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Nanotechnology is an interdisciplinary field of technology development at the atomic, molecular, or macromolecular range of approximately 1-100 nanometers to create and use structures, devices, and systems that have novel properties.
Chemists have dealt with naturally occurring nanoparticles all along. Think molecules or viruses. Toxicologists have dealt with nanoparticles that are the result of modern human life such as carbon particles in combustion engine exhaust. Without being aware of it, tire manufacturers used nanoparticles, carbon black, to improve the performance of tires as early as the 1920s. Medieval artists used gold nanoparticles to achieve the bright red color in church windows (gold particles in nanometer size are red, not golden). You might even say that we are surrounded by, and made of, nanostructures – atoms and molecules are nanoscale objects after all. So what is all the fuss about?
The ongoing quest for miniaturization has resulted in tools such as the atomic force microscope (AFM) and the scanning tunneling microscope (STM). Combined with refined processes such as electron beam lithography, these instruments allow us to deliberately manipulate and manufacture nanostructures.
Developing new instruments to be able to "see" at the nanoscale is a research field in itself. Shown in the image above is the tip of an atomic force microscope (AFM), one of the foremost tools for imaging, measuring and manipulating matter at the nanoscale. Here, a platinum electrode measuring one hundredth of a nanometer has been deposited on the tip of this pyramid shaped AFM tip via focused ion beam (FIB) deposition (Image: C. Menozzi, G.C. Gazzadi, S3 (INFM-CNR), Modena. Artwork: Lucia Covi).
The prefix nano means a factor of one billionth (10-9) and can be applied, e.g., to time (nanosecond), volume (nanoliter), weight (nanogram) or length (nanometer or nm). In its popular use “nano” refers to length, and the nanoscale usually refers to a length from the atomic level of around 0.1 nm up to 100 nm. Nanostructures or nanomaterials are forms of matter at the nanoscale.
It is hard to image things so small. Eight to 10 atoms span one nanometer. The human hair is approximately 70,000 to 80,000 nm thick. To put this in perspective: Precisely positioning a 1 nm structure inside one meter is analogous to being able to exactly position a peppercorn in the distance between New York and Miami (or if you prefer, between Copenhagen and Madrid, or Tokyo and Beijing).
Engineered nanomaterials, either by way of a top-down approach (a bulk material is reduced in size to nanoscale pattern) or a bottom-up approach (larger structures are built or grown atom by atom or molecule
by molecule), go beyond just a further step in miniaturization. They have broken a size barrier below which quantization of energy for the electrons in solids becomes relevant. The so-called “quantum size effect” describes the physics of electron properties in solids with great reductions in particle size. This effect does not come into play by going from macro to micro dimensions. However, it becomes dominant when the nanometer size range is reached.
Materials reduced to the nanoscale can suddenly show very different properties compared to what they show on a macroscale. For instance, opaque substances become transparent (copper); inert materials become catalysts (platinum); stable materials turn combustible (aluminum); solids turn into liquids at room temperature (gold); insulators become conductors (silicon).
A second important aspect of the nanoscale is that the smaller a nanoparticle gets, the larger its relative surface area becomes. Its electronic structure changes dramatically, too. Both effects lead to greatly improved catalytic activity but can also lead to aggressive chemical reactivity. The fascination with nanotechnology stems from these unique quantum and surface phenomena that matter exhibits at the nano-scale, making possible novel applications and interesting materials.
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