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QC 20190218

The magnetic domain structure of patterned antiferromagnetic/ferromagnetic Ir20Mn80/Ni80Fe20 bilayer microdisk arrays has been investigated using layer-specific polarized x-ray photoemission electron microscopy and magnetic circular dichroism. Magnetic imaging at the Fe and Mn L-edge resonances provided direct evidence of a vortex state imprinted into the antiferromagnet at the interface. The opposite magnetic contrast between the layers indicated a reversed chirality of the imprinted vortex state, and a quantitative analysis of the magnetic moment from the dichroism spectra showed that uncompensated Mn spins equivalent to about 60% of a monolayer of bulk Ir20Mn80 contributed to the imprinted information at the interface., QC 20110418 Korrigering: This article was originally published online and in print with an error in the fifth author’s name in Ref. 13; the correctspelling of the author’s name should have been E. Menéndez. AIP apologizes for this error. All online versions of the articlehave been corrected.

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 1.5 nm 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.

The surface-assisted self-assembly of one-dimensional chains using linear, rigid bipyridyl molecules of different lengths on the Cu(100) surface is presented. The chains are assembled from a stable 2-fold coordination of the terminal pyridyl groups of the molecules with Cu adatoms which diffuse from the substrate step edges. This type of interaction is selective and reversible, allowing for effective self-assembly. We observe several partially dynamic aspects of chain growth which highlight critical considerations for growth of the present system as well as other molecular nanostructures on solid substrates. The steric and electronic templating of the metal substrate leads to strictly one-dimensional bonding geometries and unusually low (2-fold) coordination. The epitaxial relation of the molecular structure with the substrate lattice has profound effects on the growth kinetics and stability of the structures. Additionally, the substrate-mediated interactions influence the stability and structure over longer ranges than can be influenced by bonding interactions, manifested here as specific interchain distances at high molecule coverages. © 2007 American Chemical Society.

(Figure Presented) Independent symmetries characterize the evolving network and the metal surface on which the network forms in the surface-assisted assembly of ligands and metal centers to 2D honeycomb networks comprising threefold coordination motifs (see picture, Co purple, N green). This type of coordination, which is rarely encountered in 3D metal-organic frameworks, is promoted by the strict confinement of a 2D environment. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.

The mesoscale induction of two-dimensional supramolecular chirality (formation of 20 organic domains with a single bandedness) 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 μm-sized strictly homochiral terraces. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA.

This article discusses different approaches to build up supramolecular nanoarchitectures on surfaces, which were simultaneously investigated by scanning tunneling microscopy (STM) on the single-molecule level. Following this general road map, first, the hydrogen-bonding guided self-assembly of two different, structural-equivalent molecular building blocks, azobenzene dicarboxylic acid and stilbene dicarboxylic acid, was studied. Secondly, the coordination chemistry of the same building blocks, now acting as ligands in metal coordination reactions, towards co-sublimed Fe atoms was studied under near surface-conditions. Extended two-dimensional tetragonal network formation with unusual Fe 2L 4/2-dimers at the crossing points was observed on copper surfaces. Complementary to the first two experiments, a two-step approach based on the solution-based self-assembly of square-like tetranuclear complexes of the M 4L 4-type with subsequent deposition on graphite surfaces was investigated. One- and two-dimensional arrangements as well as single molecules of the M 4L 4-complexes could be observed. Moreover, the local electronic properties of a single M 4L 4-complexes could be probed with submolecular resolution by means of scanning tunnelling spectroscopy (STS). © The Royal Society of Chemistry 2006.

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. Copyright © 2006 American Chemical Society.

The self-assembly of iron-coordinated two-dimensional metal - organic networks on a Cu(100) surface has been investigated by scanning tunneling microscopy under ultra-high-vacuum conditions. We applied three rodlike polybenzene dicarboxylic acid molecules with different backbone lengths as organic linkers. The three linker molecules form topologically identical rectangular networks with Fe, all comprising iron pairs as the network nodes. Whereas the length of the linker molecules defines the dimension of the networks, the substrate also significantly influences the structural details, e.g., network orientation with respect to the substrate, geometric shape of the network cavities, Fe - carboxylate coordination configuration, and iron - iron distance. © 2006 American Chemical Society.

In-situ scanning tunneling microscopy study reveals that two-dimensional metallosupramolecular receptors bind a single or a discrete number of cystine, C 60, or diphenylalanine molecules reversibly through non-covalent interactions. © The Royal Society of Chemistry 2006.

High-resolution scanning tunneling microscopy has revealed how ligand control can be successfully employed to eliminate isomeric phases and defects in 2D coordination networks that are self-assembled at a surface support by replacing symmetric dicarboxylato linker ligands to dissymmetric carboxylpyridyl linker ligands. © The Royal Society of Chemistry 2005.

We report a comparative study on the 2D self-assembly of two related ditoplc benzole acid species, which have similar shape and endgroups but different backbone symmetry. High-resolution scanning tunneling microscopy data reveal how the symmetry information of molecular building blocks is readily expressed in the resulting chiral or nonchiral supramolecular networks. The underlying square Cu(100) surface steers network orientation and accounts for carboxylate formation, resulting in an unusual intermolecular hydrogen bond motif. Our results demonstrate that symmetry and chiral resolution in 2D supramolecular assembly can be controlled via the design of functional molecules and choice of substrate. © 2005 American Chemical Society.

The self-assembly of the rodlike two-dimensional chiral molecule 4-[trans-2-(pyrid-4-yl-vinyl)] benzoic acid on the Cu(100) surface has been investigated by scanning tunneling microscopy. Upon adsorption at T ≥ 300 K, the molecules are deprotonated and assemble in parquet patterns when the coverage remains below a critical value. Corresponding high-resolution data reveal that the ordering implies mesoscopic chiral resolution as a result of chiroselective interactions (i.e., two domains comprise exclusively one enantiomer). When the critical coverage is exceeded, an abrupt transition to a single racemic phase is observed with a different lateral molecular coupling scheme. The shifting of the subtle balance between the weak lateral coupling, substrate bonding, and the packing requirements encountered with the increased molecular coverage is suggested to be the driving force for this homochiral-to-heterochiral phase transition. © 2005 American Chemical Society.

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 1,2. The so-called rational design principle - synthesis of materials with predictable structures and properties - has been explored using appropriate organicmolecular linkers connecting to metal nodes to control pore size and functionality of open coordination networks 3-9. 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.

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.

We report the construction of complex metal-organic assemblies at surfaces using concepts from coordination chemistry.(1) Well-ordered supramolecular assemblies and metalorganic coordination networks with specific topologies and a high structural stability have been fabricated under ultra-high vacuum conditions by sequential deposition of polyfunctional organic molecules and Fe atoms onto an atomically clean Cu(100) substrate(2). The structures were investigated at the molecular level by in-situ scanning tunneling microscopy. The precise control of the concentration ratio of the components and the annealing treatment allow for the assembly of distinct architectures.