herein, a methodology based on the combination of spectroscopic ellipsometry and UV-vis spectroscopy is applied to extract dielectric functions of the different components. It is shown that aromatic thiols allow a significant charge transfer at the hybrid interface with the sand d bands of the gold core that yields ``giant'' red shifts of the plasmon band, up to 40 nm for spherical particles in the size range of 3-5 nm. These results suggest that hybrid nanoplasmonic devices may be designed through the suitable choice of metal core and organic components for optimized charge exchange. more...

International audience; New generation systems are expected to include more intelligent amplifiers able to adapt to many conditions including different gains, channel load, temperature, aging and transient events.1 To face the challenge and meet these new requirements, having an accurate control on the Er environment within the fiber core matrix has never appeared to be so necessary and predominant as it is the case now. Unlike conventional solution doping techniques where Erbium ions are randomly incorporated in the fiber core, our process makes use of a soft chemical synthesis to initially produce Erbium-doped nanoparticles (NPs). Erbium ions are therefore incorporated in the fiber core together with their local environment. So far, our investigations2 first showed that, from the material point of view, quenching levels are intimately linked to the design of the NPs through their chemical composition. Then, from the system perspective, we evidenced the higher power conversion efficiencies exhibited by NP fibers when compared to their conventional counterparts in high power amplifier configurations. In this paper, we address our most recent work focusing on the NP optimisation towards quenching-free Erbiumdoped fibers with a particular focus on core-shell alumino-silicate NPs. Completing our first amplifier results obtained in high power configurations, we also explore new NP fiber profiles that extend the range of their applications. Gain and noise characteristics of typical WDM operating points serve as key indicators on the benefits our NP doping process could provide. more...