Effects of laser intensity and ambient conditions on the laser-induced plume (original) (raw)
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Modeling of plume dynamics in laser ablation processes for thin film deposition of materials
Physics of Plasmas, 1996
The transport dynamics of laser-ablated neutral/plasma plumes are of significant interest for film growth by pulsed-laser deposition of materials since the magnitude and kinetic energy of the species arriving at the deposition substrate are key processing parameters. Dynamical calculations of plume propagation in vacuum and in background gas have been performed using particle-in-cell hydrodynamics, continuum gas dynamics, and scattering models. Results from these calculations are presented and compared with experimental observations.
Modeling of laser-induced plume expansion into ambient gas for thin film deposition
1995
The expansion of laser-induced plume into an ambient gas under typical thin film deposition conditions is investigated. A simplified theoretical model has been developed to understand the dynamics of plume-ambient gas interaction under the gas pressure of typically a few tens Pa. The model is based upon the generation of a high-temperature and high-pressure plasma cloud which is initially confined to a sphere of irradiated spot radius and is then suddenly allowed to expand into a gas. The expansion is governed by the Euler system of nonstationary equations. The model has been applied to investigate the dynamics of laser ablation of YBaCuO in oxygen. Numerical results show that the series of density jumps following one after another are formed in the plume. The origin of these pulsations is attributed to the repeated reflections of the secondary shock wave due to the effect of plume overexpansion. Using the calculated data, the time-of-flight signal has been simulated to compare the numerical results with available experimental data. Surprisingly good quantitative agreement has been achieved.
Analysis of plume deflection in the silicon laser ablation process
Applied Physics A, 2007
Changes in target surface morphology and ablation plume direction have been experimentally observed during the initial stages of the silicon laser ablation process. A relationship between both phenomena can be observed upon analysing the temperature field induced by the laser beam in a rough surface material. Theoretical studies on the deflection of the ablation plume are presented. These analyses are based on the hypothesis that particles that reach evaporation temperature will exit normally to the target surface with a velocity that is proportional to the surface temperature and the amount of the ablated material. Numerical solutions and experimental results of laser ablation process of silicon targets are found to agree with theoretical studies. PACS 42.25.Lc; 79.20.Dc; 02.70.Dc
Plume dynamics during film and nanoparticles deposition by pulsed laser ablation
Physics Letters A, 2002
The gas dynamics of pulsed laser ablation of silicon target in the helium gas ambient is investigated via direct simulation Monte Carlo method with a real physical scale of target-substrate configuration. A shock driven process is clearly observed. It is shown that the interaction of the shock front with the target surface and the vapor front induce significant backward flux of ablated particles and oscillating behavior of vapor front. A confined layer mixed with high density Si and He atoms is formed around the contact front. Its behavior is important to the nanoparticle formation and deposition.
Plasma plume dynamics, rebound, and recoating of the ablation target in pulsed laser deposition
Journal of Applied Physics
The effects of the type of background gas and pressure on the spatial distributions of plume species have been investigated by time and space resolved imaging in vacuum, 1 Â 10 À2 mbar and 1 Â 10 À1 mbar O 2 and Ar. The ablation of La 0.4 Ca 0.6 MnO 3 in vacuum shows dissimilar arrival times for the different neutral species and a backscattering of the impinging species from the substrate. At 1 Â 10 À2 mbar, a species-dependent plume splitting appears and preferential scattering of the lighter elements is detected generating a cation off-stoichiometry along the plume axis. In addition at 1 Â 10 À1 mbar the plume expansion in this relatively high pressure traps a portion of the background gas against the substrate holder, thereby creating a transient high local pressure with remarkable effects once the plume reaches the substrate. In an Ar background, a rebound wave is seen, which travels backwards and recoats/contaminates the target with a different composition than the original target. In O 2 , in addition to the rebound, a long-lived volume of excited species is created, which consists mainly of LaO I. The rebound has important effects on the film composition and is background gas dependent. The same effects are also detected during Ag ablation and are probably valid for most target materials. Published by AIP Publishing.
Internal structure and expansion dynamics of laser ablation plumes into ambient gases
Journal of Applied Physics, 2003
The effect of ambient gas on the expansion dynamics of the plasma generated by laser ablation of an aluminum target has been investigated using frequency doubled radiation from a Q-switched Nd:YAG laser. The diagnostic tools include fast photography of overall visible plume emission using a 2 ns gated intensified charged coupled device and space and time resolved emission spectroscopy using a 50 cm monochromator/spectrograph and photomultiplier tube. The expansion behavior of the plasma was studied with ambient air pressure ranging from 10−6 to 100 Torr. Free expansion, plume splitting and sharpening, hydrodynamic instability, and stagnation of the plume were observed at different pressure levels. Space and time resolved emission spectroscopic studies showed a twin peak distribution for Al and Al+ species at farther distances illustrating plume splitting at pressures higher than 100 mTorr. Combining imaging together with time resolved emission diagnostics, a triple structure of the ...
Dynamical modeling of laser ablation processes
1995
Several physics and computational approaches have been developed to globally characterize phenomena important for film growth by pulsed laser deposition of materials. These include thermal models of laser-solid target interactions that initiate the vapor plume; plume ionization and heating through laser absorption beyond local thermodynamic equilibrium mechanisms; gas dynamic, hydrodynamic, and collisional descriptions of plume transport; and molecular dynamics models of the interaction of plume particles with the deposition substrate. The complexity of the phenomena involved in the laser ablation process is matched by the diversity of the modeling task, which combines materials science, atomic physics, and plasma physics.
Journal of Physics D: Applied Physics, 1998
The expansion of a laser-ablation plume into different ambient gases is investigated theoretically using a two-fluid gas-dynamic model and experimentally with time-of-flight mass spectrometry. Both calculations and measurements, performed for laser ablation of YBa 2 Cu 3 O 7−x in oxygen or noble gases, reveal an oscillatory behaviour of plume expansion dynamics which is strongly dependent on the molecular weight of the ambient gas. Simple gas-dynamic considerations based on the analogy between an ablation plume and a supersonic underexpanded gaseous jet are found to explain a number of the effects of the interaction between the plume and the background gas. The effect of plume focusing observed previously at fairly high pressures of various ambient gases is reasonably described using the phenomenology of the underexpanded jet. The analogy also predicts vortex formation at the plume periphery.
Modeling of dynamical processes in laser ablation
Applied Surface Science, 1996
Various physics and computational approaches have been developed to globally characterize phenomena important for film growth by pulsed-laser deposition of materials. These include thermal models of laser-solid target interactions that initiate the vapor plume, plume ionization and heating through laser absorption beyond local thermodynamic equilibrium mechanisms, hydrodynamic and collisional descriptions of plume transport, and molecular dynamics models of the interaction of plume particles with the deposition substrate.
Finite element analysis of the initial stages of the laser ablation process
2004
The growth of thin films by pulsed-laser deposition involves extremely complex physical processes. The study of different aspects of the basic mechanisms of the laser ablation is still in progress, with special emphasis on the modelling of the plume deflection effect and the structure formation on the irradiated surface. In this work, the initial stages of the laser ablation process have been investigated considering the surface roughness and the continuous morphological changes of the surface produced by laser irradiation. Assuming a thermal ablation model, a computational approach of the structure formation on the irradiated surface by finite elements using ANSYS (6.1) has been developed. Complementary, different ablation experiments on silicon wafers ᭨ using a XeCl excimer laser (308 nm) impinging at 458 with respect to the target were carried out. Scanning electron microscope analyses were performed to study the morphological changes of the Si surface. The validity of the model and the agreement of the numerical results are discussed.