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A sustainable future demands a successful transition from a carbon-energy dependent economy towards renewable energy schemes, many of which ultimately rely on the development of efficient electrocatalysis that either converts chemical energy into electricity or uses electrons to produce chemical energy. In general, electrocatalysis studies focus on the interactions (e.g., electron transfer) between the catalyst surface and the reaction intermediates. However, the role of electron spin, as an intrinsic property of electrons, has commonly been overlooked. Recently, controlling the electron spin polarization at the catalyst’s surface demonstrated the great potential of boosting both reaction activity and product selectivity. Molecule-induced electron spin polarization inspired by the chiral-induced spin selectivity (CISS) effect has started to have a remarkable impact in electrocatalysis. In this compact review, we summarize the latest studies that use molecule-induced electron spin polarization to enhance catalytic performance. We focus on the reactions essential to the so-called hydrogen economy, and discuss the feasibility and limitations of this effect. Finally, we share our perspective regarding the more impactful future applications.

Plasmonic nanojunctions, consisting of adjacent metal structures with nanometre gaps, can support localised plasmon resonances that boost light matter interactions and concentrate electromagnetic fields at the nanoscale. In this regime, the optical response of the system is governed by poorly understood dynamical phenomena at the frontier between the bulk, molecular and atomic scales. Here, we report ubiquitous spectral fluctuations in the intrinsic light emission from photo-excited gold nanojunctions, which we attribute to the light-induced formation of domain boundaries and quantum-confined emitters inside the noble metal. Our data suggest that photoexcited carriers and gold adatom - molecule interactions play key roles in triggering luminescence blinking. Surprisingly, this internal restructuring of the metal has no measurable impact on the Raman signal and scattering spectrum of the plasmonic cavity. Our findings demonstrate that metal luminescence offers a valuable proxy to investigate atomic fluctuations in plasmonic cavities, complementary to other optical and electrical techniques., Metallic nanojunctions support localised plasmon resonances and boost light matter interactions, but dynamical phenomena are poorly understood. Here, the authors report intrinsic photoluminescence blinking from plasmonic nanojunctions, originating from light-induced atomic scale restructuring of the metal.

Efficient catalytic water splitting demands advanced catalysts to improve the slow kinetics of the oxygen evolution reaction (OER). Earth-abundant transition metal oxides show promising OER activity in alkaline media. However, most experimental information available is either from post-mortem studies or in-situ space-averaged X-ray techniques in the micrometer range. Therefore, the composition of the active centers under operando conditions is still under debate. In this work, we combine nanoscopic and spectroscopic measurements on the hydroxylation of molecular beam epitaxy (MBE)-prepared Ni and NiFe oxides nanoislands with operando local investigations of Ni and NiFe hydroxide electrocatalysts under OER conditions to reveal the nature of active centers of Ni and Fe-doped Ni oxides in 2D OER catalysts. Our results reveal that Fe doping increases the active surface area by island fragmentation and boosts the intrinsic activity by creating optimized active centers consisting of both Ni and Fe atoms. In addition, our findings show that operando characterization at the nanoscale is crucial to reveal the dynamic nature of the interface of 2D catalysts under reaction conditions.

Surface alloying of Cu(001) by Sn deposition is a finely controllable method of tuning the degree of copper reactivity in order to drive the on-surface assembly and synthesis of metal-organic coordination networks. In this work we show that the (32×2)R45° reconstruction of the Sn/Cu(001) surface alloy acts as a weakly interacting substrate ideal for the assembly of rectangular metal-organic networks based on transition metals. As a demonstration, we have grown a two-dimensional coordination network formed by manganese and TCNQ (7,7,8,8-tetracyanoquinodimethane) with 1:1 stoichiometry. In contrast with the same structure grown on Au(111), the use of the Sn/Cu(001) substrate enables a commensurate structure with larger and more regular ordered domains. We show that the formation of a Cu-TCNQ coordination network and subsequent Mn-Cu transmetalation reactions are the key steps of the growth mechanism. Moreover, ab initio density-functional calculations indicate that the system studied in the present work is a unique example of a metal-organic coordination network weakly interacting with the substrate. Fil: Machain, Paloma. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Fuhr, Javier Daniel. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; Argentina Fil: Schneider, S.. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Carlotto, Silvia. Università di Padova; Italia Fil: Casarin, M.. Università di Padova; Italia Fil: Cossaro, A.. No especifíca; Fil: Verdini, A.. No especifíca; Fil: Floreano, L.. No especifíca; Fil: Lingenfelder, Magalí Alejandra. École Polytechnique Fédérale de Lausanne; Suiza Fil: Gayone, Julio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentina Fil: Ascolani, Hugo del Lujan. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentina

While solar-to-fuel catalysis requires the careful transfer of electrons, there are still challenges understanding how electron spin contributes to reactivity. Here, authors employ chiral fused thiadiazole-helicenes to control spin polarization in oxygen evolution electrocatalysts., A sustainable future requires highly efficient energy conversion and storage processes, where electrocatalysis plays a crucial role. The activity of an electrocatalyst is governed by the binding energy towards the reaction intermediates, while the scaling relationships prevent the improvement of a catalytic system over its volcano-plot limits. To overcome these limitations, unconventional methods that are not fully determined by the surface binding energy can be helpful. Here, we use organic chiral molecules, i.e., hetero-helicenes such as thiadiazole-[7]helicene and bis(thiadiazole)-[8]helicene, to boost the oxygen evolution reaction (OER) by up to ca. 130 % (at the potential of 1.65 V vs. RHE) at state-of-the-art 2D Ni- and NiFe-based catalysts via a spin-polarization mechanism. Our results show that chiral molecule-functionalization is able to increase the OER activity of catalysts beyond the volcano limits. A guideline for optimizing the catalytic activity via chiral molecular functionalization of hybrid 2D electrodes is given.

The electrochemical reduction of CO2 (CO2RR) into multicarbon compounds is a promising pathway towards renewable chemicals. Structure-product selectivity studies highlight that copper (100) facets favour C2+ product formation. However, the atomic processes leading to the formation of (100)-rich Cu cubes remains elusive. Herein, we use Cu and graphene-protected Cu surfaces to reveal the differences in structure and composition of common Cu-based electrocatalysts, from nano to micrometer scales. We show that stripping/electrodeposition cycles lead to thermodynamically controlled growth of Cu2O micro/nanocubes, while multi-layered Cu nanocuboids form universally during CO2RR upon polarization-driven re-organization of Cu0 atoms. A synergy of electrochemical characterization by scanning tunnelling microscopy (EC-STM), operando EC-Raman and quasi-operando X-Ray Photoemission spectroscopy (XPS) allows us to shed light on the role of oxygen on the dynamic interfacial processes of Cu, and to demonstrate that chloride is not needed for the stabilization of cubic Cu nanostructures.

Immense field enhancement and nanoscale confinement of light are possible within nanoparticle-on-mirror (NPoM) plasmonic resonators, which enable novel optically-activated physical and chemical phenomena, and render these nanocavities greatly sensitive to minute structural changes, down to the atomic scale. Although a few of these structural parameters, primarily linked to the nanoparticle and the mirror morphology, have been identified, the impact of molecular assembly and organization of the spacer layer between them has often been left uncharacterized. Here, we experimentally investigate how the complex and reconfigurable nature of a thiol-based self-assembled monolayer (SAM) adsorbed on the mirror surface impacts the optical properties of the NPoMs. We fabricate NPoMs with distinct molecular organizations by controlling the incubation time of the mirror in the thiol solution. Afterwards, we investigate the structural changes that occur under laser irradiation by tracking the bonding dipole plasmon mode, while also monitoring Stokes and anti-Stokes Raman scattering from the molecules as a probe of their integrity. First, we find an effective decrease in the SAM height as the laser power increases, compatible with an irreversible change of molecule orientation caused by heating. Second, we observe that the nanocavities prepared with a densely packed and more ordered monolayer of molecules are more prone to changes in their resonance compared to samples with sparser and more disordered SAMs. Our measurements indicate that molecular orientation and packing on the mirror surface play a key role in determining the stability of NPoM structures and hence highlight the under-recognized significance of SAM characterization in the development of NPoM-based applications.

Inert single-layer boron nitride (h-BN) grown on a catalytic metal may be functionalized with quaternary ammonium compounds (quats) that are widely used as nonreactive electrolytes. We observe that the quat treatment, which facilitates the electrochemical transfer of two-dimensional materials, involves a decomposition of quat ions and leads to covalently bound quat derivatives on top of the 2D layer. Applying tetraoctylammonium and h-BN on rhodium, the reaction product is top-alkylized h-BN as identified with high-resolution X-ray photoelectron spectroscopy. The alkyl chains are homogeneously distributed across the surface, and the properties thereof are well-tunable by the choice of different quats. The functionalization further weakens the 2D material-substrate interaction and promotes easy transfer. Therefore, the functionalization scheme that is presented enables the design of 2D materials with tailored properties and with the freedom to position and orient them as required. The mechanism of this functionalization route is investigated with density functional theory calculations, and we identify the proximity of the catalytic metal substrate to alter the chemical reactivity of otherwise inert h-BN layers.

Nickel iron oxide is considered a benchmark nonprecious catalyst for the oxygen evolution reaction (OER). However, the nature of the active site in nickel iron oxide is heavily debated. Here we report direct spectroscopic evidence for the different active sites in Fe‐free and Fe‐containing Ni oxides. Ultrathin layered double hydroxides (LDHs) were used as defined samples of metal oxide catalysts, and18O‐labeling experiments in combination with in situ Raman spectroscopy were employed to probe the role of lattice oxygen as well as an active oxygen species, NiOO−, in the catalysts. Our data show that lattice oxygen is involved in the OER for Ni and NiCo LDHs, but not for NiFe and NiCoFe LDHs. Moreover, NiOO−is a precursor to oxygen for Ni and NiCo LDHs, but not for NiFe and NiCoFe LDHs. These data indicate that bulk Ni sites in Ni and NiCo oxides are active and evolve oxygen via a NiOO−precursor. Fe incorporation not only dramatically increases the activity, but also changes the nature of the active sites.

The electroreduction of CO

The electroreduction of CO2 (CO2RR) is a promising strategy towards sustainable fuels. Cu is the only earth-abundant catalyst capable of CO2-to-hydrocarbons conversion; yet, its dynamic structure under operando CO2RR conditions remains unknown. Here, we track the Cu structure operando by electrochemical scanning tunneling microscopy and Raman spectroscopy. Surprisingly, polycrystalline Cu surfaces reconstruct forming Cu nanocuboids whose size can be controlled by the polarization potential and the time employed in their in-situ synthesis, without the assistance of organic surfactants and-or halide anions. If the Cu-surface is covered by a graphene monolayer, smaller features with enhanced catalytic activity for CO2RR can be prepared. The graphene protecting layer soften the 3D morphological changes that Cu-based catalysts suffer when exposed to aggressive electrochemical environments, and allows us to track the kinetic roughening process. This novel strategy is promising for improving Cu long-term stability and, consequently, controlling product selectivity.

By using high-speed and high-resolution Atomic Force Microscopy (AFM), it was possible to resolve within a single experiment the kinetic pathway in S-layer self-assembly at the solid-liquid interface, obtaining a model that accounts for the nucleation, growth and structural rearrangements in 2D protein self assembly across time (second to hours) and spatial scales (nm to microns). Fil: Stel, Bart. École Polytechnique Fédérale de Lausanne; Suiza Fil: Cometto, Fernando Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. École Polytechnique Fédérale de Lausanne; Suiza Fil: Rad, Behzad. Lawrence Berkeley National Laboratory; Estados Unidos Fil: De Yoreo, James J.. University of Washington; Estados Unidos Fil: Lingenfelder, Magalí Alejandra. École Polytechnique Fédérale de Lausanne; Suiza

The van der Waals (vdW) interactions of n-alkanethiols (ATs) adsorbed on planar Au(111) and Au(100) surfaces and curved Au nanoparticles of different diameters are reported. By means of electrochemical measurements and molecular dynamic calculations, the increase in the average geometrical curvature of the surface influences the global interactions, that is, decreasing vdW interactions between neighboring molecules. Small NPs do not present the same electrochemical behavior as planar surfaces. The transition between nanoparticle to flat surface electrochemical response is estimated to occur at a circa 13–20 nm diameter range. Fil: Cometto, Fernando Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina. Ecole Polytechnique Federale de Lausanne; Suiza Fil: Luo, Zhi. Ecole Polytechnique Federale de Lausanne; Suiza Fil: Zhao, Shun. Ecole Polytechnique Federale de Lausanne; Suiza Fil: Olmos Asar, Jimena Anahí. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Mariscal, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Ong, Quy. Ecole Polytechnique Federale de Lausanne; Suiza Fil: Kern, Klaus. Max-Planck-Institut für Festkörperforschung; Alemania. Ecole Polytechnique Federale de Lausanne; Suiza Fil: Stellacci, Francesco. Ecole Polytechnique Federale de Lausanne; Suiza Fil: Lingenfelder, Magalí Alejandra. Ecole Polytechnique Federale de Lausanne; Suiza

The effect of the Au crystalline plane on the adsorption of different thiols and selenols is studied via reductive desorption (RD) and X-ray photoelectron spectroscopy (XPS) measurements. Self-assembled monolayers (SAMs) using aliphatic (ATs) and aromatic thiols (ArTs) on both Au(111) and Au(100) were prepared. The electrochemical stability of these SAMs on both surfaces is evaluated by comparing the position of the RD peaks. The longer the AT chain the more stable the SAM on Au(100) when compared to Au(111). By means of XPS measurements, we determine that the binding energy (BE) of the S 2p signal corresponding to the S atoms at the thiol/Au interface, commonly assigned at 162.0 eV, shifts 0.2 eV from Au(111) to Au(100) for SAMs prepared using thiols with the C∗ (C atom bonded to S) in sp3 hybridization, such as ATs. However, when the thiol presents the C∗ with an sp2 hybridization, such as in the case of ArTs, the BE remains at 162.0 eV regardless of the surface plane. Selenol-based SAMs were characterized comparatively on both Au(100) and Au(111). Our results show that selenol SAMs become even more electrochemically stable on Au(100) with respect to Au(111) than the analogue sulfur-based SAM. According to our results, we suggest that the electronic distribution around the Au-S/Se bond could be responsible for the different structural arrangements reported in the literature (gold adatoms, etc.), which should be dependent on the crystalline face (Au(hkl)-S) and the chemical nature of the environment of the adsorbates (sp3-C∗ vs sp2-C∗ and Au-SR vs Au-SeR). Fil: Arisnabarreta, Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Ruano Sandoval, Gustavo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina Fil: Lingenfelder, Magalí Alejandra. Max Planck-EPFL Laboratory for Molecular Nanoscience; Suiza Fil: Patrito, Eduardo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Cometto, Fernando Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina

Photosynthesis is the model system for energy conversion. It uses CO as a starting reactant to convert solar energy into chemical energy, i.e., organic molecules or biomass. The first and rate-determining step of this cycle is the immobilization and activation of CO, catalyzed by RuBisCO enzyme, the most abundant protein on earth. Here, we propose a strategy to develop novel biomimetic two-dimensional (2D) nanostructures for CO adsorption at room temperature by reductionist mimicking of the Mg-carboxylate RuBisCO active site. We present a method to synthesize a 2D surface-supported system based on Mg centers stabilized by a carboxylate environment and track their structural dynamics and reactivity under either CO or O exposure at room temperature. The CO molecules adsorb temporarily on the Mg centers, producing a charge imbalance that catalyzes a phase transition into a different configuration, whereas O adsorbs on the Mg center, giving rise to a distortion in the metal-organic bonds that eventually leads to the collapse of the structure. The combination of bioinspired synthesis and surface reactivity studies demonstrated here for Mg-based 2D ionic networks holds promise for the development of new catalysts that can work at room temperature., We acknowledge the support of Dr. G. Ruano during the first phase of this project and Dr. M. Muntwiler and Dr. J. Zhang during our beamtimes at PEARL, PSI, Switzerland. A.S. and A.A. acknowledge support from the Spanish Ministerio de Ciencia e Innovacion (Grant No. FIS2016-75862-P).

Biological systems are able to control the assembly and positioning of proteins with nanoscale precision, as exemplified by the intricate molecular structures within cell membranes, virus capsids, and collagen matrices. Controlling the assembly of biomolecules is critical for the use of biomaterials in artificial systems such as antibacterial coatings, engineered tissue samples, and implanted medical devices. Furthermore, understanding the dynamics of protein assembly on heterogeneous templates will ultimately enable the control of protein crystallization in general. Here, we show a biomimetic, hierarchical bottom-up approach to direct the self-assembly of crystalline S-layers through nonspecific interactions with nanostructured block copolymer (BCP) thin-film templates. A comparison between physically and chemically patterned BCP substrates shows that chemical heterogeneity is required to confine the adhesion and self-assembly of S-layers to specific BCP domains. Furthermore, we show that this mechanism can be extended to direct the formation of collagen fibers along the principal direction of the underlying BCP substrate. The dynamics of protein self-assembly at the solid-liquid interface are followed using in situ high-resolution atomic force microscopy under continuous flow conditions, allowing the determination of the rate constants of the self-assembly. A pattern of alternating, chemically distinct nanoscale domains drastically increases the rate of self-assembly compared to non-patterned chemically homogeneous substrates.

In this work, a Mg(0001) single crystal is used as a novel template to grow 2D supramolecular nano-architectures. By using scanning tunnelling microscopy (STM) and high-resolution X-ray photoemission spectroscopy (HR-XPS), the formation of either a homo-molecular or metal–organic network is reported for carboxylic or amino functionalized molecules, respectively.

We show that Sn atoms combined with organic ligands can be used to build 2D coordination networks on Au(111) surfaces. Fil: Rodriguez, Luis Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Fuhr, Javier Daniel. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Machaín, P.. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Ascolani, Hugo del Lujan. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Lingenfelder, Magalí Alejandra. École Polytechnique Fédérale de Lausanne; Suiza Fil: Gayone, Julio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina

Carboxylic acids are prototypical building units for the creation of two-dimensional supramolecular architectures on surfaces. The formation of double (dihapto) hydrogen bonds is a common binding geometry of COOH functional groups. On surfaces, however, carboxylates and coordination bonds could also be formed due to the lowering of the activation barrier toward deprotonation of the carboxylic groups. This capacity of forming metal–ligand coordination bonds paved the road toward the creation of a wide variety of surface-confined metal–organic networks. This article is focused on the deprotonation phenomenon in connection with the generation of these types of supramolecular networks under ultra high vacuum conditions.

We use the electric field in a scanning tunneling microscope to manipulate the transition between open and close packed 2D supramolecular networks of neutral molecules in nonpolar apolar media. We found that while the magnitude of the applied field is not decisive, it is the sign of the polarization that needs to be maintained to select one particular polymorph. Moreover, the switching is independent of the solvent used and fully reversible. We propose that the orientation of the surface dipole determined by the electric field might favor different conformational-depended charge transfer mechanisms of the adsorbates to the surface, inducing open (closed) structures for negative (positive) potentials. Our results show new avenues for the use of local fields to select the polymorphic outcome of supramolecular assemblies at the solid/liquid interface. The effect has potential to control locally the capture and release of analytes in host-guest systems and the 2D morphology in multicomponent layers. Fil: Cometto, Fernando Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Institut de Physique de la Matière Condensée; Suiza. Max Planck-EPFL Laboratory for Molecular Nanoscience; Suiza Fil: Kern, Klaus. Institut de Physique de la Matière Condensée; Suiza. Max-Planck-Institut für Festkörperforschung; Alemania Fil: Lingenfelder, Magalí Alejandra. Institut de Physique de la Matière Condensée; Suiza. Max Planck-EPFL Laboratory for Molecular Nanoscience; Suiza

Supramolecular nanostructures with tunable dimensionalities are fabricated by deposition of benzene-carboxylic acids on the Cu(110) surface. By tailoring the number and position of the functional moieties, the structure of the final molecular assemblies can be rationally modified ranging from isolated one-dimensional chains to compact two-dimensional islands. Molecular units are chosen that can assemble through metal-organic and electrostatic interactions. The hierarchy between these intermolecular forces guarantees that a primary organization level, constituted by metal-organic polymeric chains, is developed by all molecular units while the secondary interchain interactions can be arbitrarily adjusted. Scanning tunneling microscopy, density functional theory calculations, and kinetic Monte Carlo simulations are used to characterize and rationalize the experimental findings. © 2013 American Chemical Society.

A new chiral nonracemic thiol derived from a popular acidic resolving agent that incorporates a cyclic disubstituted phosphate group (phencyphos) has been prepared in enantiomerically pure form. The stereochemistry and absolute configuration were established by performing a single-crystal X-ray structural analysis of a synthetic intermediate. The thiol compound was used for the preparation of self-assembled monolayers (SAMs) on both monocrystalline and polycrystalline metallic gold, which have very different surface roughness. The monolayers were used to promote the nucleation and growth of crystals from nonaqueous solutions of an organic molecule (the parent phencyphos) of similar structure to the compound present in the monolayer. The template layers influence the nucleation and growth of the phencyphos crystals despite the lack of two-dimensional order in the surfaces. Heterogeneous nucleation of phencyphos takes place upon evaporation of either CHCl(3) or isopropanol solutions of the compound on the SAM surfaces, where the evaporation rate merely influences the size and homogeneity of the crystals. The roughness of the surface also plays an important role; the polycrystalline gold produces more homogeneous samples because of the greater number of nucleation sites. Clear evidence for nucleation and growth on the surfaces is shown by scanning electron microscopy. The variation in crystal form achieved by using different surfaces and solvents suggests that the layers are applicable for the preparation of organic crystals from organic solutions.

Dynamically switchable supramolecular systems offer exciting possibilities in building smart surfaces, the structure and thus the function of which can be controlled by using external stimuli. Here we demonstrate an elegant approach where the guest binding ability of a supramolecular surface can be controlled by inducing structural transitions in it. A physisorbed self-assembled network of a simple hydrogen bonding building block is used as a switching platform. We illustrate that the reversible transition between porous and nonporous networks can be accomplished using an electric field or applying a thermal stimulus. These transitions are used to achieve controlled guest release or capture at the solution–solid interface. The electric field and the temperature-mediated methods of guest release are operative at different length scales. While the former triggers the transition and thus guest release at the nanometer scale, the latter is effective over a much larger scale. The flexibility associated with physisorbed self-assembled networks renders this approach an attractive alternative to conventional switchable systems. Fil: Lee, Shern Long. Ku Leuven-university Of Leuven; Bélgica Fil: Fang, Yuan. Ku Leuven-university Of Leuven; Bélgica Fil: Velpula, Gangamallaiah. Ku Leuven-university Of Leuven; Bélgica Fil: Cometto, Fernando Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Lingenfelder, Magalí Alejandra. Ecole Polytechnique Federale de Lausanne. Max Planck-epfl Center For Molecularnanosciencie And Technology; Francia Fil: Müllen, Klaus. Max Planck Institut für Polymer Research; Alemania Fil: Mali, Kunal. Ku Leuven-university Of Leuven; Bélgica Fil: De Feyter, Steven. Ku Leuven-university Of Leuven; Bélgica

Metal-organic supramolecular chemistry on surfaces has matured to a point where its underlying growth mechanisms are well understood and structures of defined coordination environments of metal atoms can be synthesized in a controlled and reproducible procedure. With surface-confined molecular self-assembly, scientists have a tool box at hand which can be used to prepare structures with desired properties, as for example a defined oxidation number and spin state of the transition metal atoms within the organic matrix. From a structural point of view, these coordination sites in the supramolecular structure resemble the catalytically active sites of metallo-enzymes, both characterized by metal centers coordinated to organic ligands. Several chemical reactions take place at these embedded metal ions in enzymes and the question arises whether these reactions also take place using metal-organic networks as catalysts.Mimicking the active site of metal atoms and organic ligands of enzymes in artificial systems is the key to understanding the selectivity and efficiency of enzymatic reactions. Their catalytic activity depends on various parameters including the charge and spin configuration in the metal ion, but also on the organic environment, which can stabilize intermediate reaction products, inhibits catalytic deactivation, and serves mostly as a transport channel for the reactants and products and therefore ensures the selectivity of the enzyme. Charge and spin on the transition metal in enzymes depend on the one hand on the specific metal element, and on the other hand on its organic coordination environment. These two parameters can carefully be adjusted in surface confined metal-organic networks, which can be synthesized by virtue of combinatorial mixing of building synthons. Different organic ligands with varying functional groups can be combined with several transition metals and spontaneously assemble into ordered networks. The catalytically active metal centers are adequately separated by the linking molecules and constitute promising candiates for heterogeneous catalysts.Recent advances in synthesis, characterization, and catalytic performance of metal?organic networks are highlighted in this Account. Experimental results like structure determination of the networks, charge and spin distribution in the metal centers, and catalytic mechanisms for electrochemical reactions are presented. In particular, we describe the activity of two networks for the oxygen reduction reaction in a combined scanning tunneling microscopy and electrochemical study. The similarities and differences of the networks compared to metallo-enzymes will be discussed, such as the metal surface that operates as a geometric template and concomitantly functions as an electron reservoir, and how this leads to a new class of bioinspired catalysts. The possibility to create functional two-dimensional coordination complexes at surfaces taking inspiration from nature opens up a new route for the design of potent nanocatalyst materials for energy conversion. Fil: Gutzler, Rico . Max Planck Institute for Solid State Research; Alemania Fil: Stepanow, Sebastian . Eidgenössische Technische Hochschule Zürich; Suiza Fil: Grumelli, Doris Elda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; Argentina Fil: Lingenfelder, Magali . Max Planck-Epfl Laboratory For Molecular Nanoscience; Alemania Fil: Kern, Klaus . Max Planck Institute for Solid State Research; Alemania

Recently, several research groups have reported the growth of germanene, a new member of the graphene family. Germanene is in many aspects very similar to graphene, but in contrast to the planar graphene lattice, the germanene honeycomb lattice is buckled and composed of two vertically displaced sub-lattices. Density functional theory calculations have revealed that free-standing germanene is a 2D Dirac fermion system, i.e. the electrons behave as massless relativistic particles that are described by the Dirac equation, which is the relativistic variant of the Schrodinger equation. Germanene is a very appealing 2D material. The spin-orbit gap in germanene (similar to 24 meV) is much larger than in graphene (

Self-assembled terephthalic acid adlayers on a Cu(100) surface have been studied by X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure, and scanning tunneling microscopy in the temperature range 190−400 K under ultrahigh vacuum conditions. We observe three distinct well-ordered phases evolving with increasing temperature. The combined data analysis reveals that thermally activated deprotonation of molecular carboxyl groups is decisive in the irreversible transformation of the respective structures. Their self-assembly is mediated by changing intermolecular hydrogen bond configurations, whereby a flat adsorption geometry is retained.

A combination of Scanning Tunnelling Microscopy and Density Functional Theory simulations highlights the role of van der Waals interactions in the self-assembly of an aminohelicene on Cu(100) and Au(111). Fil: Ascolani, Hugo del Lujan. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina Fil: van der Meijden, Maarten. Syncom BV; Países Bajos Fil: Cristina, Lucila Josefina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina Fil: Gayone, Julio Esteban. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina Fil: Kellogg, Richard. Syncom BV; Países Bajos Fil: Fuhr, Javier Daniel. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina Fil: Lingenfelder, Magalí Alejandra. Max Planck-epfl Laboratory For Molecular Nanoscience; Suiza

The controlled crystallization of enantiomers of an organic compound (a cyclic phosphoric acid derivative) on templated micro-patterned functionalised surfaces is demonstrated. Areas where a complementary chiral thiol has been located were effective heterogeneous nucleation centres when a solution of the compound is evaporated slowly. Various organic solvents were employed, which present a challenge with respect to other examples when water is used. The solvent and the crystallization method have an important influence on the crystal growth of these compounds. When chloroform was employed, well-defined crystals grow away from the surface, whereas crystals grow in the plane from solutions in isopropanol. In both cases, nucleation is confined to the polar patterned regions of the surface, and for isopropanol growth is largely limited within the pattern, which shows the importance of surface chemistry for nucleation and growth. The apparent dependence on the enantiomer used in the latter case could imply stereo-differentiation as a result of short-range interactions (the templating monolayer is disordered, even at the nanometre scale). The size of the pattern of chiral monolayer also determines the outcome of the crystallization; 5 μm dots are most effective. Despite the low surface tension of the samples (relative to the high surface tension of water), differential solvation of the polar and hydrophobic layers of the solvents allows crystallization in the polar regions of the monolayer, therefore the polarity of the regions in which heterogeneous nucleation takes place is indeed very important. Despite the complex nature of the crystallization process, these results are an important step towards to the use of patterned surfaces for heterogeneous selective nucleation of enantiomers.

A design strategy for fabricating a surface-supported chiral metal-organic system comprising a regular arrangement of mononuclear iron centers and nanocavities is presented. By sequential deposition of 1,2,4-benzenetricarboxylic acid (tmla) molecules and iron atoms on a Cu(100) surface under ultrahigh vacuum conditions, chiral square-planar Fe(tmla)4 metal-organic complexes are generated, which order in extended homochiral arrays. Structure formation and envisioned functionality of such metal-organic architectures are discussed.

The possibility of modifying the intermolecular interactions of absorbed benzene-carboxylic acids from coordination to hydrogen bonding by changing their surface coverage is demonstrated through a combination of scanning tunnelling microscopy, X-ray photo-emission spectroscopy and density functional theory calculations.

5 pages, 3 figures.-- Supplementary information (Sample preparation, Suppl. figures S1-S6, tables S1-S3, 17 pages) available at: http://www.nature.com/nmat/journal/vaop/ncurrent/extref/nmat2376-s1.pdf, Article in press., Magnetic atoms at surfaces are a rich model system for solid-state magnetic bits exhibiting either classical or quantum behaviour. Individual atoms, however, are difficult to arrange in regular patterns. Moreover, their magnetic properties are dominated by interaction with the substrate, which, as in the case of Kondo systems, often leads to a decrease or quench of their local magnetic moment. Here, we show that the supramolecular assembly of Fe and 1,4-benzenedicarboxylic acid molecules on a Cu surface results in ordered arrays of high-spin mononuclear Fe centres on a 1.5nm square grid. Lateral coordination with the molecular ligands yields unsaturated yet stable coordination bonds, which enable chemical modification of the electronic and magnetic properties of the Fe atoms independently from the substrate. The easy magnetization direction of the Fe centres can be switched by oxygen adsorption, thus opening a way to control the magnetic anisotropy in supramolecular layers akin to that used in metallic thin films., We acknowledge the ESRF for provision of beam time. Partial financial support was received through the EUROCORES 05-SONS-FP-009 SANMAG project of the European Science Foundation. P.G. and S.S. acknowledge financial support from the Spanish Ministerio de Educación y Ciencia (SYNSPIN-MAT2007-62341).

The adsorption of trimesic acid (TMA) on Cu(110) has been studied in the temperature range between 130 and 550 K and for coverages up to one monolayer. We combine scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), reflection absorption infrared spectroscopy (RAIRS), X-ray photoemission spectroscopy (XPS), and density functional theory (DFT) calculations to produce a detailed adsorption phase diagram for the TMA/Cu(110) system as a function of the molecular coverage and the substrate temperature. We identify a quite complex set of adsorption phases, which are determined by the interplay between the extent of deprotonation, the intermolecular bonding, and the overall energy minimization. For temperatures up to 280 K, TMA molecules are only partly deprotonated and form hydrogen-bonded structures, which locally exhibit organizational chirality. Above this threshold, the molecules deprotonate completely and form supramolecular metal-organic structures with Cu substrate adatoms. These structures exist in the form of single and double coordination chains, with the molecular coverage driving distinct phase transitions.

Herein we report on the direct observation of chiral recognition events of adsorbed diphenylalanine by scanning tunneling microscopy (STM). The interaction among individual di-d-phenylalanine (d-Phe-d- Phe) molecules and the discrimination of d-Phe-d-Phe from its enantiomer l-Phe-l-Phe on Cu(110) is followed by STM and rationalized by using first principles and classical molecular dynamics techniques. We find that the stereoselective assembly of adsorbed di-phenylalanine enantiomers into molecule pairs and chains takes place through mutually induced conformational changes, thereby illustrating at the single-molecule level the more than half a century old prediction of Pauling.

The mesoscale induction of two-dimensional supramolecular chirality (formation of 2D organic domains with a single handedness) was achieved by self-assembly of 1,2,4-benzenetricarboxylic (trimellitic) acid on a Cu(100) surface at elevated temperatures. The combination of spectroscopic [X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS)], real-space-probe [scanning tunneling microscopy (STM)], and computational [density functional theory (DFT)] methods allows a comprehensive characterization of the obtained organic adlayers, where details of molecular adsorption geometry, intermolecular coupling, and surface chemical bonding are elucidated. The trimellitic acid species, comprising three functional carboxylic groups, form distinct stable mirror-symmetric hydrogen-bonded domains. The chiral ordering is associated with conformational restriction in the domains: molecules anchor to the substrate with an ortho carboxylate group, providing two para carboxylic acid moieties for collective lateral interweaving through H bonding, which induces a specific tilt of the molecular plane. The ease of molecular symmetry switching in domain formation makes homochiral-signature propagation solely limited by the terrace width. The molecular layer modifies the morphology of the underlying copper substrate and induces mum-sized strictly homochiral terraces.

Carboxylate-bridged diiron units have been realized recently in two dimensions via metal-directed self-assembly of simple organic linkers. They represent notably a coupling motif stabilizing a series of nanoporous metal−organic coordination networks and are reminiscent of catalytically active sites in metalloproteins. To rationalize their atomic structure, chemical bonding, and electronic properties, we performed density functional theory calculations for exemplary Fe−terephthalate grids assembled on the Cu(100) surface. The obtained atomistic description and understanding is decisive for the considerate use of two-dimensional metal−organic coordination networks as templates, guest systems, or catalysts.

We present a comprehensive investigation of the modular assembly of surface-supported metal-organic coordination systems with specific topologies and high structural stability formed by vapor deposition of 1,4-benzenedicarboxylic acid molecules and iron atoms on a Cu(100) surface under ultra-high vacuum conditions. By making use of the two carboxylate moieties available for lateral linkage to Fe atoms, we succeeded in the fabrication of distinct Fe-carboxylate coordination architectures at the surface by carefully adjusting the ligand and metal concentration ratio and the temperature of the post-deposition annealing treatment. The mononuclear, 1D-polymeric and fully 2D-reticulated metallosupramolecular arrangements obtained were characterized in situ at the single-molecule level by scanning tunneling microscopy.

Metal-organic coordination networks (MOCNs) have attracted wide interest because they provide a novel route towards porous materials that may find applications in molecular recognition, catalysis, gas storage and separation. The so-called rational design principle-synthesis of materials with predictable structures and properties-has been explored using appropriate organic molecular linkers connecting to metal nodes to control pore size and functionality of open coordination networks. Here we demonstrate the fabrication of surface-supported MOCNs comprising tailored pore sizes and chemical functionality by the modular assembly of polytopic organic carboxylate linker molecules and iron atoms on a Cu(100) surface under ultra-high-vacuum conditions. These arrays provide versatile templates for the handling and organization of functional species at the nanoscale, as is demonstrated by their use to accommodate C(60) guest molecules. Temperature-controlled studies reveal, at the single-molecule level, how pore size and chemical functionality determine the host-guest interactions.