Optical absorption　in ZrO＿（2-x）-C nanocomposite films on polymer substrates:　application of an effective medium theory

摘要

RF sputtering from separate zirconia and graphite targets enables room-temperature co-deposition of ZrO_(2-x) and carbon onto polycarbonate substrates. Films consist of amorphous carbon dispersed in tetragonal nanocrystaltine zirconia; their optical properties have been determined by reflectance measurements at normal incidence and over the visible range. The optical constants of each component of the composite have been extracted; the experimental reflectance spectra have been fitted to Maxwell-Oarnett effective medium theory, leading to the effective dielectric constants of the film. Absorption is characterized by the band gap, the energy and life-rntime of the optical transition of the absorbing carbon phase. These parameters are deduced from the imaginary part of the dielectric function using Tauc-Lorentz model (TL) and from the extinction coefficient using Forouhi-Bloomer model(FB) in which an energy dependence of the matrix elemem of the transition has been introduced. Furthermore, the energies of the peak transition and the maximum of the extinction coefficient are so similar that they prove the self-consisteaey of the modified-FB model applied to the amorphous carbon phase of the composite films.