Cross-resistance between strain AFS009 metabolites (Howler EVO) and fludioxonil in .

Howler EVO is a biological fungicide based on metabolites of the bacterium Pseudomonas chlororaphis strain AFS009. One of the metabolites, pyrrolnitrin (PRN), is a chemical analogue of the phenylpyrrole fludioxonil used to manage gray mold of fruit crops caused by Botrytis cinerea. Resistance to fludioxonil in B.

Distance and Voltage Dependence of Orbital Density Imaging Using a CO-Functionalized Tip in Scanning Tunneling Microscopy.

The appearance of frontier molecular ion resonances measured with scanning tunneling microscopy (STM)─often referred to as orbital density images─of single molecules was investigated using a CO-functionalized tip in dependence on bias voltage and tip-sample distance. As model systems, we studied pentacene and naphthalocyanine on bilayer NaCl on Cu(111). Absolute tip-sample distances were determined by means of atomic force microscopy (AFM).

Real-space investigation of polarons in hematite FeO.

In polarizable materials, electronic charge carriers interact with the surrounding ions, leading to quasiparticle behavior. The resulting polarons play a central role in many materials properties including electrical transport, interaction with light, surface reactivity, and magnetoresistance, and polarons are typically investigated indirectly through these macroscopic characteristics. Here, noncontact atomic force microscopy (nc-AFM) is used to directly image polarons in FeO at the single quasiparticle limit.

Controlled single-electron transfer enables time-resolved excited-state spectroscopy of individual molecules.

An increasing number of scanning-probe-based spectroscopic techniques provides access to diverse electronic properties of single molecules. Typically, these experiments can only study a subset of all electronic transitions, which obscures the unambiguous assignment of measured quantities to specific quantum transitions. Here we develop a single-molecule spectroscopy that enables the access to many quantum transitions of different types, including radiative, non-radiative and redox, that is, charge-related, transitions.

All-optical subcycle microscopy on atomic length scales.

Bringing optical microscopy to the shortest possible length and time scales has been a long-sought goal, connecting nanoscopic elementary dynamics with the macroscopic functionalities of condensed matter. Super-resolution microscopy has circumvented the far-field diffraction limit by harnessing optical nonlinearities. By exploiting linear interaction with tip-confined evanescent light fields, near-field microscopy has reached even higher resolution, prompting a vibrant research field by exploring the nanocosm in motion.

Single-molecule electron spin resonance by means of atomic force microscopy.

Understanding and controlling decoherence in open quantum systems is of fundamental interest in science, whereas achieving long coherence times is critical for quantum information processing. Although great progress was made for individual systems, and electron spin resonance (ESR) of single spins with nanoscale resolution has been demonstrated, 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 microscopy represents a milestone towards this goal and was quickly followed by the demonstration of coherent oscillations and access to nuclear spins with real-space atomic resolution.

Charge-state lifetimes of single molecules on few monolayers of NaCl.

In molecular tunnel junctions, where the molecule is decoupled from the electrodes by few-monolayers-thin insulating layers, resonant charge transport takes place by sequential charge transfer to and from the molecule which implies transient charging of the molecule. The corresponding charge state transitions, which involve tunneling through the insulating decoupling layers, are crucial for understanding electrically driven processes such as electroluminescence or photocurrent generation in such a geometry. Here, we use scanning tunneling microscopy to investigate the decharging of single ZnPc and HPc molecules through NaCl films of 3 to 5 monolayers thickness on Cu(111) and Au(111).

Selectivity in single-molecule reactions by tip-induced redox chemistry.

Controlling selectivity of reactions is an ongoing quest in chemistry. In this work, we demonstrate reversible and selective bond formation and dissociation promoted by tip-induced reduction-oxidation reactions on a surface. Molecular rearrangements leading to different constitutional isomers are selected by the polarity and magnitude of applied voltage pulses from the tip of a combined scanning tunneling and atomic force microscope.

Spin-dependent vibronic response of a carbon radical ion in two-dimensional WS.

Atomic spin centers in 2D materials are a highly anticipated building block for quantum technologies. Here, we demonstrate the creation of an effective spin-1/2 system via the atomically controlled generation of magnetic carbon radical ions (CRIs) in synthetic two-dimensional transition metal dichalcogenides. Hydrogenated carbon impurities located at chalcogen sites introduced by chemical doping are activated with atomic precision by hydrogen depassivation using a scanning probe tip.

Exploiting Cooperative Catalysis for the On-Surface Synthesis of Linear Heteroaromatic Polymers via Selective C-H Activation.

Regiospecific C-H activation is a promising approach to achieve extended polymers with tailored structures. While a recent on-surface synthetic approach has enabled regioselective homocoupling of heteroaromatic molecules, only small oligomers have been achieved. Herein, selective C-H activation for dehydrogenative C-C couplings of hexaazatriphenylene by Scholl reaction is reported for the first time.

Current-Induced One-Dimensional Diffusion of Co Adatoms on Graphene Nanoribbons.

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.

Atomically resolved single-molecule triplet quenching.

The nonequilibrium triplet state of molecules plays an important role in photocatalysis, organic photovoltaics, and photodynamic therapy. We report the direct measurement of the triplet lifetime of an individual pentacene molecule on an insulating surface with atomic resolution by introducing an electronic pump-probe method in atomic force microscopy. Strong quenching of the triplet lifetime is observed if oxygen molecules are coadsorbed in close proximity.

Imaging Charge Localization in a Conjugated Oligophenylene.

Polaron formation in conjugated polymers has a major impact on their optical and electronic properties. In polyphenylene, the molecular conformation is determined by a delicate interplay between electron delocalization and steric effects. Injection of excess charges is expected to increase the degree of conjugation, leading to structural distortions of the chain.

Sub-cycle atomic-scale forces coherently control a single-molecule switch.

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 structures and influence chemical processes, but exploiting local dynamics to realize coherent control on the atomic scale remains an intriguing prospect. Chemical reactions, conformational changes and desorption have been followed on ultrafast timescales, but directly exerting femtosecond forces on individual atoms to selectively induce molecular motion has yet to be realized.

Gold-linked strings of donor-acceptor dyads: on-surface formation and mutual orientation.

Strings of gold-organic oligomers of polar units have been formed by on-surface synthesis and investigated with non-contact atomic force microscopy. The mutual alignment of dipoles within the strings is analyzed. While an alternating head-to-tail alignment might be expected from dipolar interactions, a more complicated alignment order is observed.

Manipulating and Probing the Distribution of Excess Electrons in an Electrically Isolated Self-Assembled Molecular Structure.

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.

Charge-Induced Structural Changes in a Single Molecule Investigated by Atomic Force Microscopy.

Intramolecular structural relaxations occurring upon electron transfer are crucial in determining the rate of redox reactions. Here, we demonstrate that subangstrom structural changes occurring upon single-electron charging can be quantified by means of atomically resolved atomic force microscopy (AFM) for the case of single copper(II)phthalocyanine (CuPc) molecules deposited on an ultrathin NaCl film. Imaging the molecule in distinct charge states (neutral and anionic) reveals characteristic differences in the AFM contrast.

Accessing a Charged Intermediate State Involved in the Excitation of Single Molecules.

Intermediate states are elusive to many experimental techniques due to their short lifetimes. Here, by performing single-electron alternate charging scanning tunneling microscopy of molecules on insulators, we accessed a charged intermediate state involved in the rapid toggling of individual metal phthalocyanines deposited on NaCl films. By stabilizing the transient species, we reveal how electron injection into the lowest unoccupied molecular orbital leads to a pronounced change in the adsorption geometry, characterized by a different azimuthal orientation.

Interface dipoles of Ir(ppy) on Cu(111).

The interplay of adsorption geometry and interface dipoles of the transition-metal complex Ir(ppy) on Cu(111) was studied using low-temperature scanning probe microscopy and density-functional-theory calculations. We find that the orientation of the molecule's intrinsic dipole moment with respect to the surface has a strong influence on the total energy of the different configurations, where the most stable one has the molecular dipole moment pointing out of the surface plane along the surface normal. Adsorption-induced redistribution of charges results in an additional dipole moment that also points out of the surface plane for all configurations.

Resolving the Unpaired-Electron Orbital Distribution in a Stable Organic Radical by Kondo Resonance Mapping.

The adsorption geometry and the electronic structure of a Blatter radical derivative on a gold surface were investigated by a combination of high-resolution noncontact atomic force microscopy and scanning tunneling microscopy. While the hybridization with the substrate hinders direct access to the molecular states, we show that the unpaired-electron orbital can be probed with Ångström resolution by mapping the spatial distribution of the Kondo resonance. The Blatter derivative features a peculiar delocalization of the unpaired-electron orbital over some but not all moieties of the molecule, such that the Kondo signature can be related to the spatial fingerprint of the orbital.

Implementing Functionality in Molecular Self-Assembled Monolayers.

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.

The Environment-Dependent Behavior of the Blatter Radical at the Metal-Molecule Interface.

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.