Numerical study of The Remittances of Axially Excited Chiral Sculptured Zirconia Thin Films

The transmission and reflection spectra from a right-handed chiral sculptured zirconia thin film are calculated using the coupled wave theory and the Bruggeman homogenization formalism in conjunction with the experimental data for the relative dielectric constant of zirconia thin film. The dielectric dispersion function effect on these spectra appeared in wavelengths shorter than the Bragg wavelength. In wavelengths larger than the Bragg wavelength, the dispersion of the dielectric function can be ignored. The results achieved in this work are consistent with the experimental data (Wu et al. (2000)). A shift towards shorter wavelengths is observed for the Bragg peak with increasing the void fraction, which is in agreement with the theoretical work of Lakhtakia (2000). Sorge et al. (2006) also found this effect in their experimental results on TiO2 chiral thin films, while they also found that unlike our results the intensity of the reflectance of the Bragg peak decreases with increasing the void fraction. This difference between our theoretical work and Sorge et al. (2006) experimental work can be related to the structural difference between idealized theoretical model for chiral films and that obtained in experimental work. In the latter, as Sorge et al. (2006) have pointed out the experimental films exhibit a large amount of scattering due to the highly complex and non-ideal structure that the individual chiral elements exhibit.Comment: 19 pages, 7 figure

Influence of annealing temperature on corrosion inhibition of Cu coated with Ni in NaCl solution

Copper substrates were coated with a 100 nm nickel thin film and post-annealed with a 300 sccm flow of nitrogen at different temperatures. The formation of nickel nitride is confirmed by x-ray diffraction analyses. Atomic force microscopy (AFM) results showed morphological changes by variation of the annealing temperature which is explained on the basis of physical processes (e.g., diffusion, penetration depth). The electrochemical behavior of the samples in 0.6 M NaCl solution was investigated by means of electrochemical impedance spectroscopy and polarization measurements. EIS data were confirmed by Kramers-Kronig transformations and by the fitting of these data with equivalent electrical circuits. Results showed that the 473 K sample has the highest corrosion inhibition efficiency (${\eta} = 98\%$ ). This can be due to the large grain size, hence a lower number of grain boundaries and the lowest surface roughness and porosity of this sample

Extinction spectra and electric field enhancement of silver chiral nano-flower shaped nanoparticle; comparison of discrete dipole approximation results with experimental results

In this work, by using the discrete dipole approximation (DDA), we have proposed a model for the growth of chiral nano-flower shaped sculptured nanoparticle in different sizes and different symmetries (e.g., 3-, 4- and 5-fold symmetries) and calculated the extinction spectra for these nanostructures identifying their plasmon peaks. Our results show that the extinction spectrum obtained experimentally for a chiral nano-flower sculptured thin film can be the result of the overlap of extinction spectra from an assembly of chiral nanoflowers forming the deposited thin film. Furthermore, we have investigated carefully the distribution of electric nearfields and have deduced the physical nature and direction of oscillations related to different plasmon peaks in the extinction spectra. Results show the existence of dipolar and quadrupolar oscillations in all structures while for the 4-fold symmetry chiral nano-flower, we have also observed octopolar oscillations. The calculated results are compared with the experimental results reported by us in [H. Savaloni, F. Haydari-Nasab, M. Malmir, Appl. Surf. Sci. 257, 9044 (2011)]. In addition, using the homogenization theory we have shown that the optical response of metallic structures is affected by a limited thickness of thin film and further increase of the film thickness has no effect on the optical spectra

Nanostructure and Optical Properties of Silver Helical Pentagon Nanosculptured Thin Films

Silver helical pentagon shaped nanosculptured thin films (HPNSTFs) were produced using oblique angle deposition method in conjunction with the rotation of sample holder under controlled conditions. The s-polarization extinction spectra obtained at different azimuthal angles (φ) and low incidence angle (i.e., 10∘) from the Ag (HPNSTF) did not show significant change in the plasmon peak position, while at higher incidence angle (i.e., 70∘) a blue shift appeared for the broad peak which was observed for lower incidence angle (i.e., 10∘) and occurred at lower wavelength. In case of p-polarized light a very broad peak was obtained for the 70∘ incidence angle and for different φ angles and when compared with the lower incidence angle results it can be concluded that it is gone under a red shift. Polar diagrams of the samples showed slight anisotropy that should be due to high symmetry of the pentagon helical structure