Molecular Dynamics Study of Fullerite Cross-Linking under keV C₆₀ and Ar_n Cluster Bombardment

Abstract

Molecular dynamics computer simulations are used to elucidate the cross-linking processes induced by 0.6− 50 keV C 60 and Ar n cluster bombardment in a C 60 fullerite solid sample. The obtained results indicate the presence of a "chemical effect" when C 60 projectile is used. Namely, the bombarding C 60 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 C 60 very similar to the case of the Ar 18 bombardment. For Ar n 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.

Re-print of “Sputtering of polymers by keV clusters: Microscopic views of the molecular dynamics”

“…For Ar n cluster bombardment, the MD study also shows that the curve of the number of crosslinks as a function of the energy per atom in the projectile has a similar shape as those reported for the sputtered masses in Fig. 2, with a strongly nonlinear evolution below 1 eV and a quasi-linear region at higher energy [69]. These simulations nicely explain the different behavior of C 60 and Ar n cluster for the depth-profiling of polystyrene [70] and materials involving fullerene molecules [57,71].…”

Fundamental aspects of Arn+ SIMS profiling of common organic semiconductors

“…likewise predicted an effect of the cluster size on cross‐linking in fullerite solids, which was found, however, to be less influential than the initial energy/atom. These findings, both experimentally and theoretically, point out that all parameter of the projectile, that is, n , E , and E / n have an effect on the chemical/physical processes initiated in the organic molecule, hence determine secondary ion yields and sputtering efficiency.…”

“…Whereas with 5 keV Ar 500 , a decent quality depth profile is obtained (left profile), a higher cluster energy (20 keV) and larger cluster size (Ar 2000 ) results in an immediate degradation of the profile and sputter efficiency (right profile). The MD simulations in Ref . likewise predicted an effect of the cluster size on cross‐linking in fullerite solids, which was found, however, to be less influential than the initial energy/atom.…”

“…These chemical modifications are, however, less pronounced on the pure polymer film, suggesting that the fullerene is more prone to structural changes than the polymer. Indeed, molecular dynamics (MD) simulations and experimental observation have shown that fullerites exhibit a strong tendency toward cross‐linking upon Ar n + beam exposure. In general, bond scission and cross‐linking in fullerite solids was found to increase with increasing E / n .…”

“…Indeed, molecular dynamics (MD) simulations and experimental observation have shown that fullerites exhibit a strong tendency toward cross‐linking upon Ar n + beam exposure. In general, bond scission and cross‐linking in fullerite solids was found to increase with increasing E / n . This general trend agrees well with the experimentally observed drop in the characteristic ion signals (Fig.…”