Study of the Optical and Thermoplasmonics Properties of Gold Nanoparticle Embedded in Al 2 O 3 Matrix

In this paper, the optical and thermoplasmonics properties of nanocomposites consisting of spherical gold nanoparticles (AuNPs) integrated in Al_2O_3 matrix are determined using the Finite Element Method (FEM). Firstly, the refractive index (n) , extinction coefficient (κ ) , absorption coefficient (μ_a) , and optical conductivity (σ ) are calculated from the effective complex permittivity obtained by solving the Laplace’s equation for different size and concentration of nanoparticles. The surface plasmon resonance (SPR) properties of AuNPs are optimized from the peak presented in the absorption coefficient spectrum. The results show that the optical parameters n, κ , μ_a , and σ undergo a strong variation around the wavelength λ_max corresponding to the SPR phenomenon. The value of λ_max increases from 560 to 600 nm when the radius of the particles varies between r=5 and r=30 nm . The effect of the AuNP concentration on the band gap energy E_g(eV) of Au- Al_2O_3 nanocomposites is also studied, a shift from Eg=5.34 to Eg=5.49 eV is observed when the concentration of the AuNPs increases from 0 to 0.82% . The electric field enhancement induced by the AuNPs at plasmonic resonance is also determined depending to the particle size; the results show that the enhancement factor increases from g=4.71 to g=6.95 when the radius of the AuNPs increases from r=5 to 30 nm . The thermal dissipation of the plasmonic energy of spherical of our system dispersed in the Al_2O_3 matrix is determined considering the Joule effect which occurs by the oscillation of the charges at the plasmonic resonance. The generated thermal power by particles is calculated for different sizes, which allows to calculate the thermal power per gram of particles depending on the intensity of the incident electric field. The results show that the plasmonic thermal power is almost identical for small particles when the radius is less than r=15 nm and increases considerably when the size increases from r=15 to 30 nm . For a fixed size and incident field amplitude, we calculated the temperature change in the nanocomposites Au- Al_2O_3 depending of time for different particle concentrations; the temperature variation curves obtained are linear as a function of time.