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Free keywords:
Aromatic compounds; Aromatization; Film preparation; Fluorine; Organic polymers; Phase transitions, Aromatic self assembled monolayers; Disordered phase; Kinetic factors; Long-term storage; Morphological transformations; Orientational orderings; Structural ordering; Substituted aromatic, Self assembled monolayers
Abstract:
By the example of 4-fluorobenzene-1-thiolate (p-FTP) films on Au(111), we show that a long-term post-preparation storage can improve significantly the quality of fluorinated aromatic self-assembled monolayers (SAMs). Whereas the freshly prepared p-FTP films exhibit a polymorphism, with a dominance of a disordered phase, the post-preparation storage triggers a gradual phase transition to a single-phase SAM of exceptional quality. This phase is characterized by the commensurate (16 × √3) structure, a molecular footprint of 23.1 Å 2 , high orientational order, and hardly perceptible borders between individual domains, with sizes exceeding 80 nm. Significantly, the phase transition is accompanied by morphological transformation of the substrate: whereas the freshly prepared films exhibit comparably large Au adatom islands, typical of aromatic SAMs, the long-storage samples rather reveal etch-pits, typical of alkanethiolate SAMs on Au(111), which generally have a high structural order immediately after the preparation. The above results suggest a deep interrelation between the structural order in the SAMs and surface morphology. A further implication is the importance of both thermodynamic and kinetic factors, a delicate interplay of which is presumably responsible for the observed evolution of p-FTP/Au in the present case. © Copyright 2019 American Chemical Society.
