Researchers at Jamia Millia Islamia, New Delhi, have developed an ultrasensitive quantum thermometer using graphene quantum dots. The thermometer can precisely measure a wide range of temperature: 27 degree C to –196 degree C. The thermometer has high sensitivity when measuring different temperatures and can measure very minute (micro Kelvin) changes in temperature.
Sensitive device
The thermometer developed by a team led by Saikh S. Islam, Director of the Centre for Nanoscience and Nanotechnology also showed extremely quick response time of just about 300 milliseconds to register a change in temperature from 27 degree C to –196 degree C. And the time taken to return to its initial temperature value was as little as about 800 milliseconds. The results of the study were published in the journal Nanoscale Advances .
“The thermometer showed excellent repeatability with negligible variation in sensing response when tested for over 50 cycles during a one-year period. The sensor was stable and responded ultra-fast when we tested it repeatedly,” says Prof. Islam.
“The device can find widespread applications in cryogenic temperature sensing. Since the sensor has high sensitivity and ability to measure minute changes in temperature, it will be useful in the pharmaceutical industry, healthcare to measure the incubation temperature of biological cells and molecules and the automobile industry to measure the ignition temperature within the engine,” he says.
The sensor can also be used for measuring high temperatures up to 100 degree C. “In the past, we have tested it up to 300 degree C. Compared with low temperature, the high-temperature sensitivity is low but it is still much higher than currently available solidstate thermometers in terms of sensitivity, resolution, response and recovery timings,” says Poonam Sehrawat from Jamia Millia Islamia and first author of the paper. “Since the sensor is stable and shows linear sensitivity behaviour, it does not need calibration.”
Sensor preparation
The researchers first prepared graphene oxide and chemically made it reduced graphene oxide. “The physical and chemical properties of reduced graphene oxide are very close to monolayer graphene. So by using reduced graphene oxide it is easy to synthesise in large-scale materials having properties similar to graphene,” says Prof. Islam. During the reduction process, quantum dots are formed in the graphene oxide. The reduced graphene oxide having quantum dots is mixed with a ceramic (aluminium oxide), to produce the sensor. The sensor does not need any encapsulation as ceramic forms the matrix.
The reduced graphene oxide flakes containing the quantum dots (measuring 3-6 nanometre in size) are dispersed in the ceramic; the ceramic does not interfere with the sensor response but provides rigidity to the film. “The graphene oxide flakes are in contact with each other in the composite. So a continuous network of current path is obtained,” he says. The temperature sensors were fabricated from this film by using small piece measuring 1x1 cm and depositing two silver electrodes to it for measuring the sensor response.
“The synthesis process is extremely cost effective, has high yield and batch fabrication is possible. One of the main advantages is that this device can be made to any shape and dimension,” Prof. Islam says.
“We are working on making a prototype of this thermometer to be used in electronic devices, as on-chip thermometers that do not even require calibrations. We will now replicate these achievements in single electron transistors (SETs) to miniaturise it for integration in integrated circuits,” he adds.
