André Maisonnat

Synthesis of tin and tin oxide nanoparticles of low size dispersity for application in gas sensing.

Nanocomposite core-shell particles that consist of a Sn0 core surrounded by a thin layer of tin oxides have been prepared by thermolysis of [(Sn(NMe2)2)2] in anisole that contains small, controlled amounts of water. The particles were characterized by means of electronic microscopies (TEM, HRTEM, SEM), X-ray diffraction (XRD) studies, photoelectron spectroscopy (XPS), and Mossbauer spectroscopy. The TEM micrographs show spherical nanoparticles, the size and size distribution of which depends on the initial experimental conditions of temperature, time, water concentration, and tin precursor concentration. Nanoparticles of 19 nm median size and displaying a narrow size distribution have been obtained with excellent yield in the optimized conditions. HRTEM, XPS, XRD and Mossbauer studies indicate the composite nature of the particles that consist of a well-crystallized tin beta core of approximately equals 11 nm covered with a layer of approximately equals 4 nm of amorphous tin dioxide and which also contain quadratic tin monoxide crystallites. The thermal oxidation of this nanocomposite yields well-crystallized nanoparticles of SnO2* without coalescence or size change. XRD patterns show that the powder consists of a mixture of two phases: the tetragonal cassiterite phase, which is the most abundant, and an orthorhombic phase. In agreement with the small SnO2 particle size, the relative intensity of the adsorbed dioxygen peak observed on the XPS spectrum is remarkable, when compared with that observed in the case of larger SnO2 particles. This is consistent with electrical conductivity measurements, which demonstrate that this material is highly sensitive to the presence of a reducing gas such as carbon monoxide.

Synthesis and characterization of monodisperse zinc and zinc oxide nanoparticles from the organometallic precursor [Zn(C6H11)2]

Abstract Decomposition of the organometallic precursor [Zn(C6H11)2] in wet anisole leads to the formation of monodisperse spherical Zn particles of 6 nm mean diameter. High resolution electron microscopy (HRTEM) indicates the crystalline nature of these particles and photoelectron studies (XPS) are consistent with the presence of both zinc and zinc oxide. In the presence of polyvinylpyrolidone (PVP), the decomposition leads to well dispersed nanoparticles for which HRTEM studies evidenced the presence of hexagonal zinc (0) surrounded by a thin layer of hexagonal zinc oxide of wurtzite type. The thermal oxidation of these zinc nanoparticles yields well-crystallized nanoparticles of ZnO without coalescence or size change. An X-ray diffraction pattern shows that the powder consists of pure hexagonal wurtzite-type phase.

Synthesis and use of a novel SnO2 nanomaterial for gas sensing

Abstract Decomposition of the organometallic precursor [Sn(NMe 2 ) 2 ] 2 in a controlled water/anisol mixture leads to the formation of monodisperse nanocomposite particles of Sn/SnO x . Full oxidation of the particles into SnO 2 occurs at 600°C without size or morphology change. These particles can be deposited onto silicon nitride covered microelectronic platforms and used as sensitive layers of gas sensors. Doping of the sensors with palladium can be achieved either by co-decomposition of organometallic precursors (doping in volume) or by deposition of palladium on preformed SnO 2 nanoparticles (doping in surface). The doped sensors display an unusually high sensitivity for CO sensing.

Synthesis and Self-Assembly of Monodisperse Indium Nanoparticles Prepared from the Organometallic Precursor [In(η5-C5H5)]

Spontaneous decomposition of [In(η5 -C5 H5 )] in the presence of poly(vinyl pyrrolidone) or trioctylphosphane oxide (TOPO) as a stabilizer gave monodisperse indium nanoparticles with a mean diameter of about 5-6 nm. In the case of TOPO, self-organization of the nanoparticles in two- and three-dimensional superlattices is observed.

Organometallic chemistry: an alternative approach towards metal oxide nanoparticles

The synthesis of nanoparticles of controlled size, shape, size distribution and surface state is nowadays recognized to be of prime importance both from a fundamental point of view and for applications. Among all nanomaterials, nanoparticles of metal oxides are very attractive as their unique characteristics make them the most diverse class of materials with properties covering almost all aspect of solid-state physics, materials science and catalysis. In this feature article, we present our efforts toward the synthesis of metal oxide nanoparticles of controlled size and shape using organometallic chemistry. We show that this approach is versatile and can be generalized to several metal oxides from semiconducting to magnetic materials as well as from monometallic to mixed-metal-oxide nanomaterials. We point out that the control over the size, the shape, and the surface state of such materials is of prime importance for understanding and controlling their physical properties. We also report the use of such semiconducting nanoparticles for two different applications, highlighting the importance of the implementation of the nanoparticles in the fabrication of devices.

Organometallic approach for the synthesis of nanostructures

Nanostructures are considered as chemical systems of high potential owing to their unusual properties at the interface of those of molecular species and bulk metals. Consequently, they are promising candidates for application in different domains such as catalysis, magnetism, medicine, opto-electronics or sensors. The control of the characteristics of nanostructures is a fundamental prerequisite if one envisages exploring their physical or chemical properties since they vary dramatically with size, shape and surface state. Thus, the development of efficient methods leading to reproducible nanostructures is presently one of the main objectives in the nanochemistry community. Although organometallic chemistry has been early involved, it arises only marginally in the field. Nevertheless, the concepts and techniques of organometallic chemistry appear to be well-adapted for the growth of well-controlled nanostructures. This will be discussed through recent advances in the synthesis of metal and metal oxide nanoparticles in terms of size dispersion, chemical composition, surface state, shape or organization, pointing out the role of ligands. Moreover their characterization at a molecular level and the development of their chemical/physical properties towards applications will be described. This review reflects more than 20 years of efforts of our team to achieve these goals.

Full Characterization of Colloidal Solutions of Long‐Alkyl‐Chain‐Amine‐Stabilized ZnO Nanoparticles by NMR Spectroscopy: Surface State, Equilibria, and Affinity

Full NMR characterization of ZnO nanoparticles (NPs) stabilized by various amines (hexadecylamine, dodecylamine, and octylamine) in C(7)D(8) demonstrated that the surface of this apparently simple system was very complex. Using different NMR spectroscopic techniques ((1)H, PGSE-NMR, diffusion-filtered (1)H NMR, NOESY, ROESY), we observed at least three different modes of interaction of the amines at the surface of the NPs, in thermodynamic equilibrium with the free amines, the relative populations of which varied with their concentration. The first mode corresponded to a strong interaction between a small amount of amine and the ZnO NPs (k(desorp)≈13 s(-1)). The second mode corresponded to a weak interaction between the amines and the surface of the ZnO NPs (k(off(2))≈50-60 s(-1)). The third, and weakest, mode of interaction corresponded to the formation of a second ligand shell by the amine around the NPs that was held together through van der Waals interactions (k(off(1))≈25×10(5) s(-1)). The second and third modes were in fast exchange on the NMR timescales with the free amines. The strongly interacting amines at the NPs surface (first mode) were in slow exchange with the other modes. A complex hydrogen-bonding network at the NPs surface was also observed, which did not only involve the coordinated amine but also THF and water molecules that remained from the synthesis.

Experimental study of LO phonons and excitons in ZnO nanoparticles produced by room-temperature organometallic synthesis

We report here the study by optical microspectroscopy of crystalline ZnO nanoparticles produced by room-temperature organometallic synthesis. We present resonant Raman scattering spectrum obtained from different sized nanostructures from which the longitudinal-optical (LO) phonon frequency has been found to be very weakly dependent on their size. Low-temperature photoluminescence measurements reveal that (i) the band-edge PL of ZnO nanoparticles is dominated by weakly bound localized exciton, and that (ii) its energy does not exhibit any spatial confinement effect. These results enlighten the need for surface passivation of the nanoparticles to improve their UV emission potential.

Raman study of E2 and surface phonon in zinc oxide nanoparticles surrounded by organic molecules

Using Raman spectrometry, we obtained results showing the influence of organic ligands on the vibrational properties of small zinc oxide nanocrystals (2.1–6.8nm). It is shown that it is possible to distinguish both mechanical and dielectric effects from the E2 nonpolar phonon mode and from a surface mode, theoretically predicted but rarely observed. It has been found that E2 phonon is not dependent on the nanocrystal size, but its frequency decreases with increasing ligand length, characteristic of a tensile stress on the nanocrystal. We report also the observation of a surface optical mode, the experimental frequency of which is in reasonable agreement with available calculations.

Self-assembly of ZnO nanocrystals in colloidal solutions.

The self-organization in solution of ZnO nanocrystals into superlattices is monitored by dynamic light scattering. When long-alkyl-chain amines or carboxylic acids are used as stabilizing ligands, no organization is observed. In contrast, when binary mixtures of long-alkyl-chain amines and carboxylic acids are used, the presence of a thermodynamic equilibrium between free and organized ZnO nanoparticles is detected in THF or toluene. The superlattices of organized ZnO nanoparticles are independently observed by TEM and SEM. The coordination mode of the ligands at the surface of the ZnO nanoparticles is evidenced by NMR studies. The presence of ion-paired ammonium carboxylate surrounding the surface of ZnO nanoparticles appears to be a necessary requirement to govern this reversible organization. This is substantiated by the absence of organization of ZnO nanoparticles when either a solvent of high dielectric constant, such as acetone, or a strong hydrogen-bond acceptor is used.