Collective electron dynamics in metallic nanoparticles

Excitation of metallic nanoparticles or artificial nanostructures leads to collective electron density fluctuations, in the elementary cases referred to as surface plasmons (SP). Insight into the dynamics of excitation, coupling and dephasing of SP modes in nanostructures is of considerable importance for the future development of nanoplasmonic devices.

The dephasing of surface plasmons can be most directly measured by real-time probing of the collective electron oscillations confined to nanometre dimensions. Imaging SP dynamics in nanoparticles calls for nanometre spatial and sub-fs temporal resolution.

Dynamical information of the SP modes will be acquired by probing the plasmonic field that has been coherently controlled by a synthesised few-cycle ligh pulse (A.1.2) by core-level photoemission from the nanoparticles induced by an attosecond XUV pulse. The momentum of the emitted photoelectrons will be measured as a function of the delay of the attosecond probe in a photoelectron emission microscope (PEEM), providing information on the plasmonic field with attosecond temporal and nanometre spatial resolution (see Fig.C.1.7). This technique will also allow element-specific imaging, as is required for more complex nanoplasmonic experiments where multicomponent materials are involved.

The cooperation with the Fritz-Haber-Institut with its extensive know-how in the preparation of size-selected clusters will be very helpful in attaining these goals. One of our long-term objectives is to realise self-affined ensembles or chains of metal nanoparticles in which the dynamics and propagation phenomena of plasmon modes can be studied. The avalanching accumulation of coherent surface plasmons in a single mode can result in a giant increase of the local field for cavity-like ensembles of metal nanolenses wich can be used for nano-optical purposes and selective photochemistry.