Paper TF+SS-TuA2
Microscopic and Spectroscopic evidence of Odd-Even Effect in Self-Assembled Monolayers of Biphenyl-Substituted Fatty Acid on Ag(111)
Tuesday, October 23, 2018, 2:40 pm, Room 102A
| Session: |
Organic/Inorganic Materials and Interfaces |
| Presenter: |
Anna Krzykawska, Jagiellonian University, Polska |
| Authors: |
A. Krzykawska, Jagiellonian University, Polska
P. Cyganik, Jagiellonian University, Poland
M. Szwed, Jagiellonian University, Poland
J. Ossowski, Jagiellonian University, Poland
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| Correspondent: |
Click to Email |
Self-assembled monolayers (SAMs) have been broadly studied as a model system for inorganic-organic interface in molecular electronics and biosensing devices. Current standard in SAMs formation is based on using sulfur as an anchoring group to the metal substrate. In our recent paper1 we have indicated that by replacing thiol headgroup by carboxylic, a highly interesting alternative is obtained, particularly when 2D ordering, SAM fabrication time and stability in ambient conditions are of great importance. Following this first observation made for a specific system, in the current work we have investigated a homolog series of SAMs based on biphenyl-substituted fatty acids on Ag(111) in the form of (C6H4)2-(CH2)n-COO/Ag (BPnCOO/Ag, n = 1-4). The series of experiments were carried out using infrared reflection absorption spectroscopy (IRRAS), scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). The results of this combined microscopic and spectroscopic analysis demonstrate very strong dependence of the structural properties on the number of the CH2 groups in the short aliphatic linker. Monolayers with n = even show highly ordered and stable structures. In contrast, SAMs with n = odd have disordered liquid-like structure with more canted orientation of the molecular backbone and the carboxylic headgroup, which results in lower packing density and film thickness compared to the even-numbered SAMs. By comparing obtained results with former odd-even effects reported for analogues SAMs based on thiols and selenols3,4, a common, qualitative model relating the odd-even effect to the monolayer stability and structure will be discussed. Our results demonstrate that for BPnCOO/Ag, this odd-even effect is particularly strong and fully controls the ability of molecules to form highly ordered structures. This observation seems to be of key importance for the design of SAMs based on the carboxylic group, which, for correctly designed molecules, forms much better 2D-ordered structures compared to commonly used thiols.
References
[1] K rzykawska, A.; Ossowski, J.; Zaba, T.; Cyganik*, P., Chem. Comm. 2017, 53, 5748-5751
[2] Krzykawska, A.; Szwed, M.; Ossowski, J.; Cyganik*, P., J. Phys. Chem. C 2018, 122, 919-928
[3] Cyganik, P.; Buck, M.; Azzam, W.; Wöll*, C., J. Phys. Chem. B. 2004, 108, 4989-4996
[4] Cyganik*, P.; Szelagowska-Kunstman, K.; Terfort, A.; Zharnikov,M., J. Phys. Chem. C. 2008, 112, 15466-15473