Comparative studies of carboranethiol self-assembled monolayers on gold surfaces

Date

2025-1-07

Author

Yalçın, Caner

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The behavior, structure, and stability of carboranethiol self-assembled monolayers on gold and, occasionally, silver substrates were investigated. Primary attention was given to how molecular structure and bonding preferences will influence the properties of these SAMs. Morphology, thickness, and chemical composition assessment were conducted through the application of a systematic analysis via contact angle measurements, spectroscopic ellipsometry, atomic force microscopy, and X-ray photoelectron spectroscopy. The experimental results show that the SAMs prepared under base-free and basic conditions do not differ much in morphology or surface characteristics, hence removing the necessity to prepare basic solutions. Comparison studies on bis-carboranethiol isomers illustrate that the para-substituted isomer, pp-SH, self-assembles into more ordered, stable, and defect-free monolayers compared to its meta-substituted isomer, mm-SH. Thickness measurements support the smoothness and homogeneity of the pp-SH surface, making this a promising precursor for applications where stable and uniform monolayers are required. Another point that was underlined is the thermodynamic preference of the bonding interactions, which means that on gold surfaces, P1C SAMs with Au-S-C bonds are much more stable than diMe-O9 SAMs containing Au-S-B bonds. The replacement experiments indeed showed that, over time, the P1C SAMs will dominate because of their favorable thermodynamic properties. On silver substrates, however, weaker binding interactions and high surface roughness lead to reduced stability and selectivity, resulting in less organized monolayers and significant intermixing.

Subject Keywords

Carboranethiol, Self-Assembled Monolayer, Contact Angle

URI

https://hdl.handle.net/11511/113442

Collections

Graduate School of Natural and Applied Sciences, Thesis