Quantitative assessment of intermolecular interactions by atomic force microscopy imaging using copper oxide tips

Abstract

Atomic force microscopy is an impressive tool with which to directly resolve the bonding structure of organic compounds. The methodology usually involves chemical passivation of the probe-tip termination by attaching single molecules or atoms such as CO or Xe (refs ). However, these probe particles are only weakly connected to the metallic apex, which results in considerable dynamic deflection. This probe particle deflection leads to pronounced image distortions, systematic overestimation of bond lengths, and in some cases even spurious bond-like contrast features, thus inhibiting reliable data interpretation. Recently, an alternative approach to tip passivation has been used in which slightly indenting a tip into oxidized copper substrates and subsequent contrast analysis allows for the verification of an oxygen-terminated Cu tip. Here we show that, due to the covalently bound configuration of the terminal oxygen atom, this copper oxide tip (CuOx tip) has a high structural stability, allowing not only a quantitative determination of individual bond lengths and access to bond order effects, but also reliable intermolecular bond characterization. In particular, by removing the previous limitations of flexible probe particles, we are able to provide conclusive experimental evidence for an unusual intermolecular N-Au-N three-centre bond. Furthermore, we demonstrate that CuOx tips allow the characterization of the strength and configuration of individual hydrogen bonds within a molecular assembly.

In-situ characterization of O-terminated Cu tips for high-resolution atomic force microscopy

“…26 We then imaged the Cu(110)-(2 Â 1)O reconstruction with the CuOx tip, as has been done in previous studies in which STM and AFM images alongside DFT-based calculations were used to determine the tip apex. 15,16 In Fig. 2(d), an STM topography image of the copper oxide domain is shown, where the maxima within the oxide coincide with AR positions in good agreement with Ref.…”

“…2(d), an STM topography image of the copper oxide domain is shown, where the maxima within the oxide coincide with AR positions in good agreement with Ref. 16. (Interestingly, the maxima were found between the added rows in Ref.…”

“…9,[11][12][13][14] Recently, M€ onig and co-workers proposed using oxygenterminated Cu tips (CuOx tips) that show a comparable spatial resolution and much higher lateral stiffness of the tip apex. 15,16 With such CuOx tips, it is for example possible to quantitatively measure intramolecular bond lengths, 16 which appear elongated when using CO tips, 9 and to scan with video rate imaging velocities theoretically. 17 While the functionalization of a metal tip with a CO molecule is a well-controlled process, 6 CuOx tips are prepared by repeated collisions of the tip with an oxidized Cu surface.…”

Atomic-scale spin sensing with a single molecule at the apex of a scanning tunneling microscope

“…To overcome this limitation, we introduce spin sensitivity by functionalazing the tip apex with a single magnetic molecule. Such a strategy has proven successful for collecting chemical and structural information on surface-supported objects otherwise inaccessible with a metallic tip [20][21][22][23][24][25]. We use here a tip decorated by a spin S = 1 nickelocene molecule ( Fig.…”

Machine learning at the (sub)atomic scale: next generation scanning probe microscopy

“…Correcting for each of these is, however, often a matter of exploiting the tacit knowledge and expertise of seasoned 'SPM-ers' , with each research group often having its own recipes for scanning, tip preparation/recovery, and atomic manipulation that have been transferred from scientist to scientist over a period of time. Although these strategies are occasionally outlined in the literature, with some groups going so far as to provide detailed reports of the efficacy of different tip preparation and functionalisation protocols [11][12][13][14], it is still very much the case that a great deal of probe microscopy relies on rather subjective criteria, Figure 1. Scanning probe microscopy in a nutshell.…”