Saturday, January 06, 2007

Carbon Nanotubes – Structure, Properties and Applications

Background

The discovery of fullerenes in 1985 by Curl, Kroto, and Smalley, culminated in their Nobel Prize in 1996. Fullerenes, or Buckminsterfullerenes, are named after Buckminster Fuller, the architect and designer of the geodesic dome, and are sometimes called bucky balls. The names derive from the basic shape that defines fullerenes; an elongated sphere of carbon atoms formed by interconnecting six-member rings, and twelve isolated five-member rings forming hexagonal and pentagonal faces. The first isolated and characterized fullerene, C60, contains 20 hexagonal faces and 12 pentagonal faces, just like a soccer ball, and possesses perfect icosahedral symmetry.
Fullerenes - Potential Industry Applications and Recent Developments

Fullerene chemistry continues to be an exciting field, generating many articles with promising new applications every year. Magnetic nanoparticles (nanomagnetic materials) show great potential for high-density magnetic storage media. Recent work has shown that C60 dispersed into ferromagnetic materials such as iron, cobalt, or cobalt iron alloy can form thin films with promising magnetic properties. A number of organometallic-fullerene compounds have recently been synthesized. Of particular note are a ferrocene-like C60 derivative and pair of fullerenes bridged by a rhodium cluster. Some fullerene derivatives even exhibit superconducting character. There has been a report of a fullerene containing a superconducting field-effect device with a Tc as high as 117K.
Structure and Different Types of Carbon Nanotubes

Carbon nanotubes (CNTs) are hollow cylinders of carbon atoms. Their appearance is that of rolled tubes of graphite, such that their walls are hexagonal carbon rings, and they are often formed in large bundles. The ends of CNTs are domed structures of six-membered rings, capped by a five-membered ring. Generally speaking, there are two types of CNTs: single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). As their names imply, SWNTs consist of a single, cylindrical graphene layer, whereas MWNTs consist of multiple graphene layers telescoped about one another.
The Unique Properties of Carbon Nanotubes

Carbon nanotubes (CNTs) were first isolated and characterized by Ijima in 1991. Since then, dozens of research articles have been published, and new applications for CNTs have been proposed every year. The unique physical and chemical properties of CNTs, such as structural rigidity and flexibility continue to generate considerable interest. Additionally, CNTs are extremely strong, about 100 times stronger (stress resistant) than steel at one-sixth the weight. CNTs can also act as either conductors or semiconductors depending on their chirality, possess an intrinsic superconductivity, are ideal thermal conductors, and can also behave as field emitters.
Carbon Nanotube-Based Nanodevices

Carbon nanotubes are a hot research area at the moment. The excitement has been fuelled by experimental breakthroughs that have led to realistic possibilities of using them commercially. Applications could include field emission-based flat panel displays, novel semiconducting devices, chemical sensors, and ultra-sensitive electromechanical sensors.
Carbon Nanotubes Used in Molecular Electronics

The utility of carbon nanotubes for molecular electronics or computers, first predicted by theory and simulations, is now being explored through experiments to fabricate and conceptualize new devices based on simulations. Carbon nanotubes are now the top candidate to replace silicon when current chip features cannot be made any smaller in 10-15 years’ time.
Semiconducting Properties of Carbon Nanotubes

Calculations show that nanotubes can have metallic or variable semiconducting properties with energy gaps ranging from a few meV to a few tenths of an eV. Experiments probing the density of states confirm these predictions. Conductivity measurements on single nanotubes have shown rectification effects for some nanotubes and ohmic conductance for others. These properties suggest that nanotubes could lead to a new generation of electronic devices.
Using Carbon Nanotubes as Electromechanical Sensors

Simulations to investigate the interaction of water molecules with a nanotube tip revealed an atomistic understanding of the interaction, which is critical in designing commercial-quality flat panel displays around carbon nanotubes. Their use as ultra-sensitive electromechanical sensors has also been explored.