Document Detail

Organic depth profiling of a binary system: the compositional effect on secondary ion yield and a model for charge transfer during secondary ion emission.
MedLine Citation:
PMID:  19645457     Owner:  NLM     Status:  MEDLINE    
In recent years, it has been demonstrated that cluster ion beams may be used to sputter some materials, particularly organic materials, without the significant accumulation of damage. It is therefore possible to use cluster ion beam sputtering in conjunction with a surface analytical technique, such as SIMS, to obtain depth profiles and three-dimensional images of the distribution of organic species in the near-surface region. For SIMS organic depth profiling to be useful as an analytical tool, it is important that it is able to measure physically meaningful quantities, such as the local concentration of a species within a blend. In this paper, we investigate a model system of a miscible binary mixture of codeine and poly(lactide). We show that there is a strong surface enrichment of poly(lactide), which provides a reference signal and permits the direct comparison of different samples in terms of secondary ion yield behavior. We demonstrate that it is possible to relate secondary ion intensities to local concentrations for a binary system and that there is a direct correspondence between the yield enhancement of one component and the yield suppression of the other. The dependence of secondary ion yield on composition is described using a model of the kinetically limited transfer of charge between secondary ions and secondary neutrals. Application of the model to pure materials under the assumption that only highly fragmented secondary ions are initially produced and interact with unfragmented secondary neutrals leads to the prediction that high molecular mass quasi-molecular ions have intensities proportional to the square of the total secondary ion yield. This relationship has been independently observed in other work (Seah, M. P. Surf. Interface Anal. 2007, 39, 634.).
Alexander G Shard; Ali Rafati; Ryosuke Ogaki; Joanna L S Lee; Simon Hutton; Gautam Mishra; Martyn C Davies; Morgan R Alexander
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  The journal of physical chemistry. B     Volume:  113     ISSN:  1520-6106     ISO Abbreviation:  J Phys Chem B     Publication Date:  2009 Aug 
Date Detail:
Created Date:  2009-10-22     Completed Date:  2010-02-22     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101157530     Medline TA:  J Phys Chem B     Country:  United States    
Other Details:
Languages:  eng     Pagination:  11574-82     Citation Subset:  IM    
Quality of Life Division, National Physical Laboratory, Teddington, Middlesex TW11 0LW, UK.
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MeSH Terms
Codeine / chemistry*
Membranes, Artificial
Models, Chemical
Polyesters / chemistry*
Spectrometry, Mass, Secondary Ion / methods*
Surface Properties
Reg. No./Substance:
0/Membranes, Artificial; 0/Polyesters; 26969-66-4/poly(lactide); 76-57-3/Codeine

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