A multifaceted approach to hydrogen storage.

The widespread adoption of hydrogen as an energy carrier could bring significant benefits, but only if a number of currently intractable problems can be overcome. Not the least of these is the problem of storage, particularly when aimed at use onboard light-vehicles. The aim of this overview is to look in depth at a number of areas linked by the recently concluded HYDROGEN research network, representing an intentionally multi-faceted selection with the goal of advancing the field on a number of fronts simultaneously. For the general reader we provide a concise outline of the main approaches to storing hydrogen before moving on to detailed reviews of recent research in the solid chemical storage of hydrogen, and so provide an entry point for the interested reader on these diverse topics. The subjects covered include: the mechanisms of Ti catalysis in alanates; the kinetics of the borohydrides and the resulting limitations; novel transition metal catalysts for use with complex hydrides; less common borohydrides; protic-hydridic stores; metal ammines and novel approaches to nano-confined metal hydrides.

Feed-forward compensation of surface potential in atomic force microscopy.

We introduce a feed-forward technique for lift-mode Kelvin probe force microscopy to minimize electrostatically induced errors in topography scans. Such errors typically occur when a grounded tip is scanned over a heterogeneous sample with differences in local work function or areas of local surface charging. To minimize electrostatic forces during the topography scan we bias the tip with the surface potential recorded in the previous Kelvin probe scan line. With this method we achieve an error free topography on samples with large variations in local surface potential. Compared to conventional tapping mode, we further observe a significant reduction of tip-induced surface charge modifications on charge patterns written in electret films.

Local surface charges direct the deposition of carbon nanotubes and fullerenes into nanoscale patterns.

This article reports on the directed deposition of carbon nanotubes (CNTs) and fullerenes onto solid surfaces using local electrostatic fields. Arbitrary patterns of local surface charges are created by charge writing with an atomic force microscope. During the subsequent development of the sample in an aqueous suspension containing surfactant-stabilized CNTs or fullerenes, Coulomb attraction guides the positioning and alignment of these particles onto the charge patterns. The surface potential of the charge patterns provides a direct control over the particle attachment. CNTs and fullerenes precisely reproduce the charge patterns, yielding structures with a lateral resolution down to the particle diameter.

Charge patterns as templates for the assembly of layered biomolecular structures.

Electric fields are used to guide the assembly of biomolecules in predefined geometric patterns on solid substrates. Local surface charges serve as templates to selectively position proteins on thin-film polymeric electret layers, thereby creating a basis for site-directed layered assembly of biomolecular structures. Charge patterns are created using the lithographic capabilities of an atomic force microscope, namely by applying voltage pulses between a conductive tip and the sample. Samples consist of a poly(methyl methacrylate) layer on a p-doped silicon support. Subsequently, the sample is developed in a water-in-oil emulsion, consisting of a dispersed aqueous phase containing biotin-modified immunoglobulinG molecules, and a continuous nonpolar, insulating oil phase. The electrostatic fields cause a net force of (di)electrophoretic nature on the droplet, thereby guiding the proteins to the predefined locations. Due to the functionalization of the immunoglobulinG molecules with biotin-groups, these patterns can now be used to initiate the localized layer-by-layer assembly of biomolecules based on the avidin-biotin mechanism. By binding 40 nm sized biotin-labelled beads to the predefined locations via a streptavidin linker, we verify the functionality of the previously deposited immunoglobulinG-biotin. All assembly steps following the initial deposition of the immunoglobulinG from emulsion can conveniently be conducted in aqueous solutions. Results show that pattern definition is maintained after immersion into aqueous solution.