Surface second harmonic generation spectra of titania coated Au NPs

Surface second harmonic generation (s-SHG) spectra of supported Au nanoparticles (NPs) with titania coating are presented. Although the optical properties of these particles are in agreement with the predictions from Mie theory and previously reported literature, s-SHG spectra over a relatively broad spectral range, allows for the extraction of additional information regarding the morphology of the sample. These geometrical findings need to be considered while interpreting the observed spectra of supported NPs. In the case of atomic layer deposition of TiO2 onto Au NPs, it is found that for the titania layers thinner than 5 nm in nominal terms, Au NPs are not fully covered, as titania preferably accumulates at the space between the particles and at particles' edges and corners. Full encapsulation of the Au NPs is achieved for titania films with a nominal thickness of more than 5 nm. Furthermore, s-SHG spectra can also be used to extract information on the size distribution of the NPs.