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Thermodynamic driving forces for substrate atom extraction by adsorption of strong electron acceptor molecules

DOI: 10.1021/acs.jpcc.2c00711 DOI Help

Authors: Paul Ryan (Diamond Light Source; Imperial College London) , Philip James Blowey (Diamond Light Source; University of Warwick) , Billal S. Sohail (University of Warwick) , Luke A. Rochford (Diamond Light Source) , David A. Duncan (Diamond Light Source) , Tien-Lin Lee (Diamond Light Source) , Peter Starrs (Diamond Light Source; University of St. Andrews) , Giovanni Costantini (University of Warwick) , Reinhard J. Maurer (University of Warwick) , David Phillip Woodruff (University of Warwick)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: The Journal Of Physical Chemistry C

State: Published (Approved)
Published: March 2022
Diamond Proposal Number(s): 17261 , 20785

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.

Journal Keywords: DFT calculations; Energy; Molecular structure; Adsorption; Molecules

Subject Areas: Chemistry, Physics

Instruments: I09-Surface and Interface Structural Analysis

Added On: 30/03/2022 09:08

Discipline Tags:

Surfaces Physics Physical Chemistry Chemistry interfaces and thin films

Technical Tags:

Diffraction Spectroscopy Low Energy Electron Diffraction (LEED) X-ray Photoelectron Spectroscopy (XPS)