Structural characterization and properties of self-assembled organic monolayers on underpotentially deposited metal substrates
- Massachusetts Institute of Technology, Cambridge, MA (United States)
Self-assembled monolayers (SAMs) are a class of chemisorbed monomolecular films that form by the spontaneous adsorption of ligating molecules onto reactive metal (or metal oxide) surfaces. We have used underpotential deposition (UPD) as a method for manipulating the structure and composition of metal surfaces at the submonolayer level. In our studies, we have characterized SAMs derived from the adsorption of n-alkanethiols onto polycrystalline gold substrates that contain underpotentially deposited films of copper, silver, and other metals by XPS, IR spectroscopy, ellipsometry, and wetting measurements. Both hydrophobic and hydrophilic surfaces can be prepared on the UPD substrates, and the assembly is compatible with tail groups such as CH2OH, CO2H, etc. The UPD layer affects the structure of the monolayer: for example, the presence of UPD layers of copper or silver atoms on gold surfaces yields SAMs derived from n-alkanethiols that arc structures distinct from those that form on copper, silver, or gold surfaces. The use of an UPD metal layer to modulate the structure of adsorbed organic films -- and consequently, the packing density of organic functionality present at the surface of the SAM -- provides a new, straightforward method for controlling an additional feature of the molecular architecture of these highly ordered, chemisorbed organic films. In addition, the UPD layer improves the level of adhesion between the adsorbate and the underlying metal substrate. The UPD layer improves the overall thermal stability of the assemblage and appears to function as a one-atom-thick {open_quotes}glue{close_quotes} at the gold/sulfur interface.
- OSTI ID:
- 466480
- Report Number(s):
- CONF-951017--
- Country of Publication:
- United States
- Language:
- English
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