Fabrication Of Ordered Two-dimensional Ag Nanoarrays And Their SPR/SERS Properties

Surface plasmon resonance (SPR) is a unique optical property possessed by metal nanomaterials, especially noble metal nanomaterials, which is different from metal bulk. SPR strongly dependents on size, shape, distribution of nanostructure and other factors. The resonance generated by surface plasma and excitating light greatly enhance local electromagnetic field of nanostructure. Built on the foundation of enhanced electromagnetic field, surface enhanced spectroscopy (SES) has been developed. Of various SES techniques, Surface Enhanced Raman Scatting (SERS) spectroscopy was is an important branch. The research of SERS mainly focused on the following four areas: (1) to discuss SERS enhancement mechanisms; (2) to expand SERS active substrates; (3) to enlarge the SERS spectral library; (4) to develop the practical application of SERS. Enlarging the range of SERS active substrates provides the prerequisite for the other studies. Nanostructured noble metal substrate is always the first choice for high SERS enhancement. Since primary contribution of SERS enhancement is caused by enhanced local electromagnetic field, it's necessary to study how the structure could influence its SPR or even its SERS. Preparation of noble metal nanomaterials with ordered structures is an effective means to achieve the aim.Lithography technique and template method possess their own advantages in the preparation of ordered structure, they are better than any other method and consequently the common methods to prepare ordered structure. Therefore, we employed both the lithography technique and the template method to prepare ordered two-dimensional array of silver nanoparticles and investigate their SPR and SERS properties. Our study is outlined as follow:1. In the fields of spectral and biological detection, composite materials composited by noble metal shell and dielectric core are valuable in practice, and highly expected. Size of polystyrene (polystyrene, PS) spheres was independently controlled by nanosphere lithography (nanosphere lithography, NSL) and reactive ion etching (reactive ion etching, RIE) technology. With etched PS spheres as templates, Ag semishell arrays with the same size and different interparticle spaces were prepared. Both local surface plasmon mode and delocalized surface plasmon mode were excited on these Ag semishell arrays. The correlation between nanoscale morphology and SERS activity of the substrates was investigated. It showed that SERS enhancement is altered with structure. Besides, the adjustability of SPR and SERS, good homogeneity and large-area ordered Ag semishell arrays suggest their promising applications as functional components in spectroscopy, immunoassay, biosensor and biochip.2. NSL is a simple and widely used method for preparation of nanoarrays. The method is of great practicality and flexibility in preparation of both biological/chemical sensor and SERS substrate.By combining NSL and template method,Ag nanocap arrays with adjustable parameters were prepared. SPR of the the arrays can be modulated from visible region to the NIR, which provides an opportunity of application for the arrays in SERS spectra. Experiments revealed that nanocap arrays with the different parameters have produced such high SERS enhancement that the enhancement factors have reached six orders of magnitude using 514.5 nm laser as the exciting light. At the same time, 785 nm laser as the exciting light was also used to estimate SERS activity of the arrays. The extreme enhancement excited by 514.5nm laser implies that it will be applied in the detection of biological analysis.3. We can prepare hollow nanostructure of various materials using PS sphere monolayer as a template. The great application value of hollow nanostructures in many fields has attracted enduring effort on hollow nano-structure. Hollow silver nanoarrays were prepared with ordered PS sphere monolayer and their SPR and SERS properties were investigated.4. Photolithography technology possesses unique advantages in the preparation of ordered structure. The advantages promote rapid technological development of photolithography in return. Laser interference lithography has overcome some shortcomings of traditional lithography and simultaneously has high resolution and large field is widely used and so on. Present laser interference lithography is used mainly in microelectronics and micromachining. Based on the advantages of laser interference lithography, we prepared a kind of square lattice in large area,, and use it as the template for SERS substrate. By Raman microscope with the optical imaging system, the corresponding relationship between SERS spectra and structure become clearer. The experiments showed that the laser interference lithography could be a new technique to study SERS.