Understanding and controlling charge states at the level of individual electrons in molecular assemblies is often hindered by system complexity and the lack of reliable theoretical framework to accurately model the underlying many-body non-equilibrium electron dynamics. To address this challenge, here we construct well-defined molecular trimers and hexamers of tetrabromo-tetraazapyrene molecules by scanning probe manipulation and show that the electron dynamics can be completely rationalized using the Anderson impurity model and master equation approach. Our analysis demonstrates that such a treatment, which goes beyond the standard single-particle picture, is essential for understanding this class of molecular systems. The model not only quantitatively reproduces all features visible in measured differential conductance maps, but also uncovers the mechanism for negative differential conductance, which arises from the non-equilibrium occupancy of collective charge states. The analysis also reveals that the charging rings are not necessarily associated with changes in the total charge of the cluster, but often originate from internal charge rearrangements between the sites. These findings provide insight into fundamental quantum many-body effects in strongly interacting molecular systems and open pathways for engineering electronic phases by controlling cluster topology and the electrostatic environment.

The Volta potential (also known as contact potential) is widely used in Kelvin probe studies of corrosion, energy materials, and biomaterials, but its relation to electrochemical behavior in solution, and its possible interpretation as an electrochemical signal, remains debated and is often inconsistent. Here, we clarify the conditions under which the electrostatic contrast revealed by Kelvin probe measurements can be meaningfully correlated with redox-related behavior, and when such interpretation is not valid. We also argue for terminology that is consistent with physical theory, interfacial chemistry, and recent methodological advances such as alternating current Kelvin probe force microscopy (AC-KPFM) and open-loop electric potential microscopy (OL-EPM).

We introduce a graphite-gated architecture for bilayer graphene devices in which the active device is completely isolated from the natural graphene edges. Using a single patterned graphite-gate layer, we realize a fully electrostatically defined Hall-bar. Longitudinal and Hall measurements reveal mesoscopic transport features, including Hall-effect quenching and magnetoresistance peaks associated with boundary scattering. The dependence of the mesoscopic features on the carrierdensity shows that the effective channel width increases with the Fermi level and the electrostatic confinement at the gate-defined boundaries, and indicates that the carriers scatter at the electrostatic boundary. Raman spectroscopy and Kelvin probe force microscopy suggest that this boundary is disordered due to the used fabrication methods. Comparably, the quantum mobility in a fieldeffect transistor fabricated with the same architecture is not limited by boundary scattering and the visibility of quantum oscillations down to 4 mT suggests a record value of 2.5 x 10^6 cm2/Vs.

We investigate the nanoscale friction behaviour of MX2 monolayers (M = Mo, W; X = S, Se) on Au(111) and Ag(111) substrates with a silicon tip using classical molecular dynamics simulations with machine-learning-based force fields. This approach enables an accurate description of tip-surface interactions and friction mechanisms at the atomic scale. We observe a pronounced non-monotonic dependence of the friction force on the applied normal load, indicating a breakdown of Amontons's law at the nanoscale. Analysis of lateral force' signals and their spatial Fourier transforms reveals the coexistence of multiple sliding modes, including longitudinal sliding, lateral slip, and zig-zag motions. We show that the overall friction response is governed by the relative contributions of these motions. While the qualitative features of friction are largely substrate-independent, both the magnitude of friction and the balance between sliding modes depend sensitively on the substrate-monolayer combination. In particular, Au/MoSe2/Si exhibits significantly reduced friction due to suppression of lateral slip motion. Our results indicate that the method is broadly applicable for probing nanoscale friction in related heterostructures.

Mixed monolayer doping (MMLD) is an attractive strategy for controllable low-dose, low-energy silicon doping via surface chemistry, yet the influence of carbon removal and surface effects on electronic properties remains unclear. In this work, silicon is doped using mixed monolayers of allyldiphenylphosphine (ADP) and 1-undecene, followed by O2 plasma ashing, SiO2 capping, and rapid thermal annealing (RTA). The plasma treatment is systematically investigated, identifying conditions that effectively remove carbon while largely preserving phosphorus in the grafted layer, as confirmed by x-ray photoelectron spectroscopy (XPS). Kelvin probe force microscopy (KPFM) reveals a pronounced decrease in work function (WF) with increasing ADP molar fraction, and the SiO2 deposition method plays a key role: evaporated SiO2 combined with O2 plasma leads to a WF consistent with enhanced n-type activation, whereas sputtered SiO2 induces strong work-function pinning, independent of ADP concentration. Four-point probe and Hall measurements confirm increasing conductivity and sheet carrier density with ADP fraction, but show no significant dependence on plasma treatment, indicating that carbon-related effects are confined to the near-surface region. These results demonstrate that surface-sensitive WF changes do not necessarily reflect bulk dopant activation, and highlight the need to combine complementary characterization techniques for a reliable assessment of MMLD processes.

Achieving rapid and flexible control of friction across different material surfaces is of great significance and remains a longstanding challenging goal in modern tribology. Here, we demonstrate dynamic structural superlubricity in monolayer MoS2-coated gold surfaces induced by external mechanical actuation. By tuning the excitation frequency to the cantilever resonance, stick-slip motion is effectively suppressed, leading to a significant reduction in friction even under high-load conditions. Experimental results, supported by a modified phononic friction model, reveal that torsional vibrations reduce energy barriers and promote transitions between atomic sites. This strategy provides a universal and reversible approach for active friction control at the nanoscale.

The moiré superlattice in twisted van der Waals heterostructures is of central importance for the modulation of the electronic and optical properties of the system, yet the mechanical dissipation of such moiré systems remains largely unexplored. Here, we report the experimental observations of energy dissipation across both vertical and lateral directions along the moiré superstructures, revealing a significant increase in dissipation at moiré ridges compared to flat domains. Comparison of the measurements with a theoretical phononic dissipation model suggests that the local increase in energy dissipation originates from nonlinear instability dynamics of the moiré superstructure. Criteria for such moiré energy dissipation are established, which are expected to be broadly applicable to other van der Waals heterostructures. Our results extend the understanding of mechanical energy loss in moiré systems and support the rational design of slidtronic and twisttronic devices and nanoelectromechanical systems in general.

High-precision molecular manipulation techniques are used to control the distance between radical molecules on superconductors. Our results show that the molecules can host single electrons with a spin 1/2. By changing the distance between tip and sample, a quantum phase transition from the singlet to doublet ground state can be induced. Due to local screening and charge redistribution, we observe either charged or neutral molecules, which couple in a sophisticated way, showing quantum spin behavior that deviates from the classical spins. Dimers at different separations show multiple Yu-Shiba-Rusinov peaks in tunneling spectroscopy of varying intensity, which are in line with the superconducting two-impurity Anderson model, where singlet (S = 0) and doublet (S = 1/2) ground states are found. The assembly of chains of 3, 4, and 5 molecules shows alternating charge patterns, where the edge molecules always host a charge/spin. The tetramer is observed in two configurations, where the neutral site is moved by one position. We show that these two configurations can be switched by the action of the probing tip in a nondestructive manner, demonstrating that the tetramer is an information unit, based on single-electron charge reorganization.

The fine control of molecules or atoms in self-assemblies on surfaces is a great challenge for future nanodevices, specially for unidimensional structure formations. In this context, our study explores the adsorption behavior of a benzo-fused double [7]thiahelicene (DT7H) on Cu(111). Using non-contact atomic force microscopy (nc-AFM) at room temperature, we prove their capability in the construction of linear-like shape adlayers. After a gentle annealing of the DT7H-copper interface, the molecules are prone to form non-covalent molecular wires which orientations are influenced by the surface symmetry. Analysis of the coverage-dependence reveals a preference for double wires at lower and intermediate densities. However, this coupling is not strong enough to prevent structural changes caused by surface mobility. Wire enlargements were induced by a further increase in surface coverage, reaching the assembly of 17 parallel molecular wires near full monolayer conditions. Finally, the electronic properties of the interface were characterized by means of Kelvin probe force microscopy (KPFM). The surface potential variations indicate a reduction of the surface work function on the regions covered by molecules, showing the functionality of this interface for optoelectronic applications.

The fullerene family is known for its unique properties, facilitating the formation of large, lubricated nano‐onions and the fragmentation into small carbon clusters through various processes. In this study, we explore the thermal evolution of islands on Pt(111), focusing on the segregation of islands, the formation of fullerene dimers, and the subsequent development of large graphene sheets. Using noncontact atomic force microscopy and scanning tunneling microscopy, we observed that after annealing at , the islands showed minimal change compared to their deposition at room temperature. However, at , pairs of separated dimers appeared, which, due to their low mobility, have the potential to transform into graphene quantum dots (GQDs). Further annealing at controlled and refined the quality and dimensions of the graphene patches. This process not only provides an effective method for producing high‐quality graphene but also permits to preserve isolated dimers on the Pt(111) surface, offering valuable insights for advanced synthesis and lubrication applications.

Topological superconductivity emerges in chains or arrays of magnetic atoms coupled to a superconductor. However, the external controllability of such systems with gate voltages is detrimental for their future implementation in a topological quantum computer. Here we showcase the supramolecular assembly of radical molecules on Pb(111), whose discharge is controlled by the tip of a scanning tunneling microscope. Charged molecules carry a spin-1/2 state, as confirmed by observing Yu-Shiba-Rusinov in-gap states by tunneling spectroscopy at millikelvin temperature. Low energy modes are localized at island boundaries with a long decay towards the interior, whose spectral signature is consistent with Majorana zero modes protected by mirror symmetry. Our results open up a vast playground for the synthesis of gate-tunable organic topological superconductors.

The tribological performance of 2D materials makes them good candidates toward a reduction of friction at the macroscale. Superlubricity has been observed for graphene, MoS2, and MXenes, whereas hexagonal boron nitride (hBN) is used to reduce or tune friction. Other materials are investigated as potential candidates for low-lubricity applications. Specifically, borophene is predicted to have ultralow friction. Here, we experimentally investigate the frictional properties of borophene and use a borophene/hBN lateral heterostructure to directly compare the tribological properties of the two complementary 2D materials. In particular, we investigate the friction between a sliding tip and (i) the weakly corrugated X6-borophene layer on Ir(111) or (ii) the hBN/Ir(111) superlattice structures with a strongly corrugated moiré reconstruction. Our experimental study performed in ultrahigh vacuum at room temperature combined with a Prandtl-Tomlinson (PT) model calculation confirms the superlubricity predicted for borophene, while hBN, which exhibits a higher friction, is nevertheless confirmed as a low friction material. Ab initio calculations show that the lower friction of X6-borophene with respect to hBN can be rationalized by weaker tip/surface interactions. In addition, we assess structural and electrical properties of borophene and hBN by using scanning probe techniques and compare their dissipation under the oscillating tip to investigate the possible path of energy dissipation occurring during friction. Our study demonstrates the low frictional properties of borophene and the potential of lateral heterostructure investigations to directly compare the properties of these 2D materials.

A comprehensive study of monolayer MoS2 on a single-crystal Au(111) surface is reported, combining ultra-high vacuum scanning probe microscopy with advanced computational methods. Kelvin probe force microscopy precisely quantified the work function of the heterointerface, while topographic analysis by contact and non-contact atomic force microscopy revealed a moiré superlattice with an interfacial twist angle of 0.45° between MoS2 and Au(111). To accurately model and predict the twist angle and out-of-plane corrugation of these moiré superlattices, a semi-anisotropic interlayer force field based on density functional theory is developed. This avoids the limitations of conventional pairwise potentials, and our results show excellent agreement with experiments. Furthermore, friction simulations revealed a non-monotonic dependence on the interfacial twist angle, with small angles exhibiting unexpectedly large shear stress, suggesting that MoS2 could serve as an effective superlubric coating for gold. This work establishes a robust framework for the investigation of van der Waals heterostructures, bridging nanoscale experimental observations with first-principles calculations, and providing insights for the design of novel nanoscale devices with tailored electronic, mechanical, and tribological properties.

Surface reconstructions play a crucial role in surface science because of their influence on the adsorption and arrangement of molecules or nanoparticles. On the Au(111) surface, the herringbone reconstruction presents favorable anchoring at the elbow sites, where the highest reactivity is found. In this work, we deposited large organic perchlorinated molecules on a Au(111) surface via high-vacuum electrospray deposition. With noncontact atomic force microscopy measurements at room temperature, we studied the molecular structures formed on the surface before and after annealing at different temperatures. We found that a supramolecular layer is formed and that a hexagonal reconstruction of the Au(111) surface is induced. After high-temperature annealing, the molecules are removed, but the hexagonal Au(111) surface reconstruction is preserved. With the hexagonal Au(111) surface reconstruction, a periodic lattice of anchoring sites is formed.

Supramolecular materials provide a pathway for achieving precise, highly ordered structures while exhibiting remarkable response to external stimuli, a characteristic not commonly found in covalently bonded materials. The design of self-assembled materials, where properties could be predicted/design from chemical nature of the individual building blocks, hinges upon our ability to relate macroscopic properties to individual building blocks - a feat which has thus far remained elusive. Here, a design approach is demonstrated to chemically engineer the thermal expansion coefficient of 2D supramolecular networks by over an order of magnitude (\boldmath 120 to \boldmath 1000 × 10-6 K-1). This systematic study provides a clear pathway on how to carefully design the thermal expansion coefficient of a 2D molecular assembly. Specifically, a linear relation has been identified between the length of decorating alkyl chains and the thermal expansion coefficient. Counter-intuitively, the shorter the chains the larger is the thermal expansion coefficient. This precise control over thermo-mechanical properties marks a significant leap forward in the de-novo design of advanced 2D materials. The possibility to chemically engineer their thermo-mechanical properties holds promise for innovations in sensors, actuators, and responsive materials across diverse fields.

Phosphorus pentamer (cyclo-P5-) ions are unstable in nature but can be synthesized at the Ag(111) surface. Unlike monolayer black phosphorous, little is known about their electronic properties when in contact with metal electrodes, although this is crucial for future applications. Here we characterize the atomic structure of cyclo-P5 assembled on Ag(111) using atomic force microscopy with functionalized tips and density functional theory. Combining force and tunneling spectroscopy, we find that a strong charge transfer induces an inward dipole moment at the cyclo-P5/Ag interface as well as the formation of an interface state. We probe the image potential states by field-effect resonant tunneling and quantify the increase of the local change of work function of 0.46 eV at the cyclo-P5 assembly. Our results suggest that the high-quality of the cyclo-P5/Ag interface might serve as a prototypical system for electric contacts in phosphorus-based semiconductor devices.

Against conventional wisdom, corrugated grain boundaries in polycrystalline graphene, grown on Pt(111) surfaces, are shown to exhibit negative friction coefficients and non-monotonic velocity dependence. Using combined experimental, simulation, and modeling efforts, the underlying energy dissipation mechanism is found to be dominated by dynamic buckling of grain boundary dislocation protrusions. The revealed mechanism is expected to appear in a wide range of polycrystalline two-dimensional material interfaces, thus supporting the design of large-scale dry superlubric contacts.

Magnetic impurities on superconductors present a viable platform for building advanced applications in quantum technologies. However, a controlled manipulation of their quantum states continues to pose a significant challenge, hindering the progress in the field. Here we show the manipulation of magnetic states in the radical molecule 4,5,9,10-tetrabromo-1,3,6,8-tetraazapyrene (TBTAP) on a Pb(111) superconducting surface using low-temperature scanning tunneling microscopy. Tunneling spectra reveal Yu-Shiba-Rusinov (YSR) states near the Fermi energy in isolated molecules. A quantum phase transition from singlet to doublet ground state is induced by changing the tip-molecule distance. Additionally, the presence of a second TBTAP molecule allows tuning of the YSR state position by altering the relative distance and can induce splitting of the YSR states for certain orientations. The construction of molecular chains up to pentamers shows periodic arrangements of charged and neutral molecules, with even-numbered chains forming a charged dimer structure at one end. Information can be encoded in these chains by switching the dimer position. These findings elucidate interactions between molecular assemblies and superconducting substrates, paving the way for advanced quantum-state engineering.

The transition from single to multiple atomic slips, theoretically expected and important in atomic-scale friction, has never been demonstrated experimentally as a function of velocity. Here we show by highresolution friction force microscopy on monolayer MoS2/Au(111) that multiple slips leave a unique footprint-a frictional velocity weakening. Specifically, in a wide velocity interval from 10 to 100 nm/s, friction surprisingly decreases. Model simulations show a similar nonmonotonic behavior at velocities in quantitative agreement with experiment. Results suggest a velocity-corrugation phase diagram, whose validity is proposed more generally.