Raman Spectroscopy

Over the past 20 years, Raman scattering has proven to be a very useful probe of carbon-based materials and has been used extensively to study the bonding and properties of pristine, metallic, and superconducting FIGURE 5.9 Raman active eigenmodes along with their frequencies for a (10,10) nanotube. The red arrows show the magnitude and displacement of the carbon atoms in the nanotube lattice, and the unit cell for this nanotube is shown in the upper right-hand corner of the figure 66 . See...

Defect Free Nanotube

There has been a tremendous amount of work studying defect-free nanotubes, including single or multiwalled nanotubes (SWNTs or MWNTs). A SWNT is a hollow cylinder of a graphite sheet whereas a MWNT is a group of coaxial SWNTs. SWNT was discovered in 1993 5,6 , 2 years after the discovery of MWNT 1 . They are often seen as straight or elastic bending structures individually or in ropes 7 by transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM),...

SWNT pn Junction as Esaki Diode

In the history of semiconductor electronics, people focused on tunnel diodes exhibiting negative differential resistance (NDR) as shown in the current-voltage characteristics in Figure 7.17, when three-terminal transistors were not fabricated reliably. With a device having an NDR and a gyrator allowing a signal to flow in a designated circulation direction (like a traffic rotary), it is possible to create a signal FIGURE 7.17 Current-voltage characteristics with a negative differential...

Structure and Symmetry

The structure and symmetry of CNTs has been described in detail in Chapter 1. In this section a summary of salient features is provided, which will be used later for understanding some of the characterization and application scenarios that form the focus of this chapter. A SWNT is best described as a rolled-up tubular shell of graphene sheet (Figure 2.1a) 4-7 . The body of the tubular shell is mainly made of hexagonal rings (in a sheet) of carbon atoms, whereas the ends are capped by...

Arc Discharge Production of MWNTs

3.2.1 General Technical Features of the Production Process The carbon arc technique for generating MWNTs appears very simple, but obtaining high yields of tubes is difficult and requires careful control of experimental conditions. In the most common laboratory scale production scheme, the direct current (DC) arc operates in a 1- to 4-mm wide gap between two graphite electrodes 6 to 12 mm in diameter that are vertically or horizontally installed in a water-cooled chamber filled with helium gas...

Chemical Functionalization Physisorption and Diffusion in Carbon Nanotubes

Many of the CNT's proposed applications in composite materials, molecular electronics, sensors, etc., require an understanding and control of the chemistry or chemical reactivity of CNTs. The efficiency of the chemical bonding of the end caps or the sidewalls of CNTs will determine where the chemically sensitive reactions occur and how these change the mechanical or electrical properties. For example, the functionalization or chemisorption on the sidewalls of CNTs can be used to increase...

Applications of CNT Emitters

The range of potential applications for CNT-based field emission is very large. Any system that uses an electron source could potentially host a CNT field emission device. CNT field emitters are particularly suited when high efficiency is necessary, such as for most space and portable applications, when fast switching or ultrahigh frequency modulation are required and also, when very high current densities are desirable. Several applications for CNT emitters are discussed below. Vacuum...

Summary and Outlook

Sensor development using CNTs is at its early stages. A summary of early results along with the basics is provided in this chapter. The potential in various sectors is outlined below. The challenges are common to all these sectors inexpensive fabrication steps, sensor robustness, reliability, reproducibility, and system integration. Carbon nanotube-based chemical sensors possess high sensitivity, small size, and low power consumption, which can be used to quickly verify incoming raw materials...

Bonding of Carbon Atoms

To understand the structure and properties of nanotubes, the bonding structure and properties of carbon atoms are discussed first. A carbon atom has six electrons with two of them filling the 1s orbital. The remaining four electrons fill the sp3 or sp2 as well as the sp hybrid orbital, responsible for bonding structures of diamond, graphite, nanotubes, or fullerenes, as shown in Figure 1.1. In diamond 2 , the four valence electrons of each carbon occupy the sp3 hybrid orbital and create four...

References

Iijima, Nature, 354, 56 1991 . 2. S. Iijima, Nature, 363, 603 1993 . 3. D.S. Bethune et al., Nature, 363, 605 1993 . 4. R. Saito, G. Dresselhaus, and M.S. Dresselhaus, Physical Properties of Carbon Nanotubes, Imperial College Press, London, 1998 . 5. M.S. Dresselhaus, G. Dresselhaus, and Ph. Avouris, Eds., Carbon Nanotubes Synthesis, Structure, Properties, and Applications, Springer-Verlag Berlin, Heidelberg, 2001 . 6. M. Meyyappan and D. Srivastava, Carbon nanotubes, in Handbook on...

Atomic Force and Scanning Tunneling Microscopy

The previous section demonstrated the usefulness of EM techniques applied to nanotube research. However, there are two other microscopic methods that are indispensable in nanotube research. These methods are atomic force microscopy AFM and scanning tunneling microscopy STM . Both methods have provided important information of nanotube structure and properties. AFM has been very useful in imaging isolated SWNTs that have either been grown directly on silicon substrates via a chemical vapor...

Structure and Microstructure of CNT Field Emitters

Carbon nanotubes have been shown to have excellent emission characteristics emission has been observed at fields lower than 1 V m, and high current densities of over 1 A cm2 have been obtained. Detailed reviews of the properties of CNT as field emitters can found in the literature 6,7 . CNT emitters can be fabricated in a variety of configurations depending on the nature of the nanotubes, their microscopic arrangement, the preparation process, and the desired emitter structure. Field emission...