It takes just about four seconds to detect lead. However, the crystal structure of silica and gallium nitride/aluminium gallium nitride is different and so they experience stress when grown on silicon. To produce a layer of gallium nitride that is stress-free, the researchers produced a stack of five layers of gallium nitride and aluminium gallium nitride on the silicon wafer base (with the percentage of aluminium in gallium nitride reducing from 100% to 0%). The sensor response time — the time taken to detect lead — is hardly affected when reused, Nigam says. “The cadmium sensor has higher sensitivity (0.255 ppb) than other electrochemical approaches and can detect cadmium in about 3 seconds.” The results of cadmium sensor were published in April 2019 in the journal IEEE Electron Device Letters.

Source: The Hindu October 19, 2019 12:45 UTC