Studies on Surface and Interface with X-ray Absorption Fine Structure (XAFS). XAFS Study of Self-Assembled Monolayers.

Abstract

The molecular orientation and the molecule-substrate interface structure of self-assembled monolayers of alkanethiol and its related molecules have been investigated by use of X-ray absorption fine structure (XAFS). The molecular orientation is mainly dependent on the molecular density, while for the ordering of molecular arrangement, which is necessary for self-assembly, the key factor is the balance between structures demanded by intermolecular and molecule/substrate interactions. The internal degree of freedom of the molecule plays an important role in the balancing. In the case of alkanethiols this condition is fulfilled at the saturated coverage, while in the case of a thiophene-substituted alkanethiol, the interaction between thiophene moieties prevent its monolayer from self-assembling at the saturated coverage but leads to form a self-assembled monolayer at a lower coverage. The molecular orientation in a monolayer exerts a strong effect on the orientation in a multilayer that is formed on the monolayer. This suggests that the structure of three-dimensionally self-assembled molecular aggregation can be controlled by using self-assembled monolayers as the template.