Structure and Hydrogen Bonding in CaSiD 1+ x : Issues About Covalent Bonding
We report here our high-resolution neutron powder diffraction and neutron vibrational spectroscopy study of ${\mathrm{CaSiD}}_{1+x}$ along with first-principles calculations, which reveal the deuterium structural arrangements and bonding in this novel alloy hydride. Both the structural and spectroscopic results show that, for $xg0$, D atoms start occupying a ${\mathrm{Ca}}_{3}\mathrm{Si}$ interstitial site. The corresponding $\mathrm{Si}\text{\ensuremath{-}}\mathrm{D}$ bond length is determined to be $1.82\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, fully $0.24\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ larger than predicted by theory. Thus, our neutron measurements are at odds with the strongly covalent $\mathrm{Si}\text{\ensuremath{-}}\mathrm{H}$ bonding in ${\mathrm{CaSiH}}_{1+x}$ that such calculations suggest, a result which may have implications for a number of ongoing studies of metal-hydrogen systems destabilized by Si alloying.
Strategies for the improvement of the hydrogen storage properties of metal hydride materials.
Metal hydrides are an important family of materials that can potentially be used for safe, efficient and reversible on-board hydrogen storage. Light-weight metal hydrides in particular have attracted intense interest due to their high hydrogen density. However, most of these hydrides have rather slow absorption kinetics, relatively high thermal stability, and/or problems with the reversibility of hydrogen absorption/desorption cycling. This paper discusses a number of different approaches for the improvement of the hydrogen storage properties of these materials, with emphasis on recent research on tuning the ionic mobility in mixed hydrides. This concept opens a promising pathway to accelerate hydrogenation kinetics, reduce the activation energy for hydrogen release, and minimize deleterious possible by-products often associated with complex hydride systems.
Submicron polymer structures with X-ray lithography and hot embossing
This article describes the process chain for replication of submicron structures with varying aspect ratios (AR) up to 6 in polymethylmethacrylate (PMMA) by hot embossing to show the capability of the entire LIGA process to fabricate structures with these dimensions. Therefore a 4.7 μm thick layer of MicroChem 950k PMMA A11 resist was spin-coated on a 2.3 μm Ti/TiOx membrane. It was patterned with X-ray lithography at the electron storage ring ANKA (2.5 GeV and λc ≈ 0.4 nm) at a dose of 4 kJ/cm3 using a Si3N4 membrane mask with 2 μm thick gold-absorbers. The samples were developed in GG/BDG and resulted in AR of 6–14. Subsequent nickel plating at 52°C resulted in a 200 μm thick nickel tool of 100 mm diameter, which was used to replicate slit-nozzles and columns in PMMA. Closely packed submicron cavities with AR 6 in the nickel shim were filled to 60% during hot embossing.