China University of Science and Technology successfully built a new type of low-symmetry nanocrystalline

China University of Science and Technology successfully built a new type of low-symmetry nanocrystalline

Recently, Professor Zeng Jie's group at the University of Science and Technology of China has made new progress in the study of plasmonic regulation of localized surface plasmons of low-symmetry metallic nanocrystals. The researchers succeeded in constructing a Pd@AuCu core-shell planar tetragonal fork structure with low symmetry based on the kinetic regulation of crystal growth and lattice mismatch between different metals, and achieved a local surface plasmon-plane in-plane coupling. The position of the polar vibration mode is precisely controlled in the range from the visible light region to the near infrared region. Due to the rich local field "hot spot", the nanocrystals also have superior surface-enhanced Raman scattering properties. The results were published in the Nano Express on May 11 [Nano Letters, 2016, 16, 3036-3041]. The first author of the dissertation was Meng Minhe, a master student, and Fang Zhicheng, a master student.

Symmetry can modulate the surface charge distribution and free electron polarization of metal nanocrystals, thereby affecting their local surface plasmon properties. In general, compared to a cubic symmetry polyhedral structure, a low-symmetry planar structure usually has more abundant vibration modes, such as in-plane and out-of-plane dipole vibration modes. In many planar metal nanocrystals, the planar branching structure has a strong local electric field at the corners, which can effectively achieve the photoelectric gain. Therefore, it has an important role in the application of local surface plasmon. However, the formation of planar branching structures requires the selective limitation of the growth of the branching structures in a two-dimensional plane, which is therefore very challenging.

Zeng Jie group researchers use the symmetry of the Pd cube as a seed crystal, through the regulation of the reaction kinetics and the degree of lattice mismatch between the core and shell to get D4h symmetry Pd@AuCu core-shell planar tetrahedral structure. By modulating the size of the nanocrystals, the researchers were able to extend the location of their local surface plasmon dipole vibrational modes from visible to near-infrared regions. At the same time, the branching characteristics of the nanocrystals make the localized electric fields at the corners form a coupled "hot spot" structure, which greatly enhances the surface-enhanced Raman scattering performance of the material, where the size is a 70 nm plane. The enhancement factor of the tetragonal fork structure has reached nearly 104 times, which has a certain potential for application in molecular ultra-sensitive detection. This work provides a new idea for the study of the local surface plasmon properties of low-symmetry metal nanocrystals.

The study was funded by projects of the Youth “973” Program of the Ministry of Science and Technology and the National Natural Science Foundation.

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