Modeling dynamic cluster SIMS experiments

Abstract

The underpinnings of two SIMS experimental findings are elucidated using the power of molecular dynamics to provide insight at the molecular level. First, the improvement of depth resolution for C 60 bombardment of Irganox delta layers and polymer layers using sample rotation is explained by molecular dynamics simulations of the repetitive bombardment of Ag surfaces with 20 keV Au 3 , C 60 , and Ar 872 at grazing angles of incidence with both single azimuthal angle and random azimuthal angles. Single azimuthal angle simulations at grazing angles show the formation of trenches and valleys parallel to the cluster beam form and are elongated with increasing incident angle. Cluster bombardment simulations with random azimuthal angles mimic sample rotation and show that under grazing angles of incidence, the surface is smoother because of the random impact angles preventing trench and valley formation. Second, depth profiles using C 60 at a 70 angle of incidence have been improved by co-bombardment with low energy Ar ions emitted at 33 from the C 60 beam and at a 45 incident angle from the surface. Molecular dynamics simulations of the bombardment of solid benzene with low energy Ar and 15 keV C 60 were used to show the depth of damage created during bombardment. For low kinetic energy (<200 eV), the damage caused by the Ar atom is in the same region as for the C 60 cluster. It is believed that for the experimental conditions used during co-bombardment, the Ar beam is breaking up the ridges created by the grazing C 60 beam.

Effect of Cosputtering and Sample Rotation on Improving C60+ Depth Profiling of Materials

“…Beside sample rotation, the cosputtering of a low-energy Ar + stream with C 60 + sputtering showed improved results for the generation of a smoother surface and suppression of carbon deposition compared to C 60 + sputtering alone. ,,− With the steadier sputtering process, multilayer organic LED devices could be profiled by the cosputtering technique, yet similar results could not be obtained with single C 60 + sputtering because of the decreased sputtering rate . This decreased sputtering rate also reflects the decaying intensity of the characteristic SIMS signals during prolonged C 60 + sputtering, while a relatively stable SIMS signal could be obtained with the optimized cosputter of 10 kV, 10 nA C 60 + and 0.2 kV, 300 nA Ar + . , MD computer simulation also provided insight that the C 60 bombardment creates an anisotropic roughened surface, while the Ar bombardment ameliorates it. , Furthermore, for lower Ar + energy and current, the effect of cosputtering is less pronounced. On the other hand, higher Ar + energy and current generate excessive damage to the remaining surface that cannot be removed by the C 60 + beam effectively; hence, signal intensity decayed.…”

“…Therefore, in this study, four sputtering methods, including C 60 + sputtering, C 60 + –Ar + cosputtering, C 60 + sputtering with sample rotation, and C 60 + –Ar + cosputtering with sample rotation, were compared for their effect on various model specimens. To compare the carbon deposition and penetration, a Si wafer, which is known to receive significant carbon deposition with C 60 + sputtering, , was utilized. To examine the sputter-induced surface roughness, bulk poly(methyl methacrylate) (PMMA), which is known to become extremely rough after C 60 + sputtering, was selected as the model target.…”

“…31,32 MD computer simulation also provided insight that the C 60 bombardment creates an anisotropic roughened surface, while the Ar bombardment ameliorates it. 36,37 Furthermore, for lower Ar + energy and current, the effect of cosputtering is less pronounced. On the other hand, higher Ar + energy and current generate excessive damage to the remaining surface that cannot be removed by the C 60 + beam effectively; hence, signal intensity decayed.…”

MD-Based Transport and Reaction Model for the Simulation of SIMS Depth Profiles of Molecular Targets

“…In recent years, secondary-ion mass spectrometry (SIMS), a well-established technique for the characterization of solid surfaces and thin films of both inorganic and organic materials, , has undergone a drastic evolution, related to the introduction of polyatomic primary ion beams, which boosted new perspectives in the analysis of organic materials and polymers. A big effort has been made to model the impact of primary cluster ions on the organic target by means of molecular dynamics (MD) simulations. − These simulations are used to model the phenomena involved in an individual cluster-target impact that typically occurs over a time scale of the order of a few tens of picoseconds . In some aspects, MD simulations can be considered as the theoretical counterpart of static-SIMS experiments.…”