Temperature Detection Made Easy with Nano-Thermometers

Transmission electron microscopy (TEM) is a powerful technique that allows researchers to observe samples at a magnification of hundreds of thousands of times by transmitting a short-wavelength electron beam through the sample. However, measuring the temperature of nanometer-sized samples within a TEM is challenging, as conventional methods have low accuracy, resolution and stability. In this article, we will introduce a novel method for measuring the temperature of nanometer-sized samples within a TEM using nano-thermometers based on cathodoluminescence (CL) spectroscopy.

What are nano-thermometers?

Nano-thermometers are nanoparticles that can emit light whose intensity or wavelength depends on the temperature of the surrounding environment. By detecting the light emitted from the nanoparticles, researchers can measure the temperature of the sample with high sensitivity and spatial resolution. Nano-thermometers can be made of various materials, such as rare-earth doped nanoparticles, semiconducting quantum dots, metal nanoclusters and small organic dyes.

How do nano-thermometers work in TEM?

One type of nano-thermometers that can work in TEM are based on cathodoluminescence (CL) spectroscopy. CL is the phenomenon of light emission from a material when it is irradiated by an electron beam. By analyzing the spectrum and intensity of the emitted light, researchers can obtain information about the physical and optical properties of the material at nanometer scales.

The newly developed nano-thermometers rely on the temperature-dependent intensity variation of a specific CL emission band of europium ions (Eu3+). Europium ions are lanthanide elements that have characteristic optical transitions that emit light in the visible range. By synthesizing nanoparticles doped with europium ions within gadolinium oxide (Gd2O3), the research team ensured minimal damage from the electron beam, enabling long-term experiments.

Through dynamic analysis, the team confirmed that the intensity ratio of the light emitting band from europium ions is a reliable indicator of temperature, with an impressive measurement error of about 4℃ using nano-thermometer particles measuring approximately 100 nanometers in size. This method offers more than twice the accuracy of conventional TEM temperature measurement techniques and significantly improves spatial resolution.

What are the applications of nano-thermometers in TEM?

The nano-thermometers can be used to measure the temperature of nanometer-sized samples within a TEM in real time, without interfering with standard TEM imaging and analysis procedures. This capability allows for the analysis of thermodynamic properties at the nanometer level in response to external stimuli, such as laser heating or electric field application.

For example, the team demonstrated the applicability of the nano-thermometers by inducing temperature changes with a laser within the TEM and simultaneously measuring temperature and structural variations in real time. They observed that the Gd2O3:Eu3+ nanoparticles underwent a phase transition from cubic to monoclinic structure at around 500℃, accompanied by a change in CL intensity ratio.

The nano-thermometers can also be used to study the thermal properties of various materials, such as metals, ceramics, polymers and biological samples, at nanoscale. They can help to understand how heat is generated, transferred and dissipated in nanostructures and devices.

Conclusion

In summary, scientists have developed a novel method for measuring the temperature of nanometer-sized samples within a TEM using nano-thermometers based on CL spectroscopy. The nano-thermometers rely on the temperature-dependent intensity variation of a specific CL emission band of europium ions doped in gadolinium oxide nanoparticles. The nano-thermometers offer high accuracy, resolution and stability for temperature measurement in TEM, without disrupting TEM imaging and analysis procedures. The nano-thermometers can be used to analyze the thermodynamic properties of fine samples and advance the development of high-tech materials.

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