Luis F. Fonseca

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A T-matrix formalism is used to calculate local electric fields around clusters of prolate spheroids in the long-wavelength regime. The calculations are performed as a function of interparticle distance as well as angle of orientation. The observed red shifts in the resonant wavelengths of the characteristic peaks are shown to obey an exponential(More)
Hydrogen sensors built with individual palladium nanowires (Pd NWs) have been achieved by integrating Pd NWs across microelectromechanical system (MEMS) electrodes, followed by assembling and bonding them to a chip carrier platform. The sensing measurements reveal that the sensors with individual Pd NWs show reverse sensing behaviors between the temperature(More)
A dual stage process of depositing bamboo-like carbon nanotubes (BCNTs) by hot filament chemical vapor deposition (HFCVD) and coating Si using Radio frequency sputtering (RFS) technique. The films were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and(More)
We report for the first time the fabrication of single-crystal metastable manganese sulfide nanowires (γ-MnS NWs) conformally coated with graphitic carbon via chemical vapor deposition technique using a single-step route. Advanced spectroscopy and electron microscopy techniques were applied to elucidate the composition and structure of these NWs at the(More)
For potential ultrafast optical sensor application, both VO 2 thin films and nanocomposite crystal-Si enriched SiO 2 thin films grown on fused quartz substrates were successfully prepared using pulsed laser deposition (PLD) and RF co-sputtering techniques. In photoluminescence (PL) measurement c-Si/SiO 2 film contains nanoparticles of crystal Si exhibits(More)
For hydrogen sensors built with pure Pd nanowires, the instabilities causing baseline drifting and temperature-driven sensing behavior are limiting factors when working within a wide temperature range. To enhance the material stability, we have developed superlattice-structured palladium and copper nanowires (PdCu NWs) with random-gapped, screw-threaded,(More)
We report universal approaches for porous nanowires (NWs), and porous NWs with spiral and meshy topologies that have been developed via anodic aluminum oxide (AAO) confined wet-chemical synthesis. Materials such as CuOx, Pd, and Cu NWs are taken as examples for porous NWs and porous NWs with spiral and meshy topologies. Immediate benefits are demonstrated(More)
A method to grow branched carbon nanostructures arrays is presented. We employ the electron-beam-induced deposition method using a transmission electron microscope in poor vacuum conditions where hydrocarbons are present in the chamber. The hydrocarbons are attracted to the substrates by the local electric fields. Saw-tooth nano-patterns were made with a(More)
The image shows an artistic version of a Pd nanowire surrounded by hydrogen molecules. The nanowire is electrically connected to the Pt electrodes of a sensor device by L. F. Fonseca and co-workers to study the effects of reduced temperature on its electrical response during hydrogen gas exposure. The TEM image shows the ordered crystal structure of the(More)
Changes in the crystal lattice of palladium nanowires (Pd NWs) upon hydrogen exposure by absorption and interstitial introduction of hydrogen atoms within the matrix can induce swelling of the nanostructure and generate dislocations through the solid that may alter the overall mechanical performance of the material. Understanding the mechanical behavior of(More)
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