Diagnostic study of laser ablated YBa2Cu3Oy plumes

Post-ablation ionisation in conjunction with a reflectron time-of-flight mass spectrometer has been used to investigate a number of species in the ablation plume from a YBa2Cu3Oy target. The experiments were carried out using a Q-switched Nd:YAG laser with typical intensities of approximate to 10(8) W cm(-2) characteristic of the fluences (1 J cm(-2)) required for the pulsed laser deposition of thin superconducting films. By varying the delay between the ablation and the ionisation laser, the velocity distributions of several of the species from the target have been measured simultaneously. It has been observed that, although some of the atoms and molecules (i.e. Cu, Ba and BaO) have similar velocities, the atoms and oxides of Y (Y and YO) have very different velocities. The yttrium atoms and oxides were observed to be slower than the barium atoms and oxides at both ablation wavelengths examined (355 and 532 nm) and at two different distances from the target surface (2 and 3 mm). It is suggested that Ba, Cu and their oxides are ablated directly from the surface as neutrals, whereas Y and YO form clusters in the ablation plume. These clusters are then fragmented by the post-ionisation laser to produce Y and YO ions. (C) 1997 Elsevier Science B.V.