Hysteresis during field emission from chemical vapor deposition synthesized carbon nanotube fibers

Abstract

Hysteresis in the field emission (FE) data of a chemical vapor synthesized carbon nanotube fiber cathode is analyzed in the regime where self-heating effects are negligible. In both the forward and reverse applied field sweeps, various FE modes of operation are identified: including Fowler-Nordheim (FN) tunneling and space-charge limited emission from the fiber tip and FN emission from the fiber sidewall. Hysteresis in the FE data is linked to the difference in the field enhancement factors in the different FE modes of operation in the forward and reverse sweeps and related to changes in the fiber morphology.

Theoretical evaluation of electronic density-of-states and transport effects on field emission from n-type ultrananocrystalline diamond films

“…Such an effect is also observed in other carbon-derived polycrystalline materials with mixed sp 2 /sp 3 hybridization 6-10 and has been speculated to be due to different phenomena, including: electron tunneling through multiple barriers, 6 an intermediate state between the field emission and thermionic emission regimes, 7,8 or due to the space-charge effect. 7,10 Moreover, the observed saturation effect is a long-known characteristic feature of conventional semiconductors [11][12][13] which has been explored theoretically. 12,14,15 a) E-mail address: chubenko@gwu.edu…”

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

“…12 If outgassing is present to change the surface chemistry of the emitter, due to either desorption of the gas adsorbates, or the back bombardment from the ionized desorbed species, the FN data typically manifests hysteresis behavior. 12,13 However, it is found that the I-V curves are symmetric when sweeping the voltage up and down (not shown) for the d = 1.75 mm case. Therefore, the slope drop in the FN plots of the present FE data is most likely due to the electrical contact resistance between the CNT fiber and the substrate.…”

“…Note that the slope drop in the high voltage regime in the FN plot is usually attributed to space charge effects, 13,40,41 or outgassing of the field emitter. 12 When the classical Child-Langmuir law…”

“…This kind of sudden drop is attributed to the self-heating effects, which can lead to a sudden failure to emit for some of the CNTs forming the fiber. 13,23 For d = 1 mm, the fiber failed to emit entirely, shortly after applying the maximum voltage of 1000 V. where A = 1.54 × 10 6 /W, B = 6.83 × 10 9 W 3/2 , S eff is the effective emission area (m 2 ) of the fiber, W is the work function (in eV) of the emitting surface, β eff is the effective field enhancement factor, D = h + d is the gap distance (in m) between the anode and the base of the CNT fiber cathode, which is the sum of the fiber length h and the fiber tip-to-anode distance d, and V g is the gap voltage. In the FN plot, Equation (1) yields a straight line when plotted as ln(I/V 2 g ) vs 1/V g , with the slope of BD/ β eff .…”

“…[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.…”