Theory and numerical modeling of the accelerated expansion of laser-ablated materials near a solid surface

Chen, Kuan-Ren; King, T. C.; J.H.Hes,; Leboeuf, J. N.; Geohegan, David B.; Wood, R. F.; Puretzky, Alexander A.; Donato, J. M.

doi:10.1103/physrevb.60.8373

Cited by 40 publications

(38 citation statements)

References 23 publications

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“…6 At time 20 ns a further increase of the radial front speed is visible. This increase can be attributed to monomer evaporation from large and relatively hot clusters, in accordance with the dynamic source model of Chen et al 8 The self-similar flow establishes at the estimated time ͑about 40 ns͒, while a few minor convexities of the curve can be attributed to the monomer evaporation from large clusters ͑see below͒.…”

Section: A Time Evolution Of the Plumesupporting

confidence: 82%

“…The following expansion of the vapor cloud has been treated either by means of analytical models, 5,6 numerically, 7,8 or in simulation. [9][10][11] Several experimental effects were explained, including strong forward peaking of the angular distribution in the plume 6 and spatial segregation of light and heavy particles in the case of a binary target.…”

Section: Introductionmentioning

confidence: 99%

“…15 Moreover, the actual speed of the expansion front is a factor of 2-3 faster than that predicted for typical vaporization temperatures. 8 Molecular dynamics ͑MD͒ simulations of laser ablation in organic solids 16 performed with the breathing sphere model 17 have provided some insights into the physical mechanisms responsible for material disintegration and ejection in laser ablation. In particular, the MD simulations have identified two distinct irradiation regimes.…”

Section: Introductionmentioning

confidence: 99%

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Combined molecular dynamics–direct simulation Monte Carlo computational study of laser ablation plume evolution

Zeifman

Garrison

Zhigilei

2002

Journal of Applied Physics

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A two-stage computational model of evolution of a plume generated by laser ablation of an organic solid is proposed and developed. The first stage of the laser ablation, which involves laser coupling to the target and ejection of molecules and clusters, is described by the molecular dynamics (MD) method. The second stage of a long-term expansion of the ejected plume is modeled by the direct simulation Monte Carlo (DSMC) method. The presence of clusters, which comprise a major part of the overall plume at laser fluences above the ablation threshold, presents the main computational challenge in the development of the combined model. An extremely low proportion of large-sized clusters hinders both the statistical estimation of their characteristics from the results of the MD model and the following representation of each cluster size as a separate species, as required in the conventional DSMC. A number of analytical models are proposed and verified for the statistical distributions of translational and internal energies of monomers and clusters as well as for the distribution of the cluster sizes, required for the information transfer from the MD to the DSMC parts of the model. The developed model is applied to simulate the expansion of the ablation plume ejected in the stress-confinement irradiation regime. The presence of the directly ejected clusters drastically changes the evolution of the plume as compared to the desorption regime. A one-dimensional self-similar flow in the direction normal to the ablated surface is developed within the entire plume at the MD stage. A self-similar two-dimensional flow of monomers forms in the major part of the plume by about 40 ns, while its counterpart for large clusters forms much later, leading to the plume sharpening effect. The expansion of the entire plume becomes self-similar by about 500 ns, when interparticle interactions vanish. The velocity distribution of particles cannot be characterized by a single translational temperature; rather, it is characterized by a spatially and direction dependent statistical scatter about the flow velocity. The cluster size dependence of the internal temperature is mainly defined by the size dependence of the unimolecular dissociation energy of a cluster.

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Section: A Time Evolution Of the Plumesupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Combined molecular dynamics–direct simulation Monte Carlo computational study of laser ablation plume evolution

Zeifman

Garrison

Zhigilei

2002

Journal of Applied Physics

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“…The value of ␥ is in agreement with the data for YBaCuO plumes and close to those of ideal gases. 23,25,26 It has been suggested 22,27,28 that the front of the plume extends in an expansive stage ͑shock wave propagation͒ in the region where its pressure exceeds the pressure of the external gas. Once these pressures are equal, the ejected particles are transported to the substrate by diffusion.…”

Section: A Structure Of the Plumementioning

confidence: 99%

Laser deposition from a nanostructured YBaCuO target: Analysis of the plume and growth kinetics of particles on SrTiO3

Huhtinen

Järvinen

Laiho

et al. 2001

Journal of Applied Physics

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The plume generated by a pulsed XeCl laser from a novel nanostructured YBaCuO target (n target) is investigated by methods of optical emission spectroscopy and atomic force microscopy. While the spectral positions of the emission lines are the same, stronger line intensities, pertinent to higher kinetic energy of the particles, are observed in the plumes generated from the n target than from a target having micron size grains (m target). The size of small clusters captured on Si plates assembled inside the plume grows in directions perpendicular to the axis of the plume. As shown by x-ray photoelectron spectroscopy investigations, in the particles deposited on a SrTiO3 substrate at Ts=700 °C in oxygen the correct 1-2-3 composition is achieved. The average ratio of the heights of the particles deposited from the n target and from the m target is hn/hm=0.6, both in the plume and on SrTiO3. This can explain the smoothness of YBaCuO films prepared by laser deposition from the n targets.

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“…13 At a later stage, away from the target surface, expansion in the radial direction will become important, and the model has to be extended to two dimensions ͑radial symmetry͒ or three dimensions. 19,20 Then, a possible solution to this problem is to employ more than one model, each suitable for a particular stage, and match them at an intermediate time. In this work, for the sake of simplicity, we use a one-dimensional description of the laser ablation process, such as it applies at early times after the end of the laser pulse, i.e., as long as lateral heat conduction can be neglected.…”

mentioning

confidence: 99%

Modeling of laser induced plasma expansion in the presence of non-Maxwellian electrons

Bennaceur-Doumaz

Djebli

2010

Physics of Plasmas

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The one-dimensional expansion into vacuum of ion-electron plasma produced by laser ablation is investigated. The ions considered as an ideal fluid are governed by a fluid model where charge quasineutrality is assumed to prevail, while electron density follows a non-Maxwellian distribution. Showing that the expansion can be described by a self-similar solution, the resulting nonlinear Euler equations are solved numerically. It is found that the deviation of the electrons from Maxwellian distribution gives rise to new asymptotic solutions of physical interest affecting the density and velocity of plasma expansion.Plasma expansion into vacuum is a basic physical problem with a variety of applications, ranging from space to laboratory scales. 1-4 Caused generally by electron pressure, it serves as an energy transfer mechanism from electrons to ions. The expansion process is often described under the assumption of Maxwellian electrons with velocities in local thermal equilibrium ͑LTE͒, known to be isotropically distributed around the average velocity. This assumption easily fails with a lack of collisions. Indeed, in many cases of astrophysical and laboratory plasmas expansion, the electron distribution functions ͑EDFs͒ are non-Maxwellian and exhibit more complex shapes showing high-energy tails, as in the weakly collisional corona and solar wind acceleration region. 5 The fundamental reason is that fast electrons collide much less frequently than slow ones. Indeed their free path is very large since proportional to v e 4 , where v e is the electron velocity, and cannot relax to a Maxwellian. The energetic electrons could have a significant effect on ionization and expansion of the plasma. As reported by many authors, 6-8 in an expanding plasma produced by laser ablation experiments, the high mobility light electrons escape faster into vacuum compared to heavier particles, thus generating a selfconsistent ambipolar electric field that accelerates the ions and slows electrons.Another phenomenon observed in plasma expansion is that the heat exchange between electrons and heavy particles such as ions is inefficient as only a fraction of the thermal energy of the order of m e / m i is transferred per collision, where m e and m i are the electron and ion mass, respectively. This causes the electron temperature T e to differ from the ion temperature T i . T e in non-LTE plasmas is higher than T i because of insufficient electron-electron collisions which provide the essential mechanism to reach thermal equilibrium. 9 This phenomenon is also crucial in pulsed laser deposition ͑PLD͒ experiments, where the efficiency of the deposited films depends on the parameters of the laser induced plasma that expands into vacuum or in an ambient environment. A very simple view of the PLD divides the process into two main stages: first, the incident laser rapidly heats the target, then a dense, warm plasma is created near the target surface, leading the plume to expand adiabatically. Finally, the plume deposits onto a substrate with nonequ...

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Theory and numerical modeling of the accelerated expansion of laser-ablated materials near a solid surface

Cited by 40 publications

References 23 publications

Combined molecular dynamics–direct simulation Monte Carlo computational study of laser ablation plume evolution

Combined molecular dynamics–direct simulation Monte Carlo computational study of laser ablation plume evolution

Laser deposition from a nanostructured YBaCuO target: Analysis of the plume and growth kinetics of particles on SrTiO3

Modeling of laser induced plasma expansion in the presence of non-Maxwellian electrons

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