Molecular dynamics bombardment

Abrams C F and Graves D B 1998 Energetic Ion bombardment of SIOj surfaces molecular dynamics simulations J. Vac. Sc/. Technol. A 16 3006-19... 

Molecular dynamics simulations yield an essentially exact (within the confines of classical mechanics) method for observing the dynamics of atoms and molecules during complex chemical reactions. Because the assumption of equilibrium is not necessary, this technique can be used to study a wide range of dynamical events which are associated with surfaces. For example, the atomic motions which lead to the ejection of surface species during keV particle bombardment (sputtering) have been identified using molecular dynamics, and these results have been directly correlated with various experimental observations. Such simulations often provide the only direct link between macroscopic experimental observations and microscopic chemical dynamics. 

Figure 7.44. Molecular dynamics simulation of the ion bombardment of a Ag crystal surface with a 15 keV Ga+ beam, and a 15 keV Cgo atomic cluster beattL The Cgo beam results in a larger crater and more material removed from the surface. In contrast, the Ga+ beam results in a destructive effect at greater sample depths, without successful sputtering of the sample. Reproduced with permission from Winograd, N. Anal. Chem. 2005, 77, 142A. Copyright 2005 American Chemical Society.

By using molecular dynamics with a reactive force field [28-30] as implemented in LAMMPS [31], we were able to analyze the side effects of ion bombardment on a sihca-supported single waUed carbon nanotube. A reactive force field enables simulating the breaking and formation of covalent bonds. Apart from observing the effective removal of carbon atoms, we found the possibility of undesired effects on the carbon nanotube sidewall, on the substrate as well as at the interface between the carbon nanotube and the substrate (Fig. 7.1). We highlight the main types of atomic defect found on carbon nanotube sidewall, vacancy defects and chemisorption. 

Restrepo OA, Delcorte A (2011) Molecular dynamics study of metal-organic samples bombarded by kiloelectronvolt projectiles. Surf Interface Anal 43 70. doi 10.1002/sia.3411... 

Postawa Z, Czerwinski B, Szewczyk M, Smiley E, Winograd N, Garrison B (2003) Enhancement of sputtering yields due to C-60 versus Ga bombardment of Ag lll as explored by molecular dynamics simulations. Anal Chem 75(17) 4402 1407... 

Taguchi M, Hamaguchi S (2006) Molecular dynamics study on At ion bombardment effects in amorphous Sio2 deposition processes. J Appl Phys 100(12) 123305... 

A classical dynamics model is used to investigate nuclear motion in solids due to bombardment by energetic atoms and ions. Of interest are the mechanisms of ejection and cluster formation both of elemental species such as Nin and Arn and molecular species where we have predicted intact ejection of benzene-CgHg, pyridine-Cs N, napthalene-CigHg, bipheny 1-0 2 10 an[Pg.43]

The classical dynamics treatment for CO on Ni 001) yields results which are in qualitative agreement with these findings. Approximately 80% of the CO molecules that eject are found to eject intact, without rearrangement. The formation of NiCO and NuCO clusters have been observed to form over the surface via reactions of Ni atoms and CO molecules. No evidence has been found for NiC and NiO clusters in the calculations. The ion bombardment approach, then, is a very sensitive probe for distinguishing between molecular and dissociative adsorption processes. 

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