Preparation Of Metal Chiral Nanostructures And Study On Their Circular Dichroism

As an important analysis method for trace detection of chiral molecules, plasmon-enhanced circular dichroism (CD) spectroscopy has great potential applications in biomedical diagnostics and pathogen detection. Improving the physical mechanism of CD enhancement and fabricating highly senstive CD detection substrates are the research emphasis in plasmon-enhanced CD spectroscopy field. It is known that chiral metal nanomaterials is one of achieving high sensitivity CD detection substrates, Meanwhile, the strong interaction of nanostructure and light make it has a strong CD effect. The CD effect of chiral metal nanostructures strongly depends on its structure parameters, which will help us study the physical mechanism of CD. In this thesis, L-shaped chiral metal nanostructures was prepared with the combination of two-dimensional ordered colloidal crystal self-assembly technique and glancing angle deposition method. The experimental results were simulated with finite element method. Different resonances on the structure caused by the changes of structure parameters were also studied. The main research and conclusions are as following:Using the highly ordered two-dimensional polystyrene microspheres, prepared by self-assembly technique, as the template, different sizes L-shaped chiral metal nanostructures were prepared with glancing angle deposition method. And the different circular dichroism of the structure caused by size changing are studied. The results show that glancing angle deposition on self-assembled nanosphere monolayers is a simple and scalable method to fabricate metal chiral nanostructures; These L shaped plasmonic helices exhibit strong chiroptical responses in the visible to near-IR region, which can be tuned by changing the diameter of nanospheres and the thickness of structure. These studies laid a solid foundation for the preparation of high sensitivity detection CD substrates.Optical activity of the chiral metal nanostructures were simulated by the Finite Element Method. The CD spectrum whit different structural parameters were calculated. The results show that the simulations confirm the experimental results; The CD spectra of the left-handed helix and right-handed helix structures are in symmetry; And the asymmetry of the structures increased with the increase of thickness difference of L-shaped nanostructure two arms, which enhances the CD response of the metal nanostructure; The shadow effect of glancing angle deposition make second floor Ag film tilted growth, and the surface electronic resonance length increases, so the CD spectra redshift. These results will help us to further understand the physical mechanism of CD.