NEMS (Nano-Electro-Mechanical Systems), which are the successors of MEMS (Micro-Electro-Mechanical Systems) that were already installed in a growing number of daily household appliances, are booming. However, until now the devices were still 'passive'. In other words, NEMS required an outside, bulky (several millimeters) source of alternating current. This is why the research of the scientists at the Laboratoire de Physique de la Matière Condensée et Nanostructures (LPMCN, laboratory of condensed matter physics and nanostructures) is so important. They have just engineered the first active NEMS that can emit a periodic electric signal, thus gaining six orders of magnitude at once. The results were published in the August 2007 issue of Nanoletters (Self-oscillations in field emission nanowire mechanical resonators: a nanometric DC-AC conversion).
Powered by a DC source, the self-oscillating NEMS is a nanowire of silicon carbide - an oscillating element similar to a pendulum - wrapped in an electric signal input wire and output wire. To make the component active, the LPMCN researchers came up with the idea of using something called field emission. When enough DC is applied to a metal, electrons can be extracted. For the NEMS, resonant voltage is applied to the nanowire. The coupling introduced by the field emission creates instability that translates into oscillations. In turn, they have an effect on the voltage that reflects on the field emission, and so on. The retroaction ensures self-sustaining oscillations.
Thanks to self-sustaining oscillations, it is now possible to generate an alternating signal on a nanometric scale based on simple DC. The results are very important because they clear the way for the development of nanometric alternating current generators that will turn NEMS into fully autonomous active components. The outlets for the devices are numerous, specifically in the telecommunications industry that needs variable signals at frequencies to the order of a gigahertz.
