Document Detail


Improvements in the characterization of the crystalline structure of acid-terminated alkanethiol self-assembled monolayers on Au(111).
MedLine Citation:
PMID:  17209609     Owner:  NLM     Status:  PubMed-not-MEDLINE    
Abstract/OtherAbstract:
We report a study of acid-terminated self-assembled monolayers of alkanethiols of different length, 11-mercaptoundecanoic acid (11-MUA) and 16-mercaptohexadecanoic acid (16-MHDA), on Au(111). Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and contact angle techniques were used for characterization, and the results were compared with those obtained from n-alkanethiols of similar chain length, providing a detailed description of the two-dimensional crystalline structure. Molecular resolution STM images show that 11-MUA forms a dense-packed monolayer arranged in a (square root 3 x square root 3)R30 degrees structure with a c(2 x 4) superlattice, where the simple hexagonal phase, the c(2 x 4) superlattice, and nonordered areas coexist. 16-MHDA assembles in a uniform monolayer with similar morphology to that of 11-MUA, but molecular resolution could not be reached in STM due to both the hydrophilicity of the acid groups and the poor conductivity of the thick monolayer. Nevertheless, the monolayer thicknesses estimated by XPS and electrochemistry and the highly blocking character of the film observed by electrochemistry as well as the low water contact angle are consistent with 16-MHDA molecules forming a compact monolayer on the Au(111) substrate with fully extended alkyl chains and acid groups pointing away from the surface. The results obtained for 16-MHDA were reproducible under different preparation conditions such as the addition or omission of acetic acid to the ethanolic solution. Contrary to other reports, we demonstrate that ordered acid-terminated self-assembled monolayers are obtained with the same preparation conditions as those of the methyl-terminated ones, without any additional treatment.
Authors:
Sandra M Mendoza; Imad Arfaoui; Simone Zanarini; Francesco Paolucci; Petra Rudolf
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Langmuir : the ACS journal of surfaces and colloids     Volume:  23     ISSN:  0743-7463     ISO Abbreviation:  Langmuir     Publication Date:  2007 Jan 
Date Detail:
Created Date:  2007-01-09     Completed Date:  2007-07-17     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9882736     Medline TA:  Langmuir     Country:  United States    
Other Details:
Languages:  eng     Pagination:  582-8     Citation Subset:  -    
Affiliation:
Materials Science Centre, University of Groningen, Nijenborgh 4, 9747AG Groningen, The Netherlands.
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