Focused ion beam fabrication of novel core-shell nanowire structures

A novel method of indirect deposition by means of a focused ion beam (FIB) is utilized to develop metal/insulator/semiconductor nanowire core-shell structures. This method is based upon depositing an annular pattern centered on a nanowire, with secondary deposition then coating the wire. Typical cross-sectional deposition area increments as a function of ion doses are 1.3 x 10(-2) mu m(2) nC(-1) for Pt and 3.5 x 10(-2) mu m(2) nC(-1) for SiO2. The structures are examined with a transmission electron microscope (TEM) using a new nanowire TEM sample preparation method that allows direct examinations of individually selected core-shell nanowires fabricated under different indirect FIB deposition conditions. Elemental analyses by means of energy dispersive x-ray spectroscopy and electron energy filtered TEM imaging verify the deposition of SiO2 and Pt layers. Relatively uniform Pt and SiO2 coatings on individual GaP nanowires can be achieved with overall thickness deviation of about 10% for deposition up to 25-30 nm thick Pt or SiO2 shells. It should be possible to extend this approach to any nanowire/nanotube system, and to a wide range of coatings in any desired layer sequences.