INVESTIGATION OF THE ABLATED FLUX CHARACTERISTICS DURING PULSED-LASERABLATION DEPOSITION OF MULTICOMPONENT OXIDES

The ablated flux characteristics of PbZr0.52Ti0.48O3 (PZT), La0.5Sr0.5 CoO3 (LSC), and MgO ceramic targets have been studied as functions of the ablation time, the ablation energy, and the chamber gas pressure. The time dependence of the ablation rate shows an initial exponential decay, reaching a steady-state value at longer times. The energy depen dence of the ablation rate (in vacuum) reveals a distinct ablation thr eshold energy for MgO ablation, while for PZT and LSC no ablation thre shold is evident. The differences in the ablation characteristics of t hese materials are explained mainly by differences in their melting po ints, thermal conductivities, and absorption coefficients. Upon adding O2 gas, a visual change in the color and shape of the PZT ablation pl ume is evident. The color change indicates a gas phase reaction of the ablated species with the O2 gas, while the shape change implies a cha nge in the angular distribution of the ablated species. We have measur ed a narrowing of the ablated flux distribution from a PZT target as O 2 is added, from a cos40 theta distribution in a low pressure, up to a cos260 theta distribution in an O2 pressure of 300 mTorr. This narrow ing, or focusing, of the ablation plume is observed with high laser en ergies and high pressures of O2 or noble gases. At low laser power, th e deposition rate decreases and the plume broadens as the gas pressure is increased. The plume narrowing and plume broadening regimes are bo th controlled by gas scattering effects. The angular distribution of d epositing species, and the ratio of deposition flux to O2 flux, are ve ry different in each of these regimes.