Near-field Optical Propertiesof Nanocomposite Films

The near-field optical properties of two kinds of nanocomposite films, including the super-resolution near-field structure (Super-RENS) and the random metal-dielectric films, have been studied.The literatures reveals that the diffraction limit in optical storage may be overcame by use of Super-RENS. In our study the super-resolution properties of Sb-type Super-RENS were determined by the static test and the scanning electron microscopy (SEM) observation. Some results that had never been reported were found: Super-RENS containing amorphous Sb film has good super-resolution properties, while that containing crystal Sb film has not; if the Sb film is replaced by an Al film, the super-resolution properties disappear. Considering the size effect and the difference in electric properties between amorphous and crystal Sb film, a three-order nonlinear response of surface plasmons is deduced. Estimation is made and the calculated results are in agreement with the experimental results.On the other hand, the optical properties of random Sb-SiN film and random Ag-SiN film were studied. Results show that the interaction between metal particles in random metal-dielectric films will cause new absorption band and influence the local enhanced field formed by the composite film when the dispersion of metal particles is dense. Considering the interaction between metal particles as the surface plasmon coupling between two or three particles, a method is developed based on the scattering theory of small particles to calculate the optical properties of random composite film with high particle dispersion. The new absorption due to the particle interaction was well explained by the calculated results. According to the calculated results, the effects of the dielectric constants, the particle size and the volume fraction on the surface plasmon coupling were given, which may effect the near-field enhancement in the same way. These results are important to predict the optical properties of random composite films. Finally, the comparison between the Super-RENS and the random metal-dielectric film was made. In both structures the surface plasmons play an important role. However, the ways in which the surface plasmons work are different. It causes the difference in the near-field optical properties.