The complex Ag nanohole structures with an Ag nanorod inside the hole are designed and investigated both numerically and experimentally. Based on finite-difference-time-domain (FDTD) calculations, these structures show strong polarization angle-dependent optical properties. Additionally, a new extraordinary optical transmission (EOT) mode with tunable resonance wavelength is observed at the near-IR region due to the enhanced local radiation of the nanorods as well as electromagnetic coupling to the nanoholes. The resonance wavelength of the new EOT mode can be red-shifted continuously from the near-IR region to the mid-IR region (~ 20μm ) by varying array periodicity and nanorod length. By combining nanosphere lithography with oblique angle deposition, large-area Ag nanorod in nanohole structures can be fabricated on glass substrates. This fabrication technique enables the production of the complex nanohole arrays with controlled hole diameter, thickness, and rod structure inside the hole. The observed transmission at the new EOT mode can increase from ~41% of the nanohole to ~78% of the compound structure. The tunable EOT wavelength and strong polarization-dependent optical properties make the structure ideal for applications such as ultrathin optical filters, polarizers, surface-enhanced spectroscopies, etc.
Surface-enhanced Raman scattering (SERS) has been proven a powerful means in detecting molecules/chemicals at trace levels due to its huge enhancement in the signal intensity of the finger prints of the molecules. The SERS experiments were carried out using Ag nanorods deposited on silicon substrates homogeneously, by e-beam glancing angle deposition (GLAD) technique, with controlled morphology and size, guranteening the homogeneity of the SERS signals from area to area. However, these substrates are facing several problems due to the thermal stability, temporal stability and chemical stability, etc. of Ag nanostructures. We proposed several approaches to solve these problems to make Ag-based nanostructures applicable as SERS substrates. In addition, we proposed a method to quantify the composition of chemical mixtures at trace levels by SERS, based on the principle components analysis (PCA), which is a statistical method normally used to distinguish chemicals in mixtures. The method was evidenced to be effective in predicting the composition of binary, ternary mixtures and even mixtures consisting of more components at trace levels by SERS, with acceptable errors.
Tungsten oxide nanorods can be fabricated in large scale at low temperatures on planar substrates. The structure and the optical properties of the nanorods are investigated by SEM, TEM, X-ray diffraction and optical spectrometers, respectively. The dependence of the orientation preference of the nanorods on the growth conditions is also investigated.
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