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Electron transfer in weakly coupled molecules typically occurs via a transient charging of the molecule by tunneling electrons. We report on the permanent electron injection into a single molecule in a controlled manner by employing low-temperature (LT) scanning tunneling microscopy (STM). Our model system is Au(III) 5,10,15,20-tetraphenylporphyrin (AuTPP) single molecules physisorbed on a single-crystal Au(111) surface. The results of our combined topographic STM images, tunnel conductance dI/dV spectra and two-dimensional spatial dI/dV mapping experiments support a switching of the molecular charge state of AuIIITPP on Au(111) induced by STM manipulation. We successfully realized STM tip-induced chemical reduction reactions in single AuTPP molecules, reducing AuIIITPP to AuIITPP, with the extra electron distributed either preferentially in a 5d state of the center gold ion or the aromatic (pi-conjugated) tetrapyrrole macrocycle of the porphyrin ligand. Details of the electron transfer process were identified and visualized with intra-molecular resolution by single-molecule tunneling spectroscopy and orbital mapping.

Electrochemical microscopy techniques have extended the understanding of surface chemistry to the micrometer and even sub-micrometer level. However, fundamental questions related to charge transport at the solidelectrolyte interface, such as catalytic reactions or operation of individual ion channels, require improved spatial resolutions down to the nanoscale. A prerequisite for single-molecule electrochemical sensitivity is the reliable detection of a few electrons per second, that is, currents in the atto-Ampere (10−18 A) range, 1000 times below today’s electrochemical microscopes. This work reports local cyclic voltammetry (CV) measurements at the solid-liquid interface on ferrocene self-assembled monolayer (SAM) with sub-atto-Ampere sensitivity and simultaneous spatial resolution < 80 nm. Such sensitivity is obtained through measurements of the charging of the local faradaic interface capacitance at GHz frequencies. Nanometer-scale details of different molecular organizations with a 19% packing density difference are resolved, with an extremely small dispersion of the molecular electrical properties. This is predicted previously based on weak electrostatic interactions between neighboring redox molecules in a SAM configuration. These results open new perspectives for nano-electrochemistry like the study of quantum mechanical resonance in complex molecules and a wide range of applications from electrochemical catalysis to biophysics.

We demonstrate here that theory-assisted near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy enables the site-sensitive monitoring of on-surface chemical reactions, thus, providing information not accessible by other techniques. As a prototype example, we have used free-base 5,10,15-tris(pentafluorophenyl)corroles (3H-TpFPC) adsorbed on Ag(111) and present a detailed investigation of the angle-dependent NEXAFS of this molecular species as well as of their thermally induced derivatives. For this, we have recorded experimental C and N K-edge NEXAFS spectra and interpret them based on XAS cross-section calculations by using a continuous fraction approach and core-hole including multiprojector PAW pseudopotentials within DFT. We have characterized the as-deposited low temperature (200 K) phase and unraveled the subsequent changes induced by dehydrogenation (at 330 K) and ring-closure reactions (at 430 K). By exemplarily obtaining profound insight into the on-surface chemistry of free-base corrolic species adsorbed on a noble metal this work highlights how angle-dependent XAS combined with accurate theoretical modeling can serve for the investigation of on-surface reactions, whereby even highly similar molecular structures, such as tautomers and isomers, can be distinguished.

We report the chemical synthesis and characterization of the stable 5,15-bis(pentafluorophenyl)-10-(trimethylsilylethynyl)corrole which serves as a precursor for the subsequent in situ sila-Sonogashira-cross-coupling reaction and metalation with copper(II) acetate. Under ambient conditions and a common catalyst system the reaction with 1-iodopyrene occurred within five hours. Due to the direct conjugation of the 18π-electronic system of the corrole macrocycle over the alkynyl group to the pyrene moiety the optical transitions in the Soret (B-) band Q-band region are significantly altered. The copper corrole exhibited complex hyperfine and superhyperfine structure in the EPR spectrum. The assignment of the EPR spectrum reveals the existence of an axial [CuII-cor∙+] species.

Radical cyclization is among the most powerful and versatile reactions for constructing mono- and polycyclic systems, but has, to date, remained unexplored in the context of on-surface synthesis. We report the controlled on-surface synthesis of stable corrole radicals on Ag(111) via site-specific dehydrogenation of a pyrrole N-H bond in the 5,10,15-tris(pentafluoro-phenyl)-corrole triggered by annealing at 330 K under ultrahigh-vacuum conditions. We reveal a thermally induced regioselective cyclization reaction mediated by a radical cascade and resolve the reaction mechanism of the pertaining cyclodefluorination reaction at the single-molecule level. Via intramolecularly resolved probing of the radical-related Kondo signature, we achieve real space visualization of the distribution of the unpaired electron density over specific sites within the corrole radical. Annealing to 550 K initiates intermolecular coupling reactions, producing an extended π-conjugated corrole system.

Corrole compounds attract increasing interest due to their potential to stabilize high-valent metal states. X-ray spectroscopy is a powerful tool for the investigation and development of functional interfaces. For corrolic species, however, the required reference data are missing. Here, we employ a multitechnique X-ray investigation of thin films of the prototypical free-base 5,10,15-tris(pentafluorophenyl)corrole (3H-TpFPC) grown on the Ag(111) surface under ultrahigh vacuum conditions. Ultrapure corrole multilayer samples are prepared and characterized by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. In parallel, the X-ray fingerprints are simulated using the continued-fraction approach within density functional theory (DFT) for extended, (quasi-)periodic molecular structures. An excellent agreement between experimental and theoretical spectra enables a thorough interpretation of the detailed spectral features and proves an accurate descripti...

Electrochemical conversion of CO2 to alcohols is one of the most challenging methods of conversion and storage of electrical energy in the form of high-energy fuels. The challenge lies in the catalyst design to enable its real-life implementation. Herein, we demonstrate the synthesis and characterization of a cobalt(III) triphenylphosphine corrole complex, which contains three polyethylene glycol residues attached at the meso-phenyl groups. Electron-donation and therefore reduction of the cobalt from cobalt(III) to cobalt(I) is accompanied by removal of the axial ligand, thus resulting in a square-planar cobalt(I) complex. The cobalt(I) as an electron-rich supernucleophilic d8-configurated metal centre, where two electrons occupy and fill up the antibonding dz2 orbital. This orbital possesses high affinity towards electrophiles, allowing for such electronically configurated metals reactions with carbon dioxide. Herein, we report the potential dependent heterogeneous electroreduction of CO2 to ethanol or methanol of an immobilized cobalt A3-corrole catalyst system. In moderately acidic aqueous medium (pH = 6.0), the cobalt corrole modified carbon paper electrode exhibits a Faradaic Efficiency (FE%) of 48 % towards ethanol production., Electrochemical conversion of carbon dioxide to ethanol is one of the most challenging energy conversion reactions. Here the authors show selective electroreduction of carbon dioxide to ethanol by using a functionalized cobalt A3-corrole catalyst immobilized on a carbon paper electrode.

Oxygen reduction and water oxidation are two key processes in fuel cell applications. The oxidation of water to dioxygen is a 4 H+/4 e− process, while oxygen can be fully reduced to water by a 4 e−/4 H+ process or partially reduced by fewer electrons to reactive oxygen species such as H2O2 and O2 −. We demonstrate that a novel manganese corrole complex behaves as a bifunctional catalyst for both the electrocatalytic generation of dioxygen as well as the reduction of dioxygen in aqueous media. Furthermore, our combined kinetic, spectroscopic, and electrochemical study of manganese corroles adsorbed on different electrode materials (down to a submolecular level) reveals mechanistic details of the oxygen evolution and reduction processes.

We report the synthesis of alkoxy-functionalized Mn(III)–A3-corrole and Mn(V)–corrole complexes. Depending on the length of the alkoxy chain attached to the meso-tetrafluoropenyl moiety, the oxidation state of the central manganese ion could either be tuned to +III in case of O–C6 or O–C12 chains, or to +V in case of O–C18 chains. The Mn(V)–corrole displays metal-centered redox chemistry in solution. Reduction with SnCl2 or Ph3P leads to the clean conversion yielding the corresponding Mn(III) derivative.

In the second half of the twentieth century, two new investigation techniques emerged that both revolutionized science and technology in their fields. The first one is (nuclear and electron) magnetic resonance (NMR, ESR), which exhibits superior energy resolution owing to the high precision of frequency measurements at resonant conditions. The second technique is scanning tunneling microscopy (STM) that has quickly established as a major investigation tool with its atomic spatial resolution. In order to benefit from both, the superior spatial resolution of the STM and the exceptional energy resolution of resonance techniques, we developed a radio-frequency (rf) STM based on a commercial low-temperature STM upgraded by a home-built rf-spectroscopic system that can be operated in active and passive modes. Here, we review recent progress in the field of rf-STM, with particular focus on our recent results on the detection and excitation of mechanical vibrations of one-dimensional molecular nanoresonators as well as of nuclear, electron, and mixed nuclear/electron spin transitions in single molecules.

Non-trivial arrangement of molecules within a molecular network complicates structure determination due to interdigitation, partial overlap, or stacking. We demonstrate that combined imaging and lateral manipulation with a scanning tunneling microscope resolves the intricate structure of a molecular network in two-dimensions in a straightforward manner. The network, formed by a monolayer of 5,10,15-tris(pentafluorophenyl)-corrole molecules on Ag(111), is manipulated for the first time with single-molecule precision. Our results reveal a shingle-like packing of partially overlapping corrole molecules. Density functional theory calculations support our findings.

Recent radio frequency scanning tunneling spectroscopy (rf-STS) experiments have demonstrated nuclear and electron spin excitations up to $\ifmmode\pm\else\textpm\fi{}12\ensuremath{\hbar}$ in a single molecular spin quantum dot (qudot). Despite the profound experimental evidence, the observed independence of the well-established dipole selection rules is not described by existing theory of magnetic resonance---pointing to a new excitation mechanism. Here we solve the puzzle of the underlying mechanism by discussing the relevant mechanistic steps. At the heart of the mechanism, periodic transient charging and electric polarization due to the rf-modulated tunneling process cause a periodic asymmetric deformation of the adsorbed qudot, enabling efficient spin transitions via spin-phonon-like coupling. The mechanism has general relevance for a broad variety of different spin qudots exhibiting internal mechanical degrees of freedom (organic molecules, doped semiconductor qudots, nanocrystals, etc.).

Corroles are versatile chemically active agents in solution. Expanding their applications toward surface-supported systems requires a fundamental knowledge of corrole-surface interactions. We employed the tip of a low-temperature scanning tunneling microscope as local probe to investigate at the single-molecule level the electronic and geometric properties of surface-supported free-base corrole molecules. To provide a suitable reference for other corrole-based systems on surfaces, we chose the archetypal 5,10,15-tris(pentafluorophenyl)corrole [H(3)(TpFPC)] as model system, weakly adsorbed on two surfaces with different interaction strengths. We demonstrate the nondissociative adsorption of H(3)(TpFPC) on pristine Au(111) and on an intermediate organic layer that provides sufficient electronic decoupling to investigate geometric and frontier orbital electronic properties of almost undisturbed H(3)(TpFPC) molecules at the submolecular level. We identify a deviating adsorption behavior of H(3)(TpFPC) compared to structurally similar porphyrins, characterized by a chiral pair of molecule-substrate configurations.

Supporting functional molecules on crystal facets is an established technique in nanotechnology. To preserve the original activity of ionic metallorganic agents on a supporting template, conservation of the charge and oxidation state of the active center is indispensable. We present a model system of a metallorganic agent that, indeed, fulfills this design criterion on a technologically relevant metal support with potential impact on Au(III)-porphyrin-functionalized nanoparticles for an improved anticancer-drug delivery. Employing scanning tunneling microscopy and -spectroscopy in combination with photoemission spectroscopy, we clarify at the single-molecule level the underlying mechanisms of this exceptional adsorption mode. It is based on the balance between a high-energy oxidation state and an electrostatic screening-response of the surface (image charge). Modeling with first principles methods reveals submolecular details of the metal-ligand bonding interaction and completes the study by providing an illustrative electrostatic model relevant for ionic metalorganic agent molecules, in general.

article The Western Tethyan estuarine oyster Crassostrea gryphoides is an excellent climate archive due to its large size and rapid growth. It is geologically long lived and allows a stable isotope-based insight into climatic trends during the Miocene. Herein we utilised the climate archive of 5 oyster shells from the Miocene Climate Optimum (MCO) and the subsequent Miocene Climate Transition (MCT) to evaluate changes of seasonality patterns. MCO shells exhibit highly regular seasonal rhythms of warm-wet and dry-cool seasons. Optimal conditions resulted in extraordinary growth rates of the oysters. δ

Stable isotope ( δ 18 O and δ 13 C) ratios were measured in successive aragonitic shell sequences of ammonoids (class Cephalopoda) to determine whether their depth distributions changed within ontogeny and whether stable isotope values differ in various morphological groups (e.g. Leiostraca vs. Trachyostraca). We concentrate mainly on δ 18 O for temperature results and added δ 13 C data to obtain information on the ontogenetic history, for which full spiral measurements were undertaken for the first time. To obtain valid stable isotope data from ammonoid shells, we measured ontogenetic sequences (full shell) within different genera. Data sets from the Jurassic ( Cadoceras ) and Cretaceous ( Hypacanthoplite s, Nowakites ) were chosen due to the pure primary aragonitic shell preservation. The study was designed to extract better information on the habitat and life cycle of fossil cephalopods (e.g. ammonoids) in comparison with recent cephalopods (e.g. Nautilus , Spirula , Sepia ) possessing equivalent or comparable hard parts. The data from three genera suggest different modes of life in at least two morphological groups. We detected and established two main groups with different ontogenetic strategies based on the δ 18 O data. The wcw -type (warm–cool–warm type) of Cadoceras resembles strategies in Nautilus and Sepia , which migrate from shallow into deeper environments and back in ontogeny ( wc-type , warm–cool-type), and the cw-type (cool–warm type) of Hypacanthoplites resembling the first two migration phases of Spirula ( cwc-type ), which migrates from deeper into shallower and back again into deeper habitats. The main (three) phases revealed by both δ 18 O and δ 13 C data sets most probably reflect diet changes in juvenile to mid-aged individuals, followed by a habitat change for spawning adults. In Cadoceras the temperatures range from 21.2 °C for juveniles down to 12.1 °C for mid-aged individuals and back up 16.9 °C in adults. The cw - type strategy of Hypacanthoplites involves a temperature range of 22.8 °C to 28.9 °C. The respective mean values are 24.2 °C (juveniles), 25.8 °C (middle phase) and 27.8 °C (adults). The δ 13 C values also revealed three ontogenetic stages in Cadoceras and Hypacanthoplites , including two major shifts from positive to negative and from negative to positive values, which probably correspond to sexual maturation, the initiation of reproduction, and concomitant changes in diet. The presented data, combined with previous ontogenetic studies (e.g. stable isotopes) on Spirula , Nautilus and Sepia can be used as proxies to directly correlate the habitats and ontogeny of recent and fossil cephalopods.

Upwelling conditions in the Early Miocene Central Paratethys SeaEvidence for regional upwelling conditions in the Central Paratethys Sea is presented for mid-Burdigalian (early Ottnangian) times. The oceanographic phenomenon is detected in clay-diatomite successions along the steep escarpment of the Bohemian Massif in the eastern North Alpine Foreland Basin. Interpretations are based on a multiproxy data-set including published sedimentological and paleontological data, newly performed stable isotope measurements (δ18O, δ13C) of foraminifers and bulk sediment samples, and analyses of dinoflagellate cyst assemblages. The revealed stable isotope values of planktonic foraminifers point to upwelling: low δ13C values indicate strong mixing of surface waters with rising nutrient-rich waters, high δ18O values reflect cool sea surface temperatures (SST). Temperature calculations give SSTs ranging from 10-14 °C. Cool SSTs and high productivity are additionally supported by bulk sediment analyses. Assemblages of dinoflagellate cysts indicate a distal-shelf environment with nutrient-rich waters. Westerly winds and tidal currents are discussed as potential driving forces behind the local upwelling event. As mid-Burdigalian geography favoured strong current patterns in the Central Paratethys as documented in the sedimentary record from the Rhône Basin to Hungary upwelling might have been a more common phenomenon in this epicontinental sea than currently known.

Stable isotopes (δ18O and δ13C) were measured in successive chambers of the aragonitic shells of the small deep-sea squid Spirula spirula (Linnaeus 1758) (class Cephalopoda, subclass Coleoidea, order Sepioidea, family Spirulidae) to determine whether their depth distributions change with age. The spiral shells, ranging in diameter from 18 to 23 mm (30–38 chambers), were collected between 2000 and 2006 from beaches in six widely separated locations in three oceans, the Atlantic (Tobago and Canary Islands), Indian (Madagascar, Maldives, and Perth, Australia), and Pacific Oceans (Ulladulla, Australia). The patterns for both isotopes were highly correlated in specimens from all six sites. The δ18O data suggest that after hatching at depths >1,000 m at temperatures of 4–6°C, the squid migrate into shallower, warmer waters at 12–14°C at depths of 400–600 m. Subsequently, the increasing δ18O values suggest a migration back into somewhat cooler, deeper habitats. The δ13C values also revealed three ontogenetic stages in all six specimens, including a major shift from positive to negative values, which probably corresponds to sexual maturation, the initiation of reproduction, and concomitant changes in diet. In three of the six specimens (from Tobago, Canary Islands, and Maldives) a fourth embryonic stage (not detected in the oxygen data) was accompanied by markedly less positive δ13C values in the first few chambers. These data, combined with the scanty life history information from previous studies of S. spirula, can be used to compare the habitat requirements of related extant and fossil cephalopod genera.

The layer growth of ultra-thin films of sexiphenyl on Au(111) has been studied as a function of substrate temperature under well-defined ultra-high-vacuum conditions. In situ X-ray photoelectron spectroscopy in combination with thermal desorption spectroscopy was applied to reveal the kinetics of layer growth and recrystallisation. Ex situ atomic force microscopy and X-ray diffraction were used to determine the film morphology and film structure. A continuous small-grain film is obtained at 93 K. The crystalline structure of the grains has been confirmed by X-ray diffraction. However, the grains are not preferentially oriented with respect to the substrate. Around room temperature, recrystallisation takes place and the molecules within the crystallites orient parallel to the substrate surface. Further small substrate temperature changes during growth lead to further changes of the film morphology and to reorientation of the crystallites. However, the molecules in the crystallites stay aligned parallel to the surface. At temperatures greater than 350 K, terraced islands of standing molecules are observed, in addition to needle-like islands with flat-lying molecules.

Adsorption of oligo-phenylenes (p-quaterphenyl (p-4P), p-sexiphenyl (p-6P)) on various gold surfaces has been investigated under ultrahigh vacuum conditions. X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and thermal desorption spectroscopy (TDS) have been applied to study the adsorbates. We have focused on the dehydrogenation of the organic molecules during thermal desorption. Whereas p-4P exhibits only a small tendency to dehydrogenate on the flat Au(1 1 1) surface, the degree of dehydrogenation on a stepped Au(4 3 3) surface or on a polycrystalline Au surface is considerable. Interestingly, p-6P shows already a strong dehydrogenation even on the flat Au(1 1 1) surface. Dehydrogenation takes place in two successive steps. The first partial dehydrogenation appears at the trailing edge of the oligo-phenyl desorption spectrum. Parallel to that stable polycyclic aromatic hydrocarbons (PAH) are formed on the surface, which eventually dehydrogenate completely at higher temperatures around 850 K. Pure carbon remains on the surface in form of a graphite like layer.

Nano-sized P4P (para-quaterphenylene) organic crystallites grown on a gold substrate were removed and redeposited using the tip of an STM. The controlled lift-off of the needle-shaped crystallites was imaged by a simultaneously operated SEM. The forces exerted by the metal STM tip on the nano-crystal during this nano-manipulation process could be determined by monitoring the deflection of the STM tip. After the lift-off process the former contact area was imaged using the STM. These STM micrographs clearly demonstrate that the region between the needles is covered by a P4P layer with a thickness of at least 3 nm.

The adsorption and growth of ordered para-hexaphenyl (6P) films have been investigated both on clean and partially carbon pre-covered Au(1 1 1) single crystal surfaces by thermal desorption spectroscopy (TDS) and low energy electron diffraction (LEED) under ultra-high vacuum conditions. The existence of a distinct first and second monomolecular 6P layer that clearly separate from the multilayer regime, which comprise lying molecules with respect to the substrate surface, could be inferred from TDS. For both the 6P mono- and multilayer grown on pure Au(1 1 1) the desorption energies have been determined based on experimental TDS data. In particular, for the monolayer regime a coverage dependence of the desorption energy has been found, which is attributed to repulsive interactions between neighbouring 6P molecules adsorbed on the gold surface. The existence of well-ordered film structures could be inferred from LEED for half monolayer and full monolayer thick 6P films. Based on the LEED and TDS data, structural models are presented for these highly ordered organic films. Multi-step dehydrogenation of 6P molecules adsorbed on clean Au(1 1 1) surfaces is reported for temperatures above 650 K together with experimental evidence for the existence of a regular overlayer composed of partially dehydrogenated polycyclic aromatic hydrocarbon (PAH) intermediates. A quite different adsorption/desorption kinetics and film growth has been observed for 6P films grown on carbon pre-covered Au(1 1 1) surfaces.

Quaterphenyl thin films were grown on Au(1 1 1) surfaces which were intentionally covered by different amounts of carbon. The films were investigated by X-ray diffraction and atomic force microscopy. An epitaxial character of the quaterphenyl crystallites could be confirmed for films grown on a clean Au(1 1 1) surface, with the (2 1 1) plane of quaterphenyl parallel to the Au(1 1 1) surface. It was found that the in-plane orientation of the quaterphenyl crystallites is determined by aligning the long molecular axes along 〈 1 1 ¯ 0 〉 Au and 〈 1 1 2 ¯ 〉 Au , facing the aromatic units of the molecules parallel to Au(1 1 1). Carbon coverages of 15% or 50% of the Au(1 1 1) surface cause a change in the orientation of the crystallites and a loss of the epitaxial orientation of the crystallites. In case of 15% carbon coverage the (2 0 1) plane of quaterphenyl crystallites develops parallel to Au(1 1 1), and 50% carbon coverage causes a (0 0 1) orientation of the crystallites. Both planes are cleavage planes of quaterphenyl. The film morphology consists of aligned needles for quaterphenyl films grown on the clean Au(1 1 1) surface, bent and randomly oriented needles at 15% carbon coverage and of uniformly distributed hillocks at 50% carbon coverage. The corresponding morphologies can be explained by the crystal structure features of quaterphenyl in combination with the orientation of the molecules within the thin films.

The influence of surface carbon on the formation of highly regular thin films of p -quaterphenyl (4P) grown on a Au(1 1 1) surface has been investigated in the mono- and multilayer regime by thermal desorption spectroscopy (TDS), X-ray photoelectron spectroscopy (XPS) and micro-channelplate low energy electron diffraction (MCP-LEED) under UHV conditions. A small carbon pre-coverage of 0.03 monolayers (ML) improves the surface mobility of adsorbed 4P molecules with respect to the clean surface by passivating Au surface defects. This enables a highly crystalline 4P film growth even at a low substrate temperature of 93 K. Otherwise, the thermodynamically stable monolayer structure is identical to that on the C-free surface, namely consisting of alternating edge/face packed, lying molecules. The structure of the first 4P monolayer grown on a 0.15 ML C covered Au(1 1 1) surface is different. Only edge-on oriented molecules accommodate in the corresponding surface unit cell. At a C coverage of 0.5 ML the first 4P monolayer is disordered, whereas for higher coverages a highly crystalline structure with upright standing molecules is adopted. Depending on the substrate temperature during film growth the surface carbon causes a different wetting behaviour of the 4P films, resulting in a different mesoscopic film morphology.

Polycrystalline films of conjugated organic semiconductors offer attractive potential for optoelectronic applications. Controlling the film morphology is essential for preparing thin films tailored for optimized devices. Here, we use atomic-force microscopy (AFM) to investigate the morphology of para -quaterphenyl (4P) films deposited under UHV conditions onto Au(1 1 1) gold surfaces and polycrystalline gold films. Films of 4P with and without additional carbon pre-coverage have been investigated on an Au(1 1 1) single crystal surface. Individual rod like 4P crystallites as well as chains of rod like and tetragonal crystallites were observed for thick films. For thin films, depending on the carbon pre-coverage either fan like arrangements of linear 4P chains, bent 4P crystallites with a distinct height distribution, or growth hillocks of upright standing molecules were found. In order to study the effect of different surface orientations on shape and arrangement of the crystallites, 4P has been deposited onto a polycrystalline Au foil. On individual gold grains, preferential orientations of the 4P crystallite chains can be found. The orientation of the chains is linked to the crystallographic orientation of the underlying Au grain. In addition, growth hillocks with 1.8 nm high terraces of upright standing 4P molecules are observed.

The adsorption, desorption, and growth kinetics as well as the thin film morphology and crystal structure of p-quaterphenyl (4P) grown under ultrahigh vacuum conditions on single crystalline Au(111) have been investigated. Thermal desorption spectroscopy (TDS) reveals two distinct first-order peaks attributed to monolayer desorption followed by a zero-order multilayer desorption. The saturation coverage of the full 4P monolayer has been quantitatively measured with a quartz microbalance to be 8 x 10(13) molecules/cm2. Using low energy electron diffraction the structures of the 0.5 and 1 ML (monolayer) adsorbates have been studied, showing highly regular arrangements of the 4P molecules, which are affected by the (111) surface structure. At the transition from 0.5 to 1 ML a structural compression of the overlayer has been observed. The behavior of thicker 4P films has been investigated by combined TDS-XPS (XPS-x-ray photoelectron spectroscopy). A temperature-induced recrystallization process at about 270 K has been observed for a 7 nm thick 4P film grown at 93 K, corresponding to a transition from a disordered layerlike growth to a crystalline island growth. Ex situ optical microscopy and atomic-force microscopy investigations have revealed needle-shaped 4P islands. Applying x-ray diffraction the crystalline order and epitaxial relationship of the 4P films with 30 nm and 200 nm mean thicknesses have been determined.

Thermal desorption spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS) have been applied to investigate the kinetics of adsorption, layer growth and desorption of p-quaterphenyl (P4P) on polycrystalline gold surfaces. Two different desorption peaks resulting from a monolayer (wetting layer) and a multilayer can be observed. The multilayer predominantly grows in form of a continuous film at 93 K, whereas at room temperature needle-like island growth is observed. A rearrangement (island formation) of the continuous multilayer takes place during heating prior to desorption. The influence of carbon on the adsorption/desorption kinetics of the monolayer has been studied in detail. On the clean surface some amount of adsorbed P4P dissociates and hydrogen is released at about 650 and 820 K, respectively. No dissociation of P4P takes place on the carbon-covered surface. The intact P4P molecules of the monolayer desorb in form of two broad peaks around 420 and 600 K, the multilayer desorbs with zero order above 350 K. Quantitative measurements with a quartz microbalance yield a mean thickness of 0.27 nm for the monolayer, suggesting that the P4P molecules are lying flat on the surface, for both the clean and the carbon-covered surface.

We probe nuclear and electron spins in a single molecule even beyond the electromagnetic dipole selection rules, at readily accessible magnetic fields (few mT) and temperatures (5 K) by resonant radio-frequency current from a scanning tunneling microscope. We achieve subnanometer spatial resolution combined with single-spin sensitivity, representing a 10 orders of magnitude improvement compared to existing magnetic resonance techniques. We demonstrate the successful resonant spectroscopy of the complete manifold of nuclear and electronic magnetic transitions of up to ΔI(z)=±3 and ΔJ(z)=±12 of single quantum spins in a single molecule. Our method of resonant radio-frequency scanning tunneling spectroscopy offers, atom-by-atom, unprecedented analytical power and spin control with an impact on diverse fields of nanoscience and nanotechnology.

We report a new type of nanomechanical resonator system based on one-dimensional chains of only 4 to 7 weakly coupled small molecules. Experimental characterization of the truly nanoscopic resonators is achieved by means of a novel radio-frequency scanning tunneling microscopy detection technique at cryogenic temperatures. Above 20 K we observe concerted oscillations of the individual molecules in chains, reminiscent of the first and second eigenmodes of a one-dimensional harmonic resonator. Radio-frequency scanning tunneling microscopy based frequency measurement reveals a characteristic length dependence of the oscillation frequency (between 51 and 127 MHz) in reasonable agreement with one-dimensional oscillator models. Our study demonstrates a new strategy for investigating and controlling the resonance properties of nanomechanical oscillators.

We have upgraded a low-temperature scanning tunnelling microscope (STM) with a radio-frequency (RF) modulation system to extend STM spectroscopy to the range of low energy excitations (1 meV). We studied single molecules of a stable hydrocarbon π-radical weakly physisorbed on Au(111). At 5 K thermal excitation of the adsorbed molecules is inhibited due to the lack of short-wavelength phonons of the substrate. We demonstrate resonant excitation of mechanical modes of single molecules by RF tunnelling at 115 MHz, which induces structural changes in the molecule ranging from controlled diffusion and modification of bond angles to bond breaking as the ultimate climax (resonance catastrophe). Our results pave the way towards RF-STM-based spectroscopy and controlled manipulation of molecular nanostructures on a surface.

Stable hydrocarbon radicals are utilized as spin standards and prototype metal-free molecular magnets able to withstand ambient conditions. Our study presents experimental results obtained with submolecular resolution by scanning tunneling microscopy and spectroscopy from monomers and dimers of stable hydrocarbon π radicals adsorbed on the Au(111) surface at 7–50 K. We provide conclusive evidence of the preservation of the radical spin-1/2 state, aiming to establish α,γ-bisdiphenylene-β-phenylallyl (BDPA) on Au(111) as a novel Kondo system, where the impurity spin is localized in a metal-free π molecular orbital of a neutral radical state in gas phase preserved on a metal support.

The crystal structure and molecular arrangement of para-quaterphenyl (4P) grown on single crystalline Au(111) was investigated over a wide thickness range. The molecular arrangement in the first monolayer, as investigated with low energy electron diffraction, shows a highly regular structure. This wetting layer is defined by adsorbate–substrate interactions and forms a prestage for the epitaxial growth of 4P single crystalline islands, as observed in x-ray diffraction. Two similar orientations of the 4P bulk phase are observed, with the (211) and (311) planes parallel to the Au(111) surface. The alignment of the molecules was kept unchanged from the first monolayers up to a film thickness of 200 nm.

Stable hydrocarbon radicals are able to withstand ambient conditions. Their combination with a supporting surface is a promising route toward novel functionalities or carbon-based magnetic systems. This will remain elusive until the interplay of radical–radical interactions and interface effects is fundamentally explored. We employ the tip of a low-temperature scanning tunneling microscope as a local probe in combination with density functional theory calculations to investigate with atomic precision the electronic and geometric effects of a weakly interacting metal support on an archetypal hydrocarbon radical model system, i.e., the exceptionally stable spin-1/2 radical α,γ-bisdiphenylene-β-phenylallyl (BDPA). Our study demonstrates the self-assembly of stable and regular one- and two-dimensional radical clusters on the Au(111) surface. Different types of geometric configurations are found to result from the interplay between the highly anisotropic radical–radical interactions and interface effects. We investigate the interaction mechanisms underlying the self-assembly processes and utilize the different configurations as a geometric design parameter to demonstrate energy shifts of up to 0.6 eV of the radicals’ frontier molecular orbitals responsible for their electronic, magnetic, and chemical properties.

The interaction of organometallic molecules with metal surfaces affects their conformation and accordingly their functionality. Surprising conformational complexity is revealed in single Au-porphyrin molecules on Au(111) exhibiting a variety of different asymmetric conformers. A combination of low-temperature scanning tunneling microscopy and spectroscopy experiments with density functional theory calculations discloses different registries of the pyrroles with the substrate lattice (determined and quantified with atomic precision) that cause asymmetric sub-\AA{} buckling of the macrocycle and, furthermore, a redshift of the frontier-orbital energy gap.

Nanomechanische Resonatoren sind winzige vibrierende Balken, die bei sehr hohen Frequenzen schwingen. Ihre Schwingungsfrequenz hangt empfindlich von ihrer Masse und Steifigkeit ab, was eine Detektion von winzigen Objekten, wie Molekulen oder Viren, durch eine genaue Frequenzmessung ermoglicht. Unserer Gruppe ist die Herstellung und Charakterisierung der kleinsten nanomechanischen Resonatoren gelungen, die aus nur vier einzelnen Molekulen bestehen. Dadurch eignen sie sich besonders als Sensoren mit Einzelmolekul-Empfindlichkeit.

Low-temperature scanning tunneling microscopy, a well-established technique for single-molecule investigations in an ultrahigh vacuum environment, has been used to study the electronic properties of Au(III) 5,10,15,20-tetraphenylporphyrin (AuTPP) molecules on Au(111) at the submolecular scale. AuTPP serves as a model system for chemotherapeutically relevant Au(III) porphyrins. For the first time, real-space images and local scanning tunneling spectroscopy data of the frontier molecular orbitals of AuTPP are presented. A comparison with results from density functional theory reveals significant deviations from gas-phase behavior due to a non-negligible molecule/substrate interaction. We identify the oxidation state of the central metal ion in the adsorbed AuTPP as Au(3+).

Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy has been applied to reveal the molecular arrangement of ultrathin oligophenyl films [p-quaterphenyl (4P) and p-hexaphenyl (6P)] on Au(111). In the half-monolayer films the molecules lie flat on the surface but still have a considerable inter-ring twist of 30 degrees -40 degrees , similar to the gas-phase conformation. In the saturated monolayer film the second half of the molecules is side-tilted by an angle of less than 66 degrees with respect to the surface. This arrangement is already similar to that in bulk net planes of thicker films parallel to the surface, that is, the 4P(211) and 6P(21-3) planes, respectively.

Radio-frequency (rf) scanning tunneling microscopy has recently been advanced to methods such as single-atom spin resonance. Such methods benefit from a frequency-independent rf voltage amplitude across the tunnel junction, which is challenging to achieve due to the strong frequency dependence of the rf attenuation in a transmission line. Two calibration methods for the rf amplitude have been reported to date. In this Note, we present an alternative method to achieve a frequency-independent rf voltage amplitude across the tunnel junction and show the results of this calibration. The presented procedure is applicable to devices that can deliver rf voltage to a tunnel junction., This replacement article is the final version published in Review of Scientific Instruments. It has been shortened to three pages by omitting the appendices. The appendices can be found in the previous version