Date of Award
Doctor of Philosophy
Michael Z. Hu, Gila E. Stein, Dibyendu Mukherjee
Metallic nanoparticles on surfaces have applications in biosensing, reaction monitoring, and solar energy harvesting etc. due their unique properties which are absent in the bulk metal. The size, spacing, shape, areal density and stability are some of the key parameters that determine suitability in applications. Metallic thin film melting in air has been investigated to produce nanoparticles as a relatively inexpensive approach with a predictable size and spacing. However, the main limitation is independent control of particle size and spacing. Recently, Yadavali and Kalyanaraman  showed that laser melting of Au films under glycerol lead to the independent control of particle size and spacing. This dissertation is focused on understanding of the behavior of nanoscale Ag metallic systems heated under bulk fluids. Ag thin films, irregular nanostructures, single and bilayer nanopyramids were fabricated using e-beam evaporation and nanosphere lithography then heating either by furnace annealing or nanosecond laser heating in vacuum, air and water-glycerol mixtures. Annealing of Ag/Co bilayer nanopyramids in air at temperature between 373 K to 573 K led to the discovery of the kinetic anchoring mechanism where the high surface energy and lower surface diffusivity of cobalt resulted in the Ag shape stabilization. Nanosecond laser heating of discontinuous Ag nanostructures under water produced a monomodal distribution of nanoparticles with smaller sizes than in air. High pressure gradients generated in the water vapor phase were attributed to this phenomenon. Pulsed laser melting of nanopyramids and thin films under water-glycerol mixtures produced nanoparticles with higher contact angles than in air. This was explained by the change of interfacial energies of quartz and metal surface by introduction of bounding fluids. Finally, nanosecond laser heating of nanopyramids and thin films beyond the boiling temperature of silver led to explosive vaporization in vacuum resulting in formation of small nanoparticles due to re-deposition onto the substrate. Overall, the thermodynamic properties and dispersive properties of the bounding fluid were found to play important roles in the Pulsed Laser Heating Under Fluids or PLHUF process.
Sandireddy, Venkatanarayana Prasad, "Mechanisms of Nanomaterial Synthesis by Pulsed Laser Heating Under Fluids (PLHUF). " PhD diss., University of Tennessee, 2019.