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Investigation of carboxyl-functionalized self-assembled monolayers on gold surfaces.

Görgülü, Salih
Thiolated derivatives of dicarba-closo-dodecaborane, HS-C 2 B 10 H 11 (carboranethiol, CT), with icosahedral molecular structure are one of the promising candidates for self-assembled monolayer (SAM) applications. CT SAMs possess various advantages relative to their organic counterparts, such as high stability towards chemical, oxidative and thermal degradations as well as having fewer defects. In this study unfunctionalized CT SAMs (M1, M9) and carboxylic group functionalized CT SAMs (M1C, M9C) as well as their corresponding mixed SAMs were investigated on template stripped gold surfaces. Wetting properties of the SAMs were studied by using contact angle (CA) measurements. The ellipsometric thickness of all SAMs were found to be about 1-2 nm which is consistent with the reported thickness, measured by scanning tunneling microscopy (STM), in the literature. In mixed SAMs, surface fraction of M1 was found to be higher than its solution fraction in the M1:M1C and M1:M9C mixtures indicating the dominant component on the surface to be M1. Similar behavior was also observed for M9 such that surface fraction of M9 was higher than its solution fraction in the M9:M1C and M9:M9C mixtures indicating the dominancy of M9 molecules on the surface. M1 and M9 molecules bind to gold surface stronger than M1C and M9C molecules. In replacement experiments of CT SAMs, M1 molecules were found to replace M9C faster than M9C replaces M1 on template stripped gold surface. Replacement experiments of CT SAMs on silver surface were also performed. It was found that M9C molecules bind to silver surfaces through carboxylic groups rather than the thiol group.