Plasma nanoparticles (such as gold, silver and aluminum particles) exhibit unique optical properties, such as local surface plasmon resonance (LSPR). The special structure of plasma nanoparticles makes it possible to regulate the plasma interaction, so its optical properties can be regulated. At present, there have been some reports about assembling plasma nanoparticles into various types of structures, such as nanoparticle clusters, chains, microspheres and arrays. In various types and combinations of plasma nanoparticles, dimer clusters of nanoparticles show strong optical near-field coupling and form hot spots, and electromagnetic fields are concentrated in hot spots. These properties depend on the interaction distance and direction of nanoparticles and the size, shape and composition of nanoparticles. These characteristics also show the great application potential of plasma nanoparticle dimer clusters in surface enhanced Raman spectroscopy (SERS) detection, maskless ultra-high resolution lithography, enhanced chemical synthesis and nano-pixel display. The existing strategies of plasma nanoparticle dimerization include assembly induced by electromagnetic interaction, site-functionalized assembly method, assembly guided by DNA folding template and nanoparticle bonding strategy controlled by quantitative reaction. However, the dimer of plasma nanoparticles assembled by these methods will be dispersed in the solution phase, and the solvent will be randomly and irregularly distributed on the surface of the substrate after volatilization. However, many plasma nanostructures need to be arranged to meet specific requirements. However, it is still very challenging to construct plasma dimer arrays with sub-wavelength resolution and arbitrary modes. This is because the construction of this plasma nanoparticle array is highly dependent on top-down technologies, such as electron beam etching, lithography and other methods. Although these methods have high accuracy, they still have great limitations. On the other hand, the bottom-up assembly method can use nano-scale chemical patterns or topological grooves as templates to synthesize plasma nanoparticles on the substrate. However, this method requires additional etching steps and limits the three-dimensional orientation of dimer.

Therefore, Professor Nie Zhihong of Fudan University has developed a strategy based on universal scanning to effectively construct the quasi-3D pattern arrangement of plasmons with controllable direction, which can be used for information encryption. The achievement was published in Advanced Materials magazine, entitled "Laser scanning-guided assembly of plastic dimensional quasi-3D patterned arrays for information encryption".

Highlights of the article:

1. This strategy combines bottom-up and top-down methods. This method is very flexible and can form high-resolution plasma dimer patterns from nanoparticles of different sizes and shapes.

2. The Z-axis direction, particle spacing, size and shape of plasma dimer nanoparticles can be accurately adjusted, so as to adjust the coupling vibration of dimer array;

3. The patterned dimer array constructed by this strategy can be used for information encryption, its plasma color can be removed by laser irradiation, and the polymer coating around nanoparticles can be repeatedly displayed and erased.

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