Study of microcontact printed patterns by chemical force microscopy

Patterned self-assembled monolayers (SAMs) on sputtered gold films prepared by microcontact printing (μCP) were studied by mapping adhesive forces with pulsed-force-mode atomic force microscopy. A stamp for μCP was fabricated by pouring polydimethylsiloxane (PDMS) over a photolithographically prepared master. The patterned SAMs were prepared by two methods. One is called the wet-inking method, in which inking was done by placing a thiol ethanol solution for 30 s on the stamp and then removing the excess ink solution under a stream of nitrogen. The other is called the contact-inking method, in which a pad made of PDMS was dipped overnight in a thiol ethanol solution and then the stamp was placed on the inker pad impregnated with the thiol ethanol solution. The second step for pattern formation was the same for both of the two different μCP methods. Namely, the gold surfaces stamped with alkanethiols were further reacted with a thiol terminating in COOH in ethanol. The resulting patterns with CH3- and COOH-terminated regions were analyzed by imaging the adhesive forces with the chemically modified gold coated AFM tips with a SAM of CH3 or COOH terminal functional groups.