Research into sensors fabricated from diamond is still at a relatively early stage but the properties of fullerenes, the so-called third form of carbon , are even less well characterised. These are a new class of compounds with unusual structural, chemical and physical properties which earned their discoverers the Nobel Prize in chemistry in 1996. They consist of cage-like structures of carbon atoms with formulae such as C ₆₀ and C ₈₀ (Figure 6) and take their name from Buckminster Fuller, inventor of the geodesic dome. Since the discovery in 1990 of ways to produce macroscopic quantities of these compounds, materials scientists have been studying their properties and investigating possible applications.

Figure 6: Schematic 3-D structures of fullerene molecules

One of the unexpected properties of fullerenes is their sizeable nonlinear optical activity. A recent survey showed that the majority of patents in this field are concerned with optical and optoelectronic applications and perhaps the most promising for immediate industrial use is optical limiting, i.e. the increase of optical absorption with light intensity. It has been suggested that this canbeusedinbroad-bandlasersafety devices and for optical sensor protection. In addition to optical limiting, substituted fullerenes may also possess a sufficiently large non-resonant nonlinearity for switching and routing applications in very high bit-rate optical telecommunication and computing systems.

In addition to anticipated uses in telecomms, molecular electronics, healthcare and solar energy conversion, sensors are already being developed. Back in 1994, Scintrex Ltd was granted a patent which describes...