Ann Arbor Times

A research team from the University of Michigan has developed a new observational technique to analyze phonons, the quantum mechanical "jiggles" in materials. This breakthrough could enhance the design of metamaterials—materials with unique properties not typically found in nature—that are reconfigurable and made from self-assembling nanoparticles.

"This opens a new research area where nanoscale building blocks—along with their intrinsic optical, electromagnetic and chemical properties—can be incorporated into mechanical metamaterials," said Xiaoming Mao, a professor of physics at U-M and co-author of the study.

Phonons are discrete packets of waves that move through materials, causing vibrations and energy transfer. They play a crucial role in various phenomena such as heat transfer and sound flow. Some materials are engineered to direct phonons along specific paths to impart certain mechanical attributes.

Qian Chen, a professor at the University of Illinois, explained that this is the first time phonon dynamics have been observed in nanoparticle self-assemblies using liquid-phase electron microscopy. The study, published in Nature Materials, integrates nanoparticle assembly with mechanical metamaterial principles.

The project was a collaboration between Chen's team at Illinois for materials science experiments, Mao's team at U-M for theoretical aspects, and Wenxiao Pan's team at the University of Wisconsin for simulations.

Chen noted that while most research focuses on macroscale structures due to ease of control and measurement, their work tackles challenges at the nanoscale using modeling techniques combined with machine learning-accelerated simulations.

The researchers examined gold nanoparticles' vibrational trajectories to determine phonon band structures and matched these with a discrete mechanical model. Pan highlighted the potential of machine learning in advancing complex particle system studies.

Funding for this research came from several sources including the Office of Naval Research and National Science Foundation. "With nanoparticle assembly," Chen stated, "we can design structures with very controlled geometry."