[show abstract][hide abstract] ABSTRACT: The dynamics of laser-excited electronic excitations (localized surface plasmons) in spherical Ag nanoparticles is studied
by phase and time resolved two photon photoemission (TR-2PPE) and photoelectron emission microscopy (TR-PEEM). A two-dimensional
array of nearly identical, parallelly oriented particles is deposited lithographically on a transparent ITO covered glass
substrate. We are able to show that the parallel acquisition mode of the PEEM enables us to resolve local variations in the
ultrafast electron dynamics in the nanoparticles with an accuracy of 1fs and a lateral resolution in the nanometer regime.
A qualitative interpretation of the mapped inhomogeneities in the local electron dynamics is provided.
[show abstract][hide abstract] ABSTRACT: Electron emission from Ag and Au nanoparticle films was studied under excitation with femtosecond-laser pulses with photon energies of 1.55 and 3.1 eV. Films were grown on a glass substrate with particle sizes from the nanometer range to a continuous layer. The transition from a continuous film to a nanoparticle film is accompanied by an increase in photoemission current by more than an order of magnitude. Pump-and-probe experiments with variable delay gave information on the lifetime of the intermediate states. At a fixed pulse power, the emission yield increases as the temporal width of the laser pulses is decreased. Experimental results are interpreted in terms of two different electron emission mechanisms, i.e., multiphoton photoemission and thermionic emission or thermally assisted multiphoton photoemission. The first mechanism prevails for con-tinuous films and larger particles with sizes above several tens of nanometers; the second one prevails for smaller nanoparticles with sizes of a few nanometers.
Physical Review B 01/2008; 77:195427. · 3.77 Impact Factor
[show abstract][hide abstract] ABSTRACT: In combining time-resolved two-photon photoemission (TR-2PPE) and photoemission electron microscopy (PEEM) the ultra-fast
dynamics of collective electron excitations in silver nanoparticles (localized surface plasmons – LSPs) is probed at fs and
nm resolution. Here we demonstrate that the sampling of the LSP dynamics by means of time-resolved PEEM enables detailed insight
into the propagation processes associated with these excitations. In phase-integrated as well as phase-resolved measurements
we observe spatio-temporal modulations in the photoemission yield from a single nanoparticle. These modulations are assigned
to local variations in the electric near field as a result of the phase propagation of a plasmonic excitation through the
particle. Furthermore, the control of the phase between the fs pump and probe laser pulses used for these experiments can
be utilized for an external manipulation of the nanoscale electric near-field distribution at these particles.
Applied Physics A 07/2007; 88(3):473-480. · 1.55 Impact Factor
[show abstract][hide abstract] ABSTRACT: We have studied the relaxation dynamics of optically excited electrons in molybdenum and rhodium by means of time resolved two-photon photoemission spectroscopy (TR-2PPE) and ab initio electron self-energy calculations performed within the GW and GW+T approximations. Both theoretical approaches reproduce qualitatively the experimentally observed trends and differences in the lifetimes of excited electrons in molybdenum and rhodium. For excitation energies exceeding the Fermi energy by more than 1 eV, the GW+T theory yields lifetimes in quantitative agreement with the experimental results. As one of the relevant mechanisms causing different excited state lifetime in Mo and Rh we identify the occupation of the 4d bands. An increasing occupation of the 4d bands results in an efficient decrease of the lifetime even for rather small excitation energies of a few 100 meV.
Physical Review B 05/2006; 74:035102. · 3.77 Impact Factor
[show abstract][hide abstract] ABSTRACT: Electron-spin relaxation at different surfaces of p-doped GaAs is investigated by means of spin, time, and energy-resolved two-photon photoemission. These results are contrasted with bulk results obtained by time-resolved Faraday rotation measurements as well as calculations of the Bir-Aronov-Pikus spin-flip mechanism. Due to the reduced hole density in the band bending region at the (100) surface the spin-relaxation time increases over two orders of magnitude towards lower energies. At the flat-band (011) surface a constant spin relaxation time in agreement with our measurements and calculations for bulk GaAs is obtained.
Physical Review B 01/2006; 73(8):081302. · 3.77 Impact Factor
[show abstract][hide abstract] ABSTRACT: In combining time-resolved two-photon photoemission (TR-2PPE) and photoemission electron microscopy (PEEM) the ultrafast dynamics of collective electron excitations in silver nanoparticles (localized surface plasmons – LSP) is probed at femtosecond and nanometer resolution. In two examples we illustrate that a phase-resolved (interferometric) sampling of the LSP-dynamics enables detailed insight into dephasing and propagation processes associated with these excitations. For two close-lying silver nano-dots (diameter 200 nm) we are able to distinguish small particle to particle variations in the plasmon eigenfrequency, which typically give rise to inhomogeneous line-broadening of the plasmon resonance in lateral integrating frequency domain measurements. The observed spatio-temporal modulations in the photoemission yield from a single nanoparticle can be interpreted as local variation in the electric near-field and result from the phase propagation of the plasmon through the particle. Furthermore, we show that the control of the phase between the used femtosecond pump and probe laser pulses used for these experiments can be utilized for an external manipulation of the nanoscale electric near-field distribution at these particles.