Chris Kiely, director of the new Nanocharacterization Laboratory in Lehigh University’s Center for Advanced Materials and Nanotechnology has revealed that when created in minute amounts gold has a range of colours including red, blue and yellow.
Just with other materials, when only hundreds or tens of atoms are combined, the material takes on different properties to its ‘bulk’ form. "As everyone knows," says Kiely, "normal bulk gold is shiny, it is gold in colour, it is inert, and it conducts electricity. If, however, you shrink gold down to a nanoparticle, its properties change dramatically. Its colour changes, it becomes a very good catalyst, and is no longer a metal - instead it turns into a semiconductor."
In partnership with CAMN director, Martin Harmer, they are taking small numbers of gold atoms and combining then with other elements to form nanoparticles of very well defined shapes and sizes. They found that the properties of the nanoparticle assemblies can be changed with variations in the size and elemental composition of the particles.
They have also used precise heating to cause a string of nanoparticles to melt into a nanowire 10 times thinner than wires made by electron beam lithography. Kiely said "The speed at which we heat and destabilize the nanoparticles is crucial. If you want to make nanowires, you have to heat very, very quickly. If you go too slowly, the result is a globby mess."
Kiely and Harmer have also found that an array of gold nanoparticles in a non-metallic super-crystal will behave like a semiconductor and alterations in the size and separation of the supercrystal nanoparticles controls its conductivity.