Angle dependent light scattering of functional nanoparticle composites

  • Datum:
  • Plats: Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala
  • Doktorand: Wang, JunXin
  • Om avhandlingen
  • Arrangör: Fasta tillståndets fysik
  • Kontaktperson: Wang, JunXin
  • Disputation

In this thesis, we mainly focus on developing approaches for the inversion of scattering and absorption coefficients from optically measured transmittance and reflectance spectra.

Varies functional nanoparticles play crucial roles in energy- and optical- related applications. The incorporation of functional nanoparticles into non-absorbing polymers to form optical absorption and scattering thin films have attracted considerable interest due to a successful selection of particles and matrices, synergistic effects of separation and fixation of particles, and controllable layer thicknesses and structures. To investigate the optical parameters, especially absorption and scattering coefficients of the nanocomposites, it is critical to evaluate and optimize those particle based functional layers.

In this thesis, we mainly focus on developing approaches for the inversion of scattering and absorption coefficients from optically measured transmittance and reflectance spectra. A two-flux radiative transfer model is robust for this purpose, but its limitation lies in failing to converge the transmittance and reflectance spectra to experimental data owing to the approximation of the completely diffuse scattering patterns. We carried out thorough characterization of angle- and wavelength-resolved light scattering on those nanocomposites with metallic Au, ferromagnetic Fe3O4 and photocatalytic TiO2 nanoparticles. We further developed an empirical scattering phase function, which can fully represent the scattering distributions for aggregated particles in the multiple scattering regime, as well as the single scattering in the Rayleigh, Mie and geometric optical scattering regimes. The incorporation of angle-resolved data into the two-flux theory to derive scattering and absorption coefficients have been validated using the functional nanoparticle composites. Several approximations are also proposed to obtain the scattering and absorption coefficients when angle resolved measurements were not available.

The optical performance was investigated on the nanocomposites mentioned above with varied sizes, shapes and concentrations using a spectrophotometer, an in-plane scatterometer and an out-of-plane goniometer. Single particle dark-field scattering spectra were also obtained for Au, Fe3O4, and TiO2 particles in the forward and backward directions.