Computed Molecular Depth Profile for C₆₀ Bombardment of a Molecular solid

Abstract

Molecular dynamics (MD) simulations have been performed for 10 keV C60 bombardment of an octane molecular solid at normal incidence. The results are analyzed using the steady-state statistical sputtering model (SS-SSM) to understand the nature of molecular motions and to predict a depth profile of a δ-layer. The octane system has sputtering yield of ~150 nm(3) of which 85% is in intact molecules and 15% is fragmented species. The main displacement mechanism is along the crater edge. Displacements between layers beneath the impact point are difficult because the nonspherically shaped octane molecule needs a relatively large volume to move into and the molecule needs to be aligned properly for the displacement. Since interlayer mixing is difficult, the predicted depth profile is dominated by the rms roughness and the large information depth because of the large sputtering yield.

Computer simulations of sputtering and fragment formation during keV C60 bombardment of octane and β‐carotene

“…The coloring scheme (from light/yellow to dark/red) represents the amount of a vertical relocation of organic material. It is interesting to note that while a significant amount of material is removed from both solids as indicated by large dimensions of the formed craters, the amount of the vertical relocation of organic material that remains in the solids is small, and it is mainly restricted to the volume near the walls of the crater . Molecular relocation is larger in β ‐carotene as compared with octane because of a more open geometrical structure of this solid.…”

“…, almost all of the fragments are created in the energized zone located in vicinity of the projectile impact. Such behavior has been reported previously . However, as also shown in Fig.…”

“…Computer studies also indicate that during cluster bombardment, most of the created fragments are ejected. Such a self‐cleaning mechanism combined with a lower fragmentation factor associated with a lower kinetic energy per atom is believed to explain why certain organic materials can be depth profiled with cluster ions . The nature of this self‐cleaning is, however, still not fully explained.…”

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

“…This is in sharp contrast with keV atoms such as Ga, which implant deeper in the solid, inducing stochastic collision cascades that are rather inefficient for sputtering. Later on, the same research teams tackled the study of depth profiling by clusters, first for silver [31] and, recently, for an octane crystal, using a combination of MD simulations and a statistical sputtering model [32]. Concerning massive solvent clusters, the fragmentation of fast water nanodroplets on inorganic substrates and the impact desolvation mechanism of IDEM were also explained by MD [33][34][35].…”

How material properties affect depth profiles – insight from computer modeling

“…Thus far, we performed numerous MD simulations for atomistic and molecular solids and interpreted the results with the SS-SSM. [7,[9][10][11][12] In this paper, we demonstrate how the SS-SSM formalism is used to explain the influence of sample material properties on depth profiling quality. The analysis is based on MD results of repetitively bombarded coinage metal samples by a keV C 60 cluster beam.…”