Bengaluru: A new thin-film material developed by researchers in Bengaluru could lead to more sensitive devices for detecting heat and temperature, including applications in thermal imaging and measuring tiny changes in heat flow.Made from scandium nitride, the material produces an unusually large electrical signal when there is a difference in temperature across it. Researchers at Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) found that it generated more than 124 millivolts of voltage response for every degree Kelvin of temperature difference near room temperature.That is nearly 100 times higher than the response conventional theory predicts for ordinary solid materials. The finding, published in Science, could also be relevant to technologies that convert otherwise wasted heat into electricity. The researchers demonstrated the effect in a prototype photon sensor, suggesting that the unusual response can be put to practical use.The study was led by Renuka Karanje and Dheemahi Rao under the guidance of Bivas Saha at JNCASR. Diksha Dadhich and Sourav Rudra of JNCASR were also part of the team, along with researchers from the University of Sydney and IISc. The researchers have filed an Indian patent application covering the thin-film materials and sensors developed in the work.The principle behind the work is relatively simple. When one side of a junction of two different materials is hotter than the other, the difference in temperature can cause electrically charged particles to move. This creates a voltage, known as the Seebeck effect.The effect is already used in temperature sensors and devices that convert heat into electricity. But the electrical signal produced by most solid materials is very small. Most inorganic materials typically produce between about 100 and 500 microvolts for every degree Kelvin of temperature difference.The JNCASR-led team found a way to make that signal much larger by altering how charges move through scandium nitride. The researchers added magnesium to the material while retaining a high concentration of charged impurities.This creates large variations in the material’s electrical properties. Instead of charges moving relatively smoothly through the material, they become concentrated in tiny conducting regions separated by barriers.When the temperature changes, the charges have to move between these regions. This produces a much larger voltage response than would normally be expected.In one experiment, a film about 200 nanometres thick produced a response of -124.6 millivolts per Kelvin at about 350 Kelvin, or 77°C. Researchers also found that making the material extremely thin could strengthen the effect. A 7.5-nanometre-thick film produced a response of -83.41 millivolts per Kelvin near room temperature.The researchers say the finding could be useful for highly sensitive temperature sensors, thermal imaging, heat-flow measurements and devices that harvest heat. Such sensors could be useful where very small temperature changes need to be detected.
