No abstract

Au/Al2O3 nanocomposite films, studied in this work, were prepared by RF-magnetron sputtering technique on glass substrate at room temperature under two different argon pressures, and subsequent heat treatment. Formation of gold nanoparticles was confirmed by X-ray diffraction patterns and UVvisible absorption spectroscopy. Au fill fraction f, changed from f=10.78% to f=25.45%, when argon pressure increased from 2x10-3 mbar to 10x10-3 mbar. For the as-deposited samples, reduction in volume fraction of gold particles causes a decrease in particle size, a lattice expansion and a blue-shift of the SPR peak position. An opposite trend is observed in the lattice parameter with respect to the gold volume fraction for the annealed samples. A small change in the sizes is observed and no significant shift of band absorption peak in samples of low Au content. However, at higher Au concentration, an appreciable red shift of the surface plasmon resonance with increasing temperature is observed. Experimental optical absorption spectra of all the samples were theoretically simulated by Maxwell-Garnett effective medium theory.

The dense attachment of silver nanoparticles (AgNPs) on indium tin oxide (ITO) surfaces was successfully synthesized and developed using a refined seed-mediated growth approach (RSMG). AgNPs/ITO film prepared was investigated using several methods such as UV-visible spectroscopy, field emission scanning electron microscope, optical absorption, electrochemical impedance spectroscopy and cyclic voltammeter, respectively. The AgNPs was attached on the ITO surface via the cysteamine molecule. Particle size and density of AgNPs/ITO film have been examined and discussed in detail. The results obtained by refined seed-mediated growth showed a narrower size distribution and much denser attachment compared with those prepared by the normal seed-mediated growth method. The particles size of Ag nanosphere have been controlled by adjusting the growth time at less than 2h, while AgNPs of larger different shape was formed after more than 3h of growth. The bridging with cysteamine was also found to be effective for denser and homogenous attachment of AgNPs on ITO surface while keeping the dispersion. The experimental optical spectra have been explained using the full Mie theory for scattering and absorption by a homogeneous Ag sphere with modified dielectric constants taking into consideration the electron mean free path limitation.

Silica films containing gold nanoparticles were grown by magnetron radio frequency (rf) sputtering technique under various deposition conditions. The structural and optical properties of the composite films deposited at 400˚C substrate temperature were compared with those deposited at room temperature. Effect of substrate temperature of AuNPs on micro structural properties of the Au/SiO 2 nanocomposite films, such as size, dislocation density (δ), strain (ε) and lattice distortion (LD) have been investigated. The face-centered cubic crystalline structure of Au nanoparticles inclusion in the amorphous silica dielectric matrix was confirmed using X-ray diffraction. The average grain size of AuNPs has been found in the range of 0.56 -0.60 nm and 1.15 -1.23 nm at 3 × 10 −3 mbar and 2 × 10 −3 mbar argon pressure respectively. The δ, ε, LD values change inversely with the increasing of the substrate temperatures. These composites exhibit the optical features of a semiconductor with direct band gap. The band gap energy of 3.85 eV and 4.1 eV achieved for gold nanoparticles when the substrate temperatures increases from 25˚C to 400˚C. A peak wavelength of the surface plasmon resonance band absorption (SPR) characteristic of gold nanoparticle was found around 500 nm for the sample deposited at 2 × 10 −3 mbar and at 400˚C substrate temperature.

Amorphous alumina films containing gold nanoparticles were grown by radio frequency (rf) magnetron sputtering technique, with a variation of area ratio of gold/Alumina target ( 2 3 ⁄ ). Effect of the gold content in the composite films on the microstructural and optical absorption have been investigated. From the X-ray diffraction (XRD) measurements, the texture coefficient, lattice parameter, grain size and strain were calculated and correlated with changing . Contrary to the melting point of free metal cluster, it is found that melting point of gold nanoparticles embedded in amorphous alumina matrix is larger than the melting point of the corresponding bulk material, decreases with increasing size of particles. The surface plasmon resonance peak wavelength, volume fraction and size of gold nanoparticles were determined from the optical absorption spectra of the samples through the MaxwellGarnett effective model fitting, considering the size dependent mean free path limitation of free electrons. The peak wavelength of the surface plasmon resonance (SPR) was found to redshift from 500 nm to 558 nm and size increases from 2.2 nm to 5.8 nm when the 2 3 ⁄ increases from 1.3% to 2.6%, and remain at the same wavelength for larger size.