In order to characterize the laser ablation process as it relates to the deposition of high Tc superconducting thin films, optical emission spectra produced during ArF excimer laser ablation of the high Tc superconductor YBa2Cu3O7 were studied. The population of excited states within the gas phase blow-off material depends strongly on excimer laser fluence at 193 nm. Ablation using relatively low excimer laser fluences produces a significant fraction of YO in the gas phase. The plasmas derived from ablation of targets made from the high Tc material are similar to plasmas observed from ablation of the individual components BaCO3, CuO, and Y2O3.
The effects of changes in experimental parameters on the plasma emission spectra produced during excimer laser ablation of YBa2Cu3O7 were investigated. Emission from YO is observed for low-incident laser fluences, but is absent for fluences at or above those used for thin film deposition by laser ablation. Excitation within the plasma appears to be primarily due to electron impact. The effects of incident laser fluence and ambient gas pressure on the plasma emission are distinct enough to allow adjustment of either parameter based on the observed change in the emission spectrum. Therefore, optical emission spectroscopy is well suited as a technique for in situ monitoring of the deposition of thin films by laser ablation.
The Raman (3900-20 cm-') and infrared (3500-50 cm-') spectra of gaseous and solid methylcyclobutane and methyl-d,-cyclobutane have been recorded. Additionally, the Raman spectra of the pure liquids have been recorded and qualitative depolarization values have been obtained. The spectra have been interpreted on the basis that both the axial and equatorial conformers are present in the fluid phases and that the equatorial form is thermodynamically preferred and the only form present in the annealed solid. All 39 of the normal vibrational modes have been assigned for both the 4 and d3 compounds. An abundance of spectral evidence is presented which indicates extensive coupling between the vibrations associated with the ring and those of the methyl group. The CH3 internal torsional mode has been observed in the Raman spectrum of the solid at 232 cm-', and utilizing this frequency the periodic threefold barrier to internal rotation has been calculated to be 1190 cm-' (3.40 kcal mol-'). The fundamental ring puckering mode has been assigned from the Raman spectra of the gases to weak features observed at 161 and 154 cm-' for the 4 and d3 compounds, respectively. All of these results are compared with the corresponding quantities for some similar molecules.
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