VUV 157nm F₂ laser irradiation of micro- and nano-scale particles

Cockcroft, Stephanie

Abstract

Micro- and nanoscale particles have recently become the focus of a great deal of research interest due to their wide-ranging potential in a number of applications.

This thesis concerns the interaction of small particles with the 157nm wavelength vacuum ultraviolet, VUV, emission from a molecular fluorine gas, F₂, laser. The laser system is introduced and an overview of laser ablation of polymers is presented.

Small particles of different materials and sizes, supported on polymeric substrates, are irradiated at a wavelength of 157nm. The silica particles are transparent to the 157nm radiation, which leads to a lens effect. The polystyrene, silicon carbide and silver particles are opaque to the 157nm radiation, leading to a substrate-shielding effect.

The lens effect results in the focussing of the incident laser beam into a hotspot at the interface between the particle and the substrate. The enhancement leads to the removal of substrate material underneath the particle to form a dimple on the surface of the substrate. The substrate-shielding effect leads to the removal of the substrate material around the opaque particle while the underlying material is left behind. This forms a polymeric support structure, with the seeding particle attached to the top. The shape of the seeding particle dictates the shape of the support structure, for example spherical particles seed composite conical structures and cylindrical particles seed linear prismatic structures. The polystyrene and silver particles are seen to undergo shape and size transformations as a result of laser irradiation. This is discussed in terms of mass loss through heating.

Finite Element Method modelling is used to investigate and support the experimental results.

Fluorescent polystyrene particles are also irradiated at a wavelength of 157nm. They retain their fluorescence after irradiation and exhibit Whispering Gallery Mode resonances, ideal for high-sensitivity sensing applications and Lab-on-a-Chip microreactors.

Citation

Cockcroft, S. VUV 157nm F₂ laser irradiation of micro- and nano-scale particles. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4214530

• Thesis Type: Thesis
• Deposit Date: Oct 2, 2013
• Publicly Available Date: Feb 23, 2023
• Keywords: Physics
• Public URL: https://hull-repository.worktribe.com/output/4214530
• Additional Information: Department of Physics, The University of Hull
• Award Date: Aug 1, 2012