Optical nano-structuring in light-sensitive AgCl-Ag waveguide thin films: wavelength effect.

Irradiation of photosensitive thin films results in the nanostructures formation in the interaction area. Here, we investigate how the formation of nanostructures in photosensitive waveguide AgCl thin films, doped by Ag nanoparticles, can be customized by tuning the wavelength of the incident beam. We found, silver nanoparticles are pushed towards the interference pattern minima created by the interference of the incident beam with the excited TEn-modes of the AgCl-Ag waveguide. The interference pattern determines the grating constant of the resulting spontaneous periodic nanostructures. Also, our studies indicate a strong dependence of the shape and size distribution of the formed Ag nano-coalescences on the wavelength of the incident beam. It also influences on the surface coverage of the sample by the formed silver nanoparticles and on period of the self-organized nano-gratings. It is found, exposure time and intensity of the incident light are the most determinant parameters for the quality and finesse of our nanostructures. More intense incident light with shorter exposure time generates more regular nanostructures with smaller nano-coalescences and, produces gratings with higher diffraction efficiency. At constant intensity longer exposure time produces more complete nanostructures because of optical positive feedback. We observed exposure with longer wavelength produces finer gratings.

High precision refractometry based on Fresnel diffraction from phase plates.

When a transparent plane-parallel plate is illuminated at a boundary region by a monochromatic parallel beam of light, Fresnel diffraction occurs because of the abrupt change in phase imposed by the finite change in refractive index at the plate boundary. The visibility of the diffraction fringes varies periodically with changes in incident angle. The visibility period depends on the plate thickness and the refractive indices of the plate and the surrounding medium. Plotting the phase change versus incident angle or counting the visibility repetition in an incident-angle interval provides, for a given plate thickness, the refractive index of the plate very accurately. It is shown here that the refractive index of a plate can be determined without knowing the plate thickness. Therefore, the technique can be utilized for measuring plate thickness with high precision. In addition, by installing a plate with known refractive index in a rectangular cell filled with a liquid and following the described procedures, the refractive index of the liquid is obtained. The technique is applied to measure the refractive indices of a glass slide, distilled water, and ethanol. The potential and merits of the technique are also discussed.

Systematic Surface Phase Transition of Ag Thin Films by Iodine Functionalization at Room Temperature: Evolution of Optoelectronic and Texture Properties.

We show a simple room temperature surface functionalization approach using iodine vapour to control a surface phase transition from cubic silver (Ag) of thin films into wurtzite silver-iodid (ß-AgI) films. A combination of surface characterization techniques (optical, electronical and structural characterization) reveal distinct physical properties of the new surface phase. We discuss the AgI thin film formation dynamics and related transformation of physical properties by determining the work-function, dielectric constant and pyroelectric behavior together with morphological and structural thin film properties such as layer thickness, grain structure and texture formation. Notable results are: (i) a remarkable increase of the work-function (by 0.9 eV) of the Ag thin layer after short a iodine exposure time (≤60 s), with simultaneous increase of the thin film transparency (by two orders of magnitude), (ii) pinning of the Fermi level at the valance band maximum upon iodine functionalization, (iii) 84% of all crystallites grain were aligned as a result of the evolution of an internal electric field. Realizing a nano-scale layer stack composed of a dielectric AgI layer on top of a metallic thin Ag layer with such a simple method has some technological implications e.g. to realize optical elements such as planar optical waveguides.