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  • 1.
    Czerwinski, Bartlomiej
    et al.
    Universite Catholique de Louvain, Institute of Condensed Matter and Nanosciences - Bio and Soft Matter, Louvain-la-Neuve.
    Delcorte, Arnaud
    Universite Catholique de Louvain, Institute of Condensed Matter and Nanosciences - Bio and Soft Matter, Louvain-la-Neuve.
    Molecular dynamics study of fullerite cross-linking under keV C 60 and Arn cluster bombardment2013Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 7, s. 3595-3604Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Molecular dynamics computer simulations are used to elucidate the cross-linking processes induced by 0.6-50 keV C60 and Arn cluster bombardment in a C60 fullerite solid sample. The obtained results indicate the presence of a "chemical effect" when C 60 projectile is used. Namely, the bombarding C60 delivers additional, highly reactive, radicals which interact with the atoms of the fullerite sample, increasing the efficiency of the cross-linking process. The omission of those interactions in the analysis makes the C60 very similar to the case of the Ar18 bombardment. For Arn cluster bombardment, the initial energy per atom in the projectile is the parameter which has the predominant influence on the cross-linking process. Furthermore, a relationship between the energy thresholds for fragmentation of the target molecules and cross-linking initiation and the size of the Ar clusters is observed. Both of these thresholds decrease with increasing size of the projectile.

  • 2.
    Czerwinski, Bartlomiej
    et al.
    Universite Catholique de Louvain, Institute of Condensed Matter and Nanosciences - Bio and Soft Matter, Louvain-la-Neuve.
    Postawa, Zbigniew
    Smoluchowski Institute of Physics, Jagiellonian University, ul. Reymonta 4, 30-059 Krakow.
    Garrison, Barbara J.
    Department of Chemistry, Pennsylvania State University.
    Delcorte, Arnaud
    Universite Catholique de Louvain, Institute of Condensed Matter and Nanosciences - Bio and Soft Matter, Louvain-la-Neuve.
    Molecular dynamics study of polystyrene bond-breaking and crosslinking under C60 and Arn cluster bombardment2013Ingår i: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, s. 22-26Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Molecular dynamics computer simulations are used to elucidate the bond-breaking and crosslinking processes induced by 2.5 keV C60 and Arn cluster bombardment in an amorphous sec-butyl-terminated polystyrene sample. The obtained results indicate that replacement of C 60 by Ar18 or Ar60 projectiles leads to the decrease of the number of broken bonds and, hence, to the decrease of formation of new intra- and intermolecular (crosslinking) bonds. When the number of atoms in the Arn cluster is increased from 60 to 250 or more, the total number of broken bonds and the total number of newly created bonds reach a zero value. Additional comparison to the case of a fullerite crystal reveals that the change of material properties leads to almost 7.5-fold reduction of the efficiency of the crosslinking process.

  • 3.
    Delcorte, Arnaud
    et al.
    Universite Catholique de Louvain, Institute of Condensed Matter and Nanosciences - Bio and Soft Matter, Louvain-la-Neuve.
    Cristaudo, Vanina
    Universite Catholique de Louvain, Institute of Condensed Matter and Nanosciences - Bio and Soft Matter, Louvain-la-Neuve.
    Lebec, V.
    Universite Catholique de Louvain, Institute of Condensed Matter and Nanosciences - Bio and Soft Matter, Louvain-la-Neuve.
    Czerwinski, Bartlomiej
    Universite Catholique de Louvain, Institute of Condensed Matter and Nanosciences - Bio and Soft Matter, Louvain-la-Neuve.
    Sputtering of polymers by keV clusters: Microscopic views of the molecular dynamics2014Ingår i: International Journal of Mass Spectrometry, ISSN 1387-3806, E-ISSN 1873-2798, Vol. 370, s. 29-38Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This article reviews the results of molecular dynamics simulations of cluster sputtering of hydrocarbon polymers obtained in the last few years and expand them with unpublished data of Ar cluster bombardment. The targets are molecular solids of linear hydrocarbons, polyethylene and polystyrene, including a polyethylene substrate decorated with adsorbed globular macromolecules. The projectiles are (hydro)carbon and Arn clusters, from small to massive, as well as Bin and Au400 clusters. The study focuses on the dynamics of cratering and sputtering, using a coarse-grained representation of the samples, on the study of molecular fragmentation, crosslinking and free H formation, using a fully atomistic model, and on the conditions of desorption of macromolecules by massive clusters. The results explain the similarities and differences between several cluster types and sizes and, to a large extent, the sputtering yields of Arn clusters and their 'universal' dependence on the scaled cluster energy, as observed in the experiments. They also demonstrate the reduction of sample fragmentation and crosslinking when going to larger clusters and the incidence angle dependence of intact macromolecule emission. Recent experimental validations obtained in our laboratory are also introduced and comparisons with data obtained by other groups are discussed in order to present a more complete picture of the physics of cluster bombardment of organic solids and polymers.

  • 4.
    Delcorte, Arnaud
    et al.
    Universite Catholique de Louvain, Institute of Condensed Matter and Nanosciences - Bio and Soft Matter, Louvain-la-Neuve.
    Czerwinski, Bartlomiej
    Universite Catholique de Louvain, Institute of Condensed Matter and Nanosciences - Bio and Soft Matter, Louvain-la-Neuve.
    Cristaudo, Vanina
    Universite Catholique de Louvain, Institute of Condensed Matter and Nanosciences - Bio and Soft Matter, Louvain-la-Neuve.
    Lebec, V.
    Universite Catholique de Louvain, Institute of Condensed Matter and Nanosciences - Bio and Soft Matter, Louvain-la-Neuve.
    Re-print of "Sputtering of polymers by keV clusters: Microscopic views of the molecular dynamics"2015Ingår i: International Journal of Mass Spectrometry, ISSN 1387-3806, E-ISSN 1873-2798, Vol. 377, nr 1, s. 580-590Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This article reviews the results of molecular dynamics simulations of cluster sputtering of hydrocarbon polymers obtained in the last few years and expand them with unpublished data of Ar cluster bombardment. The targets are molecular solids of linear hydrocarbons, polyethylene and polystyrene, includingapolyethylene substrate decorated with adsorbed globular macromolecules. The projectiles are (hydro)carbon and Arn clusters, from small tomassive, as well as Bin and Au400 clusters. The study focuses on the dynamics of cratering and sputtering, using a coarse-grained representation of the samples, on the study ofmolecular fragmentation, crosslinking and freeHformation, usingafully atomistic model, and on the conditions of desorption of macromolecules by massive clusters. The results explain the similarities and differences between several cluster types and sizes and, to a large extent, the sputtering yields of Arn clusters and their 'universal' dependence on the scaled cluster energy, as observed in the experiments. They also demonstrate the reduction of sample fragmentation and crosslinking when going to larger clusters and the incidence angle dependence of intact macromolecule emission. Recent experimental validations obtained in our laboratory are also introduced and comparisons with data obtained by other groups are discussed in order to present a more complete picture of the physics of cluster bombardment of organic solids and polymers.

  • 5.
    Verkhoturov, Stanislav V.
    et al.
    Department of Chemistry, Texas A&M University.
    Czerwinski, Bartlomiej
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Verkhoturov, Dmitriy S.
    Department of Chemistry, Texas A&M University, College Station, Texas 77843-3144, USA.
    Geng, Sheng
    Department of Chemistry, Texas A&M University, College Station, Texas 77843-3144, USA.
    Delcorte, Arnaud
    nstitute of Condensed Matter and Nanosciences - Bio and Soft Matter (IMCN/BSMA), Universit ́ e Catholique de Louvain, 1 Croix du Sud, B-1348 Louvain-la-Neuve, Belgium.
    Schweikert, Emile A.
    Department of Chemistry, Texas A&M University, College Station, Texas 77843-3144, USA.
    Ejection-ionization of molecules from free standing graphene2017Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, nr 8, artikel-id 084308Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the first data on emission of C60stimulated by single impacts of 50 keV C602+on the self-assembled molecular layer of C60deposited on free standing 2 layer graphene. The yield,Y, of C60emitted in the transmission direction is 1.7%. To characterize the ejection and ionization of molecules,we have measured the emission of C60from the surface of bulk C60(Y= 3.7%) and from a singlelayer of C60deposited on bulk pyrolytic graphite (Y= 3.3%). To gain insight into the mechanism(s) ofejection, molecular dynamic simulations were performed. The scenario of the energy deposition andejection of molecules is different for the case of graphene due to the confined volume of projectile-analyte interaction. In the case of 50 keV C602+impacts on graphene plus C60, the C atoms of theprojectile collide with those of the target. The knocked-on atoms take on a part of the kinetic energyof the projectile atoms. Another part of the kinetic energy is deposited into the rim around the impactsite. The ejection of molecules from the rim is a result of collective movement of the molecules andgraphene membrane, where the membrane movement provides the impulse for ejection. The efficientemission of the intact molecular ions implies an effective ionization probability of intact C60. Theproposed mechanism of ionization involves the tunneling of electrons from the vibrationally exitedarea around the hole to the ejecta

  • 6.
    Verkhoturov, Stanislav V.
    et al.
    Department of Chemistry, Texas AandM University, College Station.
    Geng, Sheng
    Department of Chemistry, Texas AandM University, College Station.
    Czerwinski, Bartlomiej
    Universite Catholique de Louvain, Institute of Condensed Matter and Nanosciences - Bio and Soft Matter, Louvain-la-Neuve.
    Young, Amanda E.
    Materials Characterization Facility, Texas AandM University.
    Delcorte, Arnaud
    Universite Catholique de Louvain, Institute of Condensed Matter and Nanosciences - Bio and Soft Matter, Louvain-la-Neuve.
    Schweikert, Emile A.
    Department of Chemistry, Texas AandM University, College Station.
    Single impacts of keV fullerene ions on free standing graphene: Emission of ions and electrons from confined volume2015Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 143, nr 16, artikel-id 164302Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the first data from individual C60 impacting one to four layer graphene at 25 and 50 keV. Negative secondary ions and electrons emitted in transmission were recorded separately from each impact. The yields for Cn - clusters are above 10% for n ≤ 4, they oscillate with electron affinities and decrease exponentially with n. The result can be explained with the aid of MD simulation as a post-collision process where sufficient vibrational energy is accumulated around the rim of the impact hole for sputtering of carbon clusters. The ionization probability can be estimated by comparing experimental yields of Cn - with those of Cn 0 from MD simulation, where it increases exponentially with n. The ionization probability can be approximated with ejecta from a thermally excited (3700 K) rim damped by cluster fragmentation and electron detachment. The experimental electron probability distributions are Poisson-like. On average, three electrons of thermal energies are emitted per impact. The thermal excitation model invoked for Cn - emission can also explain the emission of electrons. The interaction of C60 with graphene is fundamentally different from impacts on 3D targets. A key characteristic is the high degree of ionization of the ejecta

  • 7.
    Verkhoturov, Stanislav V.
    et al.
    Department of Chemistry, Texas A&M University, College Station, Texas, USA.
    Gołuński, Mikołaj
    Department of Physics, Jagiellonian University, Kraków, Poland.
    Verkhoturov, Dmitriy S.
    Department of Chemistry, Texas A&M University, College Station, Texas, USA.
    Czerwinski, Bartlomiej
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Eller, Michael J.
    Department of Chemistry, Texas A&M University, College Station, Texas, USA.
    Geng, Sheng
    Department of Chemistry, Texas A&M University, College Station, Texas, USA.
    Postawa, Zbigniew
    Department of Physics, Jagiellonian University, Kraków, Poland.
    Schweikert, Emile A.
    Department of Chemistry, Texas A&M University, College Station, Texas, USA.
    Hypervelocity cluster ion impacts on free standing graphene: Experiment, theory, and applications2019Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, nr 16, artikel-id 160901Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present results from experiments and molecular dynamics (MD) simulations obtained with C60 and Au400 impacting on free-standing graphene, graphene oxide (GO), and graphene-supported molecular layers. The experiments were run on custom-built ToF reflectron mass spectrometers with C60 and Au-LMIS sources with acceleration potentials generating 50 keV C2+ 60 and 440–540 keV Au4+ 400. Bombardmentdetection was in the same mode as MD simulation, i.e., a sequence of individual projectile impacts with separate collection/identification of the ejecta from each impact in either the forward (transmission) or backward (reflection) direction. For C60 impacts on single layer graphene, the secondary ion (SI) yields for C2 and C4 emitted in transmission are ∼0.1 (10%). Similar yields were observed for analyte-specific ions from submonolayer deposits of phenylalanine. MD simulations show that graphene acts as a trampoline, i.e., they can be ejected without destruction. Another topic investigated dealt with the chemical composition of free-standing GO. The elemental composition was found to be approximately COH2. We have also studied the impact of Au400 clusters on graphene. Again SI yields were high (e.g., 1.25 C /impact). 90–100 Au atoms evaporate off the exiting projectile which experiences an energy loss of ∼72 keV. The latter is a summation of energy spent on rupturing the graphene, ejecting carbon atoms and clusters and a dipole projectile/hole interaction. The charge distribution of the exiting projectiles is ∼50% neutrals and ∼25% either negatively or positively charged. We infer that free-standing graphene enables detection of attomole to zeptomole deposits of analyte via cluster-SI mass spectrometry

  • 8.
    Zarshenas, Mohammad
    et al.
    Institute of Condensed Matter and Nanosciences - Bio & Soft Matter (IMCN/BSMA), Université Catholique de Louvain.
    Moshkunov, Konstantin
    Institute of Condensed Matter and Nanosciences - Bio & Soft Matter (IMCN/BSMA), Université Catholique de Louvain.
    Czerwinski, Bartlomiej
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Leyssens, Tom
    Institute of Condensed Matter and Nanosciences - Molecules, Solids and Reactivity (IMCN/MOST) Université Catholique de Louvain.
    Delcorte, Amaud
    Institute of Condensed Matter and Nanosciences - Bio & Soft Matter (IMCN/BSMA), Université Catholique de Louvain.
    Molecular Dynamics Simulations of Hydrocarbon Film Growth from Acetylene Monomers and Radicals: Effect of Substrate Temperature2018Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, nr 27, s. 15252-15263Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In an attempt to rationalize the mechanisms occurring during plasma polymerization of acetylene, classical molecular dynamics (MD) computer simulations investigating the deposition and reaction of a mixed gas of acetylene molecules and radicals on the Ag(111) substrate were performed for a wide range of substrate temperatures. Prior to that, this article establishes a methodology for film deposition and identifies the appropriate potentials for hydrocarbons by comparison with electronic calculations using the density functional theory (DFT). Based on this preliminary study, simulations of films growth are carried out at different temperatures using the REBO potential. Our results show that the rates of creation of new C-C and C-H bonds are higher at the beginning of the film growth when the substrate is still exposed, than when it is covered with polymeric chains, and these initial reaction rates are proportional to temperature. The analysis of the hybridization of carbon atoms in the films shows that the substrate temperature increase leads to the formation of coatings containing more carbon atoms in the sp2 and sp3 configurations and less in the sp configuration with sp2 becoming dominant at high temperatures. We establish a polymerization-connectivity formalism that describes the structural transformation of the film during the deposition on the basis of each atom hybridization and bonding. Within this formalism the evolution of the polymerization and the connection character of the polymers is observed and discussed.

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