High-contrast and fast electrochromic switching enabled by plasmonics.

With vibrant colours and simple, room-temperature processing methods, electrochromic polymers have attracted attention as active materials for flexible, low-power-consuming devices. However, slow switching speeds in devices realized to date, as well as the complexity of having to combine several distinct polymers to achieve a full-colour gamut, have limited electrochromic materials to niche applications. Here we achieve fast, high-contrast electrochromic switching by significantly enhancing the interaction of light--propagating as deep-subwavelength-confined surface plasmon polaritons through arrays of metallic nanoslits, with an electrochromic polymer--present as an ultra-thin coating on the slit sidewalls. The switchable configuration retains the short temporal charge-diffusion characteristics of thin electrochromic films, while maintaining the high optical contrast associated with thicker electrochromic coatings. We further demonstrate that by controlling the pitch of the nanoslit arrays, it is possible to achieve a full-colour response with high contrast and fast switching speeds, while relying on just one electrochromic polymer.

Robust composite-shell microcapsules via pickering emulsification.

Microencapsulation technology has been increasingly applied toward the development of self-healing paints. Added to paint as a dry powder prior to spraying, the microcapsules store a liquid that can repair the protective barrier layer if released into a scratch. However, self-healing will not occur unless the microcapsules can withstand spray-painting, aggressive solvents in the paint, and long-term exposure to the elements. We have therefore developed a one-pot synthesis for the production of Pickering microcapsules with outstanding strength, solvent resistance, and barrier properties. Octadecyltrimethoxysilane-filled (OTS) microcapsules form via standard interfacial polycondensation, except that silica nanopowder (10-20 nm diameter) replaces the conventional surfactant or hydrocolloid emulsifier. Isophorone diisocyanate (IPDI) in the OTS core reacts with diethylenetriamine, polyethylenimine, and water to form a hard polymer shell along the interface. Compared to pure polyurea, the silica-polyurea composite improves the shelf life of the OTS by 10 times. The addition of SiO2 prevents leaching of OTS into xylenes and hexanes for up to 80 days, and the resulting microcapsules survive nebulization through a spray gun at 620 kPa in a 500 cSt fluid.

Crystal structure and the paraelectric-to-ferroelectric phase transition of nanoscale BaTiO3.

We have investigated the paraelectric-to-ferroelectric phase transition of various sizes of nanocrystalline barium titanate (BaTiO3) by using temperature-dependent Raman spectroscopy and powder X-ray diffraction (XRD). Synchrotron X-ray scattering has been used to elucidate the room temperature structures of particles of different sizes by using both Rietveld refinement and pair distribution function (PDF) analysis. We observe the ferroelectric tetragonal phase even for the smallest particles at 26 nm. By using temperature-dependent Raman spectroscopy and XRD, we find that the phase transition is diffuse in temperature for the smaller particles, in contrast to the sharp transition that is found for the bulk sample. However, the actual transition temperature is almost unchanged. Rietveld and PDF analyses suggest increased distortions with decreasing particle size, albeit in conjunction with a tendency to a cubic average structure. These results suggest that although structural distortions are robust to changes in particle size, what is affected is the coherency of the distortions, which is decreased in the smaller particles.

Photoinduced thermal copper reduction onto gold nanocrystals under potentiostatic control.

We study the photoreduction of adsorbed copper ions onto Au nanoparticles, on an indium tin oxide (ITO) electrode in an aqueous electrochemical cell, as a function of applied voltage and laser intensity. The photocurrent is a nonlinear function of laser intensity and increases sharply with cathodic voltage in the underpotential deposition region. The photoreduction is attributed to laser heating of the Au nanoparticles rather than "hot electron" processes. Numerical simulation of the Butler-Volmer kinetic equation using experimental parameters predicts a several orders of magnitude increase in current for a temperature rise of a few Kelvin.

Crystalline graphite from an organometallic solution-phase reaction.

We report a chemical method by which graphitic carbon is prepared at reaction temperatures as low as 110 degrees C from readily available molecular reagents. This process requires no forcing conditions such as high pressures, intense light, or electrical discharge but is a simple, catalytic organometallic reaction. The carbon forms in a variety of morphologies including graphene sheets and nanotubes. The mild reaction conditions are similar to those routinely employed in homogeneous catalysis; therefore, they will allow the subtle manipulation of reaction variables to give desired morphologies selectively.

Electrodeposition of metal nanostructures by galvanic displacement powered with insoluble crystals of a ferrocene derivative.

The deposition of metal nanostructures (wires and particles) on a graphite surface from an aqueous electrolyte solution was induced by galvanic displacement, via the oxidation of insoluble crystals of a ferrocene derivative (either n-butyl ferrocene or decamethyl ferrocene) present on the same substrate. Micron-to-millimetre-scale crystallites of decamethyl ferrocene were deposited on the graphite surface by evaporation from a solution of a nonpolar solvent (1,2-dichloroethane). Immersion of this modified surface into a dilute solution of a metal ion (e.g., CuII, AgI, PdII, PtII and others) caused the deposition of metal nanoparticles at step edges present on the graphite surface. The reducing equivalents required for the metal deposition process are provided by oxidation of the ferrocene derivative on the surface, as directly evidenced by elemental analysis and chronoamperometric experimental data presented here.

Metal nanowire arrays by electrodeposition.

We describe two related methods for preparing arrays of nanowires composed of molybdenum, copper, nickel, gold, and palladium. Nanowires were obtained by selectively electrodepositing either a metal oxide or a metal at the step edges present on the basal plane of highly oriented pyrolytic graphite (HOPG) electrodes. If a metal oxide was electrodeposited, then nanowires of the parent metal were obtained by reduction at elevated temperature in hydrogen. The resulting nanowires were organized in parallel arrays of 100-1000 wires. These nanowires were long (some > 500 microns), polycrystalline, and approximately hemicylindrical in cross-section. The nanowire arrays prepared by electrodeposition were also "portable": After embedding the nanowires in a polymer or cyanoacrylate film, arrays of nanowires could be lifted off the graphite surface thereby facilitating the incorporation of metal nanowire arrays into devices such as sensors.