Light-Dependent Nano-Thermometers Enable Real-Time Analysis of Thermodynamic Properties, Detect Temperature of Nanoparticles Within TEM

At Ulsan National Institute of Science and Technology, a group of experts led by Professor Oh-Hoon Kwon from the Department of Chemistry developed a method for measuring the temperature of nanostructures within a transmission electron microscope (TEM). Their study's results are discussed in the paper "Nanoscale Cathodoluminescence Thermometry with a Lanthanide-Doped Heavy-Metal Oxide in Transmission Electron Microscopy."

(Photo: Wikimedia Commons/ Reneegas1)

Understanding Thermodynamic Properties

A thermodynamic property refers to a parameter that describes a thermodynamic system or a portion of space with defined boundaries that separate it from its surroundings. It is a feature of a physical system that defines its state.

The thermodynamic properties of a material can be classified into derived, fundamental, and measured categories. These properties provide an understanding of the behavior of the thermodynamic system in the presence of known conditions.

Thermodynamic properties are needed for understanding chemical processes such as phase transitions or chemical reactions of substances. They provide insight into the cellular processes and in describing atmospheric processes. Aside from this, they are also helpful in optimizing geothermal power generation and in materials characterization.

New Approach to Analyzing Thermodynamic Properties

The technology developed by the Korean researchers utilizes nano-thermometers based on cathodoluminescence (CL) spectroscopy. It holds the key to analyzing fine materials' thermodynamic properties and enhancing high-tech materials' development.

Transmission electron microscopy enables researchers to observe samples at a magnification of hundreds of thousands of times. This is done by bombarding the sample with a short wavelength of an electron beam. As the light emitted from the sample through cathode ray emission spectroscopy is detected, the scientists are allowed to analyze the physical and optical properties of the sample at nanometer scales.

The newly developed nano-thermometers rely on the temperature-dependent intensity variation of a specific cathode ray emission band of europium ions. The researchers synthesized nanoparticles doped with europium ions with gadolinium oxide to enable long-term experiments.

Dynamic analysis reveals that the intensity ratio of the light-emitting band from europium ions serves as a reliable temperature indicator. When the nano-thermometer particles were used to measure samples about 100 nanometers, there was an impressive measurement error of approximately 4 degrees Celsius. This strategy provides more than twice the accuracy of traditional TEM temperature measurement approaches and significantly enhances spatial resolution.

The team also demonstrated the applicability of the nano-thermometers by triggering temperature changes with a laser within the TEM. They also simultaneously measured temperature and structural variations in real-time. This capability enabled them to analyze the thermodynamic properties at the nanometer level in response to external stimuli without any interference with standard analysis procedures.

In this study, the scientists emphasized the non-invasive nature of the temperature measurement process. They noted that the interaction between the nano-thermometer particles and transmission electron beam allows real-time temperature detection without disrupting TEM imaging.

The researchers believe that the big advantage of the developed nanometer is that temperature measurement does not interfere with the existing transmission electron microscope analysis. Since light is used in measuring temperature, it is possible to measure the image of the TEM and detect the temperature in real time.