Nathan H. Mack

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We developed a class of quasi-3D plasmonic crystal that consists of multilayered, regular arrays of subwavelength metal nanostructures. The complex, highly sensitive structure of the optical transmission spectra of these crystals makes them especially well suited for sensing applications. Coupled with quantitative electrodynamics modeling of their optical(More)
We describe a theoretical analysis of the structures of self-organizing nanoparticles formed by Pt and Ru-Pt on carbon support. The calculations provide insights into the nature of these metal particle systems-ones of current interest for use as the electrocatalytic materials of direct oxidation fuel cells-and clarify complex behaviors noted in earlier(More)
We present a new type of surface-enhanced Raman scattering (SERS) substrate that exhibits extremely large and uniform cross-section enhancements over a macroscopic (greater than 25 mm2) area. The substrates are fabricated using a femtosecond laser nanostructuring process, followed by thermal deposition of silver. SERS signals from adsorbed molecules show a(More)
In this work, we present a synthesis approach for nitrogen-doped graphene-sheet-like nanostructures via the graphitization of a heteroatom polymer, in particular, polyaniline, under the catalysis of a cobalt species using multiwalled carbon nanotubes (MWNTs) as a supporting template. The graphene-rich composite catalysts (Co-N-MWNTs) exhibit substantially(More)
In this report, we present the systematic preparation of active and durable non-precious metal catalysts (NPMCs) for the oxygen reduction reaction in polymer electrolyte fuel cells (PEFCs) based on the heat treatment of polyaniline/metal/carbon precursors. Variation of the synthesis steps, heat-treatment temperature, metal loading, and the metal type in the(More)
We describe a plasmonic crystal device possessing utility for optically transducing chemical forces. The device couples complex plasmonic fields to chemical changes via a chemoresponsive, surface-bound hydrogel. We find that this architecture significantly enhances the spectroscopic responses seen at visible wavelengths while enabling capacities for(More)
This paper describes a new type of plasmonic sensor fabricated by imprint lithography using a soft, elastomeric mold. Angle-dependent, zero-order transmission experiments demonstrate the sensing potential of this device, which uses a two dimensional plasmonic crystal. Full angle-dependent mapping shows that the sensitivity to surface chemical binding events(More)
A new non-precious metal oxygen reduction catalyst was developed via heat treatment of in situ polymerized polyaniline onto TiO(2) particles in the presence of Fe species. The TiO(2) provides for improved performance relative to a carbon black-based catalyst and, at a high catalyst loading, allows for reducing the performance gap between non-precious-metal(More)
Surface plasmon assisted catalysis (SPAC) reactions of 4-aminothiophenol (4ATP) to and back from 4,4'-dimercaptoazobenzene (DMAB) have been investigated by single particle surface enhanced Raman spectroscopy, using a self-designed gas flow cell to control the reductive/oxidative environment over the reactions. Conversion of 4ATP into DMAB is induced by(More)
Increased oxygen reduction reaction (ORR) kinetics, improved CO tolerance, and more efficient water and heat management represent significant advantages that high-temperature polymer electrolyte fuel cells (HT-PEFCs) operating with a phosphoric acid-doped polybenzimidazole (PBI) membrane offer over traditional Nafion-based, low-temperature PEFCs. However,(More)