Nanowire

As the name implies, nanowires are one-dimensional wires measured in nanometers; that is, their diameter is no more than just a few 0.000000001 meters (0.000000001 meter corresponds to 1 nanometer which is around a thousandth of a single strand of human hair). At the nano-dimension, quantum mechanics applies since the nanowires are so fine that normal (or Newtonian-scale) physics could not be relied upon to explain their behavior.

Manufacturing the Nanowire

Nanowires are manufactured from different materials. Thus, there are wires with different properties that have been acquired from the source material(s). Metallic nanowires are made from metals like nickel, platinum or gold. Semi-conducting nanowires are made from the semi-conducting silicon or indium phosphide. Insulating nanowires are made from materials like silicon dioxide or titanium dioxide. Finally, molecular nanowires are made from molecules of organic or inorganic substances.

There are several approaches to manufacturing nanowires, all of which can only be undertaken at the present time under laboratory conditions. They are the following:

Suspension

One suspension method is heating the source metal to its melting point, touching the tip of a scanning tunneling microscope (STM) on its surface, and then pulling the STM away. Some of the source material will naturally cling to the STM and a strand of ultra-fine wire will consequently be formed. This process of nanowire manufacture is somewhat akin to touching one of your fork's tines to melting cheese and then pulling the fork away; there will be a thin strand of cheese from the dish to your fork.

One other suspension method is whittling down the source material until it becomes nano-dimensional. This process of reduction is done through chemical etching (where chemical reactions are used to reduce the size of the source material) or though particle bombardment (where molecules or atoms traveling at extremely high speeds are directed towards the source material and the impact gradually reduces the material's size).

Deposition

In deposition, particles of the source material are deposited on a host material or substrate. For instance, a deposited metallic nanowire may be made by taking a piece of plastic and then depositing metallic atoms on its surface. The particles that have been deposited comprise the nanowire while the plastic merely plays 'host' to the wire.

Synthesis

The most popular approach at the moment is a process called Vapor-Liquid-Solid (VLS) synthesis which uses a source material like silane gas (the 'vapor' – this is a series of silicon atoms bound to hydrogen atoms) and a catalyst of liquid metal (the 'liquid' – liquid gold is often used) which have been manufactured or self assembled to become nano-dimensional.

The gas is exposed to the catalyst and this begins to soak into and saturate the latter. After supersaturation is attained, the gas solidifies and the wire begins to grow. Once the target length has been achieved, the gas feed is simply turned off. The synthesis part of the process comes when the original source material is, at certain intervals, alternated with other materials to form compound nanowires.