Dj. Lichtenwalner et al., INVESTIGATION OF THE ABLATED FLUX CHARACTERISTICS DURING PULSED-LASERABLATION DEPOSITION OF MULTICOMPONENT OXIDES, Journal of applied physics, 74(12), 1993, pp. 7497-7505
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.