| Summary: | 博士 === 國立成功大學 === 材料科學及工程學系 === 103 === The surface-enhanced Raman scattering (SERS) method is a technology that significantly benefits from progress in nanotechnology and nanofabrication. The optical and enhancement properties of SERS substrates have been found to be a plasmon resonant formation with novel geometries to enhance Raman signals. In the present study, the focused ion beam (FIB) method is employed to fabricate well ordered Au/Ag multilayered nanorod (NR) arrays with an embedded Au and Ag layer of various thicknesses. The number of repeated layers of NR arrays affects the detection of Raman-active species. Optimized NR arrays were applied to distinguish influenza A virus strains at very low concentrations.
The optical properties of FIB-fabricated nanostructures (NSs) may be suitable for Raman-active substrates. There still occur some drawbacks to NSs for use as photonic components. For example, FIB-fabricated NSs are strongly influenced by the residual gallium (Ga) concentration and have a limited aspect ratio. To decrease Ga concentration and lattice damage of Au/Ag NR arrays, the FIB beam was tilted at an angle. The influence of Ga concentration on the outermost surface of FIB-fabricated SERS-active NSs was studied. It is hypothesized that lower Ga content on the SERS-active surface leads to discrete multipole plasmon modes of electron oscillation along the long axis and reduces optical losses and lattice damage in the original structure. Various molecular probes, namely crystal violet (CV), malachite green isothiocyanate (MG), and rose bengal, with concentrations at a single molecule level were employed as the target species.
In addition, an annealing treatment is applied to recover the Au/Ag NSs after lattice damage and hold the formed geometry. After this treatment, some Ga remains and may diffuse into the metal matrix or remain on the outermost surface of NSs. In the Au/Ag NR arrays, diffused structures and embedded nanovoids (NV) structure were generated owing to an increase in stress, which was mostly caused by the effects of oxidation and heat expansion. In the case of Au, Ga ions interact with the Au surface structure, modifying the surface chemistry. In order to reduce Ga contamination and the formation of low-density AuGa2 on Au NR arrays were subjected to low or high-temperature treatment. The effect of temperature treatment on the SERS substrate was investigated using CV as a molecular test probe. Optimized Au NR arrays were applied to the detection of melamine cyanurate in milk solution at low concentrations.
Notably, the SERS effect highly varies with the size of the target species due to laser interaction strength. Therefore, a substrate with a high SERS effect is required for practical applications. Herein, FIB method was applied to shape a localized Au surface as Au NR arrays with a controlled ring diameter among NR. Ag nanoparticles (NPs) were coupled to bridge the gaps among NRs, tried to improve the available effect of SERS, and then paved to provide a roughened surface for detecting molecular species, especially at low concentrations of CV. Au NR was furthermore coupled with Ag NPs, as Ag NPs/Au NR to improve the effect of SERS for detecting target species such as melamine at very low concentrations. It is generally believed that obtaining high average EF can improve the sensitivity of detecting target molecules. In this case, FIB and e-beam deposition were combined for the fabrication of Ag nanoclusters (NCs) on a FIB-made ZnO nanodome (ND) arrays as a SERS-active nanosystem for high-selectivity single-molecule detection. The SERS EF of hybrid Ag NCs on ZnO ND arrays with various dimensions of Ag NCs on the side/top surface of NDs was examined with CV as the probe molecule. The effect of SERS on an optimized Ag NCs on ZnO ND arrays was then verified by sensing MG at extremely low concentrations. The results are compared with those for existing SERS-active substrates.
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