Highly porous materials such as mesoporous oxides are of technological interest for catalytic, sensing and remediation applications: the mesopores (of size 2-50 nm) permit ingress by molecules and guests that are physically excluded from microporous materials. Connecting the interior of porous materials with a nanoscale or 'molecular' wire would allow the direct electronic control (and monitoring) of chemical reactions and the creation of nanostructures for high-density electronic materials. The challenge is to create an electronic pathway (that is, a wire) within a mesoporous platform without greatly occluding its free volume and reactive surface area. Here we report the synthesis of an electronically conductive mesoporous composite--by the cryogenic decomposition of RuO4--on the nanoscale network of a partially densified silica aerogel. The composite consists of a three-dimensional web of interconnected (approximately 4-nm in diameter) crystallites of RuO2, supported conformally on the nanoscopic silica network. The resulting monolithic (RuO2//SiO2) composite retains the free volume of the aerogel and exhibits pure electronic conductivity. In addition to acting as a wired mesoporous platform, the RuO2-wired silica aerogel behaves as a porous catalytic electrode for the oxidation of chloride to molecular chlorine.

The preparation and functionalization of ITO surfaces has been studied using primarily X-ray photoemission spectroscopy and infrared reflection-absorption spectroscopy (IRRAS) and the reagents n-hexylamine and n-octyltrimethoxysilane (OTMS). Particular attention has been paid to characterization of the surfaces both before and after functionalization. Surfaces cleaned by ultraviolet (UV)/ozone treatment and subsequently exposed to room air have approximately 0.5-0.8 monolayers (ML) of adsorbed impurity C. Most is in the form of aliphatic species, but as much as one-half is partially oxidized and consists of C-OH, C-O-C, and/or >C=O groups. The coverage of these species can be reduced by cleaning in organic solvents prior to UV/ozone treatment. The OH coverage on the ITO surfaces studied here is relatively small (approximately 1.0 OH nm-2), based on the Si coverage after reaction with OTMS. A satellite feature in the O 1s XPS spectrum, often suggested to be a quantitative measure of adsorbed OH, receives a significant contribution from sources not directly related to hydroxylated ITO. n-Hexylamine adsorbs, at a saturation coverage of approximately 0.08 ML, via a Lewis acid-base interaction. The particular acid site has not been conclusively identified, but it is speculated that surface Sn sites may be involved. For OTMS, a saturation coverage of about 0.21 ML is found, and the C/Si atom ratios suggest that some displacement of preadsorbed organic impurities occurs during adsorption. The alkyl chain of adsorbed OTMS is disordered, with no preferred stereoisomer. However, the chain appears to lie mainly parallel to the surface with the plane defined by the terminal CH3-CH2-CH2- segment oriented essentially perpendicular to the surface.

Over the past decade, there has been a dramatic increase of interest in both the preparation and properties of nanocrystalline materials. This interest has been fueled by the unique properties that such materials possess when compared to bulk phases, 1 as well as the potential they hold for such varied applications as electronics, 2 catalysis, 3 and biological labeling. 4 The majority of the work in this field has focused on transition metal and semiconductor particles, with particular emphasis on gold 5 and II-VI compounds such as CdSe. 6 Although the formation of colloidal silicon 7 and germanium 8 nanoclusters has been studied, little work has been directed toward examining the preparation and fundamental properties of nanocrystalline main-group metals.Recent theoretical studies suggest that bismuth materials of reduced dimensions may exhibit enhanced thermoelectric properties at room temperature. 9 Quantum confinement has already been exploited to increase the thermoelectric figure of merit, ZT, for PbTe 10 quantum well superlattices and an even larger thermoelectric effect might be achieved with bismuth under such dimensionally restricted conditions. 9a The focus thus far has been on making these measurements on bismuth nanowires, 11 which possess diameters of 13-110 nm and lengths on the order of 10 µm.Despite the enormous potential of this material for thermoelectric applications, little work has been directed toward the solution synthesis of nanocrystalline bismuth clusters. To the best of our knowledge, only one report exists of such material being prepared as a stable colloid, 12 and these clusters were prepared at very low concentrations in an aqueous polymer, making the isolation of significant quantities of such material difficult. In addition, the size of the nanocrystals was determined to be 8 or 12 nm, sizes which are large when compared to the smallest diameters of noble metal nanoclusters. 5 Very recently, the synthesis of nanocrystalline bismuth using an in situ polymerization process was reported; 13 however, the resulting particles were even larger (20 nm) and were also suspended in a polymer matrix. Although this polymer coating protects the particles from oxidation, it once again makes the further manipulation and characterization of the product difficult. The focus of our effort has been the isolation of macroscopic quantities of bismuth nanocrystals with diameters below 10 nm that could be obtained in a more easily manipulated form.A variety of chemical methods have been reported in the literature for the preparation of noble metal nanoparticles, such as sonochemical reduction, 14 reduction in the presence of capping agents, 15 and reduction in inverse micelles. 16 We have recently examined a variety of reactions, in an attempt to prepare nanocrystalline bismuth clusters, 17 and have found difficulty in identifying a suitable capping agent. Traditional choices such as alkanethiols and TOPO have failed to provide proper control over both the nucleation and growth in our experiments with ...

Steady state and ultrafast transient absorption studies have been carried out for gold, nickel, and palladium high aspect ratio nanorods. For each metal, nanorods were fabricated by electrochemical deposition into approximately 6 microm thick polycarbonate templates. Two nominal pore diameters(10 and 30 nm, resulting in nanorod diameters of about 40 and 60 nm, respectively) were used, yielding nanorods with high aspect ratios (>25). Static spectra of nanorods of all three metals reveal both a longitudinal surface plasmon resonance (SPR(L)) band in the mid-infrared as well as a transverse band in the visible for the gold and larger diameter nickel and palladium nanorods. The appearance of SPR(L) bands in the infrared for high aspect ratio metal nanorods and the trends in their maxima for the different aspect ratios and metals are consistent with calculations based on the Gans theory. For the gold and nickel samples, time resolved studies were performed with a subpicosecond resolution using 400 nm excitation and a wide range of probe wavelengths from the visible to the mid-IR as well as for infrared excitation (near 2000 cm(-1)) probed at 800 nm. The dynamics observed for nanorods of both metals and both diameters include transients due to electron-phonon coupling and impulsively excited coherent acoustic breathing mode oscillations, which are similar to those previously reported for spherical and smaller rod-shaped gold nanoparticles. The dynamics we observe are the same within the experimental uncertainty for 400 nm and infrared (5 microm) excitation probed at 800 nm. The transient absorption using 400 nm excitation and 800 nm probe pulses of the palladium nanorods also reveal coherent acoustic oscillations. The results demonstrate that the dynamics for high aspect ratio metal nanorods are similar to those for smaller nanoparticles.

exactly 1 gallium vertex of another polyhedron. The Ga(22)-Ga(23) distance of 2.43 A is 0.1 A shorter than the next shortest Ga-Ga distance (Ga(4)-Ga(13) = 2.53 A), which when coupled with the lack of exopolyhedral bonds from Ga(22) and Ga(23) suggests a Ga( 22)=Ga( 23) double bond. If this is the case, the closed-shell electronic configuration for the edge-localized gallium satellite polyhedron depicted in Figure 2 in Ga1515-.

We report the first synthesis and characterization of nanocrystalline Bi2Te3 with particle sizes less than 10 nm. The reaction of BiOClO4·xH2O with (Me3Si)2Te in a reverse micelle formed by sodium dioctylsulfosuccinate and water in hexane has produced good yields (71%) of a black powder that has been characterized by elemental analysis, X-ray diffraction, and transmission electron microscopy.

Ultrafast transient absorption studies are reported for high-aspect-ratio gold nanorods that were fabricated by electrochemical deposition in polycarbonate templates. The nanorods are 60 nm in diameter with distribution of lengths of up to 6 μm. The average aspect ratio was ∼50, resulting in a longitudinal surface plasmon resonance (SPR L ) band in the mid-IR, as well as a transverse (SPR T ) band in the visible. The rods were excited at 400 nm and probed at a range of wavelengths from the visible to the mid-IR to interrogate both SPR bands. The dynamics observed, including the electron-phonon coupling time and coherent acoustic breathing mode oscillations, closely resemble those previously reported for gold spherical nanoparticles and smaller-aspect-ratio nanorods. The electron-phonon coupling time was similarly determined to be 3.3±0.2 ps for both of the SPR bands. Also, oscillations with a 32-ps period were observed for probing near the SPR T band in the visible region due to impulsive coherent excitation of the acoustic breathing mode, which are consistent with the 60-nm diameter of the nanorods determined by scanning electron microscopy. The results demonstrate that the dynamics for long gold nanorods are similar to those for smaller nanoparticles.

Quantum-confined nanocrystallites of GaAs are fabricated in porous Vycor glass and the bound electronic nonlinear refractive index, the two-photon absorption coefficient, and the refraction from carriers generated by two-photon absorption are simultaneously determined using the Z-scan method and compared to those of bulk GaAs. The measured nonlinear refractive index is an order of magnitude larger than that of bulk GaAs at 1060 nm.