Femtosecond Laser Interactions at Interfaces and Their Applications.

Abstract

This dissertation explores the interaction of femtosecond (fs) laser irradiation with material interfaces. The role of the interface after irradiation near the damage and material removal thresholds of metal thin films, semiconductors, insulators, and carbon nanotubes is rarely addressed in the literature and is explored here. Resulting morphologies and dynamics after irradiation are investigated using optical microscopy, atomic force microscopy, scanning electron microscopy, transmission electron microscopy, and pump-probe microscopy in order to elucidate physical models for the observed phenomena. The fundamental knowledge and mechanisms gained from studying the laser-material interactions in this thesis are used to explain phenomena observed by other researchers which were previously unexplained. For the first time, a link between homogeneous void nucleation within thin films to smooth surfaces and heterogeneous void nucleation at interfaces to rougher surfaces is shown. Formation mechanisms of Laser Induced Periodic Structures (LIPS) were investigated using single laser shots to elucidate the roles various mechanisms play in LIPS formation. To study the dynamics of LIPS formation, a new pump-probe microscopy technique with resolution limits comparable to commercially available Nomarski contrast microscopes was developed to observe the formation of LIPS after femtosecond irradiation for the first time. This technique will allow for observation of the evolution of surface features in other systems after femtosecond irradiation which are not accessible with current pump-probe techniques. The mechanisms covered in this thesis were used to improve current applications and for the creation of new devices. Thin Ni films were used to form blisters and microtubes at metal-silicon dioxide interfaces. After femtosecond irradiation of very thin Ni films, the formation of flexible microfluidics was demonstrated. New alignment mechanisms and orientations of carbon nanotubes (CNTs) on substrates were discovered using the interaction of femtosecond laser pulses with CNT-polymer composites. Finally, a nanoparticle (NP) printing technique was developed to print NPs from thin films to control NP size. The technique was used to print catalyst Ni NPs onto substrates and chemical vapor deposition was used to grow CNTs from these NPs.