Morphology dependent field emission of acid-spun carbon nanotube fibers

Abstract

Acid spun carbon nanotube (CNT) fibers were investigated for their field emission properties and performance was determined to be dependent on fiber morphology. The fibers were fabricated by wet-spinning of pre-made CNTs. Fiber morphology was controlled by a fabrication method and processing conditions, as well as purity, size, and type of the CNT starting material. The internal fiber structure consisted of CNT fibrils held together by van der Waals forces. Alignment and packing density of the CNTs affects the fiber's electrical and thermal conductivity. Fibers with similar diameters and differing morphology were compared, and those composed of the most densely packed and well aligned CNTs were the best field emitters as exhibited by a lower turn-on voltage and a larger field enhancement factor. Fibers with higher electrical and thermal conductivity demonstrated higher maximum current before failure and longer lifetimes. A stable emission current at 3 mA was obtained for 10 h at a field strength of <1 V μm(-1). This stable high current operation makes these CNT fibers excellent candidates for use as low voltage electron sources for vacuum electronic devices.

Field emission from carbon nanotube fibers in varying anode-cathode gap with the consideration of contact resistance

“…The above mentioned flash and plasma observed at the larger applied field at d = 1.25 mm may have destroyed some of the sharper features on the CNT fiber, leaving CNTs with lower field enhancement factors. As observed previously, 14 after the plasma forms at the fiber tip, the fiber tip "plumes" out, thus the field enhancement factor decreases because the fiber tip is less pointy. This would also explain the increased turn-on voltage for FE the last run at d = 1 mm (Fig.…”

“…Zhang 2017) where the resistance of the substrate R substrate and of external circuit R ext are negligible since the stainless steel substrate and electrodes are highly conductive (with resistivity of 7.2 × 10 7 Ωm), 34 the resistance of the CNT fiber R CNT fiber = ρ CNT fiber h/πr 2 = 112 Ω, with the assumption of CNT fiber's resistivity 14 being ρ CNT fiber = 1.75 × 10 6 Ωm, length h = 5 mm, and radius r = 5µm, and R contact is the contact resistance between the CNT fiber and the substrate. Therefore, the dominate component of the series resistance in Eq.…”

“…[6][7][8] Carbon materials, such carbon nanotube (CNT) fibers, [9][10][11][12][13][14][15] have demonstrated promising properties for their use as field emitters, due to their large aspect ratios, and high electrical and thermal conductivities.…”

Field Emission from Lateral Multiwalled Carbon Nanotube Yarn Emitters

“…CNT yarns/fibers, as one of the most promising CNT assemblies, have attracted extensive attention. Field emission properties from vertical configuration of yarns/fibers, using various fabrication methods, have been investigated (Wei et al, 2008;Chen et al, 2009;Jang et al, 2010;Hojati-Talemi et al, 2013;Fairchild et al, 2015). A study of field emission from the side of CNT yarn showed a similar performance to the tip of yarn induced in a scanning electron microscope, demonstrating that the field emission from lateral configuration is promising as well (Jang et al, 2010).…”

Field emission microscopy of carbon nanotube fibers: Evaluating and interpreting spatial emission

“…The fibers were fabricated using a wet spinning technique described by Behabtu et al [8]. This fabrication process ensures that the CNTs comprising the fibers are closely packed and highly aligned which ensures high electrical and thermal conductivity [9] as well as optimal performance when used as eiher wire conductors or field emission cathodes [8,[10][11][12]. Carbon nanotube yarns are made by twisting or braiding together multiple CNT fibers.…”