Metallic nanowires of cobalt, copper, and iron oxide magnetite (Fe3O4) 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.

The paper describes the use of an in-situ microscopy technique, which combines transmission electron microscopy (TEM) with scanning probe microscopy (SPM), to investigate the electrical and mechanical properties of individual silicon and germanium nanowires. Additionally, the formation of ordered arrays of size-monodisperse silicon and germanium nanowires within mesoporous silica powders and thin films using a supercritical fluid inclusion phase technique is described. In particular, we demonstrate ultra high-density arrays of germanium nanowires, up to 2 x 10(12) wires per square centimetre. These matric embedded nano-composite materials display unique optical properties such as intense room temperature ultraviolet and visible photoluminescence.