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A series of cerium samarium tungstates Ce(2– x )Sm x (WO4)3 with $x \le 0.3$ was synthesized by a coprecipitation method followed by thermal treatment at 1000 °C. The polycrystalline compounds were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) experiments. Using the Rietveld procedure, the decrease in cell parameters showed that a solid solution was obtained. A comparative analysis of diffraction profiles allowed determining structural distortions increasing with increasing composition $x$ . The PL experiments were performed under UV and XR excitations. The variations with composition $x$ of emission intensities observed in the wavelength range of 500–1000 nm, corresponding to complex charge transfers (CTs) and quenching effects, were interpreted in terms of transitions proper to Ce3+ and Sm3+ cations, accompanied by additional transitions due to oxygen vacancies and other point defects due to substitution and synthesis conditions.

Well-crystallized Ca

International audience; Having clear and deep information on the surface/interface of deposited molecules is of crucial importance for the development of efficient optoelectronic devices. This paper reports on a joint experimental/theoretical approach based on Raman spectroscopy in order to provide information on the orientation of deposited push-pull chromophores onto a gold surface. In addition, several parameters can strongly control or impede the orientation of such molecules on the surface such as: the molecular structure, the surface itself, the method of deposition and the solvents used. From this approach, additional information has been highlighted such as perpendicularly depositing the molecule on the surface, the bithiophene compounds displaying more solvent effects compared to terthiophene molecules and so on. According to the results, the joint SERS/DFT study proves to be an effective tool for probing the arrangement of push-pull chromophores and selecting right experimental conditions to tune the surface properties.

International audience; The photoluminescence of two series of A- and B-site Eu3+ substituted (SrxBa1-x)(2)CaWyMo1-yO6 double perovskite phosphor materials, (SrxBa1-x)(1.96)Eu0.02K0.02CaWyMo1-yO6 and (SrxBa1-x)(2)Ca0.96Eu0.02Li0.02WyMo1-yO6 (x and y=0, 0.25, 0.50, 0.75, and 1), were studied systematically as a function of stoichiometry and crystal structure. The Eu3+ lattice sites controlled by co-doping with either K or Li were confirmed by Raman spectroscopy. The variation in integrated emission intensity and emission colour over the experimental matrix was examined using statistical tools, and the observed trends were rationalized based on the physical and electronic structure of the phosphors. Phosphors with Eu on B-site with maximum Sr content had remarkably higher emission intensities than all other materials, but the emission was more orange than red due to domination of the D-5(0) - F-7(1) (595 nm) transition of Eu3+. The relative intensities of the D-5(0) - F-7(2) (615 nm) and D-3(0) - F-7(1) transitions of Eu3+, and thus the red-shift of the emission, decreased linearly with increasing Sr content in the A-site Eu-substituted phosphors, and reached a maximum for Sr1.96Eu0.02K0.02CaW0.25Mo0.75O6. A maximum external quantum efficiency of 17% was obtained for the phosphor Sr2Ca0.7Eu0.15Li0.15W0.5Mo0.5O6 with Eu on B-site. (C) 2016 Elsevier Inc. All rights reserved.

The solid solution Sr{sub 1−x}Pb{sub x}WO{sub 4} based on luminescent tungstates SrWO{sub 4} and PbWO{sub 4} has been synthesized by solid-state reaction for all compositions 0≤x≤1. Using Rietveld method, the structural data of all polycrystalline samples have been refined and crystal cell parameters exhibited a linear behavior as a function of x. All substituted structures are of scheelite type. Scanning electron microscopy showed that a high level of crystallization characterized the samples, with modifications in sizes and shapes depending on composition x. Infrared and Raman spectroscopy have been performed to characterize the evolution of vibrational modes with substitution rate. Finally, a systematic study of luminescence under X-ray excitation has been performed: in the composition range x=0.2 to 0.4, intensities of emission exhibited increased values. The luminescence profiles have been interpreted in terms of four Gaussian components, two of them depending on substitution rate. - Graphical abstract: Photoluminescence under X-ray excitation of Sr{sub 1−x}Pb{sub x}WO{sub 4} solid solution: (left) decomposition of emission large band into four components for composition x=0.3; (right) variation of total emission intensity with composition x. - Highlights: • Structural study of solid solution Sr{sub 1−x}Pb{sub x} WO{sub 4} using Rietveld analyses. • Variation of Debye–Waller factor withmore » composition x, disorder parameter. • Existence of four components of luminescence under X-ray excitation. • Effect of substitution of Sr by Pb on two components, due to Pb–O–W interactions. • Enhancement of luminescence intensity in a specific composition range.« less

A series of polycrystalline barium-lead tungstate Ba1-xPbxWO 4 with 0 ≤ x ≤ 1 was synthesized using a classical solid-state method with thermal treatment at 1000 °C. These materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Raman (FT-Raman) spectroscopy. X-ray diffraction profile analyses were performed using Rietveld method. These materials crystallized in the scheelite tetragonal structure and behaved as quasi ideal solid solution. Raman spectroscopy confirmed the formation of the solid solution. Structural distortions were evidenced in X-ray diffraction profiles and in vibration Raman spectra. The scanning electron microscopy experiments showed large and rounded irregular grains. Luminescence experiments were performed under X-ray excitation. The luminescence emission profiles have been interpreted in terms of four Gaussian components, with a major contribution of blue emission. The integrated intensity of luminescence reached a maximum value in the composition range x = 0.3–0.6, in relation with distortions of crystal lattice.

International audience; The bismuth lutetium tungstate series Bi(2−x)Lu(x)WO6 with 0.1 ≤ x ≤ 1 were synthesized by solid state reaction of oxide precursors at 1000 °C for 3 h. The as-prepared polycrystalline compounds were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and photoluminescence (PL) analyses. Biphasic samples were obtained in the composition range of 0.1 ≤ x ≤ 0.3. Solid solutions were obtained in the composition range of 0.4 ≤ x ≤ 1, and their monoclinic crystal structure was refined using the Rietveld method. SEM micrographs showed that solid solutions presented homogeneous morphologies. Attributions of Raman vibrational modes were proposed. A shift in the vibrational wavenumber depending on the lutetium composition was observed. The specific broadening of the spectral bands was interpreted in terms of long range Bi/Lu disorder and local WO6 octahedron distortions in the structure. The PL experiments were performed under UV-laser light irradiation. Each PL band was decomposed into three Gaussian components with energies close to 1.25, 1.80 and 2.1 eV. Their integrated intensities increased with the value of x. The presence of the near infrared band at 1.25 eV is discussed.

Nanocrystals of 20 mol % Gd3+-doped CeO2 dispersible in basic aqueous solutions were grown via hydrothermal treatment of anionic Ce(IV) and Gd(III) carbonate complexes at 125–150 °C for 6–24 h with N(CH3)4+ as a capping agent. The nanocrystals were characterized in detail using dynamic light scattering (DLS), ζ-potential measurements, X-ray diffraction (XRD), specific surface area measurements based on the Brunauer–Emmett–Teller theory (SSABET), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy, and Raman spectroscopy. DLS analysis revealed that the highly transparent product solution consisted of nanocrystals approximately 10–20 nm of hydrodynamic diameter with a very narrow size distribution, while the ζ-potential analysis results strongly suggested that the N(CH3)4+ capped negatively charged sites on the nanocrystals’ surface and provided sufficient repulsive steric effect to prevent agglomeration. Moreover, the crystallite size (dXRD) estimated from the XRD patterns and the ...

We studied the growth of SnO2 nanocrystals with a tailored structure via surface capping assisted hydrothermal approach with tetramethyl ammonium hydroxide (N(CH3)4OH; TMAH). KOH and NaOH were also used instead of TMAH for comparison. The nanocrystals with a size ranging from 3.2 ± 0.9 to 74 ± 20 nm were grown at 150 °C for 24 h depending on the pH. N(CH3)4+ capped the surface of SnO2 and improved the dispersion of the nanocrystals in basic aqueous solutions. The capping provided nanocrystals finer than those grown with KOH and NaOH because of suppressed Ostwald ripening via a reduction in surface energy. High-resolution transmission electron microscopy revealed that the nanocrystals grown in strong basic solutions with TMAH had cubic morphology terminated by the (001) and (110) faces. This strongly suggests that N(CH3)4+ preferentially caps the (001) face with the highest surface energy and decreases its surface energy to be comparable to that of the (110) face with the lowest surface energy. Anisotropic...

Hydrated nanostructured cerium dioxide CeO2, xH2O (hydrated nanoceria) has been synthesized in room conditions via a precipitation route. This hydrated nanoceria phase has been subjected to thermal decomposition in the temperature range from 25 °C to 800 °C. At least three decomposition steps have been observed in thermal and thermogravimetric analyses. Three different samples of cubic nanoceria respectively obtained at room temperature (RT-nanoceria), 80 °C (80-nanoceria) and 600 °C (600-nanoceria) have been studied by X-Ray diffraction, Raman spectroscopy and scanning electron microscopy analyses. The analyses of X-ray diffraction profiles and Raman vibrational bands have clearly shown that dehydration is accompanied by increasing crystallite size, lattice parameter contraction. The cubic structure of hydrated RT-nanoceria might be associated with a complex chemical formula unit involving Ce4+, Ce3+ mixed valences, oxygen vacancies, lattice and surface water and OH− proton species.

International audience; Increasing the activity of a photocatalyst goes through the improvement of both its absorption (light) and adsorption (reactant) properties. For a given semiconducting material, the charge carrier separation is also a very important step. Properly combining chosen phases is one option to improve this separation (example of the commercial P25) and depositing platinum on the surface of the catalyst, another one. In some cases, coupling both may nevertheless lead to a decrease of photoactivity or at least limit the potentiality of the catalyst. A third option, consisting in modifying the morphology of the photoactive phase, has shown very promising results. In this study, we have elaborated, characterized and evaluated the hydrogen evolution potentiality (through methanol assisted water splitting) of different TiO2 morphologies: nanoparticles, nanotubes and aerogels. These materials have shown different behaviours depending on both their composition and morphology. Different types of separation processes have been claimed to account for the observed different photoactivities, with more or less pronounced synergetic effects, due to: the use of Pt as a co-catalyst, the mixture of different TiO2 phases (anatase and TiO2(B) or rutile) and the specific morphology of the samples (nanotubes or aerogels). Among all the tested samples, the TiO2 aerogel supported Pt one exhibited very promising performances, three times as active as P25 supported Pt, which is already much more active than pure P25 in our testing conditions.

International audience; We compared the surface enhanced spectroscopy signal arising from dye molecules (methylene blue, crystal violet and octadecylrhodamine B) deposited on gold nanostructures fabricated onto two kinds of substrates: silicon wafer or glass. For any molecule and excitation wavelength, the observed signal was always higher on glass compared to silicon. This experimental result is confirmed by Finite-Difference Time Domain calculations: the enhancement in the electric field is much higher with gold nanoparticles on glass than on silicon, even if a thin oxide layer is present. These results clearly demonstrate that the nature of the substrate, independently of metallic nanoparticles, is important for the preparation of highly efficient SERS nanostructures.

A series of ceramics samples belonging to theCeO2-Bi2O3phase system have been prepared via a coprecipitation route. The crystallized phases were obtained by heating the solid precursors at600∘Cfor 6 hours, then quenching the samples. X-ray diffraction analyses show that forx<0.20a solid solutionCe1−xBixO2−x/2with fluorine structure is formed. For x ranging between 0.25 and 0.7, a tetragonalβ′phase coexisting with the FCC solid solution is observed. For x ranging between 0.8 and 0.9, a new tetragonalβphase appears. Theβ′phase is postulated to be a superstructure of theβphase. Finally, close tox=1, the classical monoclinicα Bi2O3structure is observed. Raman spectroscopy confirms the existence of the phase changes as x varies between 0 and 1.

In this paper, strontium lead molybdate Sr1-xPbxMoO4 polycrystalline samples with 0

International audience; Two series of A-site and B-site Eu3+ doped (SrxBa1-x)(2)CaWyMo1-yO6 double perovskite phosphor materials were prepared via a modified Pechini sol-gel route; (SrxBa1-x)(1.96)Eu(0.02)K(0.02)CaW(y)Mo(1-)yO(6) and (SrxBa1-x)(2)Ca0.96Eu0.02Li0.02WyMo1-yO6 (x and y=0, 0.25, 0.50, 0.75, 1). The Sr/Ba ratio was the main determinant for the crystal symmetry of the series, while variation in the W/Mo ratio did influence the crystal symmetry significantly. The crystal structure evolved with Sr/Ba ratio from cubic Frn (3) over barm for x=0, via tetragonal 14/m for x=0.25, to monoclinic P2(1)/n for x >= 0.5, as verified by Rietveld refinement of X-ray diffractograms as well as by Raman spectroscopy. The reported boundaries for the compositionally induced phase transitions are in very good agreement with reported optical properties. (C) 2015 Elsevier Inc. All rights reserved.

This paper reports fabrication methods for ordered metallic nanostructures such as nanowires and nanoparticles based on deoxyribonucleic acid (DNA) templates. The phosphate groups in DNA are negatively charged; consequently, the DNA conformation may mineralize metals e.g., palladium (Pd) at a relatively high metal concentration. We successfully form unique spherically shaped moss-like hybrid Pd nanoparticles using the small compacted globular state of DNA by controlling the reductive reaction [1,2]. This paper also shows the fabrications of Pd-carbon nanotube (CNT) [3,4] and silver (Ag)-CNT [5] hybrid nanomaterials as shown in Fig.1.

Biological structures harvesting sunlight have evolved for several millions of years in different ways to optimize conversion efficiency. One of the most noteworthy examples of optical bio-nanostructures is the complex silica nanoporous frustule surrounding diatoms (unicellular algae). Diatoms have recently attracted significant attention for their potential in photonic applications [1]. Coscinodiscus wailesii diatom frustules have been shown to combine photonic band gap and waveguide properties resulting in a wavelength dependent light focusing effect. Our experimental and computational results show the dependence between the spatial distribution of light transmitted through a single Coscinodiscus wailesii frustule and the wavelength. We used hyperspectral transmission mapping measurements to study the optical properties of single frustules of Coscinodiscus centralis (CC) and Coscinodiscus wailesii (CW) diatoms. Our aim is to provide a new insight on these properties using direct visualization of the light distribution after transmission through diatom frustules with different structures.

Thermochromic vanadium dioxide VO 2 exhibits a semi-conducting to metallic phase transition at T c =68 °C, involving strong variations in optical transmittance, reflectance and emissivity. However, the optical contrasts observed in thin films or nanostructured compacted samples seem to depend on both surface microstructure and surface crystal texture. In the case of opaque materials, surface defects might play a drastic role in optical reflectivity. As the high temperature metallic phase of VO 2 is opaque for infrared radiations, we used aluminum samples as standards allowing us to correlate reflectivity responses with porosity and surface defects. Then, various polycrystalline and nanostructured VO 2 samples compacted at various pressures and presenting variable surface roughness were prepared. Thin films were deposited by radio frequency sputtering process. The samples were characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Optical properties (reflectance and emissivity) were analyzed above and below the transition temperature, making use of specific FTIR equipments. In thin films, the deposited VO 2 phase was systematically oriented and surface porosity was very weak. In polycrystalline samples, as the compaction pressure increased, surface porosity decreased, and infrared optical contrast increased. In such samples, preferred orientations were favored for low applied pressures. These features clearly show that the main parameters conditioning the optical contrast should be the surface defects and porosity, not the preferred crystal orientations. As an additional interesting result, the surfaces formed from compacted nanocrystalline VO 2 powders present improved optical contrast for reflectance and emissivity properties.

The crystal structures and structure transformations of ZrAu have been investigated by means of neutron powder diffraction on as-cast ingots placed in evacuated quartz tubes to avoid oxidation. In the temperature range 300–1273 K, two structure transformations have been observed and confirmed by resistivity measurement results. The first one occurs at about 670 K and is a second-order transition as it does not yield any differential thermal analysis (DTA) event. The second one occurs at 840 K as previously reported. In each temperature interval, a complete structure model compatible with collected data was derived and used for Rietveld analysis. Between room temperature and 670 K, the structure is found triclinic (P 1 , a=11.537(8) A, b=4.841(1) A, c=11.507(7) A, α=87.42(1)°, β=104.82(1)° and γ=92.41(2)° at 300 K). Above 670 K and below 840 K, the structure is satisfactorily described in the monoclinic space group P2/m (a=11.695(16) A, b=4.828(3) A, c=11.719(18) A, β=107.090(17)° at 773 K) and finally between 840 and 1273 K, it is tetragonal, closely related to the A2-type structure (P4/mmm, a=4.835(2) A and c=3.416(3) A).

This work deals with high efficient optical switching properties at 68 °C of thermochromic vanadium dioxide ( V O 2 ) thin films deposited on amorphous silica substrates. V O 2 thin films were deposited by radio frequency reactive sputtering process. Conditions of deposition were optimized making use of parameters such as film thickness, gas ratio and substrate temperature. Process was optimized adjusting the distance between target and substrate, and dimensions of target and substrates, to obtain a good uniformity and reproducibility of the layers. X-Ray diffraction patterns and scanning electron microscopy convincingly illustrated that V O 2 thin films could grow on amorphous silica substrates with a specific preferential crystal orientation: the [001] M crystallographic direction of oxygen octahedral chains is parallel to the substrate plane and corresponds with vanadium–vanadium links (insulating state) or with a maximum of electron delocalization (metal state). Optical switching properties in the mid-infrared range are discussed: transmittance, reflectance and emissivity values are strongly modified at the thermochromic transition temperature ( Tc =68 °C). A maximum of optical transmittance contrast is observed for a thickness of 120-nm, then interpreted in terms of absorption law. Using a specific software, the n and k optical indices are determined and used to simulate the variation of transmittance vs. film thickness.

Piezoelectric ceramics for acoustic applications have been prepared by mixing the piezoelectric phase Pb1−1.5xLax□x/2(Ti1−yZry)O3 (PLZT) with variable fractions of Al2O3. The samples are in form of pellets and polarized at high temperature. After thermal treatment, X-ray diffraction and scanning electron microscopy have been used to determine the phase and morphological modifications. The morphotropic PLZT initial phase disproportionates into modified PLZT and ZrO2 phases. Using electrical impedance spectroscopy, the resonance frequencies of the composite system have been determined and analyzed. As the Al2O3 volume fractions increase, the resonance frequency and the amplitude of the electrical response both decrease. An interpretation of the role of Al2O3 additions is proposed in terms of phase and microstructure modifications. Using LRC electrical equivalent circuits, the impedance variations close to the resonance frequency are modeled: the increase of the resistance R (electrical losses) and of the capacitance C are respectively correlated to the change in microstructure and in nature of PLZT initial phase.

Optical properties of single diatom frustule valves from two different Coscinodiscus species (C. wailesii and C. centralis) are studied by transmission confocal hyperspectral imaging and numerical calculations. Light convergence, concentration, and trapping effects are observed and depend on both the wavelength and the valve orientation. These effects seem to occur independently of the incident light angle. From our results, a wavelength-dependent multifocal lens behavior can be explained by light diffraction related to the radial symmetry of the multiscaled 3D nanostructure. This is the authors' accepted and refereed manuscript to the article. Non-commercial.

Five series of compacted granular metal–polymer composites were prepared in a wide range of metal volume fractions. The metals are Al, Fe, Ni, W and Zn powders. The polymer in powder form is the poly-phenylsulfur [-C6H4S-]n, noted as PPS. Using electrical complex impedance spectroscopy (ECIS) measurements, the a.c. electrical properties of these composites were analyzed as a function of metal volume fraction and of working frequencies. Each material was characterized by scanning electron microscopy to determine the distribution and morphology of the particles. Close to the percolation threshold, abnormal electrical behavior was observed and interpreted using scanning electron microscopy (SEM) analysis. Two types of modeling calculation are proposed to describe the electrical properties.A model inspired by the Effective Medium Approximation (EMA) improves the modeling approach: the mechanically induced modification of grain size and distribution is interpreted in terms of new modeling parameters governing the evolution of the conductance. A description of electrical behavior close to the percolation threshold is proposed using percolation theory. Critical exponents are determined above and below the percolation compositions. Finally, a study of corrosion behavior for Zn based composites is presented and correlated with the initial electrical behavior of these composites. © 2002 Elsevier Science B.V. All rights reserved.

Recently, we have shown that powders containing both gold and ZrO 2 nanosized particles could be prepared by low temperature (T< 100 °C) oxidation of cast crystalline Zr-Au alloys. In this report, we present the preliminary results of a study aiming at preparing the mixed nanosized particles from thin films. In a first step, pure Zr and Au layers are alternatively deposited by RF sputtering on Si and W substrates under vacuum. Then, the intermetallic compounds are formed at high temperature under an inert atmosphere or in vacuum. The resulting samples are characterised by X-ray diffraction and by scanning electron microscopy (SEM).

We compare the Raman scattering properties of hybrid nanostructures consisting of Ag nanoparticles (NPs) in disordered and aligned arrangements on single-walled carbon nanotubes (SWCNTs) as a result of chemical and photoreduction methods. In the latter case, the unique structure of the very small Ag NP (from 4 to 7 nm) chains generated an extremely large mode at 969 cm(-1) that was assigned to the sulphate-silver interaction at the NP surface. Another strong mode was present at 1201 cm(-1) and was assigned to an IR-active mode of sodium dodecyl sulphate (SDS); this mode was observed because the symmetry changes altered the selection rules. We demonstrate that both the UV photoreduction of silver and the presence of SWCNTs are necessary to produce this very strong Raman scattering. The Raman modes of the SWCNTs are also significantly modified by the presence of Ag NP chains along the nanotubes.

The reversible metal insulator phase transition of VO 2 ( T c =68°C) is associated with strong changes in electrical, magnetic and optical properties. Recently, nanopigments were synthesized using the low temperature irreversible structural transformation of the metastable VO 2 (B). Thin films were deposited under radio-frequency sputtering conditions. The optical transparency is remarkably increased for these nanosized particles and thin films. The VO 2 transition is characterized in the mid-infrared (MIR) region, using transmittance, reflectance and normal integrated emissivity measurements. Emissivity and reflectance are analyzed from two independent experimental techniques.

The structure of the lithium metavanadate LiVO 3 has been refined at room temperature from high-resolution neutron powder diffraction data. The unit cell dimensions are a =10.1597 (4) , b =8.4155 (3) , c =5.8843 (2) A, β =110.505° (2) , and V =471.23 (1) A 3 in the monoclinic space group C 2/ c with Z =8. Conventional R p and R wp reliability factors are respectively equal to 0.030 and 0.036. The structure consists of an alternating, along the b -axis, of bands of distorted LiO 6 octahedra running parallel to the c -axis which are linked by chains of VO 4 tetrahedra which are also parallel to the c -axis. The structural behavior of the ionic conductor LiVO 3 has been studied from neutron powder thermodiffractometry in the temperature range 340–890 K in order (i) to confirm the nature of the mobile species, (ii) to characterize the diffusion mechanisms, and (iii) to link the structural disorder existing in LiVO 3 to the high observed ionic conductivity.

This work describes the first successful synthesis of nanocrystalline thermochromic VO2 powder using the low temperature irreversible structural transformation of the metastable VO2(B). At this step, the transformation is associated with a total rearrangement of VO6 octahedra, and a strong increasing of density. The reversible metal‐insulator phase transition (MIPT) of vanadium dioxide (Tta 68∞C) is associated with strong changes in electrical, magnetic and optical properties. The contrast of the optical transition in mid-infrared (MIR) region and the optical transparency are remarkably increased for these nanosized particles. Modifications in coloration are also observed. ” 2000 Elsevier Science B.V. All rights reserved.

Copper oxalate particles precipitated from copper nitrate and sodium oxalate are aggregates of small crystallites. The crystallites seem to be self-organized such that they are very well aligned crystallographically within the volume of the aggregate. The addition of various cellulose derivatives induces different particle and crystallite morphologies. Without additives, particles with a cushion-like morphology are observed. Increasing the concentration of hydroxypropylmethylcellulose (HPMC) added to the precipitating agents induces a variation of the shape from low axial ratio forms such as cubes to higher axial ratio rods. The crystallites within these particles show a more elongated shape and smaller size as the HPMC concentration is increased. The polymer additive seems to influence the three steps of copper oxalate precipitation: nucleation, crystallite growth, and aggregation. The presence of HPMC affects the copper oxalate nucleation step whereby more nuclei are created and their sizes decrease as reflected by the crystallite volume (total number of crystallites increases while the precipitate yield is constant). In this paper we describe the characterization of these well-organized aggregates and propose a mechanism for the influence of the HPMC on the crystallite and aggregate shape.

An amphiphilic poly(acrylic acid)/polystyrene graft copolymer (PAA-g-PS) has been used to form “nanoreactors” for the synthesis of gold clusters. Such copolymers tend to form stable micelles in non-polar organic solvents where the poly(acrylic acid) chains constitute the core, and the polystyrene chains, the shell. In the present study, the micellar structure of PAA-g-PS in toluene has been demonstrated by dynamic light scattering and transmission electron microscopy (TEM). The subsequent preparation of gold-graft copolymer composites involved the introduction of gold chloride (AuCl3), either in powder form or previously dissolved in ether, into the micellar cores of the PAA-g-PS in toluene. The gold salt was then reduced by ultraviolet (UV) irradiation of the emulsion, or of dried cast films. TEM and ultraviolet-visible (UV/Vis) spectroscopy were used to characterize the resulting composites. Gold particles of less than 5 nm in diameter were observed in all cases, but the size distribution and the spatial arrangement of the clusters in the cast films were modified when diethyl ether was used to introduce AuCl3 into the PAA-g-PS micellar cores. This was thought to be due to enhanced nucleation of the gold particles and partial disruption of the micellar cores in the presence of diethyl ether.

The metastable VO 2 (B) transforms irreversibly into thermochromic VO 2 (R) between 400 and 500°C. Differential scanning calorimetry (DSC) of this transition shows a broad transformation starting with a first endothermic step at 420°C followed by a second exothermic step at 455°C. During this process, the initial platelet like VO 2 (B) morphology leads to a submicronic VO 2 (R) powder. This low temperature thermal treatment avoids the grain growth commonly observed in the case of classical routes at higher temperatures. This transformation with constant mass and high increases of density has been studied by XRD, IRTF spectroscopy, thermal analyses and electronic microscopies. The structure and properties of the VO 2 (R) issued from this irreversible transition are very similar to those of the VO 2 (R) obtained by the powder metallurgy process, except the optical properties. Indeed, this thermochromic VO 2 (R) powder shows an unexpected transition contrast in the IR spectral range during the insulator–metal transition at 68°C. Experimental observations by scanning electron microscopy (SEM) correlated with calculations could explain this high efficiency by the unusual morphology of the submicronic particles.

Composites consisting of nanogold in porous alumina host membranes have been fabricated and characterized. Nanocluster size (11 nm to 60 nm radius) and shape (prolate to oblate) were varied experim ...

The optical constants nAl and kAl of a 50/50 volume fraction Au/Ag alloy were derived synthetically by application of a Bruggeman (BG) effective medium expression. The alloy data base was then inpu ...

The mass production of highly dense oxides with high-temperature and high-pressure phases allows us to discover functional properties that have never been developed. To date, the quenching of highly dense materials at the gramme-level at ambient atmosphere has never been achieved. Here, we provide evidence of the formation of orthorhombic Fe2TiO4 from trigonal FeTiO3 as a result of the high-temperature (>1250 K) and high-pressure (>23 GPa) condition induced by the high collision energy of 150 gravity generated between steel balls. Ilmenite was steeply quenched by the surrounding atmosphere, when iron-rich ilmenite (Fe2TiO4) with a high-temperature and high-pressure phase was formed by planetary collisions and was released from the collision points between the balls. Our finding allows us to infer that such intense planetary collisions induced by high-energy ball milling contribute to the mass production of a high-temperature and high-pressure phase.

International audience; A singular adaptive phenotype of a parthenogenetic insect species (Acyrthosiphon pisum) was selected in cold conditions and is characterized by a remarkable apparition of a greenish colour. The aphid pigments involve carotenoid genes well defined in chloroplasts and cyanobacteria and amazingly present in the aphid genome, likely by lateral transfer during evolution. The abundant carotenoid synthesis in aphids suggests strongly that a major and unknown physiological role is related to these compounds beyond their canonical anti-oxidant properties. We report here that the capture of light energy in living aphids results in the photo induced electron transfer from excited chromophores to acceptor molecules. The redox potentials of molecules involved in this process would be compatible with the reduction of the NAD+ coenzyme. This appears as an archaic photosynthetic system consisting of photo-emitted electrons that are in fine funnelled into the mitochondrial reducing power in order to synthesize ATP molecules.

Copper oxalate (CuOx) mesocrystalline nanostructures have been synthesized by aqueous precipitation. Several morphologies of these nanostructures could be obtained with high monodispersity dependin...

Tip-Enhanced Raman Spectroscopy (TERS) is a very promising analytical technique for high sensitivity, high spatial resolution analysis of the physical and chemical properties of nanoscale materials including nanocrystals, biomolecules, carbon-based nanostructures and nanometer-size devices. Polarized TERS, in addition, offers novel opportunities for high contrast spectroscopy and imaging of semiconductor crystals and crystalline nanostructures. This chapter reviews the current state-of-the-art in polarization-sensitive TERS focusing the attention on the experimental implementations of the technique, on the light scattering properties of the metallic probes, on the Raman signal enhancement mechanisms and, finally, on the applications of this technique.

Aggregates of Au nanoparticles have been extremely easily obtained on glass substrates by physical sputtering under primary vacuum. With such a protocol, we demonstrate that it is possible to control the surface plasmon band absorption. Surface enhanced Raman spectroscopy (SERS) experiments were performed with methylene blue, zinc octacarboxyphthalocyanine, 4-aminothiophenol and cysteamine. The correlation between the absorption band and the wavelength giving the highest SERS intensity is clearly observed for methylene blue, in accordance with the electromagnetic enhancement theory. For the other molecules, effects of the chemical enhancement are also observed. In addition, we noticed a strong influence of the nature of the adsorbed molecule on the enhancement factor for a given wavelength. The origin of this feature is discussed in terms of resonant effects or multipolar surface plasmon modes.

Copper oxalate has been precipitated in water and acetone. Raman spectroscopy is performed to validate the chemical composition of the obtained powders. Aqueous precipitation has led to micrometer-scaled agglomerates, whereas acetone precipitation has led to nanorods showing a two-dimensional (2D) self-organization when deposited on a Si substrate. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) show an anisotropic structure of the agglomerates with two kinds of faces. Nanoplatelets with self-assembly abilities are also detected in the copper oxalate aqueous suspension. These observations reveal a supracrystalline self-assembly process leading to micrometer-scaled three-dimensional (3D) superstructures. AFM measurements on nanoplatelets and nanorods are correlated to X-ray diffraction results. A kinetic study carried out by SEM highlights four main steps in the 3D self-assembly process. Each step corresponds to a specific assembly speed ratio between the two directions that define the...

1 - Article; Tip-enhanced Raman spectroscopy has proven to be a promising technique for stress/strain mapping of silicon-based semiconductor devices on the nanometer scale. Field enhancement factors of up to 104 have been reported and a spatial resolution down to 20 nm has been claimed through exploiting far-field suppression techniques based on an appropriate choice of the excitation/detection polarization states. In this paper, we show that depolarization of light due to scattering from the tip plays a key role in the selective enhancement of the one-phonon optical mode peak at 520 cm−1 with respect to the two-phonon ones. The spatial confinement of the selective enhancement has been studied by means of approach curves, and its dependence on the excitation wavelength and power further explored. Conclusions on the physical nature of the enhancement (depolarization- or plasmonic-based) are presented. Copyright © 2009 John Wiley & Sons, Ltd.

Copper oxalate 1 �m-sized nanocrystalline assemblies with several shapes (cushions, lenses, drilled cushions, and square rods) have been obtained by aqueous precipitation without additive, with glycerol, with PEG and with HPMC. Respective influences of these additives on the nanocrystals self-assembly are suggested from the obtained particles morphologies to provide a better understanding of this assembly process. Raman spectroscopy is used to highlight fluorescence occurring on the copper oxalate samples synthesized with additives. This additive induced fluorescence is suggested to result from specific interactions between the nanocrystals and the adsorbed additives.

Copper-7,7',8,8'-tetracyanoquinodimethane (CuTCNQ) is an interesting material for memory applications since it reversibly switches from high to low resistance states under external voltage. In this paper, CuTCNQ material was prepared from the gas/solid reaction between metallic copper and hot gaseous TCNQ at low pressure to form CuTCNQ nanowires. Nanowires were first grown on Au stripes and aluminum top electrode deposition enabled formation of crossbar memory structures. Electrical testing including standard current-voltage and data retention measurements were performed on the Au/CuTCNQ/AI stacks. Besides, in order to apprehend the resistive switching mechanisms, Raman spectroscopy was carried out on packaged structures enabling measurements under electrical field. Finally, in the perspective of high-density memory devices, CuTCNQ nanowires were grown in via arrays and characterized by electron transmission microscopy.

Reference LTP-ARTICLE-1998-025doi:10.1023/A:1006658415927View record in Web of Science Record created on 2005-01-12, modified on 2017-05-10

International audience; The autonomous ordering and assembly of atoms and molecules on atomically well-defined surfaces allow creating a wide range of surface nanostructures, opening an alternative 'bottom-up' route to the traditional 'top-down' fabrication methods of the microelectronics industry now approaching their fundamental limits. This review summarises some recent efforts of our team to grow molecular arrays on metal, insulating or semiconductor surfaces. In a fundamental approach, two-dimensional surface arrays of nanometre size have been obtained under ultrahigh vacuum by evaporation of molecules, functionalised to favour the intermolecular links rather than molecule-substrate ones. Intermolecular links such as hydrogen bonds, covalent or coordination bonding were profitably used to create various molecular networks. Alternatively, we also investigated molecular self-assembly from the solution whose architectures are mainly fixed by the molecule-substrate adsorption forces. Molecular assemblies were characterised using Scanning Near-Field Microscopies (Scanning Tunnelling Microscopy, non-contact-Atomic Force Microscopy), whereas electronic and vibrational properties were investigated by surface spectroscopy such as Ultra-Violet and X-ray Photoelectron Spectroscopy, infrared or Surface-Enhanced Raman Spectroscopy.

There is strong interest in the research & development of the particle/polymer composite technology for functional applications. Current activities are directed towards polymer assisted synthesis of ultrafine metal or semiconductor particles in solution, with an ultimate goal to arrange the particles in a matrix in well-controlled fashion, for possible electro-optical applications. In the present work the optical properties of poly(acrylic acid) polymers containing gold chloride have been investigated. This material system permits synthesis of gold nanoparticles by the reduction of gold chloride. The polyelectrolyte initially forming upon mixture of the reagents shows a gelating behavior. In-situ reduction into gold clusters can be achieved by several ways. Rheological properties, optical absorption/extinction spectra as well as photoluminescence and photoluminescence excitation spectra will be presented and discussed. Different possible combinations of gold ligands and co-ordinations states will be considered in the discussion. Gold may be present in the form of complexes, to the polyelectrolytes, or in form of nanoparticles or larger aggregates depending on the relative concentrations of the reagents and polymer molecular weight.