[en] Clean metal as well as C₆₀-terminated tips of an atomic force microscope probe the interaction with C₆₀ 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. (paper)

[en] The concept of spontaneous pattern formation in epitaxial growth is currently actively explored as a promising pathway for lateral nanostructuring of surfaces. Often, the origin of self-organization is traced back to the presence of an excess energy barrier for adatom diffusion associated with asymmetric features in the crystalline structure, the Ehrlich-Schwoebel barrier. Upon growth of Cu on vicinal Cu surfaces at moderate substrate temperatures a step-meandering instability develops, resulting in an in-plane patterning of the surfaces at the nanometre scale with a temperature- and flux-dependent characteristic wavelength. This meandering instability is superseded by a step-bunching instability during growth at higher temperatures. Specifically, the meandering instability acts as a precursor to the bunching instability, indicating that a one-dimensional treatment of bunching in step flow growth is not sufficient. These nanostructured surfaces might be used as templates in order to guide the growth of materials which do not show spontaneous self-organization

[en] Based on helium atom beam diffraction and scanning tunneling microscopy data, the coexistence of a meandering and a bunching instability during homoepitaxial step flow growth is established in a class of nonreconstructed, metallic vicinal surfaces, Cu (1,1,n), n=5,9,17. Specifically, the meandering instability is shown to act as a precursor to the bunching instability, indicating that a one-dimensional treatment of bunching in step flow growth is not sufficient. Our findings might be generic to step flow growth in kinetically restricted systems

[en] The conductance of single atoms and molecules is investigated with a low-temperature scanning tunnelling microscope. In a controlled and reproducible way, clean Ag(111) surfaces, individual silver atoms on Ag(111) as well as individual C₆₀ molecules adsorbed on Cu(100) are contacted with the tip of the microscope. Upon contact the conductance changes discontinuously in the case of the tip-surface junction while the tip-atom and tip-molecule junctions exhibit a continuous transition from the tunnelling to the contact regime

[en] Experiments using the tip of a scanning tunnelling microscope to contact atoms and molecules adsorbed on surfaces are reviewed. Conductance quantization upon forming or breaking a contact between the tip and surfaces as well as between the tip and specifically chosen atoms and molecular orbitals is addressed. Imaging the contact area prior to and after contact measurements allows one to monitor the status of the contacted object as well as that of the contacting electrodes. Spectroscopy with the tip in contact with individual atoms or molecules reveals the reproducibility of and control over such experiments today. (topical review)

[en] The conductance of oriented C₆₀ molecules on Au(111) and Cu(100) was investigated using a low-temperature scanning tunnelling microscope. A remarkable dependence of spectra of the differential conductance on the adsorption orientation is observed for Au(111) that is almost absent for Cu(100). For C₆₀ adsorbed on Au(111), the spatial distribution of the three lowest unoccupied molecular orbitals is revealed by maps of the differential conductance

[en] Artificially assembled linear atomic clusters, CoCu_nCoCu_m, are used to explore variations of the Kondo effect at the two Co sites. For all investigated Cu_n chain lengths () the addition of a single Cu atom to one edge Co atom of the chain () strongly reduces the amplitude of the Abrikosov–Suhl–Kondo resonance of that Co atom. Concomitantly, the resonance line width is more than halved. On the contrary, the Kondo effect of the opposite edge Co atom remains unaffected. Hybridization together with the linear geometry of the cluster are likely to drive the effect. (paper)

[en] The tip of a cryogenic scanning tunnelling microscope is used to controllably contact single atoms adsorbed on metal surfaces. The transition between tunnelling and contact is gradual for silver, while contact to adsorbed gold atoms is abrupt. The single-atom junctions are stable and enable spectroscopic measurements of, e.g., the Abrikosov-Suhl resonance of single Kondo impurities.

[en] Vibronic excitations in molecules are key to the fundamental understanding of the interaction between vibrational and electronic degrees of freedom. In order to probe the genuine vibronic properties of a molecule even after its adsorption on a surface appropriate buffer layers are of paramount importance. Here, vibrational progression in both molecular frontier orbitals is observed with submolecular resolution on a graphene-covered metal surface using scanning tunnelling spectroscopy. Accompanying calculations demonstrate that the vibrational modes that cause the orbital replica in the progression share the same symmetry as the electronic states they couple to. In addition, the vibrational progression is more pronounced for separated molecules than for molecules embedded in molecular assemblies. The entire vibronic spectra of these molecular species are moreover rigidly shifted with respect to each other. This work unravels intramolecular changes in the vibronic and electronic structure owing to the efficient reduction of the molecule–metal hybridization by graphene. (paper)

[en] Magnetic single-atom contacts have been controllably fabricated with a scanning tunnelling microscope. A voltage-dependent spin valve effect with conductance variations of ∼40% is reproducibly observed from contacts comprising a Cr-covered tip and Co and Cr atoms on ferromagnetic nanoscale islands on W(110) with opposite magnetization. The spin-dependent conductances are interpreted from first-principles calculations in terms of the orbital character of the relevant electronic states of the junction.