COMPOSITIONAL-MAPPING OF MICROPATTERNED, MIXED SELF-ASSEMBLED MONOLAYERS BY LATERAL FORCE MICROSCOPY

Lateral force microscopy (LFM) was used to image patterned organic sur faces and showed consistent changes in image contrast with surface com position. Self-assembled monolayers (SAMs) of omega-substituted alkane thiolates were patterned on surfaces of gold films coated on silicon w afers. The patterns consisted of areas of gold modified by SAMs formed from dodecanethiol (HS(CH2)(11)CH3) and areas derivatized by mixed SA Ms formed by exposure to solutions of mixtures of HS(CH2)(11)CH3 and h exaethylene glycol-terminated alkanethiol [HS(CH2)(11)(OCH2CH2)(6)OH]. Several types of patterned SAMs were investigated, each of which diff ered in the relative mole fractions of methyl- and hexaethylene glycol -terminated alkanethiolates in the mixed SAMs, Analysis of the relativ e friction measured for the different mixed SAMs suggests that LFM fan Be used as a semiquantitative technique for compositional mapping of mixed SAMs. Correlation between relative friction and the composition (as estimated by X-ray photoelectron spectroscopy) and the wettability of mixed monolayers are presented for the types of SAMs investigated. The friction is directly proportional to the fraction of hexaethylene glycol-terminated alkanethiolates present in the mixed SAMs. The corr elations can be applied in the semiquantitative estimation of the comp ositional and wetting properties or ''microscopic patterns in the mixe d SAMs. As an example, we have used the compositional correlation toge ther with LFM imaging to estimate the degree of displacement of an hex aethylene glycol-terminated SAM by a microdroplet of HS(CH2)(11)CH3.