Mixed carboranethiol self-assembled monolayers on gold surfaces

Sohrabnia, Nima
Thiolated derivatives of dicarba-closo-dodecaborane, HS-C2B10H11 (carboranethiols, CTs), with icosahedral molecular structure are one of the promising candidates for self-assembled monolayer (SAM) applications. CT SAMs possess various advantages relative to organic counterparts, such as high stability towards chemical, oxidative and thermal degradations as well as having fewer defects. In this study, pure and mixed SAMs of three different positional isomers of carboranethiols (namely M1, O1 and M9) on template stripped gold surfaces were grown from solution and characterized. Global properties of the SAMs were studied by means of contact angle (CA) and ellipsometric spectroscopy measurements. The ellipsometric thickness of all SAMs were found to be about 1 nm which is consistent with the reported thickness, measured by scanning tunneling microscopy, in the literature. In case of pure SAMs, M1 was observed to have the highest CA (85.4±1.8) whereas O1 SAMs have the lowest CA value (71.2±0.7). The dominant component that governs surface wettability was found to be M1 in mixed M1:M9 and O1:M1 SAMs. This is due to head to tail dipole-dipole interactions of M1 molecules on the surface. In case of M1:M9 co-deposited SAMs, CA was observed to increase with increasing M1 concentration in the growth solution. Such a clear trend was only present, however, in the advancing CAs for O1:M1 codeposited SAMs. On the other hand, contact angles of O1:M9 co-deposited films were observed to increase linearly with increasing M9 ratio in the growth solution. The morphological properties of the SAMs were investigated by atomic force microscopy and all SAMs were found to have similar properties with the exception of low defect concentration observed for O1:M9 films.  
Citation Formats
N. Sohrabnia, “Mixed carboranethiol self-assembled monolayers on gold surfaces,” M.S. - Master of Science, Middle East Technical University, 2017.