none

Finding materials with high stability, high yield, and excellent catalytic performance has been an outstanding research challenge. Thiol-stabilized atomically precise metal nanoclusters (NCs) have attracted a lot of interest in recent years due to their unique properties and industrial applications, including catalysis, toxic metal-ion sensing, and magnetism. Unlike classical nanoparticles (NPs) which have larger sizes ranging between 10-100 nm, the size of nanoclusters typically ranges from 1 to 3 nm. Thus, nanoclusters represent good candidates to gain fundamental insights into optical and catalytic properties from the atomic to the molecular level. The majority of nanoclusters are based on Ag, Au, and more recently Cu. The major goal of this dissertation is the synthesis and structure determination of silver and copper nanoclusters. The first part of this dissertation addresses a shape-controlled synthesis strategy based on an isomeric dithiol ligand to yield the smallest crystallized silver nanocluster to date, formulated as Ag9. The second part discusses the preparation of different sizes of copper nanoclusters using a one-pot synthesis method and attempted to understand the structure-dependent catalytic pathways at the atomic level. Moreover, three novel Cu nanoclusters were developed: Cu29, Cu45, and Cu67. In terms of size, Cu67 represents a milestone towards high-nuclearity nanoclusters with interesting optical and structural properties. In terms of catalytic properties, Cu45 was found to be promising catalyst in hydroboration reactions of alkynes/alkenes and B2pin2, which affords hydroborated products with good to excellent yield. Mechanistic studies showed single-electron oxidation of an in-situ formed ate complex ([B2pin2]OH-) by the Cu45 catalyst, enabling hydroboration of unsaturated double bonds via a boryl-centred radical. These findings motivate us to extend the library of ligand-protected nanoclusters and focus deeply on exploiting metal nanoclusters based on Cu for catalysis.

Photocarrier relaxation mechanisms in CdTe quantum dots in the strong confinement regime were investigated using femtosecond pump-probe measurements. The quantum dots were formed in films deposited on silica substrates using a sequential RF magnetron sputtering process with heat treatment to grow crystallites of various sizes. Size selection was achieved by tuning the laser to various wavelengths across the first excitation transition. The recombination mechanism showed a biexponential decay, which was fitted to a three-level model. It was shown that recombination occurs increasingly through the intermediate energy level as the size of the dots decreases. The nature of the intermediate level and the role of Auger recombination is discussed.

Since 1990, D. M. Eigler and E. K. Schweizer manipulated the xenon atoms on the Ni(110) surface to pattern the atomic scale structure. The researches about manipulation of atoms/ molecules become a major research in surface science. One of the ultimate goals of nanotechnology is manipulating or modifying the nanoclusters. In our experiment, first, deposit metal atoms on the Al2O3/NiAl(100) surface. These Co atoms will form a cluster structure because of the surface free energy. Second, use the STM manipulation technique to manipulate the clusters, and observe the differences by STM images. Closer the tip to Co clusters by reducing the bias voltage of STM. This action will induce a force to overcome the interaction between Co clusters and Al2O3 to remove the Co clusters. In the analysis of electronic spectroscopy, we can say that some of the clusters are not the Co clusters, those are formed by oxygen atom or other molecules by the difference of electronic spectroscopy curves. And we observe that the relation between Co cluster size and tunneling current gap is a linear relation. In the analysis of electronic spectroscopy, we can distinguish the cluster from the oxide surface by the difference of electronic spectroscopy curves. And we observe that the metal cluster size will be influenced the width of tunneling gap.

Photoactivated fluorescence from individual silver nanoclusters ranging in size from 2 8 atoms has been demonstrated at room temperature. The optical properties of such clusters are far superior to those of fluorescence dyes with absorption cross sections ~50 times stronger than those of even the best organic dyes. The strong oscillator strengths produced from such nanoclusters has been shown to yield comparable enhancement factors in the surface-enhanced Raman spectroscopy (SERS) process to those observed in the presence of a plasmon- supporting nanoparticle. Raman transitions are in fact so strong that antistokes scattering is also observable on a single molecule (SM) level marking the first true demonstration of SM-SERS to date. Capable of generating true scaffold specific Raman scattering on the single molecule level, the combination of fluorescence from the small nanoclusters and strong observed Raman signals in the absence of a nanoparticle strongly indicate a chemical or charge transfer SERS enhancement mechanism.

No description available.

In order to heighten the nickel content in mesoporous silica frameworks, a new direct synthesis method, called modified DS method, has been developed instead of the commonly used direct synthesis method. In addition, with the aim of incorporating a high amount of titania into SBA-15 mesoporous silica without blocking its mesopores, a multistep impregnation method, called the MSI method, has also been developed. By using the two developed methods, high nickel- and high titania-containing mesoporous silicas obtained werc synthesized. The nickel- and titania-containing mesoporous silicas were characterised by various techniques, i.e. XRD, TEM, EDX, SENI, N2-sorption, XPS, FTIR, UV-Vis-DRS, UV-VIS, TPR, and Raman spectroscopy. For nickel-containing mesoporous silicas synthesized by the modified DS method, satisfactory mesostructures were obtained and the nickel content was increased up to 14.7 wt.%. So far, no reports have been published on synthesis of mesoporous MCM-41-type silica with higher nickel content than 3.6 wt.% using DS method. Via our modified IDS method, high BET surface area (>840 rný/g) and pore volume (>-0.73 cm3/g were also achieved. Nickel was found to be incorporated into the silica frameworks. Formation of nickel phyllosilicates was also confirmed. After activation, mesostructurcs were still intact. Small nickel clusters embedded in the silica walls were found. A high amount of titania (up to 24.4 wt.%) was incorporated into the mesoporous SBA-15 silica via the multistep impregnation method. No damage to the SBA-15 silica mesostructures was caused. The existence of small titania nano-domins was confirmed to be present by Raman and UV-vis-DRS measurements. High dispersion of them was realized via this method according to the results of low-anglc XRD, TEM and N2-sorption measurements. Importantly, no blockage of mesopores was observed. Photo-activity tests showed the superiority of the materials synthesized by the MSI method to those by one-step impregnation method.

Amorphous and crystalline silicon nanocomposites have been shown to act as effective “sensitizers” for erbium ions. In the present work, a series of erbium-doped (0.2 at.%) SiOx:Er films (x = 1 - 1.8) were synthesized by physical vapor deposition and subsequently annealed at temperatures ranging from 400°C to 1100°C to induce phase separation and cluster growth. Silicon nanocluster (Si-NC) and Er3+ photoluminescence intensity spectra and dynamics were investigated as a function of SiOx composition, annealing temperature, pump wavelength and power, and specimen temperature in order to determine characteristic cross-sections and to map the efficiency of the energy transfer process between Si-NCs and Er3+ ions. Additionally, two types of optical waveguides based on SiOx:Er materials were fabricated using conventional CMOS compatible microfabrication processes. Waveguide propagation losses as well as signal absorption and enhancement were investigated under pumping conditions to evaluate the use of SiOx:Er materials as amplifying media. / Communications and Signal Processing

Mes travaux de recherche concernent la synthèse et la caractérisation des nanoclusters stabilisés pardes ligands thiolés, et plus particulièrement des nanoclusters d’or et d’argent. L’étude de ces clusterspar des méthodes de caractérisation optique en solution, séparation sur le gel d’électrophorèse et laspectrométrie de masse à haute résolution a permis de sonder quelques propriétés structurelles etélectroniques. L’originalité de ce travail de thèse vient, du couplage d’un spectromètre de masse avecun laser accordable en longueur d’onde UV/Visible pour étudier les propriétés optiques de clusters enphase gazeuse. En effet, ce travail a permis d’obtenir le premier spectre sur des mesures optiques deces espèces.Une partie de ce travail est consacrée à la synthèse et la caractérisation des nanoclusters d’or stabiliséspar les glutathions allant de Au4(SG) 4 à Au25(SG) 18. Les expériences de fragmentation induite parcollision sont réalisées sur les clusters afin de sonder leurs structures. Nous avons développé unenouvelle méthode basée sur l’analyse des structures isotopiques expérimentales pour déterminer lenombre d’électrons accommodés le coeur métallique.Ces études expérimentales ont été étendues à d’autres systèmes tels que les clusters d’argent stabiliséspar les glutathions. Deux méthodes de synthèse des clusters Agx(SG)y ont été développées aulaboratoire. Dans le cadre de ce travail, pour la première fois, nous avons pu déterminer la stichométriede ces clusters Ag31(SG) 19 et Ag15(SG) 11. / My research works concerns the synthesis and characterization of nanoclusters stabilized by thiolates(SG), particularly the gold and silver nanoclusters. The study of these clusters by opticalcharacterization techniques in solution, separation by gel electrophoresis and high-resolution massspectrometry has allowed to probe some structural and electronic proprieties. The origin of this workcome from experimental setup coupled mass spectrometry to UV/Visible optical parametric oscillatortunable laser for understanding the optical proprieties of the clusters in gas phase. In fact, this workhas allowed to get the first optical gas phase spectrum of this species. The first part of this work is dedicated to the synthesis and characterization of glutathione stabilizedgold nanoclusters with size between Au4 (SG) 4 and Au25 (SG) 18. Collision induced dissociationexperiments are performed to probe some structural proprieties of the clusters. We have developednew method based on the analysis of the experimental isotopic distribution allowed to find the numberof electrons bear in metallic core.These experimental studies have been extended to other systems such as glutathione stabilized silvernanoclusters. Two synthesis methods Agx(SG)y have been developed in the laboratory. For the firsttime, we have found the stoicheiometry of these clusters as Ag31 (SG) 19 and Ag15 (SG) 11.

Rapidly expanding research in nanotechnology has led to exciting progress in a versatile array of applications from medical diagnostics to catalysis. This success resulted from the manipulation of the desired properties of nanomaterials by controlling their size, shape, and composition. Among the most thriving areas of research about nanoparticle is the synthesis and doping of the ligand-protected atomically-precise metal nanoclusters. In this thesis, we developed three different novel metal nanoclusters, such as doped Ag29 with five gold (Au) atoms leading to enhance its quantum yield with remarkable stability. We also developed half-doped (alloyed) cluster of Ni6 nanocluster with molybdenum (Mo). This enabled enhanced stability and better catalytic activity. The third metal nanocluster that we synthesized was Au28 nanocluster by using di-thiolate as the ligand stabilizer instead of mono-thiolate. The new metal clusters obtained have been characterized by spectroscopic, electrochemical and crystallographic methods.