• Indian Institute of Science researchers have developed a highly sensitive nanometre-scale carbon monoxide sensor by employing an innovative fabrication technique.

• It is known that carbon monoxide (CO) can have adverse effects on the health of people exposed to it. Hence, it becomes necessary to have good, low-cost carbon-monoxide sensors. 

• Typically, a sensor would be a thin, current carrying plate whose resistance changes on exposure to carbon monoxide. 

• This in turn changes the value of the current flowing through it. This change when measured indicates the level of carbon monoxide in the air. 

• Most available sensors are in the micrometer range, a nanometer-sized detector would have a higher sensitivity, but the cost of manufacturing it goes up as the size decreases. 

• This is where the work of C.S. Prajapati and coworkers of Indian Institute of Science comes in.

• To build this zinc-oxide (ZnO) nanostructure on a silicon wafer substrate, the researchers first placed tiny polystyrene beads on the wafer. 

• These beads arrange themselves into what is called a hexagonal close-packed structure on the oxidised silicon wafer.

• Maintaining a reasonable level of vacuum, a high voltage is applied which “etches away” the surfaces of the beads until a gap of desired thickness is formed between adjacent beads. 

• Then zinc oxide is deposited on the system.

• This occupies the spaces between the beads, forming a honeycomb like nano-mesh that can function as a nanosenor.

• Scaling down from 10 micrometer feature size to 10 nanometer feature (used in this work) can enhance the efficiency 1,000 times. 

• However, the development cost of nanostructured gas sensors using existing lithography tools is really very high, which eventually impacts the overall cost of the device.

• This device is also easy to scale for mass production. 

• Nanostructure-based gas sensors are very promising in their performance due their high surface-to-volume ratio. The existing techniques to create honeycomb nanostructures using photolithography and e-beam lithography are expensive and time-consuming. 

• The proposed technique can potentially reduce the cost by more than 50%.

• If these sensors were at traffic intersections, we can do real time mapping of pollution hot-spots in a city. 

• This would be an enabler in realizing smart cities.

Source:TH