4.6 Microcontact printing of chemically patterned surfaces

In order to assemble two dimensionally patterned rhodium and tin porphyrin structures on surfaces using the coordination chemistry laid out in chapter 2, first it is necessary to prepare surfaces which present patterns of carboxyl and amine functionality. The microcontact printing technique21,22 provides access to patterned self assembled monolayers and preliminary experiments were carried out to pattern gold surfaces by printing a pattern of 10 mm wide lines of mercaptoundecanoic acid separated by 5 mm gaps using a PDMS stamp. Unfunctionalized gap regions were ‘filled in’ with one of either 180, 181 or 184. The resulting surfaces were imaged by atomic force microscopy operating in the friction mode as it has been reported that the frictional force between the AFM tip and a SAM is sensitive to the chemical functionality of the SAM.461 Frictional contrast consisting of 10 and 5 mm wide parallel lines was observed, indicating transfer of the pattern from the PDMS stamp to the gold surface. However the surfaces were contaminated with much particulate material and a surface patterned with mercaptododecanoic acid and dodecanethiol appeared to exhibit the opposite frictional contrast to that described in the literature,461 although this may be due to an instrumental artifact. Representative images are given in appendix 4, but will not be further discussed here. Due to time constraints and unavailability of functioning instrumentation it has not yet been possible to repeat the experiments and optimize the sample preparation and imaging.

Before proceeding to study binding of porphyrins to such monolayers it would be desirable to obtain further verification of the chemical nature of the patterned surfaces using techniques such as imaging secondary ion mass spectrometry or imaging XPS. These techniques are likely to prove invaluable when analysing more complex surfaces for which AFM will be unable to provide conclusive answers due to its limited capacity to yield compositional information.


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