| A detailed study of the interaction of a KrF beam with a Y-Ba-Cu-O high-temperature superconductor target was performed to address two principal problems associated with thin film deposition via pulsed laser evaporation: (1) formation of film surface particulates and (2) development of irregular target surface morphology. Thermodynamic chemical equilibrium and mass spectroscopic analysis were performed to determine the composition of the plasma generated by laser irradiation of Y-Ba-Cu-O during the formation and expansion stages.; The formation of film particulates was suppressed by maintaining the target bulk temperature greater than 700{dollar}spcirc{dollar}C. Such target heating eliminated the formation of spherical film particulates greater than one micron and suppressed the evolution of target surface morphology (i.e., pores, cones, and melts).; The development of surface morphology entailing the distribution of laser power via optical and conventional thermal analysis was investigated. A detailed fluence-dependent optical analysis was used to describe the surface morphology evolution which was found to be a strong function of laser fluence and pulse number. An overall energy balance showed that the phase transformation consumed one-third of the absorbed laser energy with the remainder converted to plasma kinetic energy. This kinetic energy was manifested in the redeposited plume area formed during ambient pressure evaporation; plume area was a linear function of fluence. The physical properties used in calculations were determined using thermal methods (heat capacity, transition temperatures, and thermal expansion coefficient) and laser flash technique (thermal diffusivity).; A thermodynamic equilibrium calculation (stoichiometric algorithm) was performed on a high-temperature, high-pressure, adiabatically expanding system to determine the chemical equilibrium as a function of temperature, pressure, and inert gas concentration. Ion formation was favored at high temperatures, low pressures, and high inert gas concentrations. Oxide formation was favored at high oxygen pressures and low temperatures. Chemical characterization of the plasma plume using a differentially pumped quadrupole mass spectrometer (P {dollar}le{dollar} 30 mtorr) showed the presence of mainly neutral and ionic atomic species. The result was consistent with the thermodynamic equilibrium calculation.; For comparison, the effect of KrF laser irradiation on other materials, including refractory ceramics, biocompatible materials, and polymer films, was also investigated. |
