SUPPLEMENTARY MATERIAL FOR
Hysteresis During Field Emission
From Chemical Vapor Deposition Synthesized Carbon Nanotube Fibers
M. Cahay1, P.T. Murray2,3, T.C. Back2,3, S. Fairchild4, J. Boeckl4, J. Bulmer5, K.K.K. Koziol5, G. Gruen6,
M. Sparkes7, F. Orozco7, and W. O’Neill7
1
Spintronics and Vacuum Nanoelectronics Laboratory, University of Cincinnati, Cincinnati, OH
45221 USA
2
Research Institute, University of Dayton, Dayton, OH 45469-0170 USA
3
Center of Excellence for Thin Film Research and Surface Engineering, University of Dayton,
Dayton, OH 45469-0170 USA
4
Materials and Manufacturing Directorate, Air Force Research Laboratory, WPAFB, OH 45433
USA
5
Department of Materials Science, University of Cambridge, Pembroke Street, Cambridge CB2
3QZ, United Kingdom
6
TechFlow Scientific, 2155 Louisiana Blvd. NE, Albuquerque NM 87110 USA
7
Institute for Manufacturing, University of Cambridge, 17 Charles Babbage Road, Cambridge,
UK
We used residual gas analysis (RGA) to identify the species desorbed during field FE
from a carbon nanotube fiber. The residual gas analyzer was situated in a line-of sight with
respect to the FE regime, and the distance from the FE regime to the entrance aperture of the
RGA was approximately 15 cm. The RGA and field emission scans were acquired such that the
intensity for each mass was recorded at every voltage step. Shown are the FE (Figure S1(a)) and
RGA data (Figure S1(b)) for a gap distance d = 1.75 mm. The left ordinate represents the change
in partial pressures of H2 from the base line value. The incremental changes in Δ𝑃𝐻2 is plotted as
ln(ΔP/𝐸𝑒𝑥𝑡 2) vs 1/𝐸𝑒𝑥𝑡 to show the strong correlation between the RGA and FE data. The RGA
data indicate a small, constant change in H2 partial pressure below an electric field of 𝐸𝑒𝑥𝑡 = 0.29
V/m. Above this value, there is additional desorption of H2 that correlates strongly with the four
FE regimes of operation (FN1, CL1, FN2, and CL2) described in the main text. It is interesting
to note that the change in CO and CO2 partial pressures (not shown) were approximately one and
two orders of magnitude, respectively, smaller than that of H2.
Figures S2 and S3 are scanning electron microscope images of the tip and sidewall of the
fiber taken prior to FE measurements. Figure S2 indicates the presence of a large density of
misaligned CNTs of various length and diameter at the tip after the laser cut. The separation
between the CNTs is less than twice their height which is most likely for the observation of
screening effects (mode CL1) in the FE data. Figure S3 shows a large number of CNTs
protruding from the CNF sidewall which explains the sidewall FE mode of operation (FN2)
observed in the experimental data.
As described in the main text, we have observed an increasing number of bright spots
along the sidewall of the fiber past the CL1 regime of operation (Fig.2(a)). Figure S4 shows
optical images of the fiber before the start of the FE measurements and at a voltage of 980V for
an anode to tip of the fiber spacing of 1.75mm. The number and brightness of the emitting spots
was found to increase from the tip of the fiber and going down its sidewall as the voltage across
the gap was increased beyond 750V (end of CL1 regime of operation in Fig.2(a). As the number
of spots increased and got brighter, the FE data were found to be in good agreement with the CL
expression over the 𝐸𝑒𝑥𝑡 field range from 1.75 to 1.85 µm/V (fit CL2 for forward sweep in
Fig.3(a)), indicative of space-charge limited transport from the surface emitting areas of the fiber
sidewall.
FIGURE CAPTIONS
S1.(a) FN plot of FE data showing modes of operation of a CNT fiber for fiber tip to anode
spacing of 1.75mm. The four different regimes of FE (FN1, CL1, FN2, CL2) described in the
main text are shown. (b) The incremental change in partial pressure of H2 compared to the
baseline pressure as a function of applied electric field. The incremental changes in Δ𝑃𝐻2 and
Δ𝑃𝐶𝑂 are plotted as ln(ΔP/𝐸𝑒𝑥𝑡 2) vs 1/𝐸𝑒𝑥𝑡 to show the strong correlation between the RGA and
FE data in all four regimes of FE.
S2. Scanning electron microscope images of the tip of a 30 µm diameter laser cut fiber taken
prior to FE measurements at two different resolutions.
S3. Scanning electron microscope images of the sidewall of 30 µm diameter laser cut fiber taken
prior to FE measurements at two different resolutions showing CNTs protruding from the
surface.
S4. Images of laser cut CNT fiber (a) prior to FE measurements and (b) at the maximum applied
voltage of 1000V. The latter was recorded for a fiber tip to anode distance of 1.75mm. At the
maximum applied voltage of 1000V, there is a large glowing spot at the fiber tip associated with
space-charge limited emission and also a large number of bright spots all the way down the fiber
indicative of space-charge limited emission from the sidewall of the fiber.
Fig. S1 (M. Cahay et al.)
Fig. S2 (M. Cahay et al.)
Fig. S3 (M. Cahay et al.)
Fig. S4 (M. Cahay et al.)