How material properties affect depth profiles – insight from computer modeling

Paruch, Robert J.; Postawa, Zbigniew; Garrison, Barbara J.

doi:10.1002/sia.5423

Cited by 4 publications

(5 citation statements)

References 18 publications

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“…The calculation protocol was described in detail previously . The coinage metal samples used in MD calculations were cuboid and measured from approximately 30 × 30 × 17 to 35 × 35 × 27 nm. In all cases, the (111) face was used.…”

Section: Methodsmentioning

confidence: 99%

“…We have therefore performed a number of MD simulations in which atomic and molecular solids were bombarded by Ar n clusters in order to disentangle the important physical elements of the “universal relation”. The substrate systems included in this study are the coinage metals Ag, Pt, Au, and Al, and the molecular solid octane . The elements come from three different rows of the periodic table and have a wide disparity of masses.…”

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confidence: 99%

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On Universality in Sputtering Yields Due to Cluster Bombardment

Paruch

Garrison

Mlynek

et al. 2014

J. Phys. Chem. Lett.

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Molecular dynamics simulations, in which atomic and molecular solids are bombarded by Arn (n = 60-2953) clusters, are used to explain the physics that underlie the "universal relation" of the sputtering yield Y per cluster atom versus incident energy E per cluster atom (Y/n vs E/n). We show that a better representation to unify the results is Y/(E/U0) versus (E/U0)/n, where U0 is the sample cohesive energy per atom or molecular equivalent, and the yield Y is given in the units of atoms or molecular equivalents for atomistic and molecular solids, respectively. In addition, we identified a synergistic cluster effect. Specifically, for a given (E/U0)/n value, larger clusters produce larger yields than the yields that are only proportional to the cluster size n or equivalently to the scaled energy E/U0. This synergistic effect can be described in the high (E/U0)/n regime as scaling of Y with (E/U0)(α), where α > 1.

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Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

On Universality in Sputtering Yields Due to Cluster Bombardment

Paruch

Garrison

Mlynek

et al. 2014

J. Phys. Chem. Lett.

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“…Molecular dynamics simulation is well suited for this purpose because it provides a mechanistic view of the modeled processes and allows for calculation of the parameters that are directly comparable with experimental values. The description of the computational methods were given elsewhere. − Of note is that we employed atomistic models of organic materials to properly model molecular fragmentation and internal excitation. These calculations are excessively time and computing resources consuming. , Therefore, for some substrates, especially β-carotene, a limited number of beam conditions have been calculated to confirm the observed trends.…”

Section: Introductionmentioning

confidence: 99%

Seduction of Finding Universality in Sputtering Yields Due to Cluster Bombardment of Solids

2015

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Universal descriptions are appealing because they simplify the description of different (but similar) physical systems, allow the determination of general properties, and have practical applications. Recently, the concept of universality has been applied to the dependence of the sputtering (ejection) yield due to energetic cluster bombardment versus the energy of the incident cluster. It was observed that the spread in data points can be reduced if the yield Y and initial projectile cluster kinetic energy E are expressed in quantities scaled by the number of cluster atoms n, that is, Y/n versus E/n. The convergence of the data points is, however, not perfect, especially when the results for molecular and atomic solids are compared. In addition, the physics underlying the apparent universal dependence in not fully understood. For the study presented in this Account, we performed molecular dynamics simulations of Arn cluster bombardment of molecular (benzene, octane, and β-carotene) and atomic (Ag) solids in order to address the physical basis of the apparent universal dependence. We have demonstrated that the convergence of the data points between molecular and atomic solids can be improved if the binding energy of the solid U0 is included and the dependence is presented as Y/(E/U0) versus (E/U0)/n. As a material property, the quantity U0 is defined per the basic unit of material, which is an atom for atomic solids and a molecule for molecular solids. Analogously, the quantity Y is given in atoms and molecules, respectively. The simulations show that, for almost 3 orders of magnitude variation of (E/U0)/n, there are obvious similarities in the ejection mechanisms between the molecular and atomic solids, thus supporting the concept of universality. For large (E/U0)/n values, the mechanism of ejection is the fluid flow from a cone-shaped volume. This regime of (E/U0)/n is generally accessed experimentally by clusters with hundreds of atoms and results in the largest yields. For molecular systems, a large fraction of the total energy E is consumed by internal excitation and molecular fragmentation, which are energy loss channels not present in atomic solids. For small (E/U0)/n values, the cluster deforms the surface and the ejection occurs from a ring-shaped ridge of the forming crater rim. This regime of (E/U0)/n is generally accessed experimentally by clusters with thousands of atoms and results in the smallest yields. For the molecular systems, there is little or no molecular fragmentation. The simulations indicate, however, that the representation which includes U0 as the only material property cannot be completely universal, because there are other material properties which influence the sputtering efficiency. Furthermore, neither the Y/n nor Y/(E/U0) representation includes the energy loss physics associated with molecular fragmentation in the high (E/U0)/n regime. The analysis of the universal concept implies for practical applications that if the objective of the experiment is large material removal, then the...

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“…The setup of the MD simulations was described in greater detail previously. 12,20,21 Rectangular boxes of Ag(111) samples, measuring approximately from 26 Â 26 Â 13 to 31 Â 31 Â 23 nm and containing approximately from 600 000 to 1 400 000 Ag atoms, were used depending on the projectile cluster size and impact energy. The interactions between the cluster atoms, Ar-Ar, and between the cluster atoms and the substrate atoms, Ar-Ag, were described by the Lennard-Jones potential splined with the KrC potential to account properly for high-energy collisions.…”

Section: Computationalmentioning

confidence: 99%

Physical basis of energy per cluster atom in the universal concept of sputtering

Paruch

Postawa

Garrison

2016

Journal of Vacuum Science &Amp; Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phen

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High-energy ions and atoms sputtered and reflected from a magnetron source for deposition of magnetic thin films J.The interpretation of the variables, scaled by the number of projectile cluster atoms n, in the universal relation of the sputtering yield Y versus incident energy E, that is, Y/n vs E/n, is not necessarily obvious. Following on previous works, the objective of this study is to elucidate the physical basis of the energy per atom variable E/n. The authors employ molecular dynamics simulations of Ar n cluster bombardment of Ag(111) metal samples for this study. The authors find that the energy per cluster atom quantity E/n is responsible for the fraction of the initial energy that is deposited in the solid, rather than energy per cluster mass E/m. The results show that even though there is an average loss of the energy for a cluster, each cluster atom loses a different fraction of its initial energy, thus yielding a distribution of energy loss by individual atoms. The analysis of these distributions indicates that the energy deposition process is more effective for clusters with higher E/n when compared to the clusters with lower E/n. This conclusion is supported by a visual analysis of the cluster bombardment event. The cluster atoms that lose most of their initial energy are those which split off from the cluster and penetrate into the bulk of the solid. Conversely, the atoms of the clusters with low E/n keep together during the interaction with the solid, and eventually reflect into the vacuum taking away a portion of the initial kinetic energy. In addition, the simulations indicate that the clusters of different sizes have the same distribution of energy loss for individual atoms if they have the same E/n, in other words, if the initial energy E is proportional to the cluster size n.

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How material properties affect depth profiles – insight from computer modeling

Cited by 4 publications

References 18 publications

On Universality in Sputtering Yields Due to Cluster Bombardment

On Universality in Sputtering Yields Due to Cluster Bombardment

Seduction of Finding Universality in Sputtering Yields Due to Cluster Bombardment of Solids

Physical basis of energy per cluster atom in the universal concept of sputtering

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