Influence of surface topography on alkanethiol SAMs assembled from solution and by microcontact printing

The influence of the topography of the underlying gold surface on the integ rity of self-assembled monolayers (SAMs) of hexadecanethiol (HDT) prepared by solution assembly and microcontact printing was assessed using six diffe rent gold substrates. The bare substrates were evaluated for roughness and defects using scanning tunneling microscopy (STM). The structural integrity of self-assembled monolayers on these substrates has been evaluated using both surface methods (STM) and electrochemical measurements. Perhaps not su rprisingly, the flattest substrates seem to produce the highest quality mon olayer. It is surprising to note, however, that the layer quality is not ne cessarily traceable to a variation in coverage. Despite both the solution-f ormed and printed SAMs appearing similar in STM images, electrochemical ass essment of the SAM integrity indicated the printed SAMs were inferior, form ing a less effective passivating barrier with many more pinholes. The quali ty of printed SAMs could be improved considerably by rolling the inked stam p across the gold surface rather than placing the stamp horizontally onto t he substrate. This second printing technique of rolling the stamp across th e surface produced SAMs which were still marginally inferior to those forme d from solution but were assembled in less than a minute rather than 24 h.