In nanotechnology, a particle is defined as a small object that behaves as a whole unit in terms of its transport and properties.
It is further classified according to size: in terms of diameter, fine particles cover a range between 100 and 2500 nanometers, while ultrafine particles, on the other hand, are sized between 1 and 100 nanometers.
Colorized transmission electron micrograph showing chains of cobalt nanoparticles. Image credit: G. Cheng, A.R. Hight Walker/NIST
Similar to ultrafine particles, nanoparticles are sized between 1 and 100 nanometers. Nanoparticles may or may not exhibit size-related properties that differ significantly from those observed in fine particles or bulk materials.
Although the size of most molecules would fit into the above outline, individual molecules are usually not referred to as nanoparticles.
Nanoclusters have at least one dimension between 1 and 10 nanometers and a narrow size distribution. Nanopowders are agglomerates of ultrafine particles, nanoparticles, or nanoclusters.
Nanometer-sized single crystals, or single-domain ultrafine particles, are often referred to as nanocrystals.
Nanoparticle research is currently an area of intense scientific interest due to a wide variety of potential applications in biomedical, optical and electronic fields.
The National Nanotechnology Initiative has led to generous public funding for nanoparticle research in the United States.
Although nanoparticles are generally considered an invention
of modern science, they actually have a very long history.
Nanoparticles were used by artisans as far back as the 9th century in
Mesopotamia for generating a glittering effect on the surface of pots.
Even these days, pottery from the Middle Ages and
Renaissance often retain a distinct gold or copper colored metallic
glitter. This so called luster is caused by a metallic film that was
applied to the transparent surface of a glazing. The luster can still be
visible if the film has resisted atmospheric oxidation and other
weathering.
The luster originated within the film itself, which
contained silver and copper nanoparticles dispersed homogeneously in the
glassy matrix of the ceramic glaze.
These nanoparticles were created by
the artisans by adding copper and silver salts and oxides together with
vinegar, ochre and clay, on the surface of previously-glazed pottery.
The object was then placed into a kiln and heated to about 600 °C in a
reducing atmosphere.
In the heat the glaze would soften, causing the copper and
silver ions to migrate into the outer layers of the glaze. There the
reducing atmosphere reduced the ions back to metals, which then came
together forming the nanoparticles that give the colour and optical
effects.
Luster technique showed that ancient craftsmen had a rather
sophisticated empirical knowledge of materials. The technique originated
in the islamic world. As Muslims were not allowed to use gold in
artistic representations, they had to find a way to create a similar
effect without using real gold. The solution they found was using
luster.
Michael Faraday provided the first description, in
scientific terms, of the optical properties of nanometer-scale metals in
his classic 1857 paper.
In a subsequent paper, the author (Turner)
points out that: "It is well known that when thin leaves of gold or
silver are mounted upon glass and heated to a temperature which is well
below a red heat (~500 °C), a remarkable change of properties takes
place, whereby the continuity of the metallic film is destroyed.
The
result is that white light is now freely transmitted, reflection is
correspondingly diminished, while the electrical resistivity is
enormously increased."
Further Reading
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"Nanoparticle"
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