| AVS 64th International Symposium & Exhibition | |
| Applied Surface Science Division | Wednesday Sessions |
| Session AS+2D+NS+SA-WeA |
| Session: | 2D, 3D and nD Imaging of Surfaces, Buried Interfaces and Nanostructures |
| Presenter: | Anna Krzykawska, Jagiellonian Univeristy, Poland |
| Authors: | A. Krzykawska, Jagiellonian Univeristy, Poland J. Ossowski, Jagiellonian University, Poland T. Żaba, Jagiellonian University, Poland P. Cyganik, Jagiellonian University, Poland |
| Correspondent: | Click to Email |
Self-assembled monolayers (SAMs) prepared from biphenyl-substituted molecules chemisorbed on the Ag(111) substrate via an -SH or -COOH headgroup were characterized using scanning tunneling microscopy (STM), infrared reflection absorption spectroscopy (IRRAS), and X-ray photoelectron spectroscopy (XPS). The objective of this work was to determine which of these headgroups, -SH or -COOH, will provide better 2D ordered SAMs. Importantly, to make such comparison valuable, i.e., to correlate the reduction in the concentration of surface defects with the particular headgroup, we need to compare the two systems, which are chemical analogues, and it would be desired that both systems form SAMs of similar packing density. Only under such conditions can the difference in intermolecular interactions in both systems be minimized to determine the role of headgroup bonding to the substrate in the 2D structural ordering of the resulting SAMs. Our results1 obtained for monolayers meeting the above criteria show that SAMs with carboxylic headgroups can form, at room temperature and within a very short time of just a few minutes well-ordered 2D structures on Ag(111) with surprisingly large domains. In contrast, the thiol analogue formed at the same temperature reveals poor 2D ordering, with approximately 30 times smaller structural domains. Importantly, this pronounced difference in 2D ordering is observed despite the approximately 300 times longer incubation process of the thiol analogue. We also demonstrate that formation of the thiol analogue at elevated solution temperature (60°C) can significantly increase the size of its domains, which is, however, still approximately 5 times smaller in comparison to the carboxylic analogue formed at room temperature. Moreover, the structure of the carboxylic analogue on Ag(111) also shows better 2D order compared with the former data obtained for the thiol analogue SAMs formed on the Au(111) substrate at room temperature. Only the formation of thiol analogue SAMs at elevated solution temperature (60°C) on the Au(111) substrate with 300 times longer formation time provides comparable 2D ordering to that obtained at the room temperature for the carboxylic analogue SAMs on the Ag(111) substrate.
Our results indicate, therefore, that SAMs based on carboxylic head group can be considered an interesting alternative for the curren t standard based on the sulfur headgroups, particularly when 2D ordering, SAM fabrication time and stability in the ambient conditions are of great importance.
References
[1] A. Krzykawska, J. Ossowski, T. Żaba and P. Cyganik, Chem Comm2017 accepted