Characterisation of carbon nanotube pastes for field emission using their sheet resistances

Carbon nanotube (CNT) pastes for field emitters were fabricated by varying the milling speed, CNT amount and glass frit (GF) powder size. The CNTs remained agglomerated at lower milling speeds while they were damaged and shortened at higher speeds. Increasing the amount of CNTs improved the field emission properties, but excessive CNTs led to increased removal of the CNT paste with surface activation because of lower cohesion strength. Small GF particles were incorporated to provide a flat surface to the CNT paste, which improved its field emission uniformity and lifespan. The dispersion, density and milling damage characteristics of CNTs in the pastes were assessed by their sheet resistances under the assumption of equal printed thicknesses. Tape activation reduced the thickness of the CNT pastes by different amounts that depended on the cohesion strength of the paste. This reduction caused the sheet resistance to increase. For all cases in this study, the field emission properties of the CNT pastes were closely related to their sheet resistances, suggesting that sheet resistance could be used as a figure-of-merit for the evaluation of CNT pastes for field emission applications.