AFM Imaging of Mercaptobenzoic Acid on Au(110): Submolecular Contrast with Metal Tips

Abstract

A self-assembled monolayer of mercaptobenzoic acid (MBA) on Au(110) is investigated with scanning tunneling and atomic force microscopy (STM and AFM) and density functional calculations. High-resolution AFM images obtained with metallic tips show clear contrasts between oxygen atoms and phenyl moieties. The contrast above the oxygen atoms is due to attractive covalent interactions, which is different than previously reported high-resolution images, where Pauli repulsion dominated the image contrast. We show that the bonding of MBA to the substrate occurs mainly through dispersion interactions, whereas the thiol-Au bond contributes only a quarter of the adsorption energy. No indication of Au adatoms mediating the thiol-Au interaction was found in contrast to other thiol-bonded systems. However, MBA lifts the Au(110)-(2 × 1) reconstruction.

Stability of functionalized platform molecules on Au(111)

“…[27][28][29][30][31][32][33][34] Here we show that even on well-ordered Au(111) surfaces, some functionalized trioxatriangulenium (TOTA) platform molecules fragment despite the fact that they physisorb. 35,36 We functionalized TOTA platforms with methyl, ethyl, ethynyl, propynyl, and hydrogen. After sublimation onto Au(111), all methyl-TOTA and >99% ethyl-TOTA on Au(111) are intact.…”

Molecular Identification, Bond Order Discrimination, and Apparent Intermolecular Features in Atomic Force Microscopy Studied with a Charge Density Based Method

“…Guo et al pointed out, from DFT calculations, that the replacement of one C–H group by a N atom in a pentacene molecule modifies the charge density and locally distorts the image, making the N substitutional distinct from the image of the remaining C atoms. These distortions have been observed in hydrocarbon rings with heteroatoms ,− and surfaces with dopants, but it is still unclear what causes them. ,,,− Furthermore, 3D-force spectroscopy data on organic molecules obtained with CO probes exhibits a characteristic, local contrast that could be used for chemical recognition . However, the possibility to get this atom by atom chemical identification with CO probes has been questioned as the contrast depends on the environment, hybridization, and oxidation state of the sample molecule …”

Rasterkraftmikroskopie für die molekulare Strukturaufklärung

“…Mit ihnen erhält man daher meist keine atomare Auflçsung fürM oleküle,k ann aber in gewissen Fällen, wie kürzlich gezeigt wurde,s ubmolekularen Kontrast erreichen. [48] 2) Funktionalisierung mit Halogenen wie Cl, Br und I, die,w ie bei Cl [9,46] aus NaCl, aus einem dünnen Film extrahiert werden oder vor der Aufnahme mit der Spitze von einem Molekül dissoziiert werden (Br und I). [29] Diese Messspitzen eignen sich fürd ie Bildgebung in atomarer Auflçsung und produzieren weniger verzerrte Bilder als die CO-Messspitzen.…”

“…[48] 2) Funktionalisierung mit Halogenen wie Cl, Br und I, die,w ie bei Cl [9,46] aus NaCl, aus einem dünnen Film extrahiert werden oder vor der Aufnahme mit der Spitze von einem Molekül dissoziiert werden (Br und I). Mit ihnen erhält man daher meist keine atomare Auflçsung fürM oleküle,k ann aber in gewissen Fällen, wie kürzlich gezeigt wurde,s ubmolekularen Kontrast erreichen.…”