SURFACE MODIFICATION OF LASER-ABLATED YBCO TARGET

A modified surface layer of YBa2Cu3O7-x (YBCO) target was systematical ly observed in the process of pulsed laser deposition (PLD) by scannin g electron microscopy (SEM). We observed that the size of cones formed on the YBCO target by a pulsed laser became larger with increasing nu mber of laser shots. The major effect of the surface modification like cone formation on PLD is a reduction of the deposition rate. To elimi nate cones, we have used the method of rotating the target by 180 degr ees to shoot the same number of laser beams on the same spot from oppo sing angles, Experimental results of losing the directionality and cha nging the shape of cones formed on YBCO target surface by laser beams incident on the same spot from opposing angles are obtained. These res ults are mainly due to altering irradiation geometry because cones dev elop only under a unidirectional laser beam. Raman spectroscopy illust rates that the target phase is less degraded by the laser beams incide nt from opposing angles than the laser beams incident from only one di rection.