RESUMEN
Metallic molybdenum (Mo(o)) wires with diameters ranging from 15 nanometers to 1.0 micrometers and lengths of up to 500 micrometers (0.5 millimeters) were prepared in a two-step procedure. Molybdenum oxide wires were electrodeposited selectively at step edges and then reduced in hydrogen gas at 500 degrees C to yield Mo(o). The hemicylindrical wires prepared by this technique were self-uniform, and the wires prepared in a particular electrodeposition (in batches of 10(5) to 10(7)) were narrowly distributed in diameter. Wires were obtained size selectively because the mean wire diameter was directly proportional to the square root of the electrolysis time. The metal nanowires could be embedded in a polystyrene film and lifted off the graphite electrode surface. The conductivity and mechanical resiliency of individual embedded wires were similar to those of bulk molybdenum.
RESUMEN
Hydrogen sensors and hydrogen-activated switches were fabricated from arrays of mesoscopic palladium wires. These palladium "mesowire" arrays were prepared by electrodeposition onto graphite surfaces and were transferred onto a cyanoacrylate film. Exposure to hydrogen gas caused a rapid (less than 75 milliseconds) reversible decrease in the resistance of the array that correlated with the hydrogen concentration over a range from 2 to 10%. The sensor response appears to involve the closing of nanoscopic gaps or "break junctions" in wires caused by the dilation of palladium grains undergoing hydrogen absorption. Wire arrays in which all wires possessed nanoscopic gaps reverted to open circuits in the absence of hydrogen gas.
RESUMEN
Low-temperature growth of AlxGa1-xAs by the solution-liquid-solid mechanism affords nanowhiskers having two specific overall compositions: x = 0.1 and 0.8. Intermediate compositions (0.1 < x < 0.8) are inaccessible by the method employed. Examination of the nanowhiskers by transmission electron microscopy, photoluminescence spectroscopy, electron energy loss spectroscopy, and annealing studies indicates that they possess compositionally modulated nanostructures. The observed compositional modulation consists of alternating comparatively Al-rich and Ga-rich AlxGa1-xAs domains with dimensions of 3-20 nm. The spontaneous phase separation, which occurs during growth, appears to be kinetically driven, and the resulting phase-separated nanostructures appear to be, therefore, metastable rather than stable. Spontaneous phase separation in AlxGa1-xAs, which strongly influences its photoemission behavior, is not well understood theoretically.