Order in Microcontact Printed Self-Assembled Monolayers

Self-assembled monolayers (SAMs) on Au(111) formed by microcontact printing of dodecanethiol and investigated by scanning tunneling microscopy and wettability measurements have, under certain conditions, characteristics indistinguishable from SAMs formed from solutions of dodecanethiol in ethanol. The monolayer product of microcontact printing demonstrates a sensitivity to the concentration of thiol used to ink a poly(dimethyl siloxane) (PDMS) stamp needed to make the print, and an insensitivity to its duration of contact, for times >0.3 s, with the gold substrate. The wettability of the SAM, the distribution of domains within the monolayer, their size and organizational state, and the pattern of depressions on the surface each are reproducibly controlled by simply changing the concentration of dodecanethiol applied to the stamp. The inferred mode of growth of printed SAMs shares many features of monolayer formation through the gas phase of a thiol and corresponds to a highly controlled and self-limiting delivery of thiol from the interior parts of the PDMS. Our study shows that printed SAMs provide a wonderful opportunity to observe the emergence of order in monolayers at the nanometer scale and its effects on microscopic and macroscopic properties of these films and suggests strategies towards control over this order.