Posted in | Nanoelectronics

A Non-Invasive Quantum-Light-Based Method to Measure Temperature at the Nanoscale

The capability of measuring, and tracking, temperatures and temperature variations at minuscule scales—within a cell or in micro and nano-electronic components—has the potential to influence a number of areas of research from disease detection to a core challenge of contemporary computation and communication technologies, how to compute scalability and performance in electronic components.

A joint team, led by researchers from the University of Technology Sydney (UTS), created an extremely-sensitive nano-thermometer that uses atom-like inclusions in diamond nanoparticles to exactly measure temperature at the nanoscale. The sensor manipulates the properties of these atom-like diamond inclusions on the quantum level, where the boundaries of classical physics do not apply.

Diamond nanoparticles are very small particles—up to 10,000 times smaller than the width of a human hair—that fluoresce when irradiated with a laser.

Senior Investigator, Dr Carlo Bradac, UTS School of Mathematical and Physical Sciences, said the new method was not merely a "proof-of-concept realisation."

"The method is immediately deployable. We are currently using it for measuring temperature variations both in biological samples and in high-power electronic circuits whose performance strongly rely on monitoring and controlling their temperature with sensitivities and at a scale hard to achieve with other methods," Dr Bradac said.

The research paper published in Science Advances, is a partnership between UTS scientists and international collaborators from the Russian Academy of Science (RU), Nanyang Technological University (SG) and Harvard University (US).

Lead author, UTS physicist Dr Trong Toan Tran, explained that though pure diamond is transparent it "usually contains imperfections such as inclusions of foreign atoms."

"Beyond giving the diamond different colours, yellow, pink, blue, etc. the imperfections emit light at specific wavelengths [colours] when probed with a laser beam," says Dr Tran.

The team learned that there is an unusual regime—called Anti-Stokes—wherein the intensity of the light produced by these diamond color impurities relies very robustly on the temperature of the neighboring environment. Since these diamond nanoparticles can be as tiny as just a few nanometers they can be employed as miniature nano-thermometers.

We immediately realised we could harness this peculiar fluorescence-temperature dependence and use diamond nanoparticles as ultra-small temperature probes. This is particularly attractive as diamond is known to be non-toxic—thus suitable for measurements in delicate biological environments—as well as extremely resilient—hence ideal for measuring temperatures in very harsh environments up to several hundreds of degrees.

Dr Carlo Bradac, School of Mathematical and Physical Sciences, UTS

The scientists say that a key advantage of the method is that it is all-optical. The measurement just necessitates placing a droplet of the nanoparticles-in-water solution in touch with the sample and then measuring—non-invasively—their optical fluorescence as a laser beam is shone on them.

Although analogous all-optical methods using nanoparticles have effectively measured temperatures at the nanoscale, the study team believes that none have been able to attain both the sensitivity and the spatial resolution of the method put forth at UTS.

We believe our sensor can measure temperatures with a sensitivity which is comparable—or superior—to that of the current best all-optical micro- and nano-thermometers, while featuring the highest spatial resolution to date.

Dr Trong Toan Tran, Physicist, UTS

The UTS researchers emphasized that nanoscale thermometry was the most apparent—yet far from the only—application manipulating the Anti-Stokes regime in quantum systems. The regime can develop the foundation for investigating important light-matter interactions in isolated quantum systems at energies conventionally unexamined. It makes way for new possibilities for a surplus of practical nanoscale sensing technologies, a few as exotic as optical refrigeration where light is applied to cool down objects.

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