Applied Technology of CNT

Figure 1 shows the various applications of carbon nanotubes. Carbon nanotubes have been intensive attentions as the new high technological materials that can be used in various industry such as the latest electron information industry.

  • The Applications of Emitters FEDs
    The research on the applications of carbon nanotubes as the electron emitter and FED(Field Emission Display) is one of the intensively researched areas in many countries. It is expected that LCD (Liquid Crystal Display), LED (Light Emitting Diode), PDP (Plasma Display Panel), FED (Field Emission Display), followed by the CRT (Cathode Ray Tube) that can be used as a display device until now, will be used in the next high technological electronic information periods. The FEDs have been highly attentions as the next generation electronic information devices. The main technology of the FEDs is the based on the polishing technology and stabilities of emitter tips.
    The silicon tips and molybdenum tips have the large problems on the lifetimes and the stabilities and the efficiencies on the electron emitions.  Thus, there are serious attentions on the use of carbon nanotubes as the emitter tips because of their high conductivities and sharp tips. Figure 2 shows the schematics of FEDs using  carbon nanotubes.The FED constructions using carbon nanotubes are initiated by De Heer after Smalley confirmed the SWNT’s FED electron emitter capacities. Chang and et. al. constructed the diode typed FEDs using screen printing with carbon nanotube conductive epoxy and expressed the characters on the screen by the methods of controlling on-off with applying pulse signals on each pixel. They also showed the possibilities of stable electron emission in the low 106 torr. Saito and et. at. showed the possibilities of FEDs using MWNTs. Samsung Advanced Institutes of Technology successfully developed the realization of moving pictures on 9 inch FEDs using screen printing methods and showed the higher brightness (1800 cd/cm2 at 3.7 V/μm) than conventional Spindt-type FED in the low voltages
  • The Applications of Carbon Nanotubes as the secondary batteries and Fuel batteries
    We expect many anticipated effects in the case of applications of carbon nanotubes as the secondary batteries and fuel cell batteries. If we use the carbon nanotubes instead of currently used hydrogen attached alloys, we can reduce the weight of the secondary batteries severely and increase the effectiveness of charging batteries. Thus, carbon nanotubes have the great possibilities of using secondary battery electrodes in automobile batteries, charging batteries, notebook computers. The empty spaces of carbon nanotubes are used for improving the capacity of hydrogen storage. Carbon nanotubes have advantages in not only the light weight but also much space to store hydrogen so that carbon nanotubes are outstanding for the charge storage per unite weight. It is expected that carbon nanotubes fuel cell can be in the highlights as the replaceable energy source.  Table 1. summarized the hydrogen storage capacities of carbon materials including carbon nanotubes.

    Material

    max. wt % H2

    T(K)

    P(MPa)

    SWNTs (low purity) 5-10 133 0.040
    SWNTs (high purity) -4 300 0.040
    GNFs (tubular) 11.26 298 11.35
    GNFs (herringbone) 67.55 298 11.35
    GNFs (platelet) 53.68 298 11.35
    graphite 4.52 298 11.35
    GNFs 0.4 298-773 0.101
    Li-GNFs 20.0 473-673 0.101
    Li-graphite 14.0 473-673 0.101
    K-GNFs 14.0 313 0.101
    K-graphite 5.0 313 0.101
    SWNTs (high purity) 8.25 80 7.18
    SWNTs (-50 % pure) 4.2 300 10.1
    SWNTs (50 % pure) 2 293

    0.101

    <Table 1.>

    Rodrigueze and et. al. announced that the maximum hydrogen storage capacities of herringbone structured carbon nanotubes are 67.55 wt % at the temperature of 298 K and the pressure of 11.35 MPa. If this fact is confirmed, we expect enormous applications of carbon nanotubes as the hydrogen storages. In the case of SWNTs, they stated that the maximum hydrogen storage capacities of carbon nanotubes are 5-10 wt % in the temperature of 133 K and the pressure of 0.040 MPa. It is considered that the low temperature and low pressure conditions are the severe problems to overcome for the real applications. For the references, the goal of Department of Energy (DOE) in U.S.A. is to make electrical automobiles to consume 6.5 wt % and 65 kg H2/m3 per 500 km driving distances. 

  • The Applications of electron switching nano devices
    The metallic and semiconductor properties of carbon nanotubes are controlled by the diameters and the wound structures. It is expected that carbon nanotubes with several tens nm diameters will replace the present silicon devices, developing Tera memory devices. Dekker in university of Delft in Netherland constructed the single molecule nano-devices at the room temperatures using SWNTs as shown in Figure 3
    In this device, the 1 nm carbon nanotubes with semiconductor properties is connected between two metallic electrodes on the Si substrates sputtered with SiO2 with 400 nm spaces. They confirmed that there are two kinds of carbon nanotubes showing different current-voltage (I-V bias) characteristics according to the gate voltages. One is a metallic carbon nanotube showing linear I-V bias characteristics without the relations of gate voltages, and the other is a semiconducting carbon nanotube showing nonlinear I-V bias characteristics with the highly affected relation of Gate voltages.
    Figure 4 shows the I-V bias courves of CNT-based devices that indicate the semiconductor characteristics and the switching efficiency is about 106 on/off ratio. Based on these characteristics, it is considered that the applied Field-Effect Transistor (FET) technologies using carbon nanotubes have advantages not only on device execution speed, but also on the minute size. Recently it is announce that professor Im-Ji Sun and et.al. developed 10 nm size triod type carbon nanotube transistors through the cooperative research with University of California at Berkeley in U.S.A. It is revaluated that this technologies reduce the currently used 256 MDRAM semiconducting devices to 1 over 10 thousand sizes and we expect the appearance of Terabit Dram in the future.
  • The Mechanics and the applications of high functional composites
    Carbon nanotubes can be used in the tips of SPM, STM and AFM using the excellent electronic transport and mechanical strength. Now, the current AFM tips consisted of Si or SiN materials have disadvantages due to the limitation in the observation of minute defects inside samples. In the case of the use of carbon nanotube tips, these disadvantages can be solved. It is anticipated that the minute sized carbon nanotubes can be applied to the nano connections of nano systems, the nano pipes, the nano liquid injection systems, the gas sensors employed the gas adhesion properties of carbon nanotubes, and the applications of the medical system devices used the affinity between carbon and biological tissues.  
    Especially, Liber and et. al. suggested the possibilities of special sensors detecting special applicants on the surface of materials. These carbon nanotubes visualize the chemically patterned surfaces with various molecules, oxidizing and deleting the tips of carbon nanotubes, and attaching carboxyl functionals on the tips. Carbon nanotubes are also applied in observing the correspondence reactions of liquid ?receptors in biological and chemical ways.
    On the other side, it is expected that the applications of high functional composites will give a great affection on the whole industrial areas.
    As the existing carbon black and carbon fibers are employed for the purpose of the electron transport of high molecule composite, recent research is in progress on the composite materials for the purpose of optoelectronic applications using high electron transport of carbon nanotubes.
    Until now, it is considered that the carbon nanotube composite research had a limitation because of the high manufacturing expense. However, the carbon nanotube composite research will be boosted due to the publications of the low cost of carbon nanotube synthesis.