On the Plasmonic Photovoltaic

The conversion of sunlight into electricity by photovoltaics is currently a mature science and the foundation of a lucrative industry. In conventional excitonic solar cells, electron–hole pairs are generated by light absorption in a semiconductor and separated by the “built in” potential resulting from charge transfer accompanying Fermi-level equalization either at a p–n or a Schottky junction, followed by carrier collection at appropriate electrodes. Here we report a stable, wholly plasmonic photovoltaic device in which photon absorption and carrier generation take place exclusively in the plasmonic metal. The field established at a metal–semiconductor Schottky junction separates charges. The negative carriers are high-energy (hot) electrons produced immediately following the plasmon’s dephasing. Some of the carriers are energetic enough to clear the Schottky barrier or quantum mechanically tunnel through it, thereby producing the output photocurrent. Short circuit photocurrent densities in the range 70–120 μA cm^–2 were obtained for simulated one-sun AM1.5 illumination with devices based on arrays of parallel gold nanorods, conformally coated with 10 nm TiO₂ films and fashioned with a Ti metal collector. For the device with short circuit currents of 120 μA cm^–2, the internal quantum efficiency is ∼2.75%, and its wavelength response tracks the absorption spectrum of the transverse plasmon of the gold nanorods indicating that the absorbed photon-to-electron conversion process resulted exclusively in the Au, with the TiO₂ playing a negligible role in charge carrier production. Devices fabricated with 50 nm TiO₂ layers had open-circuit voltages as high as 210 mV, short circuit current densities of 26 μA cm^–2, and a fill factor of 0.3. For these devices, the TiO₂ contributed a very small but measurable fraction of the charge carriers

Characterization of Superparamagnetic “Core−Shell” Nanoparticles and Monitoring Their Anisotropic Phase Transition to Ferromagnetic “Solid Solution” Nanoalloys

The structure, magnetism, and phase transition of core−shell type CoPt nanoparticles en route to solid solution alloy nanostructures are systematically investigated. The characterization of CocorePtshell nanoparticles obtained by a “redox transmetalation” process by transmission electron microscopy (TEM) and, in particular, X-ray absorption spectroscopy (XAS) provides clear evidence for the existence of a core−shell type bimetallic interfacial structure. Nanoscale phase transitions of the CocorePtshell structures toward c-axis compressed face-centered tetragonal (fct) solid solution alloy CoPt nanoparticles are monitored at various stages of a thermally induced annealing process and the obtained fct nanoalloys show a large enhancement of their magnetic properties with ferromagnetism. The relationship between the nanostructures and their magnetic properties is in part elucidated through the use of XAS as a critical analytical tool

Bimodal Mesoporous Titanium Nitride/Carbon Microfibers as Efficient and Stable Electrocatalysts for Li–O₂ Batteries

Bimodal Mesoporous Titanium Nitride/Carbon Microfibers as Efficient and Stable Electrocatalysts for Li–O2 Batterie

Redox−Transmetalation Process as a Generalized Synthetic Strategy for Core−Shell Magnetic Nanoparticles

Although multicomponent core−shell type nanomaterials are one of the highly desired structural motifs due to their simultaneous multifunctionalities, the fabrication strategy for such nanostructures is still in a primitive stage. Here, we present a redox−transmetalation process that is effective as a general protocol for the fabrication of high quality and well-defined core−shell type bimetallic nanoparticles on the sub-10 nm scale. Various core−shell type nanomaterials including Co@Au, Co@Pd, Co@Pt, and Co@Cu nanoparticles are fabricated via transmetalation reactions. Compared to conventional sequential reduction strategies, this transmetalation process has several advantages for the fabrication of core−shell type nanoparticles:  (i) no additional reducing agent is needed and (ii) spontaneous shell layer deposition occurs on top of the core nanoparticle surface and thus prevents self-nucleation of secondarily added metals. We also demonstrate the versatility of these core−shell structures by transferring Co@Au nanoparticles from an organic phase to an aqueous phase via a surface modification process. The nanostructures, magnetic properties, and reaction byproducts of these core−shell nanoparticles are spectroscopically characterized and identified, in part, to confirm the chemical process that promotes the core−shell structure formation