Abstract
Technological advancements in the simultaneous observation of ultrafine structures and temperature changes in materials are paving the way for the development of advanced materials. This innovation is expected to facilitate the analysis of the correlation between specific structures and the thermodynamic properties of samples.
A research team, led by Professor Oh-Hoon Kwon in the Department of Chemistry at UNIST announced the development of a versatile nanothermometer, capable of accurately measuring the temperature of micro-samples in transmission electron microscopy (TEM). This newly-designed nanothermometer measures temperature by analyzing the cathodoluminescence (CL) spectrum emitted by nanoparticles that serve as thermometers when subjected to an electron beam. In TEM, the electron beam acts as a source of illumination for observing the microstructure of a sample and is also employed for temperature measurements.
While previously developed nanothermometers could be used alongside in situ TEM for observing microstructure changes, they required adjustments based on the strength of the electron beam, which posed significant challenges to researchers.
Figure 1. Schematic image describing the basic principle of temperature measurement of the developed nanothermometer.
In this study, the research team enhanced the reliability and versatility of the thermometer by selecting different nanothermometer materials. They chose dysprosium ions (Dy3+) as the active material for cathode ray emission, allowing for improved performance.
Researcher Won-Woo Park, the lead author of the study, explained, "The distribution of quantum states in the CL spectrum of Dy³⁺ follows a Boltzmann distribution that is solely dependent on temperature, regardless of the strength of the electron beam." The Boltzmann distribution is a statistical distribution that describes the phenomenon by which the proportion of high-energy quantum states increases with rising temperature.
The research team incorporated Dy3+ into yttrium vanadate (YVO4), a material capable of withstanding the high energy of the electron beam, to synthesize nanothermometer particles measuring 150 nm. When evaluated over a temperature range from -170°C to 50°C, the measurement error of the developed thermometer was within approximately 4°C.
Figure 2. Figure 6. In situ temperature measurements under laser heating.
Additionally, the team successfully raised the temperature by irradiating the sample with a laser beam and tracked the spatial distribution of temperature changes. This achievement underscores the effectiveness of the technology for simultaneously observing temperature and structural changes in real time due to external stimuli.
Professor Kwon remarked, "By redesigning the material for the nanothermometer, we have significantly improved the reliability of temperature measurements and enhanced versatility." He added, "This innovation will also contribute to the development of temperature-sensitive secondary battery materials and display materials for charging and discharging applications."
The study was co-authored by Dr. Pavel K. Olshin, the primary author, and Professor Ye-Jin Kim, a UNIST graduate appointed to the Department of Chemistry at Seoul National University last year, as a co-author.
The research findings were published in the December 2024 issue of ACS Nano, a prestigious journal in the nanotechnology field. The work was supported by the Samsung Future Technology Promotion Project and the National Research Foundation of Korea (NRF).
Journal Reference
Pavel K. Olshin, Won-Woo Park, Ye-Jin Kim, et al., "Boltzmann-Distribution-Driven Cathodoluminescence Thermometry in In Situ Transmission Electron Microscopy," ACS Nano, (2024).
