Making the light fantastic
INNOVATION PROFILE/Science Foundation Ireland:IMPROVED SOLAR cells, anti-bacterial surfaces for medical equipment, more efficient lasers, enhanced battery life for smartphones, and coatings to render objects invisible are just a few of the applications of the work being done by the Science Foundation Ireland-funded Advanced Materials Surfaces Group (AMSG) at the Tyndall Institute at UCC.
Led by Prof Martyn Pemble, the group has gained global recognition through numerous national and international collaborative research projects in the areas of advanced chemical vapour deposition (CVD) systems and atomic layer deposition (ALD) systems.
The group is made up of about 20 researchers and recently received additional SFI funding for one of its main strands of research which involves materials known as photonic crystals.
“These are materials which are analogues of natural materials, the most commonly cited of which are opal gemstones,” explains Pemble. “The colours of these stones change when you look at them. This happens because the structure of the material enables it to reflect and refract light in different ways. We call this opalescence.”
He points out that opals and photonic crystals are the optical equivalents of semiconductors. In the case of a semiconductor there are areas or energies where electrons can’t normally be placed – this is known as the electron band gap. In photonic crystals the equivalent is known as the photonic band gap and it is an energy region where light can’t exist.
“These are areas where light can’t pass through and it must be reflected,” says Pemple. “The colour of the reflected light varies as a function of the angle from which you view it. Nature makes this in opals or butterfly wings.”
Opals are made up of balls of silicon dioxide which were formed millions of years ago and during the formation process arranged themselves in an ordered structure. “The scale of this structure is comparable to the wavelength of light and this can have interesting refractive and diffractive effects,” he notes.
“We are trying to make these things in the lab and exploit the fact that they can control the way light is reflected, diffracted and refracted. For example, if we can trap light in a solar cell for longer we can get more energy from the cell. Also, we could make it travel in curves and go around corners and make optical circuits using light instead of electrons.”
In theory, this could mean having a computer operating at the speed of light if its transistors were connected by optical circuits. But this might not be as fast as it might appear.
