Energetic ion bombardment of Ag surfaces by C60+ and Ga+ projectiles (original) (raw)
Related papers
Energy distributions of atomic and molecular ions sputtered by C60+ projectiles
Applied Surface Science, 2006
In the process of investigating the interaction of fullerene projectiles with adsorbed organic layers, we measured the kinetic energy distributions (KEDs) of fragment and parent ions sputtered from an overlayer of polystyrene (PS) oligomers cast on silver under 15 keV C 60 + bombardment. These measurements have been conducted using our TRIFT TM spectrometer, recently equipped with the C 60 + source developed by Ionoptika, Ltd. For atomic ions, the intensity corresponding to the high energy tail decreases in the following order: C + (E À0.4 ) > H + (E À1.5 ) > Ag + (E À3.5 ). In particular, the distribution of Ag + is not broader than those of Ag 2 + and Ag 3 + clusters, in sharp contrast with 15 keV Ga + bombardment. On the other hand, molecular ions (fragments and parent-like species) exhibit a significantly wider distribution using C 60 + instead of Ga + as primary ions. For instance, the KED of Ag-cationized PS oligomers resembles that of Ag + and Ag n + clusters. A specific feature of fullerene projectiles is that they induce the direct desorption of positively charged oligomers, without the need of a cationizing metal atom. The energy spectrum of these PS + ions is significantly narrower then that of Ag-cationized oligomers. For characteristic fragments of PS, such as C 7 H 7 + and C 15 H 13 + and polycyclic fragments, such as C 9 H 7 + and C 14 H 10 + , the high energy decay is steep (E À4 À E À8 ). In addition, reorganized ions generally show more pronounced high energy tails than characteristic ions, similar to the case of monoatomic ion bombardment. This observation is consistent with the higher excitation energy needed for their formation. Finally, the fraction of hydrocarbon ions formed in the gas phase via unimolecular dissociation of larger species is slightly larger with gallium than with fullerene projectiles. #
Sputtering of Ag under C 60 + and Ga + projectile bombardment
Applied Surface Science, 2004
Cluster ion bombardment often results in large secondary ion yield enhancements relative to atomic ion bombardment. The yields of neutral particles and secondary ions sputtered from a silver surface were investigated through experiments and molecular dynamics (MD) computer simulations. The results show that the neutral Ag yield produced by 15 keV C 60 þ bombardment is 5.6-fold higher than that found for 15 keV Ga þ bombardment, which is in agreement with simulations. The enhancement effect is observed to be about the same for both neutral species and their corresponding secondary ions. Experimental results also indicate that the Ag neutral species produced by C 60 þ bombardment have emission velocity distributions that maximize at much lower values than those observed by Ga þ bombardment, suggesting the presence of non-linear collision cascades. #
Analytical Chemistry, 2003
The mechanism of enhanced desorption initiated by 15-keV C 60 cluster ion bombardment of a Ag single crystal surface is examined using molecular dynamics computer simulations. The size of the model microcrystallite of 165 000 atoms and the sophistication of the interaction potential function yields data that should be directly comparable with experiment. The C 60 model was chosen since this source is now being used in secondary ion mass spectrometry experiments in many laboratories. The results show that a crater is formed on the Ag surface that is ∼10 nm in diameter, a result very similar to that found for Au 3 bombardment of Au. The yield of Ag atoms is ∼16 times larger than for corresponding atomic bombardment with 15-keV Ga atoms, and the yield of Ag 3 is enhanced by a factor of 35. The essential mechanistic reasons for these differences is that the C 60 kinetic energy is deposited closer to the surface, with the deeply penetrating energy propagation occurring via a nondestructive pressure wave. The numbers predicted by the model are testable by experiment, and the approach is extendable to include the study of organic overlayers on metals, a situation of growing importance to the SIMS community.
MeV atomic ion sputtering of fullerenes: a radial velocity distribution study
International Journal of Mass Spectrometry and Ion Processes, 1996
We report swift heavy-ion-induced sputtering of carbon cluster ions from fullerene-containing and polymer thin films (pure C60, fluorinated C60(C60Fm, 24 < m < 48), blends of pure C60 with polystyrene (PS/Cro), and poly(vinylidene fluoride) (PVDF)). Intact C60 molecular ions and their fragments (C60-2,, 1 < n < 5), together with a series of higher mass carbon cluster ions (C60+2,, n from 1 to at least 100) are ejected as a result of the interaction of an individual MeV ion with the various targets. The intensity patterns of the higher mass carbon cluster ion series depend on the type of bombarded target. For pure C60 targets the high mass clusters have higher yields around multiples of 60 (Ci20 and C180). In the case of PS/C60, C60F m and PVDF targets, the cluster intensity decreases continuously with increasing cluster size. Measurements of the initial radial velocity distributions of such cluster ions have been performed in a reflectron time-offlight mass spectrometer, using 72.3 MeV 127113+ as primary ions. The radial velocity distributions of the sputtered ions are indicative of the processes of their formation: condensation of hot carbon atom "gas" in the core of the ion tracks versus coalescence of C60 molecules, most probably in the gas phase.
Microscopic Insights into the Sputtering of Ag{111} Induced by C60 and Ga Bombardment
The Journal of Physical Chemistry B, 2004
Molecular dynamics computer simulations have been utilized to compare the differences in the mechanism of sputtering of Ag{111} by kiloelectronvolt Ga and C 60 projectiles. The calculated kinetic energy distributions of Ag monomers and Ag 2 dimers compare favorably with experimental results. The damage caused by the C 60 particle left in the sample is less than the depth of material that the next impinging C 60 particle would remove, thus supporting the preliminary experimental observations that molecular depth profiling is possible with C 60 projectile beams.
Ejection of molecular clusters from ion-bombarded surfaces
Vacuum, 1980
We have modeled, using classical dynamics, the dissipation of momentum of a 600-eV Ar+ ion as it bombards a metal single crystal. The model correctly predicts relative sputtering yields, secondary particle energy distributions, and angular distributions. In addition, it also gives considerable insight into the mechanism of molecular cluster• formation. For the three low index faces of copper, for example, the observed dimers, trimers, and higher multimers form over the surface but within interaction range of the solid. The clusters show rearrangement of their constituent atoms from their original surface positions, but do arise from a localized region of radius ~5 A. We have also examined oxygen atoms and CO molecules adsorbed on copper and nickel, respectively. For the chemisorbed O atoms, the clusters Cu 2 , CuO, 0 2 , Cu 3 , Cu 2 O, CuO 2 , and 0 3 have all been observed to form over the surface, analogous to the clean metal case. For CO, however, most of the ejection occurs molecularly due to the strong carbon-oxygen bond (~ 11 eV). The formation of NiCO and Ni 2 CO clusters occurs over the surface.
An experimental and theoretical view of energetic C 60 cluster bombardment onto molecular solids
Surface and Interface Analysis, 2013
Recent experimental measurements and calculations performed by molecular dynamics computer simulations indicate, for highly energetic C 60 primary ions bombarding molecular solids, the emission of intact molecules is unique. An energy-and angle-resolved neutral mass spectrometer coupled with laser photoionization techniques was used to measure the polar angle distribution of neutral benzo[a]pyrene molecules desorbed by 20-keV C 60 + primary ions and observed to peak at off-normal angles integrated over all possible emission energies. Similarly, computer simulations of 20-keV C 60 projectiles bombarding a coarse-grained benzene system resulted in calculations of nearly identical polar angle distributions. Upon resolving the measured and calculated polar angle distributions, sputtered molecules with high kinetic energies are the primary contributors to the off-normal peak. Molecules with low kinetic energies were measured and calculated to desorb broadly peaked about the surface normal. The computer simulations suggest the fast deposition of energy from the C 60 impact promotes the molecular emission by fluid-flow and effusive-type motions. The signature of off-normal emission angles is unique for molecules because fragmentation processes remove molecules that would otherwise eject near normal to the surface. Experimental measurements from a Ni {001} single crystal bombarded by 20-keV C 60
Collisions of fullerenes with surfaces at the 5–100 eV impact energy range
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2002
In this paper, we will present recent studies on the scattering dynamics of neutral and charged fullerenes from surfaces at the hyperthermal impact energy range. The energy range for the neutral colliders is 5-50 eV (aerodynamic acceleration in seeded beams) while with negatively charged ions we extend it up to 100 eV. The smooth overlap of the two energy regions using neutral and charged C 60 is demonstrated. The translational energy of the scattered particles (both C 60 0 and C 60 −) was found to scale linearly with impact energy for both near normal and near grazing scattering angles. Kinetic energy losses varied with scattering angle from 15% (near normal incidence) to 40% (near grazing incidence). Analysis of the results in terms of simple kinematical models demonstrates nearly complete decoupling between normal and tangential energy losses. Furthermore, the accuracy of our energy measurements (90.1 eV) enables us to extract, for the first time, molecule-surface binding energies from kinetic energy losses measured in molecular beam-surface scattering experiments. We compare this dynamically determined value with the equilibrium one as measured by temperature-programmed desorption experiments. The yield of C 60 − negative ions following scattering of hyperthermal neutral C 60 molecules from a graphite monolayer on nickel surface (Ni/C) was measured as a function of impact energy. An increase of two orders of magnitude was observed going from 4 to 42 eV. Energy and angle distributions of both scattered ions (C 60 −) and neutrals (C 60 0) were measured and compared for this impact energy range. The C 60 − ion yield was found to obey an exponential dependence on the inverse of the outgoing normal velocity component similar to that observed before for atom-surface collisions at much higher energies. The shifts observed between the angular and energy distributions maxima of the neutral and negative ion could be analysed and explained in terms of image charge effects on the outgoing trajectory (deflection) and exit energy (retardation) of the C 60 −. A large critical distance for ion formation was extracted from the results. The charge transfer dynamics is consistent with final charge state exclusively determined along the exit trajectory.
International Journal of Mass Spectrometry, 2019
The formation probability of secondary ions released from a metal surface under bombardment with a 20-keV cluster ion beam is investigated using combined time-of-flight secondary ion and neutral mass spectrometry (Tof-SIMS/SNMS) experiments. The emitted neutral atoms and clusters are post-ionized after their ejection using strong-field photoionization in an intense short infrared laser pulse. Comparing the secondary ion signal with that of the corresponding neutral particles, the ionization probability of sputtered indium atoms and In n clusters with n = 2-4 is determined. The results are compared between two different projectile cluster ions, namely i) C 60 + and ii) Ar n + with n∼1000. It is shown that the ionization probability obtained with the fullerene cluster is by roughly a factor 4 larger than that obtained with the rare gas cluster, thereby indicating that there is no nonlinear enhancement of the transient electronic excitation generated by a cluster impact.
Journal of Applied Physics
We compare various sputtering simulation methods to experimental results in both the low energy (<1 keV) and high energy (≥1 keV) impact regimes for argon ions impacting a pure copper substrate at normal incidence. Our results indicate that for high energy impacts, both binary collision approximation (BCA) and molecular dynamics methods can be used to generate reasonable predictions for the yield and energy distribution of the sputtered atoms. We also find reasonable agreement between the theoretical and experimental results down to impact energies of 600 eV. However, at 200 eV impact energies, significant discrepancies appear between the experimental and theoretical ejecta energy distributions in the peak position, the width of the energy distribution, and the magnitude of the high energy tail. These discrepancies appear to arise from the experimental results being only for atoms sputtered normal to the substrate surface, whereas the theoretical results are integrated over all 2π solid angles above the surface. Using the BCA code SDTrimSP and limiting the results to only atoms emitted within ±15°of the surface normal brings theory and experiment into reasonable agreement. These results suggest that for low energy impacts, the energy distribution of sputtered atoms is highly dependent on the emission angle of the ejecta.