Modification of cleaved surfaces of Bi Sr CaCu O single 2 2 2 8 crystals induced by ArF excimer laser irradiation

The variation of surface morphology and chemical composition of cleaved surfaces of 001.Bi2Sr2CaCu2O8 BSCCO. crystals was investigated following irradiation in vacuum with an ArF excimer laser. Results were obtained for laser fluences in the range from 20 to 500 mJrcm2. Distinctive surface structures of BSCCO have been observed having a strong correlation with the laser fluence and number of pulses delivered to the site. The development of a relatively smooth surface d;20 nm.has been observed for irradiation at 500 mJrcm2. The formation of a ‘hexatic’ micro-structure on the surface of ablated crystals suggests that a two-dimensional phase transition has occurred. At lower laser fluences, rough surfaces 0.05 mm-d-3 mm. were developed with characteristic pyramids andror cone-shape islands. The results indicate that surface modification is due to different mechanisms corresponding to the surface temperature being raised by direct laser irradiation and laser heated plasma. q1999 Elsevier Science B.V. All rights reserved.