Effects of oxygen background pressure on the stoichiometry of a LaGaO3 laser ablation plume investigated by time and spectrally resolved two-dimensional imaging

The plume expansion dynamics strongly affects the growth and the chemistry of pulsed laser
deposited thin films. The interaction with the background gas determines the kinetic energy of the
species impinging on the substrate, their angular broadening, the plasma chemistry, and eventually
the cations stoichiometric ratio in oxide films. Here, we exploit two-dimensional, spectrally
resolved plume imaging to characterize the diverse effects of the oxygen background pressure on
the expansion dynamics of La, Ga, and LaO species during pulsed laser deposition of LaGaO
3
. The
propagation of the ablated species towards the substrate is studied for background oxygen pressures
ranging from high vacuum up to

10

1
mbar. Our experimental results show specie-dependent
effects of the background gas on the angular distribution of the precursors within the plume. These
findings suggest that even in the presence of a stoichiometric ablation and of a globally stoichio-
metric plume, cations off-stoichiometry can take place in the forefront portion of the plume im-
pinging on the substrate. We show that such effect can be compensated by a proper choice of
process parameters.