Helping bridge the gap between photonics  and electronics, researchers from Purdue University have coaxed a thin film of titanium nitride  into transporting plasmons, tiny electron excitations coupled to light that can direct and manipulate optical signals on the nanoscale. Titanium nitride's addition to the short list of surface-plasmon-supporting materials, formerly composed only of metals, could point the way to a new class of optoelectronic  devices with unprecedented speed and efficiency. "We have found that titanium nitride is a promising candidate for an entirely new class of technologies based on plasmonics and metamaterials," said Alexandra Boltasseva, a researcher at Purdue and an author on a paper published March 27 in the Optical Society's (OSA) open-access journal Optical Materials Express. "This is particularly compelling  because surface plasmons  resolve a basic mismatch between wavelength-scale optical devices and the much smaller components of integrated electronic circuits."

Metals carry electricity with ease, but normally do nothing to transmit light waves. Surface plasmons, unusual light-coupled oscillations that form on the surface of metallic materials, are the exception to that rule. When excited on the surface of metals by light waves of specific frequencies, plasmons are able to retain that same frequency, but with wavelengths that are orders-of-magnitude smaller, cramming visible and near-infrared light into the realm of the nanoscale.

In the world of electronics and optics, that 100-fold contraction is a boon. Circuits that direct the paths of electrons operate on a much smaller scale than optical light waves, so engineers must either rely on small but relatively sluggish  electrons for information processing or bulk up to accommodate the zippy photons. Plasmons represent the best of both worlds and are already at the heart of a number of optoelectronic devices. They have not had widespread use, however, due to the dearth of materials that readily generate them and the fact that metals, in most cases, cannot be integrated with semiconductor devices.