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Source of Image Contrast in STM Images of Functionalized Alkanes on Graphite:  A Systematic Functional Group Approach

Claypool, Christopher L. and Faglioni, Francesco and Goddard, William A., III and Gray, Harry B. and Lewis, Nathan S. and Marcus, R. A. (1997) Source of Image Contrast in STM Images of Functionalized Alkanes on Graphite:  A Systematic Functional Group Approach. Journal of Physical Chemistry B, 101 (31). pp. 5978-5995. ISSN 1520-6106. https://resolver.caltech.edu/CaltechAUTHORS:20150422-091143996

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Abstract

A series of functionalized alkanes and/or alkyl alcohols have been prepared and imaged by scanning tunneling microscopy (STM) methods on graphite surfaces. The stability of these ordered overlayers has facilitated reproducible collection of STM images at room temperature with submolecular resolution, in most cases allowing identification of individual hydrogen atoms in the alkane chains, but in all cases allowing identification of molecular length features and other aspects of the image that can be unequivocally related to the presence of functional groups in the various molecules of concern. Functional groups imaged in this study include halides (X = F, Cl, Br, I), amines, alcohols, nitriles, alkenes, alkynes, ethers, thioethers, and disulfides. Except for −Cl and −OH, all of the other functional groups could be distinguished from each other and from −Cl or −OH through an analysis of their STM metrics and image contrast behavior. The dominance of molecular topography in producing the STM images of alkanes and alkanols was established experimentally and also was consistent with quantum chemistry calculations. Unlike the contrast of the methylene regions of the alkyl chains, the STM contrast produced by the various functional groups was not dominated by topographic effects, indicating that variations in local electronic coupling were important in producing the observed STM images of these regions of the molecules. For molecules in which electronic effects overwhelmed topographic effects in determining the image contrast, a simple model is presented to explain the variation in the electronic coupling component that produces the contrast between the various functional groups observed in the STM images. Additionally, the bias dependence of these STM images has been investigated and the contrast vs bias behavior is related to factors involving electron transfer and hole transfer that have been identified as potentially being important in dominating the electronic coupling in molecular electron transfer processes.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1021/jp9701799 DOIArticle
http://pubs.acs.org/doi/abs/10.1021/jp9701799PublisherArticle
ORCID:
AuthorORCID
Faglioni, Francesco0000-0002-3327-8848
Goddard, William A., III0000-0003-0097-5716
Gray, Harry B.0000-0002-7937-7876
Lewis, Nathan S.0000-0001-5245-0538
Marcus, R. A.0000-0001-6547-1469
Additional Information:© 1997 American Chemical Society. Received: January 7, 1997; In Final Form: April 16, 1997. We acknowledge the NSF, grants CHE-9634152 (N.S.L.), CHE-9522179 (W.A.G.), CHE-9610164 (H.B.G.), and ASC-9217368 (W.A.G.), for partial support of this work. C.C. acknowledges the NIH for a training grant, and we also acknowledge helpful discussions with Dr. J. Miller of Argonne National Laboratory regarding orbital coupling issues.
Funders:
Funding AgencyGrant Number
NSFCHE-9634152
NSFCHE-9522179
NSFASC-9217368
NIHUNSPECIFIED
Issue or Number:31
Record Number:CaltechAUTHORS:20150422-091143996
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20150422-091143996
Official Citation:Source of Image Contrast in STM Images of Functionalized Alkanes on Graphite:  A Systematic Functional Group Approach Christopher L. Claypool, Francesco Faglioni, William A. Goddard III, Harry B. Gray, Nathan S. Lewis, and R. A. Marcus The Journal of Physical Chemistry B 1997 101 (31), 5978-5995 DOI: 10.1021/jp9701799
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:56855
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:22 Apr 2015 16:35
Last Modified:09 Mar 2020 13:18

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