Ultrafast photophysical properties of Au on STO (001)

We have determined the ultrafast carrier dynamics the Gold nanostructures on Strontium Titanate SrTiO₃ (STO) (001) single crystal substrate. The Gold was deposited on the STO by thermal evaporation. We have carried out the studies by transient absorption spectroscopy using femtosecond lasers. The nonlinear absorption has been determined by Z-scan technique using both open aperture and closed aperture method. The structural information of the film deposited was obtained by FESEM. From the ultrafast TA spectroscopy, it was determined that the band gap for STO is about 2.04 eV, a band gap shift and subsequent renormalization is observed in the crystal due to excitons. A phonon bottle-neck phenomenon is observed when the samples are pumped at higher energies. On 10 nm gold films grown on STO very low frequency plasmonic phonons primarily of frequency 0.6 GHz were observed. (author)