Monte Carlo simulation of pulsed laser ablation from two-component target into diluted ambient gas T. E. Itinaa) Laboratoire Interdisciplinaire Ablation Laser et Applications, IRPHE-LP3 UMR CNRS 6594, Parc Scientifique et Technologique de Luminy, 163 avenue de Luminy, Case 918, Marseille 13009, France
W. Marine Laboratoire Interdisciplinaire Ablation Laser et Applications, GPEC UMR CNRS 6631, Parc Scientifique et Technologique de Luminy, 163 avenue de Luminy, Case 918, Marseille 13009, France
M. Autric Laboratoire Interdisciplinaire Ablation Laser et Applications, IRPHE-LP3 UMR CNRS 6594, Parc Scientifique et Technologique de Luminy, 163 avenue de Luminy, Case 918, Marseille 13009, France
~Received 25 March 1997; accepted for publication 30 May 1997! Laser ablation from a binary target into a diluted gas background is studied by means of a Monte Carlo simulation. The influence of the ambient gas on the spatial and mean energy distribution of particles deposited at the distant detector is considered. Thermalization of the particles, the random scattering effect and the backscattering of particles were observed. Considerable modification of the deposited film thickness profiles due to collisions of the ablated particles with the ambient gas is shown. The increase of the ambient gas pressure was found to affect the stoichiometry distribution of deposited and backscattered particles. The study is of a particular interest for the development of the thin film growing technique known as pulsed laser deposition. © 1997 American Institute of Physics. @S0021-8979~97!04617-3#
I. INTRODUCTION
Pulsed laser deposition ~PLD!1,2 for growing thin films is one laser application that has progressed rapidly over past few years. Interest in this field was brought about by the success of in situ growth of high-temperature superconducting films.3 Numerous experiments were carried out and rich scientific information of the ablation process was obtained. Of particular interest was the influence of various laser parameters, system geometry, target material and ambient gas on the film thickness profile and film stoichiometry. Experimental and theoretical studies4–17 show the formation of a forward-peaked angular distribution of the ablated particles. In vacuum, collisions of the plume particles among themselves were found9–17 to determine the plume angular distribution. The effects of the background gas on the deposition process were considered in a number of papers. The experimental results on ablation in the presence of ambient gas8,18–20 revealed the dependence of the deposition rate on the ambient gas parameters. The comparison between the results obtained for the deposition in inert and reactive atmospheres ensured that part of these effects is not chemical in nature.8 In the presence of ambient gas, additional plume particle collisions with the background gas must be considered.21 Previous investigations show that the effect of background gas depends on the pressure regime and on the laser parameters used in PLD. For an accurate description of this effect one must distinguish between two cases. In the first case the density of the ablated particles is so high that the plume can be described in terms of a continues medium. As a rule, the a!
On leave from The Moscow Institute of Physics and Technology, Russia. Electronic mail:
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J. Appl. Phys. 82 (7), 1 October 1997
ambient gas pressures of a few hundreds of mTorr are used in these experiments. For this regime shock wave models22–24 are found to describe the interaction well. Fast photographic techniques were used to study the process and forward focusing of the plume was often observed. When the density and the energy of the ablated particles are not very high, plume-background gas interaction can be considered as the scattering of a molecular beam by the particles of the background gas. For very low ambient gas pressure ~P
