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Understanding and controlling decoherence in open quantum systems is of fundamental interest in science, whereas achieving long coherence times is critical for quantum information processing1. Although great progress was made for individual systems, and electron spin resonance (ESR) of single spins with nanoscale resolution has been demonstrated2–4, the understanding of decoherence in many complex solid-state quantum systems requires ultimately controlling the environment down to atomic scales, as potentially enabled by scanning probe microscopy with its atomic and molecular characterization and manipulation capabilities. Consequently, the recent implementation of ESR in scanning tunnelling microscopy5–8represents a milestone towards this goal and was quickly followed by the demonstration of coherent oscillations9,10and access to nuclear spins11with real-space atomic resolution. Atomic manipulation even fuelled the ambition to realize the first artificial atomic-scale quantum devices12. However, the current-based sensing inherent to this method limits coherence times12,13. Here we demonstrate pump–probe ESR atomic force microscopy (AFM) detection of electron spin transitions between non-equilibrium triplet states of individual pentacene molecules. Spectra of these transitions exhibit sub-nanoelectronvolt spectral resolution, allowing local discrimination of molecules that only differ in their isotopic configuration. Furthermore, the electron spins can be coherently manipulated over tens of microseconds. We anticipate that single-molecule ESR-AFM can be combined with atomic manipulation and characterization and thereby paves the way to learn about the atomistic origins of decoherence in atomically well-defined quantum elements and for fundamental quantum-sensing experiments.

One-dimensional diffusion of Co adatoms on graphene nanoribbons has been induced and investigated by means of scanning tunnelling microscopy (STM). To this end, the nanoribbons and the Co adatoms have been imaged before and after injecting current pulses into the nanoribbons, with the STM tip in direct contact with the ribbon. We observe current-induced motion of the Co atoms along the nanoribbons, which is approximately described by a distribution expected for a thermally activated one-dimensional random walk. This indicates that the nanoribbons reach temperatures far beyond 100 K, which is well above the temperature of the underlying Au substrate. This model system can be developed further for the study of electromigration at the single-atom level.

The interaction of a molecule with a specific surface has been shown to produce consistent unidirectional motion driven by voltage pulses. The mechanism can even facilitate the transport of molecular cargo.

Scanning probe techniques can leverage atomically precise forces to sculpt matter at surfaces, atom by atom. These forces have been applied quasi-statically to create surface structures1–7and influence chemical processes8,9, but exploiting local dynamics10–14to realize coherent control on the atomic scale remains an intriguing prospect. Chemical reactions15–17, conformational changes18,19and desorption20have been followed on ultrafast timescales, but directly exerting femtosecond forces on individual atoms to selectively induce molecular motion has yet to be realized. Here we show that the near field of a terahertz wave confined to an atomically sharp tip provides femtosecond atomic-scale forces that selectively induce coherent hindered rotation in the molecular frame of a bistable magnesium phthalocyanine molecule. Combining lightwave-driven scanning tunnelling microscopy21–24with ultrafast action spectroscopy10,13, we find that the induced rotation modulates the probability of the molecule switching between its two stable adsorption geometries by up to 39 per cent. Mapping the response of the molecule in space and time confirms that the force acts on the atomic scale and within less than an optical cycle (that is, faster than an oscillation period of the carrier wave of light). We anticipate that our strategy might ultimately enable the coherent manipulation of individual atoms within single molecules or solids so that chemical reactions and ultrafast phase transitions can be manipulated on their intrinsic spatio-temporal scales.

Exploiting single electrical charges and their mutual interactions for computation has been proposed as a concept for future nanoelectronics. Controlling and probing charge transfer in electrically isolated atomic-scale structures are fundamental to push its experimental realization. Here, we controllably inject individual excess electrons and study their distribution in a self-assembled structure supported on a nonconductive substrate. The self-assembly ensures structural order down to the atomic scale. Depending on the charge state of the molecular assembly, intermolecular electron hopping and specific electron distributions have been resolved by atomic force microscopy, clarifying the charge-transfer pathways in the tunnel-coupled structure. When mutual charge interactions were exploited, control over specific charge distributions in the self-assembled structure has been achieved with single-molecule precision, paving the way toward the design of data processing platforms based on molecular nanostructures.

The planar heterocyclic molecules 1,6,7,12-tetraazaperylene on a Ag(111) metal substrate show different charging characteristics depending on their local environment: next to vacancies in self-assembled islands, molecules can be charged by local electric fields, whereas their charge state is fixed otherwise. This enables the activation of selected molecules inside islands by vacancy creation from scanning-probe-based manipulation. This concept allows for combining the precise mutual atomic-scale alignment of molecules by self-assembly, on one hand, and the implementation of specific functionality into otherwise homogeneous monolayers, on the other. Activated molecules in the direct neighborhood influence each other in their charging characteristics, suggesting their use as molecular quantum cellular automata. Surprisingly, only very few interacting molecules exhibit a rich spectroscopic signature, which offers the prospect of implementing complex functionality in such structures in the future.

Stable organic radicals have potential applications for building organic spintronic devices. To fulfill this potential, the interface between organic radicals and metal electrodes must be well characterized. Here, through a combined effort that includes synthesis, scanning tunneling microscopy, X-ray spectroscopy, and single-molecule conductance measurements, we comprehensively probe the electronic interaction between gold metal electrodes and a benchtop stable radical—the Blatter radical. We find that despite its open-shell character and having a half-filled orbital close to the Fermi level, the radical is stable on a gold substrate under ultrahigh vacuum. We observe a Kondo resonance arising from the radical and spectroscopic signatures of its half-filled orbitals. By contrast, in solution-based single-molecule conductance measurements, the radical character is lost through oxidation with charge transfer occurring from the molecule to metal. Our experiments show that the stability of radical states can be very sensitive to the environment around the molecule.

Electron transfer plays a crucial part in many chemical reactions1,2, including photosynthesis, combustion and corrosion. But even though redox-state transitions change the electronic structure of the molecules involved, mapping these changes at the single-molecule level is challenging. Scanning tunnelling microscopy provides insights into the orbital structure3of single molecules and their interactions4,5, but requires the use of a conductive substrate that keeps molecules in a given charge state and thereby suppresses redox-state transitions. Atomic force microscopy can be used on insulating substrates to obtain structural6and electrostatic7,8information but does not generally access electronic states. Here we show that when synchronizing voltage pulses that steer electron tunnelling between a conductive atomic force microscope tip and a substrate with the oscillation of the tip, we can perform tunnelling experiments on non-conductive substrates and thereby map the orbital structure of isolated molecules as a function of their redox state. This allows us to resolve previously inaccessible electronic transitions in space and energy and to visualize the effects of electron transfer and polaron formation on individual molecular orbitals. We anticipate that our approach will prove useful for the investigation of complex redox reactions and charging-related phenomena with sub-ångström resolution.

The bonds in metal organic networks on surfaces govern the resulting geometry as well as the electronic properties. Here, we study the nature of these bonds by forming phenazine–copper complexes on a copper surface by means of atomic manipulation. The structures are characterized by a combination of scanning probe microscopy and density functional theory calculations. We observed an increase of the molecule–substrate distance upon covalent bond formation and an out-of-plane geometry that is in direct contradiction with the common expectation that these networks are steered by coordination bonds. Instead, we find that a complex energy balance of hybridization with the substrate, inhomogeneous Pauli repulsion, and elastic deformation drives the phenazine–copper interaction. Most remarkably, this attractive interaction is not driven by electron acceptor properties of copper but is of completely different donation/back-donation mechanism between molecular π-like orbitals and sp-like metal states. Our findings show that the nature of bonds between constituents adsorbed on surfaces does not have to follow the common categories.

Intermolecular single-electron transfer on electrically insulating films is a key process in molecular electronics1–4and an important example of a redox reaction5,6. Electron-transfer rates in molecular systems depend on a few fundamental parameters, such as interadsorbate distance, temperature and, in particular, the Marcus reorganization energy7 . This crucial parameter is the energy gain that results from the distortion of the equilibrium nuclear geometry in the molecule and its environment on charging8,9. The substrate, especially ionic films10 , can have an important influence on the reorganization energy11,12. Reorganization energies are measured in electrochemistry13 as well as with optical14,15and photoemission spectroscopies16,17, but not at the single-molecule limit and nor on insulating surfaces. Atomic force microscopy (AFM), with single-charge sensitivity18–22, atomic-scale spatial resolution20 and operable on insulating films, overcomes these challenges. Here, we investigate redox reactions of single naphthalocyanine (NPc) molecules on multilayered NaCl films. Employing the atomic force microscope as an ultralow current meter allows us to measure the differential conductance related to transitions between two charge states in both directions. Thereby, the reorganization energy of NPc on NaCl is determined as (0.8 ± 0.2) eV, and density functional theory (DFT) calculations provide the atomistic picture of the nuclear relaxations on charging. Our approach presents a route to perform tunnelling spectroscopy of single adsorbates on insulating substrates and provides insight into single-electron intermolecular transport. An atomic force microscope is used as an ultralow current sensor to measure the reorganization energy of a single naphthalocyanine molecule during a redox reaction on a NaCl film.

Watching a single molecule move on its intrinsic timescale has been one of the central goals of modern nanoscience, and calls for measurements that combine ultrafast temporal resolution with atomic spatial resolution. Steady-state experiments access the requisite spatial scales, as illustrated by direct imaging of individual molecular orbitals using scanning tunnelling microscopy or the acquisition of tip-enhanced Raman and luminescence spectra with sub-molecular resolution. But tracking the intrinsic dynamics of a single molecule directly in the time domain faces the challenge that interactions with the molecule must be confined to a femtosecond time window. For individual nanoparticles, such ultrafast temporal confinement has been demonstrated by combining scanning tunnelling microscopy with so-called lightwave electronics, which uses the oscillating carrier wave of tailored light pulses to directly manipulate electronic motion on timescales faster even than a single cycle of light. Here we build on ultrafast terahertz scanning tunnelling microscopy to access a state-selective tunnelling regime, where the peak of a terahertz electric-field waveform transiently opens an otherwise forbidden tunnelling channel through a single molecular state. It thereby removes a single electron from an individual pentacene molecule’s highest occupied molecular orbital within a time window shorter than one oscillation cycle of the terahertz wave. We exploit this effect to record approximately 100-femtosecond snapshot images of the orbital structure with sub-ångström spatial resolution, and to reveal, through pump/probe measurements, coherent molecular vibrations at terahertz frequencies directly in the time domain. We anticipate that the combination of lightwave electronics and the atomic resolution of our approach will open the door to visualizing ultrafast photochemistry and the operation of molecular electronics on the single-orbital scale.

Einzelne Moleküle, die auf ultradünnen Isolatorfilmen adsorbiert sind, bieten eine Spielwiese für Experimente mit dem Rastertunnelmikroskop (RTM).Das Beispiel des Pentazen zeigt, dass diese Experimente die Grenzorbitale der Moleküle ganz direkt abbilden können. Besonders interessant ist dies bei der Synthese neuer Moleküle. Mit dem Tunnelstrom lässt sich ein Gold-Atom chemisch an das Pentazen binden und bildet so einen Gold-Pentazen-Komplex. Dabei verändern sich die Struktur, Energie und Besetzung der Orbitale. Das RTM kann diese Änderungen direkt messen und abbilden. Solche Experimente eröffnen besonders der molekularen Elektronik neue Möglichkeiten.

The scanning tunnelling microscope, initially invented to image surfaces down to the atomic scale, has been further developed in the last few years to an operative tool, with which atoms and molecules can be manipulated at will at low substrate temperatures in different manners to create and investigate artificial structures, whose properties can be investigated employing spectroscopic dI/dVmeasurements. The tunnelling current can be used to selectively break chemical bonds, but also to induce chemical association. These possibilities give rise to startling new opportunities for physical and chemical experiments on the single atom and single molecule level. Here we provide a short overview on recent results obtained with these techniques.

With the scanning tunneling microscope (STM) it became possible to perform controlled manipulations down to the scale of small molecules and single atoms, leading to the fascinating aspect of creating manmade structures on atomic scale. Here we present a short review of our work in the last five years on atomic scale manipulation investigations. Upon soft lateral manipulation of adsorbed species, in which only tip/particle forces are used, three different manipulation modes (pushing, pulling, sliding) can be discerned. We show that also manipulation of highly coordinated native substrate atoms is possible and demonstrate the application of these techniques as local analytic and synthetic chemistry tools with important consequences on surface structure research. Vertical manipulation of Xe and CO is presented, leading to improved imaging and even chemical contrast with deliberately functionalized tips. For the transfer of CO it is shown that beside tip voltage current effects play also an important role. This is also the case for the dissociation of molecules. With CO transferred deliberately to the tip we have also succeeded to perform vibrational spectroscopy on single molecules. Furthermore, first experiments aiming for the transfer of all manipulation modes to thin insulating films are described.

Die meisten Eigenschaften von Atomen sind durch die Zahl der Elektronen in ihrer äußeren Hülle bestimmt. Deshalb sind Messungen, die verschiedene Ladungszustände atomar aufgelöst unterscheiden können, von großer Bedeutung für die Grundlagenforschung. Auch für die Entwicklung zukünftiger, miniaturisierter Bauteile der Informationstechnik, die auf Speicherung und Transport einzelner Elektronen basieren soll, sind solche Messungen von fundamentalem Interesse. Unserer Gruppe ist es gelungen, den Ladungszustand von einzelnen Gold und Silberatomen mit dem Rasterkraftmikroskop zu untersuchen.

Auf der Suche nach immer kleineren elektronischen Geräten greifen die Wissenschaftler nach einzelnen Molekülen als elektronische Bauteile. Naphthalocyanin-Moleküle eignen sich als molekulare Schalter, die man – anders als die bisher bekannten molekularen Schalter – untereinander koppeln kann.

Mit einem Rastertunnelmikroskop lassen sich nicht nur Oberflächen atomar abbilden, es kann auch dazu genutzt werden, Atome auf einer Oberfläche zu manipulieren. Auf diese Weise ist es erstmals gelungen, den Ladungszustand einzelner Goldatome zu verändern, ohne diese dabei seitlich zu verschieben.