The substrate cooling method was used in glancing angle deposition to grow a slanted silver nanorod array (NRA). Liquid nitrogen was allowed to flow under the substrate during deposition, and we compared the morphologies of Ag NRAs deposited with and without cooling. The cooling reduced the average width of the nanorods. A Z-shaped nanostructure array composed of three sections of silver NRAs was then deposited under the same cooling conditions. The average tilt angle of the nanorods from the surface normal was varied from the bottom section to the top section with the nanorods of the top section made to lie almost parallel to the substrate. Under normal illumination, the rods in the top section exhibit distinct longitudinal and transverse plasmon modes that cause strong polarization-dependent transmittance and reflectance.
A metal-dielectric (M-D) multilayer has been applied as a subwavelength structure to exhibit the negative index of refraction. Periodic MD multilayer or symmetrical five layered MDMDM multilayer has been arranged to exhibit an equivalent complex refractive index with negative real part. As the extinction coefficient is much smaller than the index of refraction, the wave vector and Poynting vector are in opposite directions. How to reduce the extinction coefficient and raise the transmittance becomes an issue. In this work, the metal films within the multilayer are not arranged with the same thickness as well as dielectric films. The thickness of each layer is tuned to increase the transmittance. The previous example of a five layered MDMDM as a negative index metamaterial at a wavelength of 363.8nm is adopted here to do the improvement of loss. The near field simulation is also adopted here to observe the backward wave propagation as a negative refraction phenomenon.
The substrate cooling technique was introduced in glancing angle deposition to grow a slanted silver nanorod array (NRA) by introducing liquid nitrogen to flow under the substrate. The morphologies of NRAs deposited with cooling and without cooling are compared in this paper. During deposition, the temperature on the backside of substrate was kept at -140°C. A three-sectional zig-zag nanostructured array (ZNA) was then deposited under the same cooling condition. The polarization dependent transmittance and reflectance spectra of both NRA and ZNA were also measured and compared in this work.
Gold nanohelical structured thin films (NHFs) were tried to be deposited on a glass substrate using glancing angle deposition technique. At a deposition angle of 89°, gold NHFs were fabricated by introducing liquid nitrogen to flow under the backside of BK7 glass substrate holder. The temperature of substrate was reduced to be less than -140°C before deposition. The spin rate was controlled with respect to the deposition rate to grow three different sized nanohelices. The morphology and optical properties of Au NHFs were measured and compared between the three samples. The strong g-factor implies high sensitivity of deposited helixes in biosensing in the future.
A traditional high-reflection optical coating was applied to enhance the directional radiation of nanoantennas. A highly reflective multilayer upon the top lateral side of a horizontally lying silver nanorod enhances the forward scattering when an optical wave is incident on the bare bottom side of the nanorod. Enhanced forward scattering can thus be observed from a glancing deposited silver nanorod array (NRA). An effective method for coupling the energy of incident light into a NRA involves arranging the NRA in a prism coupling. The highly efficient light coupling effect over a broadband and a wide range of angles results in extra-strong forward light scattering.
In this work, the equivalent Herpin index and phase thickness of a symmetrical film stack that consists of a dielectric
film D and a metal film M are analyzed using the film matrix method. Five-layered symmetrical MDMDM film stacks in
which the thickness of each film is less than 1/10 of the incident wavelength are utilized. The positive real part of the
equivalent Herpin index and the negative real part of the phase thickness result in a negative real part of the equivalent
refractive index. The range of refractive indices of D and M that lead to a negative refractive index of the overall
material is developed as a procedure. When a p-polarized light wave obliquely propagates into the material with the
negative refractive index, negative refraction and backward wave propagation occur. To reduce the loss in the negative
index metamaterial, a porous metal film is introduced as a substitute for the metal film M in MDMDM to increase the
feasibility of the use of the metamaterial as an optical coating.
A slanted silver nanorod array (NRA) deposited with glancing angle of deposition around 89°. By controlling the
deposition angle, SiO2 and Ta2O5 grow on sliver rods in different morphologies. The multilayer designed as high
reflective multilayer by arranging SiO2 and Ta2O5 alternatively on a cylindrical silver rod with diameter of 80 nm and a
length of 200 nm would enhance the local field intensity and scattering when the rod is illuminated by s-polarized and ppolarized
light waves. In this work, the reflective multilayer is designed at wavelengths of 450nm and 750nm that are
associated with transverse plasmonic mode and longitudinal plasmonic mode, respectively. It is demonstrated
experimentally that the intensity of light scattering from the capped NRA is enhanced due to the local field confinement
around silver rod.
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