Photo- and thermionic emission from potassium-intercalated carbon nanotube arrays
(Color online) Predicted electron EEDs for pure thermionic emission [Eq. (1)] and for two simple photoemission models. One photoemission model [Eq. (4)] assumes that all of the photon energy is converted into “normal energy” while the other photoemission model (Ref. 9) assumes that has an equal probability of being absorbed as kinetic energy in any direction. All curves are normalized to facilitate comparison: and .
(Color online) (a) Tilted cross-sectional FESEM showing the PAA surface with SWCNTs extending from pores. (b) FESEM of the area in the yellow box in (a). White material in the bottom of the pores is palladium and provides electrical contact to the SWCNTs. The inset shows a Pd-contacted SWCNT in a PAA pore. Scale bar is in (a) and 200 nm in (b).
FESEM images of K/MWCNTs, showing metal, presumably potassium, inside individual MWCNTs. Scale bars are 500 nm, , and 100 nm, in (a), (b), and (c), respectively.
X-ray photoemission intensity of a K/MWCNT sample as a function of binding energy at temperatures of 300 and 570 K. XPS data were obtained by Zemlyanov of the Surface Analysis Laboratory, Birck Nanotechnology Center, Purdue University.
(Color online) Schematic of hemispherical energy analyzer and vacuum system used to measure energy distributions of emission electrons. Labels have the following meanings: (a) incident laser, (b) electron multiplier, (c) pyrometer temperature probe, (d) movable metal plate, (e) direct-current voltage supply , and (f) sample heater.
Normalized EED data from single-crystal tungsten (100) at approximately 1140 K. The work function of tungsten (100) is known to be approximately 4.56 eV, indicating that the analyzer’s work function is 3.98 eV.
(Color online) (a) EEDs from a K/SWCNT/PAA sample showing effects of electron pass energy and laser illumination. (b) Normalized data curves from (a). Data with laser shuttered are not shown in (b) because they are dominated by noise. Theoretical EEDs based on thermionic emission [Eq. (1), solid line] and photoemission [Eq. (4), dashed line] assuming are included in (b) for comparison: and .
(Color online) Thermionic and laser-assisted EEDs from the same K/SWCNT/PAA sample featured in Fig. 7. In (a) the EED magnitudes have been adjusted to account for the energy analyzer’s settings and in (b) the EEDs have been normalized and theoretical fits based on Eq. (1) have been included. Data in (a) dominated by background noise are not shown in (b); .
(Color online) Thermionic and laser-assisted EEDs from a potassium-intercalated multiwalled CNT (K/MWCNT) sample. In (a) the EED magnitudes have been adjusted to account for the energy analyzer’s settings and in (b) the EEDs have been normalized and theoretical fits included based on Eq. (1). Data in (a) dominated by background noise are not shown in (b): .
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