Influence of laser energy density on the plasma expansion dynamics and film stoichiometry during laser ablation of BiSrCaCuO

The plasma expansion dynamics and the composition of films deposited during laser ablation of BiSrCaCuO at laser energy densities in a broad interval (1-6 J/cm(2)) have been studied by means of spatially resolved real time optical emission spectroscopy and Rutherford backscattering and nuclear reactive analysis, respectively. In vacuum, the velocity of the ejected species is found to increase as the energy density increases whereas the compositional and angular distribution of the deposited films remain unchanged. When an oxygen pressure of 10(-1) mbar is applied, the film composition and angular distribution depend on the laser energy density, The results are analyzed in the frame of a collisional mechanism between the ejected and gas species, the effect of increasing the laser energy density being similar to that of decreasing the oxygen pressure. Finally, this competitive influence of the oxygen pressure and the energy density is discussed within the adiabatic expansion model. (C) 1996 American Institute of Physics.