Optical Selectivity Enhancement of Carbon-based nanocomposites: Simulation and Experiments

Carbon-based metal nanocomposites have been shown to be good material candidates for applications requiring optical selectivity. However their true potential usage largely depends on the optimization of their composition and microstructure. Diamond Like Carbon with different transition metals were grown on stainless steel and Inconel substrates using pulse filtered cathodic arc deposition from two repetitively pulsed cathodic arc sources with separate macroparticle filters. The influence of several transition metals (Ti, Zr, Cr, W, Mo, V and Nb) on their optical selectivity was investigated. Carbon metal-containing samples were prepared using two cathodic arc sources provided with a carbon cathode and a pure transition metal cathode. Different metal concentrations in the coatings were obtained by varying the average arc current of the metal pulsed cathodic arc source (Imetal). The volume fraction of metal was determined by combined Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA) measurements. The structure of the deposited films was analyzed by Transmission Electron Microscopy (TEM), X-ray diraction (XRD) and Raman spectroscopy. In this study, the computer simulation program Coating Design (CODE) has been used to calculate optical properties of the different carbon-transition metal nanocomposites. The optical constants of various carbon-based nanocomposites were simulated using a physical model proposed by Bruggeman and Maxwell Garnett which averages the dielectric function of the components of the composite, which allows treating the composite system as an effective medium. The performed simulations allowed calculating the solar absorptance and thermal emittance of the nanocomposites. Varying the nanocomposite material configurations such as layer thickness, volume metal fraction, number of layers and multilayer stack resulted in new configurations that enhance the optical selectivity of these materials. Simulated reflectance was compared with spectrophotometry measurements of the deposited films with good agreement between them.