Optimization of electron field emission from carbon nanotube paste

Photosensitive organic binder was mixed with well-dispersed arc discharged single-walled carbon nanotubes (CNTs). The CNT-paste was screen-printed on the Cr-patterned glass substrate. Following back-side UV exposure, binder burn-out processes were carried out for accurate and fine patterning of paste. Emission images were obtained from a cathode successively: (a) as-prepared, (b) just after rubber-roll treatment and (c) after multiple I-V cycling. Improvement of emission properties with I-V cycling was observed from scanning electron micrographs (SEM) and I-V curves. The morphology of printed-CNTs was remarkably changed after I-V cycling. Parallel alignment of CNTs to the field direction become permanent after multiple field emission cycles. The field emission threshold was about 2.5 V·μm^-1 for the first measurement. In the successive emission cycles, the threshold fields decreased gradually to 1.9 V·μm^-1 for the final 13^th cycle. From the corresponding Fowler-Nordheim plots, the field enhancement factor (β) of each line was evaluated. The average β values monotonically increased (from 1366 to 2120) with field emission repetition, which again confirmed the gradual vertical alignment of CNTs by multiple I-V cycles.