Polymer Diffraction Gratings Modified with Silver Nanoparticles

Abstract

In the present research we have modified polymer gratings with silver nanoparticles deposited from colloidal solutions.
Silver colloids were produced by chemical reduction of silver salt (silver nitrate AgNO3) solution using different
components. We have chosen two different preparation methods: modified Volski method – Ag1 (we have modified it)
and Lee and Meisel – Ag2. UV-VIS spectrometry was used to control formation of nanoparticles in colloids.
Comparison of theoretical (Mie light scattering theory) and experimental results showed that the diameter of silver
nanoparticles in colloidal solution varies in the range 50 nm – 100 nm. The polymer 4 μm period grating was formed by
replication of silica matrix by photopolymer and using UV hardening of the structure. The modification with silver
nanoparticles was performed using a dip – coating technique. Dipping was performed for 72 hours in two solutions
separately. Analysis of modified structures was performed with UV-VIS spectroscopy, atomic force microscope (AFM)
and scanning electron microscope (SEM). Optical properties of diffraction grating before and after modification were
investigated measuring diffraction efficiency. The diffraction efficiency was measured using three wavelengths: He-Ne
(λ = 632.8 nm), DPSS (λ = 532 nm), He-Cd (λ = 441.6 nm). It was found that using different colloidal solutions it is
possible selective deposition of the nanoparticles. AFM and SEM results indicate that silver nanoparticles from the
solution Ag1 were assembling on the grooves of the grating whereas particles from the solution Ag2 were assembling in
the valleys of the grating. Resonant plasmonic response of the grating/silver nanoparticles system enabled to control
diffraction efficiency of the final grating.