Robust CNT field emitters: patterning, growth, transfer, and in situ anchoring

Robust carbon nanotube (CNT)-based cold cathodes were fabricated on titanium (Ti) substrates. Methods to grow vertically aligned CNTs  directly on Ti substrates were developed. These cathodes can be treated post-growth at elevated temperatures under inert atmosphere which causes the surface-grown CNTs to become anchored to the substrate surface. These samples offer improvements in field emission properties over previously studied silicon (Si) substrate-based cathodes with no anchoring, displaying low threshold voltages, high field enhancement factors, and long operating lifetimes. Current densities of 25 mA cm^-2 were held for over 24 h with anchored samples at low electric fields (observed thresholds as low as 0.5 V μm^-1) and more current stability. Higher current densities of up to 150 mA cm^-2 could be reached with anchored samples, limited only by the experimental setup. In efforts to generate even more stable and reproducible field emission, a transfer process of CNTs from polished Si to Ti with copper (Cu) was developed (flipCNTs). These cathodes display extreme improvements over previous results, with observed thresholds as low as 0.2 V μm^-1 and γ-factors as high as 30 000. To demonstrate the utility of these robust cathodes, a flipCNT-based cathode was assembled into a fully functioning vacuum triode.