Martin Couillard

Nanocrystalline intermetallics on mesoporous carbon for direct formic acid fuel cell anodes.

Shape- and size-controlled supported metal and intermetallic nanocrystallites are of increasing interest because of their catalytic and electrocatalytic properties. In particular, intermetallics PtX (Xxa0=xa0Bi, Pb, Pd, Ru) are very attractive because of their high activity as fuel-cell anode catalysts for formic acid or methanol oxidation. These are normally synthesized using high-temperature techniques, but rigorous size control is very challenging. Even low-temperature techniques typically produce nanoparticles with dimensions much greater than the optimum <6xa0nm required for fuel cell catalysis. Here, we present a simple and robust, chemically controlled process for synthesizing size-controlled noble metal or bimetallic nanocrystallites embedded within the porous structure of ordered mesoporous carbon (OMC). By using surface-modified ordered mesoporous carbon to trap the metal precursors, nanocrystallites are formed with monodisperse sizes as low as 1.5xa0nm, which can be tuned up to ∼3.5xa0nm. To the best of our knowledge, 3-nm ordered mesoporous carbon-supported PtBi nanoparticles exhibit the highest mass activity for formic acid oxidation reported to date, and over double that of Pt-Au.

Annealing Effects on the Chemical Configuration of Uncapped and (Poly-Si)-Capped HfO x N y Films Deposited on Si(001)

We use spatially resolved spectroscopy in a scanning transmission electron microscope to study the thermal stability of the HfO x N y /Si(001) system with and without an in situ capping layer of silicon. The films were deposited by metallorganic chemical vapor deposition using the amide precursor tetrakis(diethylamido)hafnium with NO as the oxidant. A SiO x N y interfacial layer (∼1.8 nm) is observed at the HfO x N y /substrate interface for films directly exposed to air. In addition, the N loss in the HfO x N y film for the uncapped sample is significant. In contrast, in situ capping is found to reduce the thickness of the interfacial layer and to keep the N content in the final dielectric film high. The capped HfO x N y films are quasi-amorphous, whereas uncapped films are polycrystalline following exposure to air. Oxinitridation at both interfaces is observed following a rapid thermal annealing process (900°C in N 2 for 30 s) of the capped HfO x N y film. However, the interfacial layers remain thin (∼1 nm) and a significant amount of N is present in the HfO x N y film. The rapid thermal annealing leads to the partial crystallization of the HfO x N y film and the Si capping layer. No Hf silicate is detected on a scale of ∼6 A in the electron energy loss spectroscopy analysis.

Mapping Local Optical Densities of States in Finite Si Photonic Structures with Monochromated, Nanoscale Electron Spectroscopy

* School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853 ** Department of Electrical Engineering, Stanford University, Stanford, CA, 94305 *** Department of Physics, Columbia University, New York, NY 10027 † Current address: Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305 ‡ Current address: Department of Materials Science and Engineering and Canadian Centre for Electron Microscopy, McMaster University, Hamilton, ON, Canada, L8S 4L7