Grain rotation breakthrough for electronics

Utilising advanced microscopy housed at the UC Irvine Materials Research Institute, the team heated samples of platinum nanocrystalline films to observe grain rotation mechanisms in fine detail. Their findings, recently published in Science, are groundbreaking for understanding atomic-scale behaviours in these materials. Through four-dimensional scanning transmission electron microscopy (4D-STEM) and high-angle annular dark-field STEM, researchers captured the movement at grain boundaries with unprecedented clarity. To interpret the complex 4D-STEM data, they developed a machine learning algorithm that enabled extraction of critical information, identifying the role of disconnections at grain boundaries as a driving force behind grain rotation.

"Scientists have speculated and theorised on phenomena occurring at the boundaries of crystalline grains for decades," said Xiaoqing Pan, UC Irvine Distinguished Professor and UC IMRI director. "Now – through the use of the most advanced instruments available to the scientific community – we have been able to transition from theory to observation."

In polycrystalline materials, grain boundaries are interfaces that impact material efficiency due to imperfections. The study found that grain rotation happens through the motion of disconnections, line defects that combine step and dislocation characteristics. This discovery advances the understanding of microstructural changes in nanocrystalline substances.

The research also revealed, through machine learning analysis, a correlation between grain rotation and changes in grain size – either growth or shrinkage – caused by shear-coupled migration along grain boundaries. Observed via STEM and supported by atomistic simulations, this finding highlights the mechanisms governing grain rotation and nanomaterial dynamics. Pan noted: "Our results provide unequivocal, quantitative and predictive evidence of the mechanism by which grains rotate in polycrystals on an atomic scale. Understanding how disconnections control grain rotation and grain boundary migration processes can lead to new strategies for optimising the microstructures of these materials. This knowledge is invaluable for advancing technologies in various industries, including electronics, aerospace, and automotive sectors."

The study opens new possibilities for enhancing polycrystalline material performance, offering potential improvements in efficiency and durability for various applications.