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Simulation of isotopic mass effects in sputtering

Shapiro, M. H. and Haff, P. K. and Tombrello, T. A. and Harrison, Don E., Jr. (1985) Simulation of isotopic mass effects in sputtering. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 12 (1). pp. 137-146. ISSN 0168-583X. http://resolver.caltech.edu/CaltechAUTHORS:20141104-145427348

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Abstract

The multiple interaction, molecular dynamics code SPUT1 has been used to simulate the effects of isotopic mass differences on atoms sputtered from single crystal Cu targets by normally incident Ar ions. Calculations were carried out for 1 keV and 5 keV ions incident on natural Cu targets (69.1% ^(63)Cu, 30.9% ^(65)Cu). and for 5 keV ions incident on pseudo-Cu targets composed of mixtures of natural Cu (63.546 amu) and “very light” Cu (50.837 amu) in the abundance ratios 1:3, 1:1, and 3:1. In all cases the sputtered ejecta showed an overall enrichment in the light isotope relative to the isotopic composition of the target. Preferential enrichment of the light isotope in the normal direction was pronounced. Material ejected at oblique angles was either depleted in the light isotope or had a much lower enrichment of the light isotope compared to material ejected normal to the target. Studies with the pseudo-Cu targets showed that smaller enrichments were obtained when the incident ion recoiled immediately back through the first layer of the target, while larger enrichments were associated with deeper penetration of the incident ion into the target crystallite. In both cases, the average energy of the light atoms in the collision cascade was found to be higher than that of the heavy atoms. However, this effect was enhanced with deeper penetration of the incident ion into the target. The preferential enrichment of the light ejected atoms normal to the target is largely the result of a strong momentum asymmetry in the collision cascades. Light atoms in the cascades, on average, carry far greater momentum towards the surface of the target than do the heavy atoms. A limited number of simulation runs also were carried out with heavy ions (74 amu) incident on pseudo-Cu targets. Overall enrichment of the light atoms in the sputtered material was reduced, but the angular variation of the isotopic yields persisted.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://www.sciencedirect.com/science/article/pii/0168583X85907098PublisherArticle
http://dx.doi.org/10.1016/0168-583X(85)90709-8DOIArticle
Additional Information:© 1985 Published by Elsevier B.V. Received 10 December 1984 and in revised form 27 March 1985. Supported in part by the National Science Foundation [DMR83-06541 (Caltech) and DMR83-06548 (CSUF)], by a Schlumberger-Doll Research Corp. grant (Caltech), by an Office of Naval Research Special Research Opportunity Grant (NPG), and by the Foundation Research Program of the Naval Postgraduate School. The author wish to thank Mr. Gene Dippel and Mr. Dick Bednar of the CSU-Fullerton computer center for their assistance. We also are very grateful to the State University Data Center for providing the many hundreds of hours of CYBER-760 CPU time needed for these calculations.
Funders:
Funding AgencyGrant Number
NSFDMR83-06541
NSFDMR83-06548
Schlumberger-Doll ResearchUNSPECIFIED
Office of Naval Research (ONR)UNSPECIFIED
Naval Postgraduate School FoundationUNSPECIFIED
Record Number:CaltechAUTHORS:20141104-145427348
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20141104-145427348
Official Citation:M.H. Shapiro, P.K. Haff, T.A. Tombrello, Don E. Harrison Jr, Simulation of isotopic mass effects in sputtering, Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 12, Issue 1, August 1985, Pages 137-145, ISSN 0168-583X, http://dx.doi.org/10.1016/0168-583X(85)90709-8. (http://www.sciencedirect.com/science/article/pii/0168583X85907098)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51254
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:05 Nov 2014 00:14
Last Modified:05 Nov 2014 00:14

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