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The influence of ligands on the low frequency vibration of different thicknesses cadmium selenide colloidal nanoplatelets is investigated using resonant low frequency Raman scattering. The strong vibration frequency shifts induced by ligand modifications as well as the sharp spectral linewidths make low frequency Raman scattering a tool of choice to follow ligand exchange as well as the nano-mechanical properties of the NPLs, as evidenced by a carboxylate to thiolate exchange study. Apart from their molecular weight, the nature of the ligands, such as the sulfur to metal bond of thiols, induces a modification of the NPLs as a whole, increasing the thickness by one monolayer. Moreover, as the weight of the ligands increases, the discrepancy between the massload model and the experimental measurements increase. These effects are all the more important when the number of layers is small and can only be explained by a modification of the longitudinal sound velocity. This modification takes its origin in a change of lattice structure of the NPLs, that reflects on its elastic properties. These nanobalances are finally used to characterize ligands affinity with the surface using binary thiols mixtures, illustrating the potential of low frequency Raman scattering to finely characterize nanocrystals surfaces., Comment: Nanoscale, Royal Society of Chemistry, 2021

International audience; Nanomaterials have a huge potential in research fields from nanomedicine to medical devices. However, surface modifications of nanoparticles (NPs) and thus of their physicochemical properties failed to predict their biological behavior. This requires investigating the "missing link" at the nano-bio interface. The protein corona (PC), the set of proteins binding to the NPs surface, plays a critical role in particle recognition by the innate immune system. Still, in vitro incubation offers a limited understanding of biological interactions and fails to explain the in vivo fate. To date, several reports explained the impact of PC in vitro but its applications in the clinical field have been very limited. Furthermore, PC is often considered as a biological barrier reducing the targeting efficiency of nano vehicles. But the protein binding can actually be controlled by altering PC both in vitro and in vivo. Analyzing PC in vivo could accordingly provide a deep understanding of its biological effect and speed up the transfer to clinical applications. This review demonstrates the need for clarifications on the effect of PC in vivo and the control of its behavior by changing its physicochemical properties. It unfolds the recent in vivo developments to understand mechanisms and challenges at the nano-bio interface. Finally, it reports recent advances in the in vivo PC to overcome and control the limitations of the in vitro PC by employing PC as a boosting resource to prolong the NPs half-life, to improve their formulations and thereby to increase its use for biomedical applications.

International audience; We report the synthesis of long narrow gold nanocrystals and the study of their vibrational dynamics using inelastic light scattering measurements. Rich experimental spectra are obtained for monodomain gold nanorods and pentagonal twinned bipyramids. Their assignment involves diameter-dependent non-totally symmetric vibrations which are modeled in the framework of continuum elasticity by taking into account simultaneously the size, shape and crystallinity of the nanocrystals. Light scattering by vibrations with angular momenta larger than 2 is reported. It is shown to increase with the ratio of the nanocrystals diameter to the interparticle separation. It originates from the plasmonic coupling due to the self-assembly of the nanocrystals after deposition.

Au nanoparticles (NPs) characterized by distinct surface chemistry (including dodecanethiol or oleylamine as capping agent), different sizes (∼5 and ∼10 nm) and crystallinities (polycrystalline or single crystalline), were chosen as seeds to demonstrate the versatility and robustness of our two-step core–shell Au@Ag NP synthesis process. The central component of this strategy is to solubilize the shell precursor (AgNO3) in oleylamine and to induce the growth of the shell on selected seeds under heating. The shell thickness is thus controlled by the temperature, the annealing time, the (shell precursor)/(seed) concentration ratio, seed size and crystallinity. The shell thickness is thus shown to increase with the reactant concentration and to grow faster on polycrystalline seeds. The crystalline structure and chemical composition were characterized by HRTEM, STEM-HAADF, EELS and Raman spectroscopy. The plasmonic response of Au@Ag core–shell NPs as a function of core size and shell thickness was assessed by spectrophotometry and simulated by calculations based on the discrete dipole approximation (DDA) method. Finally, the nearly monodisperse core–shell Au@Ag NPs were shown to form micrometer-scale facetted 3D fcc-ordered superlattices (SLs) after solvent evaporation and deposition on a solid substrate. These SLs are promising candidates for applications as a tunable surface-enhanced Raman scattering platform.

Phonons in hybrid lamellar supercrystals are investigated by Raman scattering. Special attention is paid to low-frequency vibrations as a mean to shed some light onto the structure at the nanometer scale. In particular, little is known about the structure of the organic capping agents in supercrystals made of colloidal nanopoarticles. This is due to the fact that characterization tools such as electron microscopy and X-ray diffraction are mostly sensitive to the inorganic phase due to its larger electronic density. Raman scattering does not suffer from this limitation. In this class of materials, synthesized following the “benzyl alcohol route”, the inorganic layers are kept together by π–π conjugated interactions. Low-frequency Raman spectra have been measured for yttrium and neodymium oxide-based lamellar organic–inorganic supercrystals synthesized with three benzyl alcohol derivatives. The spectra strongly depend on the nature of both the inorganic and organic phase despite the resulting lamellar struc...

Understanding the mechanisms of interaction between proteins and noble metal nanoparticles (NPs) is crucial to extend the use of NPs in biological applications and nanomedicine. We report the synthesis of Ag-NPs:protein bioconjugates synthesized in total absence of citrates or other stabilizing agents in order to study the NP-protein interaction. Four common proteins (lysozyme, bovine serum albumin, cytochrome-C and hemoglobin) were used in this work. Transmission electron microscopy (TEM) and surface enhanced Raman spectroscopy (SERS) were mainly used to study these bioconjugated NPs. TEM images showed Ag NPs with sizes in the 5–40 nm range. The presence of a protein layer surrounding the Ag NPs was also observed by TEM. Moreover, the composition at different points of single bioconjugated NPs was probed by electron energy loss spectroscopy (EELS). The thickness of the protein layer varies in the 3–15 nm range and the Ag NPs are a few nanometers away. This allowed to obtain an enhancement of the Raman signal of the proteins in the analysis of water suspensions of bioconjugates. SERS results showed a broadening of the Raman bands of the proteins which we attribute to the contribution of different configurations of the proteins adsorbed on the Ag NPs surface. Moreover, the assignment of an intense and sharp peak in the low-frequency range to Ag–N vibrations points to the chemisorption of the proteins on the Ag-NPs surface.

International audience; Mesoporous materials may be considered as the negative image of a collection of nanoparticles. In both cases, the large surface area induces an increase of the system energy. Pressure-induced phase transitions are used to study the differences between mesoporous TiO 2 and a collection of TiO 2 nanoparticles. The synthesis and characterization of mesoporous TiO 2 with a nanosponge-like structure are presented and the inputs of different spectroscopic techniques (Terahertz, Brillouin and Raman) are highlighted. The results show that the phase stability of mesoporous TiO 2 under pressure is very similar to that observed in nanoparticles. 2

Nanoscale advances 1(8), 3139 - 3150 (2019). doi:10.1039/C9NA00222G, Nanostructured iron-oxide based materials with tailored mechanical and magnetic behavior are produced inbulk form. By applying ultra-fast heating routines via spark plasma sintering (SPS) to supercrystalline pellets,materials with an enhanced combination of elastic modulus, hardness and saturation magnetization areachieved. Supercrystallinity – namely the arrangement of the constituent nanoparticles into periodicstructures – is achieved through self-assembly of the organically-functionalized iron oxide nanoparticles.The optimization of the following SPS regime allows the control of organics' removal, necking, iron oxidephase transformations and nano-grain size retention, and thus the fine-tuning of both mechanicalproperties and magnetic response, up until the production of bulk mm-size superparamagnetic materials., Published by Royal Society of Chemistry, Cambridge

Cisplatin (cis-diaminedichloroplatinum(II), CDDP) plays a crucial role in the treatment of various malignant tumors. However, its clinical efficacy and applicability are restricted by issues of toxicity and resistance. Here, for drug delivery purposes, the outer surface of MCM-41 mesoporous silica nanoparticles (MSNs) was functionalized with poly(ethylene glycol) (Mw = 10 000 g/mol) or low-molecular-weight (Mw = 1800 g/mol) branched polyethyleneimine (PEI). Given the strong affinity of sulfur for platinum, thiol-functionalized MSNs were synthesized for comparison by co-condensation with (3-mercaptopropyl)triethoxysilane. CDDP loading was performed either by adsorption or impregnation in aqueous media without the use of dimethyl sulfoxide as a solubilizer. CDDP loading capacities obtained by impregnation were higher than those obtained by adsorption and varied from 3.9 to 16.1 wt %, depending on the functional group. Loaded nanomaterials were characterized by scanning electron microscopy, scanning transmission electron microscopy–high-angle annular dark-field, and Raman spectroscopy. Depending on the functional groups, platinum-based species were either dispersed in the nanomaterials as nanocrystals or uniformly distributed as molecular species. The spectral signature of CDDP was strongly modified when platinum species were homogeneously distributed within the nanomaterials. Preliminary drug release studies performed at 37 °C showed that the behavior of CDDP-loaded MSNs strongly depends on the nature of the present functional groups. Among the functionalization routes investigated in this paper, PEI-based functionalization showed the most promising results for further applications in controlled drug release with the absence of burst release and a sustained release over 72 h.

Resonant acoustic modes of ultrathin CdS and CdSe colloidal nanoplatelets (NPLs) with varying thicknesses were probed using low frequency Raman scattering. The spectra are dominated by an intense band ascribed to the thickness breathing mode of the 2D nanostructures. The measured Raman frequencies show strong deviations with respect to the values expected for simple bare plates, all the more so as the thickness is reduced. The deviation is shown to arise from the additional mass of the organic ligands that are bound to the free surfaces of the nanoplatelets. The calculated eigen frequencies of vibrating platelets weighed down by the mass of the organic ligands are in very good agreement with the observed experimental behaviours. This finding opens up a new possibility of nanomechanical sensing such as nanobalances.

Dielectric ceramic materials (1 − x) KNbO3 − xK0.5Bi0.5TiO3 (0 ≤ x ≤ 0.3) have been successfully synthesized via a stirred (dynamic) hydrothermal method. The microstructure, relative density and dielectric properties were studied as a function of KBT doping. The structure of the solid solutions changed from orthorhombic (x = 0; 0.05) to tetragonal (x = 0.1; x = 0.3) at room temperature. The morphotropic phase limit was obtained at x = 0.075 where we have noted the coexistence of the orthorhombic and tetragonal structures. The mean value of the measured dielectric permittivity er was 700 and dielectric loss tanδ was about 0.06 at room temperature. The dielectric properties of the studied ceramics, from 80 to 450 K, depend not only on their microstructure but also on their relative density. A relaxation behavior was observed for the tanδ curves at temperature below 150 K. The activation energy (Ea) of this phenomenon increases from 0.15 to 0.34 eV with the increase of KBT amount. The conductivity σac remains constant at about 10−6 S m−1.

International audience; The vibrations of gold nanowires and nanorods are investigated numerically in the framework of continuum elasticity using the Rayleigh-Ritz variational method. Special attention is paid to identify the vibrations relevant in Raman scattering experiments. A comprehensive description of the vibrations of nanorods is proposed by determining their symmetry, comparing with standing waves in the corresponding nanowires and estimating their Raman intensity. The role of experimentally relevant parameters such as the anisotropic cubic lattice structure, the presence of faceted lateral surfaces and the shape of the ends of the nanorods is evaluated. Elastic anisotropy is shown to play a significant role contrarily to the presence of facets. Localized vibrations are found for nanorods with flat ends. Their evolution as the shape of the ends is changed to half-spheres is discussed.

International audience; 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 modifiessignificantly 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 obtain information hardly reachable by other means such as electron microscopy or absorption spectroscopy.

International audience; Studies of the mechanical contact between nanometer-scale particles provide fundamental insights into the mechanical properties of materials and the validity of contact laws at the nanoscale which are still under debate for contact surfaces approaching atomic dimensions. Using in situ Brillouin light scattering under high pressure, we show that effective medium theories successfully predict the macroscopic sound velocities in nanopowders if one takes into account the cementation of the contacts Our measurements suggest the relevance of the continuum approach and effective medium theories to describe the contact between nanoparticles of diameters as small as 4 nm, i.e. with radii of contact of a few angstroms. In particular, we demonstrate that the mechanical properties of nanopowders strongly depend on the surface state of the nanoparticles. The presence of molecular adsorbates modifies significantly the contact laws.

Mesoporous silica nanoparticles were synthesized at high pH using CTAB as a template and TEOS as a silica precursor. It was shown that varying the NaOH concentration between 5 and 27.5 mM allows the size, pore and silica structure of mesoporous nanoparticles to be precisely tuned. In particular, monodisperse nanoparticles with the MCM-41 structure with size ranging from 90 nm to 450 nm were obtained by increasing the NaOH concentration from 12.5 to 22.5 mM. It thus demonstrates that NaOH concentration must range between 12.5 and 15 mM in order to prepare MCM-41 silica nanoparticles with optimal size for nanovectorization. We also found that under usual conditions the aggregation of the obtained MSNs was due to the presence of carbonates and ethanol in the reaction mixture. Careful elimination of these species by using carbonate-free NaOH and purging with a N2 flow allows a highly stable suspension of non-aggregated MSN–MCM-41 to be obtained. After a complete CTAB extraction which was confirmed by Raman spectroscopy, cytotoxicity assays carried out in SW480 cancer cells show that these nanoparticles are not toxic up to 100 μg/mL.

In this study we report various new efficient ways to synthesize and modify in situ magnetite (Fe3O4) iron oxide nanoparticles (NPs). Thanks to an apparatus especially developed for this new method of grafting, the NPs have been synthesized and functionalized by 3,4-dihydroxyhydrocinnamic acid (DHCA) or 3,4-dihydroxy-L-phenylalanine (LDOPA) in one step and under hydrothermal conditions using varying concentration ratios ([organic molecules]/[ferrous and ferric ions]). The organic molecules were added before or after the NP synthesis. The addition of these organic molecules modifies the structure, the morphology, the oxidation degree and the growth of the crystallites. Adding the organic molecules before the synthesis step and under acidic conditions increases the average crystallite size and prevents further oxidation whereas under basic conditions the growth is stopped but a partial oxidation of magnetite to maghemite NPs is observed. Adding DHCA or LDOPA after the synthesis step results in a modification of the lattice structure and oxidation degree of the NPs but does not change the average size. This study underlines the importance of the sequence of the addition of organic molecules on the synthesis of NPs.

International audience; Resonant acoustic modes from ultrathin CdS colloidal nanoplatelets (NPLs) are probed under high pressure using low frequency Raman spectroscopy. In particular we focus on the characterization of the recently evidenced mass load effect that is responsible for a significant downshift of the NPL breathing frequency due to the inert mass of organic ligands. We show that a key parameter in the observation of the mass effect is whether the surrounding medium is able to support THz acoustic wave propagation, at a frequency close to that of the inorganic vibrating core. At low pressures, surface organic molecules show a single particle-like behavior and a strong mass effect is observed. Upon pressure loading the ligands are compacted together with the surrounding medium and slowly turned into a solid medium that supports THz acoustic phonons. We observe a continuous transition towards a fully embedded NPL with a frequency close to that of a freely vibrating slab and a progressive loss of the mass effect. The quality factor of the detected vibration significantly decreases as a result of the appearance of a "phonon-like" behavior of the environment at the origin of damping and energy dissipation. Resonant acoustic modes arise from a structure when the phonon wavelength becomes comparable to the confinement dimension. These modes have been investigated in the past few years for various geometries of nanomaterials such as spherical metallic, 1,2 semiconducting 3,4 and dielectric NPs. 5 Low frequency Raman experiments have essentially focused on nano-objects embedded in solid environments such as glassy matrices, which aroused theoretical studies to understand the coupling with the matrix. 6,7 This coupling essentially results in a damping of the modes i.e., a broadening of the Raman peaks without significant shifting of the resonance frequency as compared to a free vibration. The damping mainly originates from energy dissipation in the matrix due to the emission of THz acoustic waves. Inorganic materials can accommodate acoustic phonons with relatively high frequencies. For instance in inorganic glass, 8 metallic, 9 CdS and CdSe systems, the maximum of acoustic phonon frequency reaches several THz at the maximum of the dispersion relations. For this reason, experimental Raman spectra of embedded NPs (position and width of the resonances) have been so far well explained by core-shell 10 or core-matrix 11 models. However, the recent finding of a mass load effect from CdS and CdSe NPLs loaded with oleic acids at their surfaces suggests that the sound propagation within the organic molecules should be neglected. This is the basis of the mass loaded model where only the inertial mass of the ligands is taken into account to explain the lowering of the NPL breathing frequencies. 12 The discovery of this effect with two-dimensional nano-objects was recently extended to QDs explaining the temperature dependence of acoustic vibrations of CdSe and CdSe-CdS core-shell nanocrystals 13 and the modulation of QD acoustic vibration frequencies through the choice of surface ligands. 14 It can also provide insights into more complex geometries such as nanorod heterostructures. 15 Resonant acoustic modes in finite size structures arise when the phonon wavelength matches the confinement dimension. In the case of nanomaterials with a 3D confinement , such as nanoparticles, breathing acoustic modes with an angular momentum ℓ = 0 have been extensively studied in particular because they are Raman active. The breathing motion of a free sphere involves a radial displacement of the surface with a frequency given by ν 3D ' 0:9=D ffiffiffiffiffiffiffiffiffiffiffiffi C 11 =ρ p where D, C 11 and ρ are the sphere diameter, elastic constant and density, respectively. 1D confinement geometries such as

International audience; The onset of the sintering of 5 nm ZrO2 and TiO2 nanoparticles is investigated by various methods including inelastic light scattering. A special attention is paid to low-frequency Raman spectra where scattering from confined acoustic vibrations and quasielastic scattering manifest. Significant changes are observed between samples sintered at different temperatures or applied forces. A detailed analysis of the spectra enables to follow the variation of the size of the nanoparticles, the surface area, and the formation of internanoparticles necks in the sintered materials. Finally, low-frequency scattering is shown to be more sensitive to the onset of sintering than most other experimental methods.

International audience; A facile and rapid localized electrochemical reduction of colloid copper particles is proposed using the scanning electrochemical,microscope (SECM), technique. In this purpose, thin films of composite silica :glass containing copper salts were prepared by the sol-gel method via the dip coating technique. Acid-catalyzed tetraethylorthosilane (TEOS) solutions charged with copper nitrate were used as precursors. This one-pot experiment can be performed in mild conditions. The localized generation of copper metallic nanostructures on silica film has been performed by electroreduction of methyl viologen on an ultramicroelectrode (UME). The UME generates reducing species, which in turn diffuse:toward the silica matrix and reduce the metal ions. The diameter of the working electrode and the electrolysis period Were taken into account to study the size of the generated dotted micropatterns. The compositions of the modified silica films were characterized by X-ray diffraction (XRD), scanning,electronic microscopy (SEM), optical microscopy,, and vibrational (IR-ATR and Raman) and X-ray photoelectron spectroscopies (XPS).

Nanocomposites consisting of noble metal nanoparticles (NPs) embedded in TiO2 thin films are of great interest for applications in optoelectronics, photocatalysis and solar-cells for which the plasmonic properties of the metal NPs play a major role. This work investigates the first stages of the formation of gold NPs by thermal annealing of Au-doped TiO2 thin films grown by magnetron sputtering. A low concentration of gold in the films is considered (5 at.%) in order to study the first stages of the formation of the NPs. Raman spectroscopy is used to follow the crystallization of TiO2 when increasing the annealing temperature. In addition, low-frequency Raman scattering (LFRS) is used to investigate the formation of gold NPs and to determine their size. Resonant LFRS measurements obtained by using a laser wavelength matching the surface plasmon resonance of the metallic NPs significantly enhances the Raman peak intensity enabling to focus on the first stages of the NPs formation. A double size distribution is observed at Ta = 800 °C calling for additional investigations by transmission electron microscopy (TEM). TEM observations reveal an inhomogeneous in-depth size distribution of gold NPs. The annealed films are structured in two sublayers with bigger NPs at the bottom and smaller NPs at the top. At Ta = 800 °C, a double size distribution is confirmed near the surface. A mechanism is proposed to explain the formation of the sublayers. The modification of the diffusion of gold atoms by stresses in the film near the substrate is assumed to be responsible for the observed two layers structure.

International audience

International audience; Acoustic vibrations of assemblies of gold nanoparticles were investigated using ultralow frequency micro-Raman scattering and finite element simulations. When exciting the assemblies resonantly with the surface plasmon resonance of electromagnetically coupled nano-particles, Raman spectra present an ultralow frequency band whose frequency lies below the lowest Raman active Lamb mode of single nanoparticles that was observed. This feature was ascribed to a Raman vibration mode of gold nanoparticle " supermolecules " , that is, nanoparticles mechanically coupled by surrounding polymer molecules. Its measured frequency is inversely proportional to the nanoparticle diameter and sensitive to the elastic properties of the interstitial polymer. The latter dependence as well as finite element simulations suggest that this mode corresponds to the out-of-phase semirigid translation (l = 1 Lamb mode) of each nanoparticle of a dimer inside the matrix, activated by the mechanical coupling between the nanoparticles. These observations were permitted only thanks to the resonant excitation with the coupling plasmon excitation, leading to an enhancement up to 10^4 of the scattering by these vibrations. This enhanced ultralow frequency Raman scattering thus opens a new route to probe the local elastic properties of the surrounding medium.

The ferroelectric compounds Pb 2 Na 1− x La x Nb 5− x Fe x O 15 and Pb 0.5(5− x ) La x Nb 5− x Fe x O 15 (0≤ x ≤1) with the tungsten bronze type structure have been investigated using Raman spectroscopy. The evolution of the spectra as a function of composition at room temperature is reported. In the frequency range 200–1000 cm −1 three main A 1 phonons around 240 ( υ 1 ), 630 ( υ 2 ) and 816 ( υ 3 ) cm −1 were observed. The broadening of the Raman lines for high values of x originates from a significant structural disorder. This is in good agreement with the relaxor character of these compositions. The lowest-frequency part of the spectra, below 180 cm −1 , reveals a structural change in the studied solid solutions. The behaviour of the Raman shift of the υ 1 mode confirms that in Pb 2 Na 1− x La x Nb 5− x Fe x O 15 , a clear anomaly occurs in the vicinity of x =0.4.

Lead free Na0.5Bi0.5TiO3(NBT) and (Na0.5Bi0.5TiO3)1-x(CaTiO3)x (NBT-CT) piezoelectric ceramics with the perovskite structure were studied. The NBT and NBT-CT samples were synthesized using a solid-state reaction method and characterized with X-ray diffraction (XRD), Raman spectroscopy and dielectric measurements for several compositions (x = 0, 0.07, 0.15) at room temperature. The XRD analysis showed a stabilization of a rhombohedral phase at a low concentration of Ca (0 < x

International audience; Au nanocrystals (NCs) with different crystalline structures and related morphologies are unselectively synthesized using an organometallic route. The acoustic vibrations of these NCs are studied by plasmon mediated low-frequency Raman scattering (LFRS). A splitting of the quadrupolar vibration mode is pointed out in the LFRS spectrum. Comparison of the measured frequencies with calculations and careful examination of the NCs morphologies by transmission electron microscopy ascertain this splitting as being an effect of crystallinity. The excitation dependence of the LFRS spectra is interpreted by the shape-selection of the NCs via plasmon−vibration coupling. These results give new insights into the crystallinity influence on both the vibrations of the NCs and their coupling with plasmons and demonstrate the relevance of elastic anisotropy in monodomain NCs.

International audience; Control of nanocrystal (NC) crystallinity currently raises great interest because of its potential benefits in both physics modeling and technological applications. Advances in methods for synthesizing perfect single-crystalline NCs are recent, so that the effect of crystallinity on NC properties has received only limited study and still needs to be properly investigated. Here, we report that crystallinity of gold NCs dramatically modifies their vibrations. Using low-frequency Raman scattering, we clearly demonstrate that single-domain NCs vibrate differently than their multiply twinned counterparts, through the splitting of the quadrupolar vibrations, which is only observed for the former. Using the resonant ultrasound approach, we calculate the vibrational frequencies of a gold sphere and show that elastic anisotropy induces a lift of degeneracy of the quadrupolar mode in good agreement with our experimental measurements. These findings open up challenging perspectives on using Raman spectroscopy to characterize nanocrystallinity.

International audience; A nanoparticle in aqueous solution is modeled as a homogeneous elastic isotropic continuum sphere in contact with an infinite viscous compressible Newtonian fluid. The frequencies and damping of the confined vibrational modes of the sphere are calculated for the material parameters of a CdSe nanoparticle in water and a poly(methyl methacrylate) nanosphere in water. Although the effects of viscosity are found to be negligible for macroscopic objects, for nanoscale objects, both the frequency and damping of the vibrational modes are significantly affected by the viscosity of the liquid. Furthermore, both shear viscosity and bulk viscosity play an important role. A model of the spherical satellite tobacco mosaic virus consisting of outer solid layers with a water core is also investigated, and the viscosity of the water core is found to significantly damp the free vibrational modes. The same approach can be applied for nonspherical geometries and also to viscoelastic nanoparticles.

International audience; Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL or Apo2L) is a member of the tumor necrosis factor (TNF) superfamily. This type II transmembrane protein is able to bound specifically to cancer cell receptors (i.e., TRAIL-R1 (or DR4) and TRAIL-R2 (or DR5)) and to induce apoptosis without being toxic for healthy cells. Because membrane-bound TRAIL induces stronger receptor aggregation and apoptosis than soluble TRAIL, we proposed here to vectorize TRAIL using single-walled carbon nanotubes (SWCNTs) to mimic membrane TRAIL. Owing to their exceptional and revolutional properties, carbon nanotubes, especially SWCNTs, are used in a wide range of physical or, now, medical applications. Indeed due to their high mechanical resistance, their high flexibility and their hydrophobicity, SWCNTs are known to rapidly diffuse in an aqueous medium such as blood, opening the way of development of new drug nanovectors (or nanocarriers). Our TRAIL-based SWCNTs nanovectors proved to be more efficient than TRAIL alone death receptors in triggering cancer cell killing. These NPTs increased TRAIL pro-apoptotic potential by nearly 20-fold in different Human tumor cell lines including colorectal, nonsmall cell lung cancer, or hepatocarcinomas. We provide thus a proof-of-concept that TRAIL nanovector derivatives based on SWCNT may be useful to future nanomedicine therapies.

Équipe 103 : Composés intermétalliques et matériaux hybrides; International audience; The ability of some materials with a perfectly ordered crystal structure to mimic the heat conduction of amorphous solids is a remarkable physical property that finds applications in numerous areas of materials science, for example, in the search for more efficient thermoelectric materials that enable to directly convert heat into electricity. Here, we unveil the mechanism in which glass-like thermal conductivity emerges in tetrahedrites, a family of natural minerals extensively studied in geology and, more recently, in thermoelectricity. By investigating the lattice dynamics of two tetrahedrites of very close compositions (Cu12Sb2Te2S13 and Cu10Te4S13) but with opposite glasslike and crystal thermal transport by means of powder and single-crystal inelastic neutron scattering, we demonstrate that the former originates from the peculiar chemical environment of the copper atoms giving rise to a strongly anharmonic excess of vibrational states.

We introduce an adapted method for calculating the acoustic vibrational frequencies of arbitrarily shaped nanoparticles to high precision. Molecular dynamics simulation results are tested against exact solutions for a free sphere, a hollow sphere and a spheroid. This permits theoretical predictions of the frequencies of peaks in low frequency Raman spectra. Our results demonstrate that vibrational frequencies can be calculated for a wide range of low frequency modes with accuracies on the order of a tenth of a percent.

A one-step hydrothermal treatment of TiO2 powders under strongly basic conditions has been used to synthesize titanate nanoribbons. The nanoparticles were thoroughly characterized using several methods including transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectrometry (XPS) to determine their morphological, structural and chemical characteristics. The influence of the nature and size of the TiO2 precursor and of the reaction duration on the formation of the nanoribbons was investigated. The conditions required to obtain only titanate nanoribbons with a width ranging from 100 to 200 nm and several tens of micrometers in length were determined: the optimum precursor's grain size is about 25 nm and the reaction duration should be at least 20 h. Starting from our experimental results, we propose a multi-step mechanism of formation. In addition, a study of the integrity of the titanate nanoribbon structure reveals that they are made of an assembly of smaller ribbons juxtaposed and piled up on top of one another.

In this research we study optical absorption and morphology of silver films prepared with a sputtering method. Silver granular films are obtained on a glass substrate for films with thickness smaller than about 60 Å. Superficial silver clusters of around 100 nm in diameter are clearly seen in the atomic force micrographs. The absorption of these samples are characterized by plasmon excitation in the 450-650 nm spectral range, which differs from the known excitation of silver nanoparticles fabricated by different techniques. The optical absorption of silver granular films depend on sputtering conditions like substrate temperature or deposition rate and correlates with the surface morphology.

A solid-matrix-embedded spherical nanoparticle has acoustic vibrational frequencies which are shifted and damped relative to modes of a free sphere. Not only the longitudinal plane wave acoustic impedances, but also the Poisson ratios of nanoparticle and matrix are important in determining the Q-factor of the “breathing” mode, for which frequencies and Q-factors with different material combinations are presented. High matrix sound speed (e.g. silica, titania, alumina, diamond) increases Q.

Thin films of CoFe 2 O 4 have been fabricated by pulsed laser ablation of a metallic CoFe 2 target at two different temperatures (200 and 400 °C) and in various O 2 :N 2 , 20:80 pressures [from 0.7 Pa (5×10 -3 Torr) up to 26.7 Pa (2×10 -1 Torr)]. Too low pressures resulted in an insufficient oxidation of the deposited material and an antiferromagnetic (Fe,Co)O phase is observed together with CoFe 2 O 4 . A minimum pressure of 6.7 Pa was found necessary to obtain pure CoFe 2 O 4 films with magnetic properties close to the bulk. The higher the pressure and the temperature, the larger was the roughness of the films. The optimum deposition temperature and pressure to obtain flat (3 nm rms roughness) CoFe 2 O 4 films were, respectively, 200 °C and 6.7 Pa.

Arbitrary waves incident on a solid embedded nanoparticle are studied. The acoustic vibrational frequencies are shown to correspond to the poles of the scattering cross section in the complex frequency plane. The location of the poles is unchanged even if the incident wave is nonplanar. A second approach approximating the infinite matrix as a very large shell surrounding the nanoparticle provides an alternate way of predicting the mode frequencies. The wave function of the vibration is also provided., Comment: Accepted for publication in physica status solidi (c) (C) (2003) WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Proceedings of Phonons2004

The growth of paratellurite single crystals by the vertical-gradient freezing technique is reported for the first time. Boules of 120 mm long and 25 mm in diameter were obtained under a temperature gradient of 10°C cm −1 and translation rates lower than 0.6 mm h −1 . The spatial distribution of defects along the growth axis reveals a continuous evolution of the free convective fluid-flow regime as growth proceeds. Gas bubbles and dark inclusions rejected to the periphery in the upper part of the crystal are observed to lay preferentially in (1 0 0), (0 0 1), ( 1 1 ¯ 0 ) and (1 1 2) crystallographic planes. Among them, SEM and microprobe analyses evidenced the presence of metallic platinum, while micro-Raman experiments allowed to assess oxygen as being actually the gas content of occluded bubbles, originated at the crucible wall through Pt-induced dissociation of Te–O bonds.

The effects of the physical aging on the vibrational density of states (VDOS) of a polymeric glass is studied. The VDOS of a poly(methyl methacrylate) glass at low-energy (, To be published in Europhys. Lett

When silicon thin films are deposited by plasma enhanced chemical vapor deposition in a plasma regime close to powder formation, a new type of material, consisting of an amorphous matrix in which silicon nanocrystallites are embedded is obtained. This material, named hydrogenated polymorphous silicon (pm-Si: H), exhibits enhanced transport properties with respect to state-of-the-art hydrogenated amorphous silicon (a-Si: H). In order to understand the origin of such improved properties, we investigated structural characterization of pm-Si:H films. High resolution transmission electron microscopy (HRTEM) micrograph, micro-Raman and infrared spectra of the films are presented. The crystallite sizes deduced from the Raman spectra are supported by the HRTEM measurements. The infrared stretching modes of pm-Si:H films present a band at similar to2030 cm(-1) attributed to hydrogen platelets. Two approaches are then given in order to explain the enhanced photoconductivity properties. The first one, qualitative, appeals to low density of states at the Fermi level N(E-F) and low capture cross-section of electrons sigma(c) due to the improved amorphous matrix. The second, more quantitative, suggests that recombination mainly occur at dangling bonds at the surface of the crystallites. Considering the dangling bond density at silicon surface passivated by hydrogen and the description of multiphonon carrier capture, both given in the literature, we derive N(E-F) and sigma(c) values in good agreement with experiments.

The effect of aging following different treatments on the high frequency dynamics of a polymeric glass was measured by means of low frequency Raman scattering and inelastic neutron scattering. The spectra, in particular the Boson peak, are consistent with the discontinuous network model at the nanometric scale. The effects of similar aging procedures on slow dynamics are investigated by low frequency mechanical spectroscopy. The set of results is discussed within a multiscale description of the glassy state disorder.

TiO 2 thin films were deposited on (100) GaAs substrates by LP-MOCVD with deposition temperatures ( T d ) ranking from 450 to 750 °C. The structure of these layers was studied by X-ray diffraction (XRD) and Raman spectroscopy. The growth of the TiO 2 anatase phase was observed for T d T d >600 °C. Finally, X-ray photoelectron spectrometry (XPS) and secondary ion mass spectroscopy (SIMS) experiments showed the presence of small quantities of Ga and As through the whole film thickness, slightly increasing at the surface of the layers. This result was related to the SEM observations and explained by considering the growth conditions.

International audience; The effect of an applied high pressure on the optical and acoustic vibrations of small anatase TiO2 nanoparticles is studied using Raman scattering. All the Raman peaks show a significant variation of their frequency with pressure, except for the low-frequency peak which is due to acoustic vibrations confined in the nanoparticles. These variations (or lack thereof) are compared to first-principles calculations of the stiffness tensor and phonons of bulk anatase TiO2 as a function of pressure. In particular, the variation of the shape of the low-frequency peak is explained by the increase of the elastic anisotropy of anatase TiO2 as pressure is increased.

International audience; Low-frequency Raman scattering experiments have been performed on metal nanoparticles embedded in two different thermally treated matrices. In addition to the well-known Raman scattering by the nanoparticle quadrupolar vibrational mode, the spectra measured in the $3–40 cm^{−1}$ frequency range exhibit several new bands. They are ascribed to resonant scattering by the nanoparticle breathing mode and its harmonics, in very good agreement with time-resolved measurements.

International audience; We report sharp low-frequency Raman spectral features of supercrystals synthesized via the "benzyl alcohol route" and consisting of either yttrium-stabilized or pure zirconia (ZrO2) nanocrystals. In situ formed benzoate species control the nanocrystal growth and act as organic glue leading to the assembly of the nanocrystals in highly ordered 3D supercrystals. We attribute some Raman peaks to THz acoustic vibrations of individual nanocrystals which are only weakly coupled due to the strong acoustic mismatch between the capping ligands and the nanocrystals. Peak positions are consistent with nanocrystal sizes estimated from transmission electron microscopy and X-ray powder diffraction studies. Narrow size distribution, together with uniform morphological and structural features of the nanocrystals, leads to sharp Raman peaks in the THz spectral region. After removing the ligands by annealing, the acoustic vibrations of the nanocrystals couple resulting in an increase of their frequency. These findings suggest that 3D supercrystals of zirconia nanocrystals can be used for manipulating THz phonons.