Effects of thermal energy deposition on material ejection in poly(methyl methacrylate)

Conforti, Patrick F.; Prasad, Mahesh; Garrison, Barbara J.

doi:10.1016/j.apsusc.2007.01.052

Cited by 16 publications

(27 citation statements)

References 21 publications

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“…12,59 The interpretation of energy density for a polymer, however, is complex because there are strong covalent bonding interactions within the chains as well as weaker van der Waals interactions between the chains. In our earlier work, based on the same simulation setup, 61 it was shown that imparting 5 eV/monomer ͑8 mJ/cm 2 ͒ in the surface layer of one penetration depth only led to surface evaporation and insufficient void generation or fragmentation of the substrate and no ablation. At a higher fluence, with 5.9 eV/monomer ͑10 mJ/ cm 2 ͒, ablation was initiated which corresponded to a critical energy density of 0.037 eV/ Å 3 .…”

Section: Ejection Mechanismsmentioning

confidence: 98%

On the role of chemical reactions in initiating ultraviolet laser ablation in poly(methyl methacrylate)

Prasad

Conforti

Garrison

2007

Journal of Applied Physics

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The role of chemical reactions is investigated versus the thermal and mechanical processes occurring in a polymer substrate during irradiation by a laser pulse and subsequent ablation. Molecular dynamics simulations with an embedded Monte Carlo based reaction scheme were used to study ultraviolet ablation of poly͑methyl methacrylate͒ at 157 nm. We discuss the onset of ablation, the mechanisms leading to ablation, and the role of stress relaxation of the polymer matrix during ablation. Laser induced heating and chemical decomposition of the polymer substrate are considered as ablation pathways. It is shown that heating the substrate can set off ablation via mechanical failure of the material only for very short laser pulses. For longer pulses, the mechanism of ejection is thermally driven limited by the critical number of bonds broken in the substrate. Alternatively, if the photon energy goes towards direct bond breaking, it initiates chemical reactions, polymer unzipping, and formation of gaseous products, leading to a nearly complete decomposition of the top layers of substrates. The ejection of small molecules has a hollowing out effect on the weakly connected substrates which can lead to lift-off of larger chunks. Excessive pressure buildup upon the creation of gaseous molecules does not lead to enhanced yield. The larger clusters are thermally ejected, and an entrainment of larger polymer fragments in gaseous molecules is not observed.

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Section: Ejection Mechanismsmentioning

confidence: 98%

On the role of chemical reactions in initiating ultraviolet laser ablation in poly(methyl methacrylate)

Prasad

Conforti

Garrison

2007

Journal of Applied Physics

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“…This indicates that the bond scissions occur, which results in the ejection of PMMA monomers as well as COOCH 3 radicals from the surface irradiated with the water clus- ter ion beams. Thus, the sputtering of PMMA surfaces by the water cluster ion irradiation represents unique features, which are different from the ablation and scission of PMMA surfaces during monomer ion and photon deposition induced surface modification [19][20][21]. Figure 7 shows the micro-patterning of PMMA substrate demonstrated with water cluster ion beams.…”

Section: Resultsmentioning

confidence: 99%

Chemical Modification of Solid Surfaces at Nano-level by Water Cluster Ion Irradiation

Takaoka

Ichihashi

Ryuto

et al. 2011

e-J. Surf. Sci. Nanotechnol.

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We have investigated impact-process of water cluster ions on solid surfaces. Various kinds of substrates such as Si(100), SiO2 and PMMA substrates were irradiated by adjusting the acceleration voltage and the ion dose. The sputtered depth of these substrates increased with increase of the acceleration voltage, and it was 37 nm for Si, 49 nm for SiO2, and 2.9 µm for PMMA substrates, respectively at an acceleration voltage of 9 kV and an ion dose of 1.0×1016 ions/cm 2 . The sputtering yield calculated was 19 atoms per ion for Si and 13 molecules per ion for SiO2, which was approximately ten times larger than that for Ar monomer ion irradiation. The XPS measurement showed that the Si substrate surfaces sputtered at an ion dose of 1.0×1016 ions/cm 2 had an oxide layer such as SiOx. The oxide layer thickness increased with increase of the acceleration voltage, and it was approximately 10 nm at an acceleration voltage of 6 kV. On the other hand, at lower ion doses such as 1.0×1014 ions/cm 2 , the ratio of the sputtered depth of Si surface to SiO2 surface became approximately 10. This indicated that the chemical erosion such as silicon hydride occurred, resulting in enhancement of chemical sputtering of Si substrates. Furthermore, for the case of PMMA substrates, the chemical erosion of the substrate surfaces occurred probably through the exchange between CH3 and H radicals, and the chemical sputtering by the ejection of methacrylic acid molecule was enhanced. The surface roughness of PMMA substrates irradiated was less than 2 nm, and the smooth surface at the nano-level was obtained. In addition, micro-patterning was demonstrated with the water cluster ion beams on the PMMA substrates.

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“…Ablation is realized once a sufficient number of bonds are broken and there is adequate energy in the system to provide propel the cleaved material from the remaining substrate [16]. The efficiency of this process is influenced by factors such as the amount of chemistry present, the number of photons, the laser pulse width, and the penetration depth [16][17][18]. To assess the possible effects of dopants on the ablation process in PMMA, additional simulations were performed with dopant-like particles dispersed within the polymer matrix [19].…”

Section: Introductionmentioning

confidence: 99%

A technique to study doped ablation in polymethyl methacrylate using molecular dynamics simulation

Conforti

Prasad

Garrison

2009

Applied Surface Science

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Effects of thermal energy deposition on material ejection in poly(methyl methacrylate)

Cited by 16 publications

References 21 publications

On the role of chemical reactions in initiating ultraviolet laser ablation in poly(methyl methacrylate)

On the role of chemical reactions in initiating ultraviolet laser ablation in poly(methyl methacrylate)

Chemical Modification of Solid Surfaces at Nano-level by Water Cluster Ion Irradiation

A technique to study doped ablation in polymethyl methacrylate using molecular dynamics simulation

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