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N. Shimoi
CNTs especially possess excellent physicochemical properties, including high electrical and thermoconductivity, rigidness, and chemical stability. Single-walled carbon
nanotubes (SWCNTs) can be grown to have metallic, semiconducting or semimetal
characteristics by controlling a chirality of a tube rolling up a graphene sheet. The
selection of the two types is available for developing and designing electronic devices
(Hamada et al. 1992; Saito et al. 1992; Tanaka et al. 1992; Kim et al. 2002). SWCNTs,
which express unique effects confined within low-dimensional structure, can be
employed as quantum wires (Ebbesen et al. 1997; Wildoerm et al. 1998; Odom
et al. 1998). Among the different types of CNTs, SWCNTs show particularly high
Young’s modulus (Treacy et al. 1996). SWCNTs have been used various applications, including electron sources as field emitters (Rinzler et al. 1995; Saito et al.
1998), probes of scanning probe microscopy (Dai et al. 1996), gas storage (Dillon
et al. 1997), and electrically conductive materials for secondary batteries (Niu et al.
1997).
The crystal of SWCNTs as grown, including other CNTs, has some defects in their
carbon networks, expressing their unstable physicochemical and electrical properties,
and the crystal defects of CNTs have rendered their problem to use in electronic
devices requiring stable reliability. The crystallization of untreated CNTs, mainly
those grown by chemical vapor deposition, super growth, or laser ablation, has been
paid no attention to develop in electronic devices; as it has proven that it was very
difficult to handle CNTs artificially and manually. Also it was important that the
control of their crystallinity and purity to obtain the good durability and stability in
CNTs required for electron conductivity. Tohji et al. established purification methods
of raw synthesized SWCNTs (Tohji et al. 1996) to obtain a perfect carbon network,
and they improved the crystallinity of SWCNTs synthesized by arc discharge and
succeeded in obtaining highly pure and crystalline SWCNTs by annealing them at
over 1350 K and a low pressure under 10–5 Pa (Yamamoto et al. 2006). Together
with Iwata et al., they succeeded to establish a method to analyze the crystallinity
of highly crystalline SWCNTs by absorption of H 2 gas to their surface (Iwata et al.
2007). Based on these results, a process for synthesizing high crystallized CNTs,
especially SWCNTs, has been gradually developed; however, a technical skill to
employ high crystallized SWCNTs is yet unsatisfactory to use as assembly parts in
an electrical device.
The application using high crystallized SWCNTs as field emitters is gradually
promising and approaching practical utilization industrially. We have developed field
emission (FE) devices employing high crystallized SWCNTs (Shimoi et al. 2013) and
succeeded in employing FE electron sources with SWCNTs as the planar cathodic
element of an artificial lighting device (Garrido et al. 2014). From these achievements, we believe that high crystallized SWCNTs will be necessary to decrease
loading energy of FE devices, increasing their radioactive half-time independent of
FE current density, and thereby correcting the FE electron emission homogeneity
of planar artificial lighting devices (Garrido et al. 2014) with extremely low power
consumption.
N. Shimoi
CNTs especially possess excellent physicochemical properties, including high electrical and thermoconductivity, rigidness, and chemical stability. Single-walled carbon
nanotubes (SWCNTs) can be grown to have metallic, semiconducting or semimetal
characteristics by controlling a chirality of a tube rolling up a graphene sheet. The
selection of the two types is available for developing and designing electronic devices
(Hamada et al. 1992; Saito et al. 1992; Tanaka et al. 1992; Kim et al. 2002). SWCNTs,
which express unique effects confined within low-dimensional structure, can be
employed as quantum wires (Ebbesen et al. 1997; Wildoerm et al. 1998; Odom
et al. 1998). Among the different types of CNTs, SWCNTs show particularly high
Young’s modulus (Treacy et al. 1996). SWCNTs have been used various applications, including electron sources as field emitters (Rinzler et al. 1995; Saito et al.
1998), probes of scanning probe microscopy (Dai et al. 1996), gas storage (Dillon
et al. 1997), and electrically conductive materials for secondary batteries (Niu et al.
1997).
The crystal of SWCNTs as grown, including other CNTs, has some defects in their
carbon networks, expressing their unstable physicochemical and electrical properties,
and the crystal defects of CNTs have rendered their problem to use in electronic
devices requiring stable reliability. The crystallization of untreated CNTs, mainly
those grown by chemical vapor deposition, super growth, or laser ablation, has been
paid no attention to develop in electronic devices; as it has proven that it was very
difficult to handle CNTs artificially and manually. Also it was important that the
control of their crystallinity and purity to obtain the good durability and stability in
CNTs required for electron conductivity. Tohji et al. established purification methods
of raw synthesized SWCNTs (Tohji et al. 1996) to obtain a perfect carbon network,
and they improved the crystallinity of SWCNTs synthesized by arc discharge and
succeeded in obtaining highly pure and crystalline SWCNTs by annealing them at
over 1350 K and a low pressure under 10–5 Pa (Yamamoto et al. 2006). Together
with Iwata et al., they succeeded to establish a method to analyze the crystallinity
of highly crystalline SWCNTs by absorption of H 2 gas to their surface (Iwata et al.
2007). Based on these results, a process for synthesizing high crystallized CNTs,
especially SWCNTs, has been gradually developed; however, a technical skill to
employ high crystallized SWCNTs is yet unsatisfactory to use as assembly parts in
an electrical device.
The application using high crystallized SWCNTs as field emitters is gradually
promising and approaching practical utilization industrially. We have developed field
emission (FE) devices employing high crystallized SWCNTs (Shimoi et al. 2013) and
succeeded in employing FE electron sources with SWCNTs as the planar cathodic
element of an artificial lighting device (Garrido et al. 2014). From these achievements, we believe that high crystallized SWCNTs will be necessary to decrease
loading energy of FE devices, increasing their radioactive half-time independent of
FE current density, and thereby correcting the FE electron emission homogeneity
of planar artificial lighting devices (Garrido et al. 2014) with extremely low power
consumption.