A technique for growing single metallic nanowires through a process of field-emission from a pointed structure is described. The field-emission of electrons in the presence of metal-carbonyls results in the deposition and growth of nanowires with diameters typically ranging from 3 to 30 nm, depending on the precursor used and growth conditions. Lengths range typically from several to tens of microns. Transmission electron microscope analysis of the nanowires shows that they are overcoated with a thin (~nm) layer of carbon which prevents the oxidation and corrosion of the encapsulated wire. Tungsten, iron and cobalt nanowires have been grown from their respective carbonyls. Current-voltage measurements of tungsten nanowires show ohmic behaviour at room temperature, yielding resistivity values 11-17 times that of bulk tungsten. Tungsten wires with inner core diameters of 4-5 nm are able to withstand current densities of greater than 5×1011Am-2 before failure. Free-standing nanowires thus grown from vertically-aligned nanostructures such as carbon nanotubes can be made to contact a substrate electrode by electrostatic attraction. The technique opens up the possibility of making electrical contacts to nanostructures that are otherwise not easily contactable.
A table top SEM design has been presented which is based upon the use of permanent magnets. The SEM's height can be designed to be below 12 cm. Computer simulations predict that the SEM should be able to provide high spatial resolution and operate at primary beam voltages above 100 kV for thin specimens.
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