Many targets are too small to be observed with optical instruments as electronic, thermoelectric and computer technologies have been scaled to nanometer scale.
Using cutting-edge electron microscopes and novel techniques, a team of researchers at the University of California, Irvine, the Massachusetts Institute of Technology and other institutions has found a way to map phonons.
The researchers used a transmission electron microscope to look at the dynamic behavior of phonons near a single quantum dot of Silicon-germanium. A paper about the results of the project is in Nature.
Xiaoqing Pan is a professor of materials science and engineering and physics at the University of California at Irvine. It's the first time we've been able to show that the interplay between diffusive and specular reflection depends on the atomistic structure.
The wave of atoms displaced from their equilibrium position as heat moves away from the thermal source is called the atomic wave. In crystals, wave packets of atomic displacements carry thermal energy equal to their frequencies of noise.
The structure of the SiGe alloy impeded the efficient propagation of phonons. The alloy stretches the Silicon atoms because they are closer together than germanium atoms. The strain and alloying effect engineered within thenanostructure was found to be the cause of the softened phonons.
Pan said that softened phonons have less energy which means that they carry less heat. One of the ways that thermoelectric devices impede the flow of heat is due to the softened of vibrations.
The development of a new technique for mapping the direction of thermal carriers was one of the key outcomes of the project. He said it's similar to counting how many phonons are going up or down and taking the difference. The technique allowed us to see the reflection from the interface.
Electronics engineers have succeeded in miniaturizing structures and components in electronics to such a degree that they are now down to the order of a billionth of a meter, so these structures are invisible to optical techniques.
With this research, we are beginning the process of catching up with progress in other areas, said co-author Chaitanya Gadre, a graduate student in Pan's group.
The field that will benefit from this research is thermoelectrics. Co-author Ruqian said, "Developers of thermoelectrics technologies attempt to design materials that either impede thermal transport or promote the flow of charges, and atom-level knowledge of how heat is transmitted through solids embedded as they often are with faults, defects and imperfections, will aid in this
More than 70% of the energy produced by human activities is heat, so it is imperative that we find a way to recycle this back into a usable form.
More information: Chaitanya A. Gadre et al, Nanoscale imaging of phonon dynamics by electron microscopy, Nature (2022). DOI: 10.1038/s41586-022-04736-8 Journal information: Nature
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