ELSEVIER Supramokcular Science 4 (1997) 247-253 F ’ 1997 Elsevier Science Ltd Printed in Great Britain. All rights reserved zyxwvutsrqp PII: SO968-5677(97)00011-4 0968-5677/97/%17.00 X-ray photoelectron spectroscopy of partial and stamped thiol-based self-assembled monolayers S. D. Evans*, S. D. Cooper, S. R. Johnson and T. M. Flynn Department of Physics, University of Leeds, Leeds LS2 9JT, UK and A. Ulmanl Department of Chemistry, Polytechnic University at Brooklyn, Brooklyn, NY 11201, USA (Received 6 September 1996; revised 16 December 1996) X-ray photoelectron spectroscopy was used to explore the local environment of a perfluorinated thiol derivative incorporated into an alkanethiol matrix. The alkanethiol octadecylmercaptan (ODT) was formed via a printing p.rocedure and samples taken at various stages of stamp depletion were investigated. Compared with the spectra obtained from a monolayer of the pertluorinated material adsorbed directly from solution, one can see distinct differences in the shape of the F 1s peak. We present possible interpretations of this behaviour from a molecular perspective. 0 1997 Elsevier Science Ltd. All rights reserved. zyxwvutsrqponmlkjihgfedcbaZYXWV (Keywords: X-ray photoelectron spectroscopy; self-assembled monolayers) INTRODUCTION One of the most significant breakthroughs in the relatively short history of alkanethiol-derivatized self- assembled monolayers (SAMs) has been the development of patterning techniques to produce multi-functional surfaces. The two techniques being most widely advocated, at present, are: (1) a ‘stamping’ procedure in which an alkylthiol derivative (either in ethanol as a solution or in its neat form) is absorbed into an elastomeric stamp and subsequently transferred by bringing it into contact with a clean gold surface; and (2) a ‘photo-patterning’ procedure in which a pre-formed monolayer is irradiated with UV radiation through a mask to oxidize the thiol (in a specified region) to the sulfoxide, which is subsequently removed by washing with wate?. Both techniques have their relative merits and both significantly widen the range of applications for which SAMs may be used. Monolayers formed by using the ‘stamping’, or ‘printing’, technique tend to yield films with slightly lower average thicknesses than their counterparts formed via direct adsorption from solution5. This probably arises as a result of the significantly shorter contact time used for transfer of the ‘thiol ink’ compared with the much longer adsorption times usually used for the formation of monolayers. If a * To whom correspondence should be addressed substrate patterned in such a way is placed into a solution containing a second alkylthiol derivative, then this derivative will adsorb not only on the regions in which the first monolayer was deliberately not printed but will also penetrate the previously ‘stamped’ region. Such penetration of the second component into the first patterned region may be either a benefit or a hindrance, depending on the desired application and on the form of the penetration; i.e. whether one has island formation (on the meso scale) or homogeneous penetration can be either useful or a nuisance. During a recent study of two-component SAM systems formed by using the ‘stamping’ (or ‘printing’) procedure, we observed that upon placing an octadecylthiol (ODT) stamped monolayer into a solution of perfluorinated thiol (PFl), molecules of PFl penetrated into the ODT region of the film6. This was interesting for two reasons: (1) the F 1s peak (measured by X-ray photoelectron spectroscopy, XPS) from regions of PFl in the ODT film was different from that found for the pure regions of PFl (i.e. adsorbed from solution) and (2) because it showed the usefulness of XPS in its imaging mode for mapping the uniformity of SAMs. It is the former point, however, that we address here. That is, why should there be a difference in the F 1s peak for single-component SAMs of PFl adsorbed from solution compared with the cases where molecules of PFl have penetrated a stamped ODT SUPRAMOLECULAR SCIENCE Volume 4 Numbers 3-4 1997 247