Experimental study of ultrafast carrier dynamics and plasmons in nanostructures

[摘要] This thesis is devoted to the experimental investigation of ultrafast dynamics in silicon nanostructures and surface plasmonics by means of femtosecond lasers. First part of the research, ultrafast carriers dynamics in silicon nano-structures, is based on the time-resolved pump-probe reectivity method. A change in the density of excited carriers, as a response to the change of the excitation intensity, was extracted from the time-resolved re ectivity of crystalline nanopillars and nano-inclusions. The measurements were performed mainly in the sub-melting uence regime, at nearly normal incidence to the sample surface plane of the pump and probe beams. Both types of nano-structures have shown strong intensity dependent response comparing to bulk crystalline silicon. This enhanced response is attributed to a suppression of the diffusion processes in nanopillars and nonlinear response due to a constructive multilayer interference between the host matrix material, where silicon inclusions have been embedded, and the sublayers. Electron-phonon and recombination characteristic decay-times are extracted. The second part is devoted to sub-nanosecond decay of photoluminescence from siliconnitride amorphous structures. Particular structures have shown two radiative decay peaks. The second radiative peak is addressed to deep subband tail states, originated by the open bonds of the amorphous structure leading to the long radiative transition. The last part describes femtosecond-resolved plasmon-assisted dissociation of diatomic oxygen molecules in ultrahigh vacuum conditions. Asymmetric gold gratings have been utilised to create enhanced local electric elds originated from the optically excited surface plasmon resonances. Charged products of the dissociation process have been analysed by time-of-light linear drift mass spectrograph, while two-dimensional distribution has been achieved deploying Velocity Map Imaging technique. The dissociation process is found intensity dependent with strong non-linear prole. No correlation has been observed with background plasmon-enhanced electron emission.

[发布机构] University:University of Birmingham;Department:School of Physics and Astronomy

[关键词] Q Science;QC Physics