Picosecond dynamics of Cu nanoparticle composites embedded in insulators by 60 keV negative ion implantation

摘要

Steady-state and laser-induced transient absorption around the surface plasmon resonance of copper nanoparticle composites, fabricated by ion implantation, have been studied by optical measurements. Negative ion implantation has been applied to generate the Cu nanoparticles in amorphous SiO_2, crystalline MgOn(Al_2O_3), LiNbO_3, SrTiO_3 and TiO_2 with various refractive indices and optical energy gaps. The surface plasmon resonance in the steady-state absorption resulted from formation of nanoparticles in the substrates and shifted to red with increasing refractive index of the matrix. The nanoparticle fabrication by the negative ion implantation was succeeded in all the insulating substrates used and it is capable to tune the resonance band to 1.7 - 2.2 eV (730 - 560 nm) by selecting of the matrix. However, there remained a problem that the plasmon band in LiNbO_3, SrTiO_3 and TiO_2 with narrow energy gap overlapped radiation-induced defect band. Laser-induced transient absorption was measured with a technique of pump-probe femtosecond spectroscopy. The bleaching plasmon band recovered in several picoseconds due to energy transfer from the excited electron system to the phonon system via the electron-phonon interaction. The transient absorption is also affected by radiation damage in the matrices with the narrow energy gap.