Effect of Sputtering Area Ratio of Gold/Silica Target and Thermal Annealing on Structural and Optical Absorption Properties of Au Nanoparticles Dispersed in Amorphous Silica Dielectric Films

Abstract

Gold-containing silica films were prepared by magnetron radio frequency (rf) co-sputtering technique, by varying the area ratio of gold/silica target $(r_{Au/SiO_2})$ and subsequent thermal annealing. The effect of deposition conditions on the formation of Au nanoparticles were studied by X-ray diffractometry (XRD) and optical absorption measurements. From the observation of measured spectra of the as-grown composite films, the presence of broad Au diffraction peaks in the XRD spectrum in addition to the amorphous silica pattern and absence of surface plasmon resonance band in the optical absorption spectra, suggests that the size of Au nanoparticles dispersed in silica films is less than 2 nm. After annealing at different tempertures up to 500 $^\circ$C, no significant changes in structural and optical absorption spectra was observed in the case of the samples deposited at $(r_{Au/SiO_2}=1.3\%)$, while for samples synthesized at $(r_{Au/SiO_2}=2.6\%)$, a weak but relatively broad absorption band in the absorption spectra starts appearing revealing that Au nanoparticles with size larger than 2 nm exists in $SiO_2$ matrix. With increase of annealing temperature, the intensity of absorbance peak increases and showed a red shift on the SPR position. Experimental optical absorption spectra were theoretically simulated by modified Mie theory.