Silver nanoparticles on graphite studied by femtosecond time-resolved multiphoton photoemission

Time-resolved multiphoton photoelectron spectroscopy is employed to study c ollective excitations and their decay dynamics in silver nanoparticles on h ighly oriented pyrolytic graphite. Resonant excitation of the surface plasm on in the silver nanoparticles with 400 nm femtosecond radiation allows to distinguish between photoemission from the nanoparticles and the substrate. This extends the method of time-resolved two-photon photoemission spectros copy to inhomogeneous surfaces and permits to probe the dynamics of a confi ned electron gas. The multiphoton photoelectron spectra, the polarization d ependence of the photoelectron yield and the time-resolved measurements rev eal the double excitation of the surface plasmon and allow the identificati on of two different decay channels of the collective excitation. The multip ly excited plasmon transfers its total excitation energy to a single photoe lectron or decays into at least two single-particle excitations which share the total energy. (C) 2000 American Institute of Physics. [S0021-9606(00)7 0711-2].