Optical properties of nickel nanoparticles in systems with a statistically inhomogeneous structure

The analysis and further development of the experimental-analytical approach for determining the values of the optical parameters of nanosized particles for a system with a statistically inhomogeneous structure is presented. An improved experimental-analytical method for determining the complex specific electric polarizability of nanosized particles in systems with a statistically inhomogeneous structure is based on spectrophotometric and electron-microscopic measurements on two-dimensional structures and application of analytical solution of Rosenberg’s spectrophotometric equations with the consideration of analysis of particle size distribution. Experimental spectrophotometric and electron-microscopic studies of nickel islet films with weight thickness from 0.3 nm to 2.0 nm deposited by high-vacuum sputtering on quartz substrates in the range of the spectrum 0.2 ÷ 1, 1 μm are performed. Islands nickel film presented morphological microstructure in the form of monolayers isolated from each other nanoislands spherical surface nickel concentration (0.8 ÷ 2.0) · 1012 cm-2 and an average particle diameter 2.5 ÷ 7 nm. The optical characteristics, namely, the complex specific electric polarizability, optical electric conductivity of nanosized nickel particles are determined in the spectral range 0.2 ÷ 1.1 μm with the help of the improved experimental-analytical method. A significant increase to one order of magnitude of the absolute values of complex specific electric polarizability of nickel particles with a decrease in their size and in comparison with absolute values of complex specific electric polarizability of model spheres with refractive index and absorption index of nickel in macroscopic volumes was revealed. It is established that in the spectral dependences of optical electric conductivity of nickel nanoparticles in the range 0.2 ÷ 1.1 μm there is a band that diminishing size is shifted to a high-frequency region. In this case, the value of optical electric conductivity of nickel nanoparticles monotonically decreases with a decrease in the size by 1-2 orders of magnitude. Comparison of the obtained values of optical electric conductivity of particles in the range of the considered interval with the values of optical electric conductivity of macroscopic samples of nickel in the studied range of the spectrum shows that in particles the value of optical electric conductivity is 2-3 orders of magnitude smaller than that of massive metals. It is shown that in the nanoparticles of nickel absorption of “Drude” type in the near infrared region the spectrum is suppressed. The reason for this phenomenon may be the change of the mechanism of low-frequency electromagnetic response in nanosized metal particles in comparison with macroscopic metals. The research results are of interest for the development and optimization of nanostructured systems with the inclusion of nanosized nickel particles and functional devices based on them with given electromagnetic characteristics. Ref. 22, fig. 4