Structure Determination of F₄TCNQ on Ag(111): A Systematic Trend in Metal Adatom Incorporation.

Abstract

A structure determination of the commensurate phase formed by 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (F₄TCNQ) absorbed on Ag(111) is reported. Initial characterization was performed using low-energy electron diffraction and synchrotron radiation photoelectron spectroscopy, with quantitative structural data being provided by normal incident X-ray standing waves (NIXSW) and surface X-ray diffraction (SXRD). NIXSW data show the F₄TCNQ molecule to adopt a "twisted" conformation on the surface, previously found to be associated with metal adatom incorporation into a 2d-metal-organic framework for F₄TCNQ on Au(111), Ag(100), and Cu(111). SXRD results provide direct evidence of the presence of Ag adatoms that are found to occupy near-bridge or fcc hollow sites with respect to the underlying surface, at an adsorption height of 2.69 ± 0.10 Å. The results show a consistent pattern of behavior for F₄TCNQ adsorption on the (111) surfaces of Cu, Ag, and Au.