Formation and Characterization of a Molecule–Metal–Molecule Bridge in Real Space

Albrecht, Florian; Neu, Mathias; Quest, Christina; Swart, Ingmar; Repp, Jascha

doi:10.1021/ja404084p

Cited by 75 publications

(80 citation statements)

References 34 publications

(54 reference statements)

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“…Whereas different tip functionalizations have been reported [2,3], CO was used most often, and is now being widely applied [2][3][4][5][6][7][8][9][10][11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Image correction for atomic force microscopy images with functionalized tips

et al. 2014

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It has been demonstrated that atomic force microscopy imaging with CO-functionalized tips provides unprecedented resolution, yet it is subject to strong image distortions. Here we propose a method to correct for these distortions. The lateral force acting on the tip apex is calculated from three-dimensional maps of the frequency shift signal. Assuming a linear relationship between lateral distortion and force, atomic force microscopy images could be deskewed for different substrate systems.

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“…Whereas different tip functionalizations have been reported [2,3], CO was used most often, and is now being widely applied [2][3][4][5][6][7][8][9][10][11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Image correction for atomic force microscopy images with functionalized tips

et al. 2014

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“…Compound 2 was deposited on Cu(111), NaCl(100), and Xe(111) surfaces to generate triangulene (1) by means of atomic manipulation. STM/AFM is an ideal combination to study on-surface synthesis ranging from individual molecules 9,10 to graphene nanoribbons 11,12 . The chemical structure of reactants and products can be resolved by means of AFM with functionalized tips 13 .…”

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confidence: 99%

Synthesis and characterization of triangulene

et al. 2017

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* These authors contributed equally to this workTriangulene, the smallest triplet ground state polybenzenoid (also known as Clar's hydrocarbon), has been an enigmatic molecule ever since its existence was first hypothesized isomers (2, also denoted as dihydrotriangulenes) as precursor molecules. Compound 2 was deposited on Cu(111), NaCl(100), and Xe(111) surfaces to generate triangulene (1) by means of atomic manipulation. STM/AFM is an ideal combination to study on-surface synthesis ranging from individual molecules 9, 10 to graphene nanoribbons 11,12 . The chemical structure of reactants and products can be resolved by means of AFM with functionalized tips 13 . Even molecules too elusive to be studied by other means 14,15 can be stabilized by using an ultrathin insulating film as a decoupling 2 layer. A decoupling layer also facilitates studying the frontier molecular orbitals of the free molecule by means of STM and scanning tunnelling spectroscopy (STS) 16 .Figure 2 presents STM and AFM images of four different molecular species of compound 2 adsorbed on NaCl. As expected, different isomers of dihydrotriangulene are observed. This observation can be discussed by a comparison of Fig. 2e and Fig. 2f, showing the non-equivalent isomers 2a and 2b which we found on the surface, respectively. Because the former isomer is prochiral with respect to adsorption, we also observed its surface enantiomer (see Supplementary Fig. 5). Note that 2a is about three times more abundant than the highly symmetric 2b, although two Clar sextets can be drawn for both species. This difference can be rationalized by the resonance energy of its aromatic Remarkably, the ketone 3 in Fig. 2g represents an oxidized structure of 2 that was already reported by Clar and Stewart 1. A comparison of STM and AFM data reveals that in the STM images a tiny sharp kink arises at the position of a single CH 2 group. In contrast, a ketone group leads to a fainter bulge in STM images (Figs. 2c, d) and a lower contrast of the hexagon involved. The central carbon of the three adjacent CH 2 group in 3 adopts the expected tetrahedral bond angle for sp 3 carbon leading to sharp ridges in both STM and AFM mode (Figs. 2c, g) because of strong tilting of the CO molecule at the tip apex.We dehydrogenated promising candidates (2a and 2b molecules) to obtain triangulene by means of atomic manipulation 14,15,19 . To this end, we first positioned the tip above a molecule. Then, we opened the feedback loop and retracted the tip by 0.5 to 0.7 nm to limit the tunnelling current to a few picoamperes. Finally, we increased the voltage to values ranging from 3.5 to 4.1 V for several seconds. In many cases, this procedure also resulted in a lateral displacement of the molecule. When a subsequent STM image indicated a change in the appearance of the molecule, we recorded AFM 3 images to obtain its structure. Using this procedure, we did not observe any changes in the molecular structure other than the removal of single hydrogens from a CH 2 groups throughout our experiment...

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“…Tip termination with a CO molecule has made studies of inter-and intramolecular bonding possible (7)(8)(9)(10)(11). The CO-terminated tip itself, however, has proven to be difficult to characterize, despite experimental and theoretical approaches (12, 13), in part because it is challenging to characterize lateral forces and stiffnesses with AFM.…”

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Quantifying Molecular Stiffness and Interaction with Lateral Force Microscopy

Weymouth

Hofmann

Giessibl

2014

Science

127

117

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True atomic resolution was demonstrated for AFM more than 15 years ago, but only recently has it been possible to atomically engineer the tip apex (1-4), a technique pioneered in the STM community (5,6). Tip termination with a CO molecule has made studies of inter-and intramolecular bonding possible (7-11). The CO-terminated tip itself, however, has proven to be difficult to characterize, despite experimental and theoretical approaches (12, 13), in part because it is challenging to characterize lateral forces and stiffnesses with AFM. With any study of shortrange interactions, AFM requires that the long-range background interaction of the macroscopic tip and surface be subtracted (14). Although a full three-dimensional (3D) dataset can reconstruct the potential energy, lateral forces and stiffnesses are only accessible by taking a numerical derivative of experimentally determined energies (15), which results in substantial noise in the data.In LFM, the tip is oscillated parallel to the surface (16,17), and the recorded frequency shift (Δf) is a direct measure of the lateral stiffness (18). The subtraction of long-range contributions, necessary in normalforce AFM (where the tip oscillates normal to the surface) to identify the short-range force components, is obsolete in LFM, rendering LFM particularly appealing for measurements in which the short-range interaction is the signal of interest (e.g., Ref. (19)). We have used both normalforce AFM and LFM to characterize a CO terminated tip and quantify parameters of a model incorporating torsional springs to account for the response of the CO molecules to lateral forces.When the CO tip was first used to image pentacene, it was remarked that the image seemed to be distorted due to CO relaxation (7). Further experiments showed that the relaxation of the CO molecule on the tip was an important part of the tip-surface interaction (13). This relaxation is usually characterized as a torsional spring, with the CO bending around the metal atom to which it is bound (12).We used a CO-terminated tip to probe a single CO molecule on Cu(111). CO on Cu(111) has been well-studied and the system offers a high degree of symmetry. The asymmetry in a normal-force AFM image of a CO with a CO-terminated tip (Fig. 1A) is the result of the slight asymmetry of the tip with respect to the surface, amplified by the bending of both tip and surface CO molecules. Images collected at further distances [e.g., those shown in Fig. S1 (20)] do not show this degree of asymmetry.We acquired a 3D dataset by collecting constant-height normal-force AFM images at various distances from the surface (21). To isolate the shortrange interaction, we subtracted the raw Δf data from the Δf signal above the bare Cu surface (14). The data were then deconvoluted and integrated twice along the z-direction (where z denotes the distance to the surface) to yield the potential energy (21-23). The potential energy map of the short-range interaction at closest approach is shown in Fig. 1B.A plot of the energy as a functio...

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Formation and Characterization of a Molecule–Metal–Molecule Bridge in Real Space

Cited by 75 publications

References 34 publications

Image correction for atomic force microscopy images with functionalized tips

Image correction for atomic force microscopy images with functionalized tips

Synthesis and characterization of triangulene

Quantifying Molecular Stiffness and Interaction with Lateral Force Microscopy

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