Efficient field emission of gold and platinum nanowire patch arrays

Metallic nanostructures with controllable dimension and high aspect ratio provide an interesting alternative to carbon nanotubes for triode applications which require highly efficient and homogeneous field emission cathodes. Noble metal nanowires (NW) were electrochemically synthesized into the randomly distributed cylindrical pores of polycarbonate templates fabricated by GeV-ion irradiation, selective pore etching and subsequent metallization with a stable backing layer. After dissolution of the polycarbonate, freestanding solitary or clustered gold NW were found depending on the irradiation fluence and the NW length. Systematic studies of Au-NW cathodes revealed promising field emission properties. Therefore, regular patch arrays of gold or platinum NW were fabricated by using shadow masks during irradiation. A test mask with four quadratic arrays of patches of 50 mum diameter and different pitch size (100 and 150 mum) was used to optimize the fluence (10⁶-10⁸/cm²) and NW length (7-28 mum) with respect to emitter efficiency and alignment. A second mask with a hexagonal array of 150 mum diameter patches and 320 mum pitch was then employed to develop cathodes suitable for triode devices.