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| Artificial bilayer membranes are platforms for basic ion channel research as well as for detection and analyte sensing. The formation of bilayer membranes on semiconductor surfaces is an important step in device integration for transistor and sensor arrays. Here Langmuir-Blodgett deposition in conjunction with vesicle fusion is used to form bilayers on single crystal silicon. Lipids and peptides are spread on the Langmuir trough and deposited onto a silicon wafer. Pressure - area isotherms are used to determine the area per molecule. Impedance spectroscopy is used to characterize the conduction due to ion channels in the membrane. |
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| Nanoporous gold nanowires are fabricated by template synthesis of Au-Ag alloy nanowires. After etching the Ag from the aloy, the Au ligaments are 5 - 10 nm in size, less than the mean free path for electrons (about 50 nm). Lithography is used to pattern contacts to each end of the nanowire. The resistance is dominated by surface scattering and hence chemisorption (in this case with octodecanethiol) results in ineleastic scattering and an increase in the resistance. |
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| Novel ordered macroporous materials can be fabricated by electrodeposition into colloidal crystal templates. The colloidal crystal templates are formed by self-assembly of nanoparticles into an ordered (usuallly fcc) lattice. The plan view image shows the surface of a gold replica fabricated by electrodeposition into a colloidal crystal fabricated from 500 nm polystyrene particles. First depositing a Ag release layer (see cross-section image) allows the gold structure to be removed from the substrate. Cyclic voltammetry for 2µm thick porous structures show increasing peak current (surface area) with decreasing particle size. The interconnections can be smaller than the mean free path for electrons and hence these structures can be used for sensing. |
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| Shape anisotropy is an example of a degree of freedom in controlling properties of nanoparticles. The ability to introduce multiple segements allows additional degrees of freedom associated iwth the aspect ratio of each segement. In multilayer nanowires with alternating ferromagnetic (FM) and non-magnetic segements, the magnetic easy axis is dependent on the aspect ratio of the ferromagnetic nickel segment. Nanowires with rod-shaped FM segments have an easy axis parallel to the wire axis whereas nanowires with disk-shaped FM segments have their easy axis perpendicular to the nanowire axis. Multisegment nanowires with the same length, diameter can respond very differently to an external magnetic field depending on the aspect ratio of the FM segments. |
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| The ability to fabricate patterned features on a substrate using low-cost, low-tech processing is a key challenge in nanoscience. The combination of soft lithography and electrodeposition provides a method to fabricate a wide range of materials and structures. The AFM image shows a patterned monolayer of octadecanethiol on gold used as a template for electroseposition. Under certain conditions, materials such as cobalt can be electrodeposited onto the patterned surface with high fidelity. In many cases features as high as several hundred nanometers can be grown with no lateral growth. Confinement of nucleation during electrodeposition can be used to produce arrays of silver islands. |
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| The electrochemical desoprtion of self-assembled monolayers can be used to achieve programmed release of biomolecules and noparticles with spatial and temporal control. The fluorescence image shows gold electrodes functionalized with fluorescenntly labelled avidin. On applying a suitable voltage to two of the electrodes, the protein is released from the surface. |
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| Electronically conducting polymers can be switched between a neutral state and a doped state by a redox reaction. The removal of electrons from the polymer and the insetion of a negatively charged anion is caled p-doping, while the injection of electrons and the insertion of a positvely charged cation is called n-doping. P-doping can be quite reversible whereas n-doping is usually irreversible due to the highly reducing conditions. The molecular engineering of monomers that exhibit n-doping with reasonable reversibility open the pssibility of an all-polymer battery. Fluorophenyl substituted thiophenes exhibit both n- and p-doping with a potential difference of about 2.5 V. We have fabricated prototype bateries with no metallic components. |
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