Laser-induced polymer ablation: photochemical decay plus thermal desorption

Kalontarov, L. I.; Marupov, R.

doi:10.1016/0009-2614(92)85922-w

Cited by 17 publications

(4 citation statements)

References 13 publications

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“…Detailed models of photochemical modification of material are found in the literature. 8,17,[54][55][56] The model of Kalonartov proposes that ablation happens in two steps beginning with the photolytic decomposition of material followed by thermally activated ejection of material. 55 Our simulation data fit well to the model; however, the small molecules are not accounted in our fits because their ejection is not described by this model.…”

Section: Microscopic Physics and Bulk Ablation Modelsmentioning

confidence: 99%

“…8,17,[54][55][56] The model of Kalonartov proposes that ablation happens in two steps beginning with the photolytic decomposition of material followed by thermally activated ejection of material. 55 Our simulation data fit well to the model; however, the small molecules are not accounted in our fits because their ejection is not described by this model. 43 As discussed in the previous sections, the formation and ejection of small molecules are important contributors to the ablation process, and a more complete description is warranted.…”

Section: Microscopic Physics and Bulk Ablation Modelsmentioning

confidence: 99%

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Elucidating the Thermal, Chemical, and Mechanical Mechanisms of Ultraviolet Ablation in Poly(methyl methacrylate) via Molecular Dynamics Simulations

2008

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[Figure: see text]. Laser ablation harnesses photon energy to remove material from a surface. Although applications such as laser-assisted in situ keratomileusis (LASIK) surgery, lithography, and nanoscale device fabrication take advantage of this process, a better understanding the underlying mechanism of ablation in polymeric materials remains much sought after. Molecular simulation is a particularly attractive technique to study the basic aspects of ablation because it allows control over specific process parameters and enables observation of microscopic mechanistic details. This Account describes a hybrid molecular dynamics-Monte Carlo technique to simulate laser ablation in poly(methyl methacrylate) (PMMA). It also discusses the impact of thermal and chemical excitation on the ensuing ejection processes. We used molecular dynamics simulation to study the molecular interactions in a coarse-grained PMMA substrate following photon absorption. To ascertain the role of chemistry in initiating ablation, we embedded a Monte Carlo protocol within the simulation framework. These calculations permit chemical reactions to occur probabilistically during the molecular dynamics calculation using predetermined reaction pathways and Arrhenius rates. With this hybrid scheme, we can examine thermal and chemical pathways of decomposition separately. In the simulations, we observed distinct mechanisms of ablation for each type of photoexcitation pathway. Ablation via thermal processes is governed by a critical number of bond breaks following the deposition of energy. For the case in which an absorbed photon directly causes a bond scission, ablation occurs following the rapid chemical decomposition of material. A detailed analysis of the processes shows that a critical energy for ablation can describe this complex series of events. The simulations show a decrease in the critical energy with a greater amount of photochemistry. Additionally, the simulations demonstrate the effects of the energy deposition rate on the ejection mechanism. When the energy is deposited rapidly, not allowing for mechanical relaxation of the sample, the formation of a pressure wave and subsequent tensile wave dominates the ejection process. This study provides insight into the influence of thermal, chemical, and mechanical processes in PMMA and facilitates greater understanding of the complex nature of polymer ablation. These simulations complement experiments that have used chemical design to harness the photochemical properties of materials to enhance laser ablation. We successfully fit the results of the simulations to established analytical models of both photothermal and photochemical ablation and demonstrate their relevance. Although the simulations are for PMMA, the mechanistic concepts are applicable to a large range of systems and provide a conceptual foundation for interpretation of experimental data.

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Section: Microscopic Physics and Bulk Ablation Modelsmentioning

confidence: 99%

Section: Microscopic Physics and Bulk Ablation Modelsmentioning

confidence: 99%

Elucidating the Thermal, Chemical, and Mechanical Mechanisms of Ultraviolet Ablation in Poly(methyl methacrylate) via Molecular Dynamics Simulations

2008

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“…The introduction of ultraviolet (UV) laser ablation has been effective in advancing many applications such as drilling ink-jet nozzles and developing lab-on-chip devices − A full microscopic insight, however, has eluded these investigations due to the complex interplay between the laser and the material. Molecular dynamics (MD) simulation is ideal for this fundamental task as it can resolve the irradiation process into microscopic details and shed light on the mechanisms that contribute to material ejection. − …”

Section: Introductionmentioning

confidence: 99%

Simulations of Laser Ablation of Poly(methyl methacrylate): Fluence versus Number of Photons

2007

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Using molecular dynamics simulations with an embedded chemical reaction scheme, two pathways of chemical decomposition of poly(methyl methacrylate) leading to ablation are independently investigated using two photon energies. The model employed in this study uses a coarse-grained substrate with predetermined reaction channels and a fixed penetration depth. The simulations allow for single-photon absorption per site with the possibility of photochemical bond cleavage. Within these parameters, the absorption of 7.9 and 5 eV photons (equivalent to 157 and 248 nm radiation, respectively) is simulated over a range of fluences to demonstrate the fundamental photochemical effects of the number of photons versus the total energy absorbed. Above the ablation threshold, similar mechanisms of ejection occur using either photon energy, but, at equal fluences, more material is ejected with a larger number of lower energy photons. When more photons are absorbed cleaving a greater number of bonds, more transformation occurs deeper within the substrate, and the amount of ejected material increases. If thermal as well as photochemical processes occur, the ablation threshold is shifted to a higher fluence. The amount of residual photon energy following the bond scission affects the ablation plume composition.

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“…The removal of material is often rather violent, as flash photographs shows. ,, Gaseous and particulate matter are ejected on a short time scale, frequently during the laser pulse which is in the 10 -8 −10 -12 s range. The details of the ablation mechanism are still a matter of debate; both photochemical and thermal processes and several photothermal mechanisms were suggested in the literature. − …”

Section: Introductionmentioning

confidence: 99%

Laser-Induced Dissociation of an Energetic Polymer: A Spectroscopic Study of the Gaseous Products

et al. 2000

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Previous studies of GAP (glycidyl azido polymer) laser-induced decomposition (Propellants, Explosives, Pyrotechnics 1996, 21, 258), revealed that the shock wave produced from a diluted polymer is more energetic than from the neat polymer. In this paper, direct measurement of the energy disposal into molecular products is reported using spectroscopic methods. Chemiluminescence probes electronically excited species, and laser-induced fluorescence, ground-state radicals. It is found that the initial velocity and internal energy content of small diatomic molecules is larger in some diluted polymers than in the neat one. This finding is in line with a simple model based on the assumption of a self-sustained reaction following initial laser excitation.

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Laser-induced polymer ablation: photochemical decay plus thermal desorption

Cited by 17 publications

References 13 publications

Elucidating the Thermal, Chemical, and Mechanical Mechanisms of Ultraviolet Ablation in Poly(methyl methacrylate) via Molecular Dynamics Simulations

Elucidating the Thermal, Chemical, and Mechanical Mechanisms of Ultraviolet Ablation in Poly(methyl methacrylate) via Molecular Dynamics Simulations

Simulations of Laser Ablation of Poly(methyl methacrylate): Fluence versus Number of Photons

Laser-Induced Dissociation of an Energetic Polymer: A Spectroscopic Study of the Gaseous Products

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