Laser Spectroscopy and
Nanoparticle Research
at The University of Texas in Austin

Nanoparticles and Nanostructured Materials


A Cluster of a few hundred to ten million atoms with a large surface area-to-bulk volume ratio is called a nanoparticle, since its size can be measured in nanometers (1-100nm). Materials made from nanoparticles are often described as "Nanostructured".
Due to their finite size small particles have totally different structures and material properties than their bulk crystalline counterparts. Even more, these properties sometimes change drastically whenever a single atom is added to or removed from the cluster. This opens the pathway for a whole new world of tailor made materials in the future.
Nanomaterials already have numerous commercial and technological applications in areas like analytical chemistry, drug delivery, bioencapsulation, and in electronic, magnetic, optical and mechanical devices.
Laser has produced a list of specific features for nanoparticles and –materials:

Small with respect to visible wavelength

Because Nanoparticles are small with respect to visible wavelength they show characteristic absorption and scattering properties (plasmon resonance due to the motion of the ‘free’ electrons in the cluster).
The corresponding excitations and their distinctive differences due to the small size have been exploited technologically for many centuries.
The colored glass used already by the ancient Romans or the fantastically colored glass of the church windows from the Middle Ages owe their color to finely dispersed silver, copper, or gold particles embedded by special fabrication procedures into the glass.
The physics was first explained by Gustav Mie at the beginning of the last century, when he developed the electrodynamic treatment and the theory describing the optical properties of small metal particles.
Today these features are exploited to create nano sized devices (sensors, switches and modulators) with optical signatures that are tunable and can measure changes in their environment.

Large surface area to volume ratio (surface effect)

The ratio of surface area to volume of a particle is inversely proportional to the diameter for a sphere, and follows roughly the same trend for other shapes. For the smallest particles, this means that most of the atoms are at the surface (a spherical particle 1 nm in diameter, consisting of atoms 0.2 nm in diameter, consists of almost 80% surface atoms, as does a cube of the same size).
It turns out that the vast majority of all industrial chemical reactions involve surfaces as the catalysts. Catalysis involves the enhancement of the rate of a reaction by a substance, which is not consumed in the reaction. The kind of processes involved range from hydrogenation of hydrocarbons to detoxification of exhaust gases. The catalytic converter in an automobile is a classic example


Quantum confinement of carriers (volume effect)

Certain properties, such as electron transport (electrical conduction), magnetic domains, charge carrier coherence in superconductors, have a characteristic length. As one makes particles smaller, their diameter becomes smaller than a characteristic length, so that new behavior should arise. One type of such behavior is the quantum size effect, which has to do with the fact that an electron confined in a small region is restricted to have particular energies corresponding to standing waves in its motion through the particle (particle in the box -> electron in the nanoparticle problem).
Semiconductor Nanoparticles are especially suitable to demonstrate visibly this effect in the transition range between the bulk state and the atom. The absorption shifts to shorter wavelengths with decreasing particle size, which indicates that the band gap of the semiconductor becomes larger.
The possibility of shifting electronic bands in semiconductor particles allows the tailoring of semiconductors for special purposes.


Small numbers of grains per particle

Nanomaterials (here nanocrystalline materials) are materials possessing grain sizes on a nanometer scale. They manifest extremely fascinating and useful properties, which can be exploited for a variety of structural and non-structural applications.
All materials are composed of grains, which in turn comprise many atoms. These grains are usually invisible to the naked eye, depending on their size. Conventional materials have grains varying in size anywhere from 100s of microns (µm) to millimeters (mm).
A nanocrystalline material has grains on the order of 1-100 nm.  The average size of an atom is on the order of 1 to 2 angstroms (Å) in radius. 1 nanometer comprises 10 Å, and hence in one nm, there may be 3-5 atoms, depending on the atomic radii.  Nanocrystalline materials are exceptionally strong, hard, and ductile at high temperatures, wear-resistant, erosion-resistant, corrosion-resistant, and chemically very active.  Nanocrystalline materials are also much more formable than their conventional, commercially available counterparts.

This page was last updated : April, 2006.
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