Thermodynamic Driving Forces for Substrate Atom Extraction by Adsorption of Strong Electron Acceptor Molecules

Ryan, Paul; Blowey, Philip James; Sohail, Billal S.; Rochford, Luke A.; Duncan, David A.; Lee, Tien-Lin; Starrs, Peter; Costantini, Giovanni; Maurer, Reinhard J.; Woodruff, David Phillip

Abstract

A quantitative structural investigation is reported, aimed at resolving the issue of whether substrate adatoms are incorporated into the monolayers formed by strong molecular electron acceptors deposited onto metallic electrodes. A combination of normal-incidence X-ray standing waves, low-energy electron diffraction, scanning tunnelling microscopy, and X-ray photoelectron spectroscopy measurements demonstrate that the systems TCNQ and F4TCNQ on Ag(100) lie at the boundary between these two possibilities and thus represent ideal model systems with which to study this effect. A room-temperature commensurate phase of adsorbed TCNQ is found not to involve Ag adatoms, but to adopt an inverted bowl configuration, long predicted but not previously identified experimentally. By contrast, a similar phase of adsorbed F4TCNQ does lead to Ag adatom incorporation in the overlayer, the cyano end groups of the molecule being twisted relative to the planar quinoid ring. Density functional theory (DFT) calculations show that this behavior is consistent with the adsorption energetics. Annealing of the commensurate TCNQ overlayer phase leads to an incommensurate phase that does appear to incorporate Ag adatoms. Our results indicate that the inclusion (or exclusion) of metal atoms into the organic monolayers is the result of both thermodynamic and kinetic factors.

Citation

Ryan, P., Blowey, P. J., Sohail, B. S., Rochford, L. A., Duncan, D. A., Lee, T.-L., Starrs, P., Costantini, G., Maurer, R. J., & Woodruff, D. P. (2022). Thermodynamic Driving Forces for Substrate Atom Extraction by Adsorption of Strong Electron Acceptor Molecules. Journal of Physical Chemistry C, 126(13), 6082-6090. https://doi.org/10.1021/acs.jpcc.2c00711

• Journal Article Type: Article
• Acceptance Date: Mar 13, 2022
• Online Publication Date: Mar 28, 2022
• Publication Date: Apr 7, 2022
• Deposit Date: Feb 19, 2025
• Publicly Available Date: Feb 26, 2025
• Journal: Journal of Physical Chemistry C
• Print ISSN: 1932-7447
• Electronic ISSN: 1932-7455
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 126
• Issue: 13
• Pages: 6082-6090
• DOI: https://doi.org/10.1021/acs.jpcc.2c00711
• Public URL: https://nottingham-repository.worktribe.com/output/41932703
• Publisher URL: https://pubs.acs.org/doi/10.1021/acs.jpcc.2c00711#