Effect of Sputtering Area Ratio of Gold/Alumina Target on Microstructure and Optical Absorption Properties of Au Nanoparticles dispersed in Amorphous Alumina Dielectric films

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 ( 𝑟𝐴𝑢/𝐴𝑙2𝑂3 ). 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 𝑟𝐴𝑢/𝐴𝑙2𝑂3. 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 Maxwell-Garnett 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 𝑟𝐴𝑢/𝐴𝑙2𝑂3 increases from 1.3% to 2.6%, and remain at the same wavelength for larger size.