Researchers at the University of California, Irvine have developed a new electron microscopy technique that allows scientists to image atomic vibrations in specific directions for the first time. This method provides insight into vibrational anisotropy, which refers to how atoms in crystalline materials vibrate differently depending on direction. Such properties are important because they affect how materials behave in electronics, semiconductors, optics, and quantum computing.
The research team’s findings were published in Nature. The group used their momentum-selective electron energy-loss spectroscopy (EELS) system to examine strontium titanate and barium titanate—two perovskite oxides with different thermoelectric, optical, piezoelectric, and ferroelectric characteristics. By measuring atom-by-atom vibrational signals along selected directions, they identified differences in the anisotropic behavior of acoustic and optical phonons between the two materials.
“The altered anisotropic vibrations offer measurements totally different from those obtained from the whole crystals and integrated across full energy ranges,” said co-author Xiaoqing Pan, Henry Samueli Endowed Chair in Engineering and Distinguished Professor of materials science and engineering as well as physics and astronomy at UC Irvine and director of the campus’s Materials Research Institute. “Our results also clearly demonstrated that the collective atomic vibrations in crystals undergo atomic-level fluctuations depending on the elements and atomic sites, challenging the traditional model that assumes a uniform distribution of phonon wave functions.”
Pan also stated that this new microscopy approach enables researchers to map vibrational anisotropy with high spatial and energy resolution across many types of materials.
“The team’s findings align closely with theoretical predictions,” said senior co-author Ruqian Wu, UC Irvine professor of physics and astronomy. “This work opens the door for further studies of critical phonon-related phenomena, including ferroelectric phase transitions, the origins of ferroelectricity and the role of oxygen sites in shaping electron-phonon interactions in high-temperature superconductors.”
Scientists from Uppsala University in Sweden as well as Nanjing University and Ningbo Institute of Materials Technology and Engineering in China collaborated on this project. Funding was provided by the U.S. Department of Energy’s Office of Basic Energy Sciences along with support from the National Science Foundation.
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