Tunable optical properties of plasmonic Au/Al2O3 nanocomposite thin films analyzed by spectroscopic ellipsometry accounting surface characteristics.

In the present work, we have fabricated plasmonic gold/alumina nanocomposite (Au/Al2O3 NC) thin films on a glass substrate at room temperature by RF magnetron co-sputtering. The influence of the film thickness (∼10-40 nm) on the optical and other physical properties of the samples was investigated and correlated with the structural and compositional properties. The X-ray diffractometer measurement revealed the formation of Au nanoparticles with average crystallite size (5-9.2 nm) embedded in an amorphous Al2O3 matrix. The energy-dispersive X ray and X-ray photoelectron spectroscopy results confirmed the formation of Au/Al2O3 NC quantitatively and qualitatively and it was observed that atomic% of Au increased by increasing thickness. The optical constants of the plasmonic Au/Al2O3 NC thin films were examined by variable angle spectroscopic ellipsometry in the wide spectral range of 246-1688 nm, accounting the surface characteristics in the optical stack model, and the obtained results are expected to be unique. Additionally, a thickness-dependent blueshift (631-590 nm) of surface plasmon resonance peak was observed in the absorption spectra. These findings of the plasmonic Au/Al2O3 NC films may allow the design and fabrication of small, compact, and efficient devices for optoelectronic and photonic applications.

Determination of optical constants including surface characteristics of optically thick nanostructured Ti films: analyzed by spectroscopic ellipsometry.

In the present work, optically thick nanostructured titanium (Ti) films of thickness ranging from ∼100 to 900 nm were deposited on a glass substrate by DC magnetron sputtering at room temperature. Microstructural and surface properties of the samples were studied by x-ray diffraction and x-ray photoelectron spectroscopy (XPS). The morphological results revealed a systematic normal grain growth mechanism with increasing thickness analyzed by a scanning electron microscope. The influence of thickness on film surface roughness has been investigated by atomic force microscopy (AFM). The optical dispersion behavior was examined by spectroscopic ellipsometry (SE) over the long wavelength range of 246-1688 nm. The experimentally observed SE parameters were theoretically fitted with Drude-Lorentz and Bruggeman effective medium approximation theory. The surface properties of the Ti film measured by XPS and AFM were further accounted for in the optical model to determine optical constants (n and k) and the obtained results are expected to be the best available for bulk Ti metal.