Depending on what it's made from, a nanowire can have the properties of an insulator, a semiconductor or a metal. Insulators won't carry an electric charge, while metals carry electric charges very well. Semiconductors fall between the two, carrying a charge under the right conditions. By arranging semiconductor wires in the proper configuration, engineers can create transistors, which either acts as a switch or an amplifier.
Some interesting -- and counterintuitive -- properties nanowires possess are due to the small scale. When you work with objects that are at the nanoscale or smaller, you begin to enter the realm of quantum mechanics. Quantum mechanics can be confusing even to experts in the field, and very often it defies classical physics (also known as Newtonian physics).
For example, normally an electron can't pass through an insulator. If the insulator is thin enough, though, the electron can pass from one side of the insulator to the other. It's called electron tunneling, but the name doesn't really give you an idea of how weird this process can be. The electron passes from one side of the insulator to the other without actually penetrating the insulator itself or occupying the space inside the insulator. You might say it teleports from one side to the other. You can prevent electron tunneling by using thicker layers of insulator since electrons can only travel across very small distances.
Another interesting property is that some nanowires are ballistic conductors. In normal conductors, electrons collide with the atoms in the conductor material. This slows down the electrons as they travel and creates heat as a byproduct. In ballistic conductors, the electrons can travel through the conductor without collisions. Nanowires could conduct electricity efficiently without the byproduct of intense heat.
At the nanoscale, elements can display very different properties than what we've come to expect. For example, in bulk, gold has a melting point of more than 1,000 degrees Celsius. By reducing bulk gold to the size of nanoparticles, you decrease its melting point, because when you reduce any particle to the nanoscale, there's a significant increase in the surface-to-volume ratio. Also, at the nanoscale, gold behaves like a semiconductor, but in bulk form it's a conductor.
Other elements behave strangely at the nanoscale as well. In bulk, aluminum isn't magnetic, but very small clusters of aluminum atoms are magnetic. The elemental properties we're familiar with in our everyday experience -- and the ways we expect them to behave -- may not apply when we reduce those elements down to the size of a nanometer.
We're still learning about the different properties of various elements at the nanoscale. Some elements, like silicon, don't change much at the nanoscale level. This makes them ideal for transistors and other applications. Others are still mysterious, and may display properties that we can't predict right now.
In the next section, we'll find out how engineers make nanowires.