Materials: Soft, flexible polymer semiconductors; photonic topological phase transition; solving the mystery of aluminum oxide surface structure.
Stanford University materials scientists used a specialized electron microscope – cryo-electron microscopy (Cryo 4D-STEM) – to explore the microstructure of soft semiconductors that could lead to new-generation electronics.
Organic mixed ionic-electronic conductors (OMIECs) are soft, flexible polymer semiconductors with promising electrochemical qualities. A liquid electrolyte is infused between layers of OMIEC polymer, like water in a car battery. The electrolyte is the medium through which ions move between positive and negative poles creating electrical current.
“When OMIEC polymers are immersed in liquid electrolyte, they swell, like an accordion, yet maintain electronic functionality,” said Alberto Salleo, the Hong Seh and Vivian W. M. Lim Professor in the School of Engineering and senior author on the paper, said in a release. “We’ve learned that the long molecular chains of the polymer material are able to stretch and gently curve, creating a continuous path, even as the material swells by 300% with the electrolyte.” [1]
NTT Corporation (NTT) and Tokyo Institute of Technology researchers achieved photonic topological phase transition by material phase transition by employing novel hybrid nanostructures consisting of a phase-change material and a semiconductor nanostructure, demonstrating that it is possible to change the photonic topological phase by using material phase transition in a reconfigurable manner.
“This achievement paves the way for novel research fields of combining material phase transition and photonic topological phase transition, and is promising for reconfigurable functional photonic integrated circuits which may lead to novel photonic information processing technologies,” according to the release.
“Previously, there have been many studies to manipulate the photonic topological properties in a variety of ways, but none of them achieved the photonic topological phase transition because of the difficulty of band inversion.” [2]
TU Wien and University of Vienna scientists uncovered the detailed structure of the aluminum oxide surface, which is one of the best insulators used in electronic components, as a support material for catalysts, or as a chemically resistant ceramic.
The strongly insulating nature of alumina has prevented experimental studies. The surface structure remained a mystery for over 50 years and was listed in 1997 as one of the “Three mysteries of surface science.” The team used noncontact atomic force microscopy (ncAFM) to analyze the surface structure.
“In an ncAFM image, one can see the location of atoms, but not their chemical identity,” said Johanna Hütner, who performed the experiments, in a release. “We overcame the lack of chemical sensitivity by precisely controlling the tip. Attaching a single oxygen atom to the tip apex allowed us to distinguish between oxygen and aluminum atoms on the surface. The oxygen atom on the tip is repelled from other oxygen atoms at the surface and attracted to aluminum atoms of the Al2O3 surface. Mapping the local repulsion or attraction enabled us to visualize the chemical identity of each surface atom directly.”
[1] Tsarfati, Y., Bustillo, K.C., Savitzky, B.H. et al. The hierarchical structure of organic mixed ionic–electronic conductors and its evolution in water. Nat. Mater. (2024). https://doi.org/10.1038/s41563-024-02016-6
[2] Takahiro Uemura et al., Photonic topological phase transition induced by material phase transition.Sci. Adv.10, eadp7779 (2024). https://www.science.org/doi/10.1126/sciadv.adp7779
[3] Johanna I. Hütner et al., Stoichiometric reconstruction of the Al2O3(0001) surface.Science385,1241-1244(2024). https://www.science.org/doi/10.1126/science.adq4744
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