provide stable emission, long lifetimes, and low emission threshold potentials
[185, 188]. Current densities as high as 4 A cm
À2 have been obtained, compared
with the 10 mA cm
À2 needed for flat panel field emission displays and the >0.5
A cm
À2 required for microwave power amplifier tubes [193]. Flat panel displays are
one of the more lucrative nanotube applications being developed by industry.
However, they are also technically the most complex, requiring concurrent advances in electronic addressing circuitry, the development of low-voltage phosphors, methods for maintaining the required vacuum, spacers withstanding the
high electric fields, and the elimination of faulty pixels. The advantages of nanotubes over liquid crystal displays are a low power consumption, high brightness, a
wide viewing angle, a fast response rate, and a wide operating temperature range.
Samsung has produced several generations of prototypes (Figure 8.14), including
a 9 in (23 cm) red–blue–green color display that can reproduce moving images
[187].
Aligned carbon nanotubes are considered to be ideal for the purpose because
of the high packing density and hence their use as high brightness field emitters. MWNT-based field emission lighting devices have been built and their luminescence characteristics studied [194]. One such field emission lighting device
is shown in Figure 8.15. Choi et al. [195a] have assembled a sealed 4.5 in
2
field-emission display device using vertically aligned SWNTs along with organic
binders. The display in three primary colors has an emission current of 1.5 mA at
3 V mm
À1 , with a brightness of 1800 Cd m
À2 . Lee et al. [195b] have just shown that
aligned nanotube bundles exhibit a high emission current density of around 2.9
mA cm
À2 at 3.7 V mm
À1 . Lovall et al. [196] have investigated the emission properties of SWNT ropes by employing field ion microscopy. The field-emitted electron
energy distribution (FEED) of SWNT field emitters shows a large density of states
near the Fermi energy. Emission characteristics of CVD produced MWNTs as well
as SWNTs have been examined by Groning et al. [197], who obtained as emission
site density of 10000 emitters cm
À2 at fields around 4 V mm
À1 . A work function of
5 eV was obtained with MWNTs, and a smaller value with the SWNTs.
The use of dense, quasi-aligned carbon nanotubes produced by the pyrolysis of
ferrocene on a pointed tungsten tip exhibit high emission current densities with
good performance characteristics [198]. In Figure 8.16(a) we show a typical I–V
plot for the carbon nanotube covered tungsten tip for currents ranging from 0.1 nA
to 1 mA. The applied voltage was 4.3 kV for a total current of 1 mA and 16.5 kV for
1000 mA. The Fowler–Nordheim (F–N) plot shown in Figure 8.16(b) has two distinct regions. The behavior is metal-like in the low-field region, while it saturates
at higher fields as the voltage is increased. We have obtained a field emission current density of 1.5 A cm
À2 at a field of 290 V mm
À1 , a value considerably higher
than that found with planar cathodes. Accordingly, the field enhancement factor
calculated from the slope of the F–N plot in the low-field region is also large. The
field emission micrographs reveal the lobe structure symmetries typical of carbon
nanotube bundles. The emission current is remarkably stable over an operating
period of more than 3 h for various current values in the 10–500 mA range. The
relative fluctuations decrease with increasing current level, and the emitter can be
8.2 Carbon Nanotubes 235
[185, 188]. Current densities as high as 4 A cm
À2 have been obtained, compared
with the 10 mA cm
À2 needed for flat panel field emission displays and the >0.5
A cm
À2 required for microwave power amplifier tubes [193]. Flat panel displays are
one of the more lucrative nanotube applications being developed by industry.
However, they are also technically the most complex, requiring concurrent advances in electronic addressing circuitry, the development of low-voltage phosphors, methods for maintaining the required vacuum, spacers withstanding the
high electric fields, and the elimination of faulty pixels. The advantages of nanotubes over liquid crystal displays are a low power consumption, high brightness, a
wide viewing angle, a fast response rate, and a wide operating temperature range.
Samsung has produced several generations of prototypes (Figure 8.14), including
a 9 in (23 cm) red–blue–green color display that can reproduce moving images
[187].
Aligned carbon nanotubes are considered to be ideal for the purpose because
of the high packing density and hence their use as high brightness field emitters. MWNT-based field emission lighting devices have been built and their luminescence characteristics studied [194]. One such field emission lighting device
is shown in Figure 8.15. Choi et al. [195a] have assembled a sealed 4.5 in
2
field-emission display device using vertically aligned SWNTs along with organic
binders. The display in three primary colors has an emission current of 1.5 mA at
3 V mm
À1 , with a brightness of 1800 Cd m
À2 . Lee et al. [195b] have just shown that
aligned nanotube bundles exhibit a high emission current density of around 2.9
mA cm
À2 at 3.7 V mm
À1 . Lovall et al. [196] have investigated the emission properties of SWNT ropes by employing field ion microscopy. The field-emitted electron
energy distribution (FEED) of SWNT field emitters shows a large density of states
near the Fermi energy. Emission characteristics of CVD produced MWNTs as well
as SWNTs have been examined by Groning et al. [197], who obtained as emission
site density of 10000 emitters cm
À2 at fields around 4 V mm
À1 . A work function of
5 eV was obtained with MWNTs, and a smaller value with the SWNTs.
The use of dense, quasi-aligned carbon nanotubes produced by the pyrolysis of
ferrocene on a pointed tungsten tip exhibit high emission current densities with
good performance characteristics [198]. In Figure 8.16(a) we show a typical I–V
plot for the carbon nanotube covered tungsten tip for currents ranging from 0.1 nA
to 1 mA. The applied voltage was 4.3 kV for a total current of 1 mA and 16.5 kV for
1000 mA. The Fowler–Nordheim (F–N) plot shown in Figure 8.16(b) has two distinct regions. The behavior is metal-like in the low-field region, while it saturates
at higher fields as the voltage is increased. We have obtained a field emission current density of 1.5 A cm
À2 at a field of 290 V mm
À1 , a value considerably higher
than that found with planar cathodes. Accordingly, the field enhancement factor
calculated from the slope of the F–N plot in the low-field region is also large. The
field emission micrographs reveal the lobe structure symmetries typical of carbon
nanotube bundles. The emission current is remarkably stable over an operating
period of more than 3 h for various current values in the 10–500 mA range. The
relative fluctuations decrease with increasing current level, and the emitter can be
8.2 Carbon Nanotubes 235