Depth profiling by cluster projectiles as seen by computer simulations

Abstract

Molecular dynamics computer simulations are used to probe the development of the surface morphology and the processes that determine the depth resolution in depth profiling experiments performed by secondary ion and neutral mass spectrometry (SIMS/SNMS). The Ag(111) surface is irradiated by an impact of 20-keV Au 3 , C 60 and Ar 872 clusters that represent a broad range of cluster projectiles used in SIMS/SNMS experiments. Improvements in the simulation protocol including automation and optimal sample shape allow for at least 1000 consecutive impacts for each set of initial conditions. This novel approach allows to shrink the gap between single-impact simulations and real experiments in which numerous impacts are used.

Cluster TOF‐SIMS imaging as a tool for micrometric histology of lipids in tissue

“…Moreover, these works motivate the future use of high energy cluster primary ions for SIMS, since an enhanced molecular sputtering yield was observed at beam energies of ∼25 keV/atom. This has also been demonstrated and explained by molecular dynamics simulation (Garrison & Postawa, ; Postawa et al, ).…”

“…This representation helps to measure the effect of the sputtering process and permits to classify cluster ion beams. This type of work was done by Postawa et al for C 60 , Au 3 , and Ar 872 projectiles, and showed the differences of size of the crater, length and depth, produced by these three different ion beams (Postawa et al, ). This study concludes to the possible limit of the damage induced to the deeper layers of a sample, by using argon clusters but with a larger crater than in the case of gold clusters or C 60 ions.…”

“…Among the primary ion beam parameters in a TOF‐SIMS instrument, the most important is the damage cross‐section and it must be measured to prove the analytically useful molecular ion yield. Plots of molecular secondary ions as a function of primary ion dose allows intercomparison of the secondary molecular ion yield between cluster type (Tempez et al, ; Novikov et al, ; Touboul et al, ) which often guides and motivates computational studies (Postawa et al, ). This representation helps to measure the effect of the sputtering process and permits to classify cluster ion beams.…”

Modeling and simulation of dynamical contact of asperities between flat rough surfaces

“…With the statistical parameters, automatic fitting with 3D microscopic surface topography is available, as shown in Figure 10(b). For the testing rectangular surface, the 3D topographical height parameters (the average height m and the standard deviation s) and feature parameters (the average radius of the asperities R and the distribution density of asperities D) are respectively 0.6107 mm, 0.7607 mm, 85.4 mm, and 111.6690 mm 22 . Based on these topography parameters, the following simulation experiments a-f with single variable were designed to analyze the influence of each factor (as shown in equation (16)) on the number of asperity contacts between two rough planes, wherein the topographical parameters (R, D, and s) of the upper and lower surfaces are the same.…”

Molecular depth profiling

“…Even so, using a clever scheme whereby non-overlapping trajectories can be computed simultaneously with parallel processors, considerable progress has been made with multi-hit computer simulations. Postawa and coworkers have been able to show that the material pushed out of an impact crater bottom leads to lateral motion on the nm scale (17). As this material interacts with neighboring impacts, topography begins to be observed.…”