Arf Laser Ablation of Yba 2 Cu 3 O 7-X as Studied by Emission Spectroscopy, Sem and Edax
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AS STUDIED BY ArF LASER ABLATION OF YBa Cu 0 EDAX EMISSION SPECTROSCOPa, SEM'ND ALON HOFFMAN* AND RAFAEL R. MANORY** *Dept. of Applied Physics, Royal Melbourne Institute of Melbourne, Australia. ** Metallurgical Engineering Group, Royal Melbourne Institute G.P.O.Box 2476V, Melbourne VIC 3001, Australia.
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ABSTRACT The fluorescence emission spectra from the plasma plume induced by ArF excimer laser irradiation of YBa 2 Cu 3 O Tx was studied and compared to the spectra 7 of Y, YO, Cu, CuO, and YCuO under similar conditions. The only compound detected in the Y-Ba-Cu-O ablated material spectra was YO. Spatially resolved measurements from the plasma plume emanating from the irradiated superconducting material were performed also as a function of distance from the surface. The effect of laser ablation on the morphology and composition of the irradiated YBa 2 Cu 3 OT 7 x material was studied by SEM and EDAX. It was found that the 1-2-3 composition ratio of the near surface region was maintained after ablation. Changes in the morphology were observed in the track region and three distinctive regions could be identified as a function of distance from the beam center. INTRODUCTION Laser evaporation has been applied successfully for the deposition of stoichiometric YBa 2 Cu 3 O 7Tx films by excimer laser (1,2). Photoluminescence spectroscopy of the plasma plume of YBa 2 Cu 3 O7 x induced by an ArF excimer laser (193 nm) has been recently performed by a number of groups (3,4). It was generally agreed that the emission lines observed could 0be assigned to Y, Y+, YO, Ba, Ba+ and Cu. Plasma temperatures in the 6000-13000 K range were reported for laser fluences of -1 J/cm (3). It was found that as the distance. from the surface increased the continuum fluorescence decreased, indicating a lowering in plasma temperature (4). The nature of the photon/target interaction was addressed and found to be of a highly non-equilibrium nature (5,6). In the present work a systematic measurement of the fluorescence emission 0 spectra for superconducting YBa Cu 3 7.x was performed. In these measurements the light emitted up to 5 mm above the ablated surface was analysed in the 20006500 A range. Spatially resolved measurements were performed to study variations in the plasma as a function of distance from the surface, and the morphology of the ablated surface was studied by SEM and EDAX. EXPERIMENTAL The laser beam was aligned perpendicular to the surface, and to avoid local heating the sample was rotated. By focusing the beam a spot of approximately 200 um diameter was obtained. The ArF (193 nm) pulsed laser was operated for 30 nsec at a repetition rate of 12 Hz at an average •luence per pulse of 7 J/cm . The optical spectra of the induced plasma (at 10.ý torr) was measured by focusing the plume image into the spectrometer slit. The fluorescence light detected by the photomultiplier was gated for 20 usec. For each spectral range the spectrum was normalized to the most intense line. SEM and EDAX analysis were performed
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