Probing relaxations of atomic-scale junctions in the Pauli repulsion range

Abstract

Clean metal as well as C 60 -terminated tips of an atomic force microscope probe the interaction with C 60 molecules adsorbed on Cu(111) and Pb(111). The force measurements unveil a monotonic shift of the point of maximum attraction with the bias voltage. The conventional superposition of long-range van der Waals and electrostatic forces with short-range Pauli repulsion does not reproduce the shift. By phenomenologically including bias-dependent relaxations of the electrode geometry in the analytical expression for the short-range force the experimental data can qualitatively be described.

Charge Transfer-Mediated Dramatic Enhancement of Raman Scattering upon Molecular Point Contact Formation

“…The j STM –Δ z curve is in agreement with previous experiments on Cu(111) . The absence of a jump-to-contact behavior in the contact regime is explained by a gradual transition of the interaction between two C 60 molecules from the attractive (van der Waals) to repulsive (Pauli) range . This result shows that chemical interactions at the MPC play a critical role in the enhancement mechanism.…”

Extraction of Chemical Reactivity and Structural Relaxations of an Organic Dye from the Short-Range Interaction with a Molecular Probe

“…7,8 With these tools at hand, the chemical bond order was determined 9 and intramolecular changes upon chemical reactions were identified. 10 The subpicometer control of the distance between an intentionally terminated AFM tip and the surface further enabled the observation of the interaction between reaction partners at the single-atom and singlemolecule level, such as the coupling between two CO molecules, 11 the bending of molecular adsorbates in the vicinity of a CO-terminated tip, 12 the probing of physisorbed and chemisorbed states in a CO−Fe contact, 13 relaxations 14 and nonequilibrium bond forces 15 in C 60 −C 60 junctions, the identification of chemically reactive Fe cluster sites, 16 the probing of acidity of surface hydroxyl groups with a OHterminated tip, 17 the motion of atomic 18 and molecular 19 terminations of the tip apex in the vicinity of the surface as well as forces and energies at the verge of a chemical reaction. 20 Moreover, insights into the force fields atop adsorbed molecules, 21 the resolution of H atoms at the onset of Pauli repulsion between the functionalized probe and the imaged molecule 22 as well as the anisotropic charge distributions at surfaces 23 were reported.…”

“…Previously, shifts of the PMA were likewise interpreted as a manifestation of intramolecular adsorption heights 46 or as electric-field-induced relaxations of the junction. 14 In conclusion, the spatial resolution of a CO-terminated AFM tip can be used to explore via pointwise spectroscopy of the short-range interaction the chemical reactivity of intramolecular moieties as well as their relaxed adsorption heights. The PMA magnitude is interpreted as a measure for the local reactivity, while its position reflects the variation of atomic adsorption heights.…”

“…Simulated adsorption heights (squares in Figure e,f) likewise exhibit an essentially linear behavior with a variation of the adsorption heights by 51 and 65 pm perpendicular and parallel to , respectively. Previously, shifts of the PMA were likewise interpreted as a manifestation of intramolecular adsorption heights or as electric-field-induced relaxations of the junction …”