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Michael Faraday, arguably, the greatest experimental physicists of all times, became famous for his works on electro-magnetisms. What is less known is that he made the first experiments with nanoparticles (gold colloids) and thus initiated the fields of nanoscience and nanotechnology. |
Nano-cluster is a small metallic particle with dimensions of just a few nanometers. The smallest such particles usually contain a so-called "magic" number of atoms, usually such that all atomic shells in the particle are completely filled. Metallic nanoparticles were first reported in 1847 by Michael Faraday. He discovered that their optical properties are different from those of bulk metals. This was perhaps the first observation of the quantum size effect. Thus nanotechnology and nanoscience were born.
Today metallic nanoparticles, made of magnetic, semiconducting and superconducting materials are used in various branches of nanoscience. Faraday’s gold is in fact a colloid, which is, by definition, a mixture of two or more solids, liquids, or gases together. The particular type of colloid that Faraday was interested in was a dispersion of very fine gold particles suspended in a liquid. This type of preparation is known as a colloidal suspension or, as Faraday named it, gold sol. Other more familiar examples of sols include paint, mud, and toothpaste. The particles of gold present in the sol are on the nanometer scale - each is one billionth of a meter in length.
Faraday made some attempt to explain what was causing the vivid coloration in his gold mixtures, saying that known phenomena seemed to indicate that a mere variation in the size of [gold] particles gave rise to a variety of resultant colors. (2) He did not explain why changing the size of the gold particles altered the color, but described his work as a useful experimental entrance into certain physical investigations respecting the nature and action of a ray of light.(3) Read more about Michael Faraday in the sites listed below.
[1] M. Faraday, The Bakerian lecture: experimental relations of gold (and other metals) to light, Philosophical Transactions of the Royal Society of London, Vol. 147 (1847), 145-181, p. 159.
[2] Same reference as above, p. 146.
[3] Same reference as above, p. 146.
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