29 A Novel Approach to Artificial Energy-Loss Free Field Emitters …
417
SWCNTs by annealing at 1400 K and under 10–5 Pa, SWCNTs annealed at 1400 K
and over 10–2 Pa, and un-annealed SWCNTs having crystal defects as a reference,
respectively. The SWCNTs annealed at over 10–2 Pa, had more crystal defects in
their carbon networks than SWCNTs annealed at 1400 K and under 10–5 Pa. After
the treatment by annealing at a high temperature and vacuum, the SWCNTs synthesized by arcing had hardly crystal defects. These cathode electrodes were assembled
into simple diode structures with conductive anodes and then a voltage of 580 V DC
was applied, and they could obtain FE currents of 10 mA/ cm
2 as initial DC current
in a vacuum of 10–4 Pa. The FE cathodes with the high crystallized SWCNTs and
SWCNTs annealed at over 10–2 Pa were activated with FE loading, and FE current
densities of each SWCNT increased to over 30 and 17 mA/ cm
2 , respectively. The
cause for this was assumed to arise from the cleaning of the surfaces of the SWCNTs’
tips by flushing. This result expressed that the FE current density by the high crystallized SWCNTs was not attenuated at over 1000 h; otherwise, the radioactive halftime of SWCNTs annealed at over 10–2 Pa was 482 h, and the reference sample
of un-annealed SWCNTs with crystal defects had a shorter emission lifetime of
105 h compared to those of the other SWCNTs. The control of the crystallinity of
each SWCNT as field emitters is an effective improvement method for FE current
durability.
Before verification of the FE lifetime, the IV characteristics for each SWCNT
was initially measured, as shown in Fig. 29.3a. The turn-on field for the un-annealed
SWCNTs was 2.01 V/µm. In contrast, the turn-on field for the high crystallized
SWCNTs was 1.07 V/µm on the FE current density 0.01 mA/ cm
2 . As shown in the
lighting spot homogeneity of Fig. 29.3b, the probability densities of each SWCNT
in the cathode films to induce FE resemble almost the SWCNTs with crystal defects
and the highly crystalline SWCNTs.
The distribution of emission spots in the highly crystalline SWCNTs and untreated SWCNTs are shown in Fig. 29.3b. The planar images on the right side in
Fig. 29.3 show enlarged views indicated in the circled regions on the left zoom
out images. We can find the FE curve properties in Fig. 29.3a depend on the crystallinity of each SWCNT. When the current density is uniform with the same supplied
field, the densities of lighting spots having high- and low-brightness and the homogeneity of the planar lighting surface are almost similar between the two crystal types,
i.e., highly crystalline SWCNTs and the un-treated SWCNTs with crystal defects.
SWCNTs synthesized by arc discharge coexist with metallic and semiconductive
properties from previous reports (Dresselhaus et al. 2005; Wu et al. 2011), and it is
surmised that the high-brightness spots in Fig. 29.3b originate from the FE of semiconductive SWCNTs and the low-brightness spots originate from SWCNTs having
metallic conduction. The chirality to roll up a graphene sheet comprising a SWCNT
does not change, nor does the mixing ratio between SWCNTs with metallic properties and semiconductive SWCNTs with the increase of the crystallinity of SWCNTs
(Wallace (1947); Saito et al. (1993); Dresselhaus et al. (1996); Spindt et al. (1976);
Czerw et al. (2003)).
From the above-mentioned results, the SWCNTs’ bundle size and the dispersion
density of these bundles protruded from the cathode film were similar for the two
417
SWCNTs by annealing at 1400 K and under 10–5 Pa, SWCNTs annealed at 1400 K
and over 10–2 Pa, and un-annealed SWCNTs having crystal defects as a reference,
respectively. The SWCNTs annealed at over 10–2 Pa, had more crystal defects in
their carbon networks than SWCNTs annealed at 1400 K and under 10–5 Pa. After
the treatment by annealing at a high temperature and vacuum, the SWCNTs synthesized by arcing had hardly crystal defects. These cathode electrodes were assembled
into simple diode structures with conductive anodes and then a voltage of 580 V DC
was applied, and they could obtain FE currents of 10 mA/ cm
2 as initial DC current
in a vacuum of 10–4 Pa. The FE cathodes with the high crystallized SWCNTs and
SWCNTs annealed at over 10–2 Pa were activated with FE loading, and FE current
densities of each SWCNT increased to over 30 and 17 mA/ cm
2 , respectively. The
cause for this was assumed to arise from the cleaning of the surfaces of the SWCNTs’
tips by flushing. This result expressed that the FE current density by the high crystallized SWCNTs was not attenuated at over 1000 h; otherwise, the radioactive halftime of SWCNTs annealed at over 10–2 Pa was 482 h, and the reference sample
of un-annealed SWCNTs with crystal defects had a shorter emission lifetime of
105 h compared to those of the other SWCNTs. The control of the crystallinity of
each SWCNT as field emitters is an effective improvement method for FE current
durability.
Before verification of the FE lifetime, the IV characteristics for each SWCNT
was initially measured, as shown in Fig. 29.3a. The turn-on field for the un-annealed
SWCNTs was 2.01 V/µm. In contrast, the turn-on field for the high crystallized
SWCNTs was 1.07 V/µm on the FE current density 0.01 mA/ cm
2 . As shown in the
lighting spot homogeneity of Fig. 29.3b, the probability densities of each SWCNT
in the cathode films to induce FE resemble almost the SWCNTs with crystal defects
and the highly crystalline SWCNTs.
The distribution of emission spots in the highly crystalline SWCNTs and untreated SWCNTs are shown in Fig. 29.3b. The planar images on the right side in
Fig. 29.3 show enlarged views indicated in the circled regions on the left zoom
out images. We can find the FE curve properties in Fig. 29.3a depend on the crystallinity of each SWCNT. When the current density is uniform with the same supplied
field, the densities of lighting spots having high- and low-brightness and the homogeneity of the planar lighting surface are almost similar between the two crystal types,
i.e., highly crystalline SWCNTs and the un-treated SWCNTs with crystal defects.
SWCNTs synthesized by arc discharge coexist with metallic and semiconductive
properties from previous reports (Dresselhaus et al. 2005; Wu et al. 2011), and it is
surmised that the high-brightness spots in Fig. 29.3b originate from the FE of semiconductive SWCNTs and the low-brightness spots originate from SWCNTs having
metallic conduction. The chirality to roll up a graphene sheet comprising a SWCNT
does not change, nor does the mixing ratio between SWCNTs with metallic properties and semiconductive SWCNTs with the increase of the crystallinity of SWCNTs
(Wallace (1947); Saito et al. (1993); Dresselhaus et al. (1996); Spindt et al. (1976);
Czerw et al. (2003)).
From the above-mentioned results, the SWCNTs’ bundle size and the dispersion
density of these bundles protruded from the cathode film were similar for the two