Optical analysis of single- and double-layer thin film using nickel and chromium transition metal as a neutral density filter

Abstract Nickel, nichrome and Cr/Ni double-layer thin film with optimum thickness 10 nm was fabricated using E-beam evaporation coating system at the same deposition parameter. The deposition was operated in a high vacuum environment on the borosilicate glass substrate. The optical analysis was done using UV-Visible spectrophotometer (LAMBDA 750 (Perkin Elmer) with step of 1 nm in the visible range of spectrum. The transmittance data were used to calculate the optical density of filter. The optical density of Cr/Ni double layer was found to be higher than another sample, i.e. , 0.84 and has more neutrality, i.e. , Δ . The variation in transmission of nickel, nichrome and Cr/Ni was 9%, 6% and only 2%, respectively. The transmittance was uniform throughout the visible range. The optical parameters such as refractive index and extinction coefficient were derived from the reflectance and absorbance data. From AFM analysis it was depicted that surface roughness and RMS value were also decreases with double layer of transition metal for stable and durable Neutral Density Filter (NDF). The reduced roughness indicates that there is no loss of scattering of light in the filter. The topographical analysis of thin films confirmed that uniform and smooth coating was achieved. XRD analysis confirms the thin film exhibits amorphous nature.