Metallic nanowires of cobalt, copper, and iron oxide magnetite (Fe 3 O 4 ) have been synthesized within the pores of mesoporous silica using a supercritical fluid inclusion technique. The mesoporous matrix provides a means of producing a high density of stable, hexagonally ordered arrays of highly crystalline nanowires. The formation of the metal and metal oxide nanowires within the silica mesopores was confirmed by transmission electron microscopy (TEM), N 2 adsorption experiments, and powder X-ray diffraction (PXRD). The mechanism of nanowire formation within the mesopores appears to occur through the initial binding and coating of the pore walls with the metal atoms to form tubelike structures within the mesoporous template. The thickness of these tubes subsequently increases with further metal deposition until nanowires are formed. Additionally, the crystal structure of the cobalt nanowires formed within the mesoporous template can be readily changed by manipulating the density of the supercritical fluid phase.

A unique supercritical fluid inclusion-phase technique has been developed to embed silicon nanowires, with size monodispersed diameters, within the pores of mesoporous silica hosts. These nanocomposite materials displayed quite intense room temperature ultraviolet and visible photoluminescence (PL), and the emission wavelength maximum was found to be dependent on the diameter of the encased nanowires. This previously unobserved wavelength dependence of the ultraviolet PL with decreasing nanowire size is explained using a continuum strain model resulting from confinement of the wires within the host lattice.

Access to the full text of the published version may require a subscription. Rights

No abstract

In the near future physical and economic constraints are expected to limit the continued miniaturisation of electronic and optical devices using current "top-down" lithography-based methods. Consequently, nonlithographic methods for synthesising and organising materials on the nanometre scale are required. In response to these technological needs a number of research groups are developing new supercritical fluids methodologies to synthesise and self-assemble "building blocks" of nanomaterials, from the "bottom-up", into structurally complex device architectures. This concept paper highlights some of the recent advances in the synthesis of metal and semiconductor nanoparticles and nanowires by using supercritical fluids. In addition, we describe an efficient supercritical fluid approach for constructing ordered arrays of metal and semiconductor nanowires within mesoporous silica templates.

No abstract

The aim of this study is to contribute to understanding the mechanisms underlying the formation of biologically relevant minerals by comparing the properties of solid phases formed in calcium phosphate (CaP) or calcium carbonate (CaCO 3 ) precipitation systems, at defined initial experimental conditions: supersaturation, constituent ions ratio, ionic strength, and/or presence of relevant inorganic ions. Thus, three systems of different chemical complexities were investigated: (a) system containing constituent ions, (b) system containing additional co-ions, and (c) system with higher ionic strength and addition of Mg 2+ . The respective precipitation diagrams were constructed, and supersaturation domains of different CaP and CaCO 3 solid phases formation were identified. The obtained results may have implications not only for biomineralization and geochemistry, but also for materials science in general.

Herein is described the first detailed study of ceria surfaces using 1 H MAS NMR techniques to probe the nature of hydroxyl species formed after exposure to water. The 1 H MAS NMR signal deriving from adsorbed hydroxyl species was used to probe the surface of ceria and crystalline mesoporous powders as a function of calcination temperature. It was found that the signals from all samples were well-resolved and of high intensity and showed easily observed chemical shifts depending on their environment. High surface areas were evidenced by large hydroxyl-derived 1 H peak integrals for the mesoporous samples compared to that of ceria prepared by traditional precipitation techniques. It is suggested that surface-adsorbed hydroxyl species generally occupy two distinct structural environments (on-top and bridge) on ceria surfaces. Hydroxyl groups assigned to ontop positions were found to be more mobile and desorbed at lower temperatures than those held in bridging positions. In addition, the mesoporous surface appears to comprise of two distinct regions assigned to external surfaces and internal pore and cavity surfaces. We also highlight a more general point that adsorbate probe MAS NMR techniques can provide important analysis of surface chemistry in favorable circumstances. Ceria is an ideal example in which very well-resolved intense 1 H signals from adsorbed hydroxyl species are observed, and consequently MAS NMR methods provide unique details of the surface chemistry. The relevance of these data is discussed in the context of current knowledge of the properties of ceria.