Field-Controlled Photoemission from Spatially Tailored Plasmonic Nanostructures

Addhya, Anchita (2019) Field-Controlled Photoemission from Spatially Tailored Plasmonic Nanostructures. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

Spatially tailored plasmonic nanostructures are widely known for their diverse applications as an ultrafast source of electrons, at the same time they are extremely useful for studying plasmonic field enhancement. The variation in geometries of such structures in responsible for a wide spectrum of observable effects. Metallic nanoparticles sustain surface charge oscillations, priamrily known as surface plasmon polaritons (SPPs). These SPPs not only play an important role in tailoring the electric field but are also responsible for electron emission from metallic surfaces, namely gold and silver. Previous works (Dombi et al, Putnam et al) have demonstrated this phenomena of controlled near-field enhanced electron emission primarily from nanotriangles, nanorods and nano bow-ties. In this dissertation, I have aimed to establish polarization controlled electron emission from plasmonic nanoparticles based on their surface plasmon resonance phenomena due to the effect of geometric phase. Gold nanospirals, being chiral structures are responsive to opposite helicities of incoming light, due to their spin and orbital angular momentum inter-conversion. Along with that, due to the plasmonic resonance it is highly likely that they are exceptionally good electron emitters as well. Thus exploiting these two phenomena and by using a completely new technique of detection via the Velocity Map-Imaging (VMI) Spectrometer for solids, I succesfully showed that electron emission is indeed affected by the effect of azimuthal phase on the nanospirals. Gold nanospirals were thus fabricated on ITO deposited on fused silica and two sets of experiments were conducted, first to confirm the helicity-dependent field phenomena exploiting the angular momenta of light and second to demonstrate that electron emission occurs via the four-photon absorption process using the Fowler-Dubridge model. Both theoretical simulations and experimental verifications were conducted to confirm the phenomena. Parallely, I have also partially modelled the VMI spectrometer as an electrostatic lens system to obtain position-momentum correlation of the electron emission with the help of an analytical formalism. These structures have initial evidence of Orbital Hall Effect which is being investigated currently.

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