Quantitative mapping of nanoparticle distribution in composite thin films by terahertz time-domain spectroscopy imaging

Terahertz Time-Domain Spectroscopy (THz-TDS) imaging is employed for the non-invasive, quantitative mapping of nanoparticle distribution in composite thin films. Chitosan–silver nanoparticle films are used as a model system to validate the methodology. The complex refractive index of pure chitosan films is first determined and used to generate high-resolution thickness maps, confirming film homogeneity in its central region. Silver nanoparticle suspensions are independently characterized by THz-TDS, and their complex dielectric function was extracted using effective medium theory, supported by TEM-based size analysis. The dielectric functions of both matrix and inclusions are then used to invert the effective medium relation and retrieve local volumetric concentrations in the composite film. This approach enabled quantitative spatial mapping of the nanoparticle distributions in composite structures.