Mya Le Thai

A lithographically patterned capacitor with horizontal nanowires of length 2.5 mm.

A symmetrical hybrid capacitor consisting of interdigitated, horizontal nanowires is described. Each of the 750 nanowires within the capacitor is 2.5 mm in length, consisting of a gold nanowire core (40 × ≈200 nm) encapsulated within a hemicylindrical shell of δ-phase MnO2 (thickness = 60-220 nm). These Au@δ-MnO2 nanowires are patterned onto a planar glass surface using lithographically patterned nanowire electrodeposition (LPNE). A power density of 165 kW/kg and energy density of 24 Wh/kg were obtained for a typical nanowire array in which the MnO2 shell thickness was 68 ± 8 nm. Capacitors incorporating these ultralong nanowires lost ≈10% of their capacity rapidly, during the first 20 discharge cycles, and then retained 90% of their maximum capacity for the ensuing 6000 cycles. The ability of capacitors consisting of ultralong Au@δ-MnO2 nanowires to simultaneously deliver high power and high capacity with acceptable cycle life is demonstrated.

Sub-6 nm Palladium Nanoparticles for Faster, More Sensitive H2 Detection Using Carbon Nanotube Ropes

Palladium (Pd) nanoparticle (NP)-decorated carbon nanotube (CNT) ropes (or CNT@PdNP) are used as the sensing element for hydrogen gas (H2) chemiresistors. In spite of the fact that Pd NPs have a mean diameter below 6 nm and are highly dispersed on the CNT surfaces, CNT@PdNP ropes produce a relative resistance change 20-30 times larger than is observed at single, pure Pd nanowires. Thus, CNT@PdNP rope sensors improve upon all H2 sensing metrics (speed, dynamic range, and limit-of-detection), relative to single Pd nanowires which heretofore have defined the state-of-the-art in H2 sensing performance. Specifically, response and recovery times in air at [H2] ≈ 50 ppm are one-sixth of those produced by single Pd nanowires with cross-sectional dimensions of 40 × 100 nm Pd. The LODH2 is <10 ppm versus 300 ppm, and the dynamic range (10 ppm -4%) is nearly twice that afforded by the Pd nanowire. CNT@PdNP rope sensors are prepared by the dielectrophoretic deposition of a single semiconducting CNT rope followed by the electrodeposition of Pd nanoparticles with mean diameters ranging from 4.5 (±1) nm to 5.8 (±3) nm. The diminutive mean diameter and the high degree of diameter monodispersity for the deposited Pd nanoparticles are distinguishing features of the CNT@PdNP rope sensors described here, relative to prior work on similar systems.

Electrodeposited, Transverse Nanowire Electroluminescent Junctions

The preparation by electrodeposition of transverse nanowire electroluminescent junctions (tn-ELJs) is described, and the electroluminescence (EL) properties of these devices are characterized. The lithographically patterned nanowire electrodeposition process is first used to prepare long (millimeters), linear, nanocrystalline CdSe nanowires on glass. The thickness of these nanowires along the emission axis is 60 nm, and the width, wCdSe, along the electrical axis is adjustable from 100 to 450 nm. Ten pairs of nickel-gold electrical contacts are then positioned along the axis of this nanowire using lithographically directed electrodeposition. The resulting linear array of nickel-CdSe-gold junctions produces EL with an external quantum efficiency, EQE, and threshold voltage, Vth, that depend sensitively on wCdSe. EQE increases with increasing electric field and also with increasing wCdSe, and Vth also increases with wCdSe and, therefore, the electrical resistance of the tn-ELJs. Vth down to 1.8(±0.2) V (for wCdSe ≈ 100 nm) and EQE of 5.5(±0.5) × 10(-5) (for wCdSe ≈ 450 nm) are obtained. tn-ELJs produce a broad EL emission envelope, spanning the wavelength range from 600 to 960 nm.