The construction of electronic devices from single molecular building blocks, which possess certain functions such as switching or rectifying and are connected by atomic-scale wires on a supporting surface, is an essential goal of molecular electronics. A key challenge is the controlled assembly of molecules into desired architectures by strong, that is, covalent, intermolecular connections, enabling efficient electron transport between the molecules and providing high stability. However, no molecular networks on surfaces 'locked' by covalent interactions have been reported so far. Here, we show that such covalently bound molecular nanostructures can be formed on a gold surface upon thermal activation of porphyrin building blocks and their subsequent chemical reaction at predefined connection points. We demonstrate that the topology of these nanostructures can be precisely engineered by controlling the chemical structure of the building blocks. Our results represent a versatile route for future bottom-up construction of sophisticated electronic circuits and devices, based on individual functionalized molecules.

AgBiI4 powder, crystals, and polycrystalline films were synthesized by sealed tube solid state reactions, chemical vapor transport (CVT), and solution processing, respectively, and their structural, optical and electronic properties are reported. The structure of AgBiI4 is based unambiguously upon a cubic close packed iodide sublattice, but it presents an unusual crystallographic problem: we show that the reported structure, a cubic defect-spinel, cannot be distinguished from a metrically cubic layered structure analogous to CdCl2 using either powder or single crystal X-ray crystallography. In addition, we demonstrate the existence a noncubic CdCl2-type polymorph by isolation of nontwinned single crystals. The indirect optical band gap of AgBiI4 is measured to be 1.63(1) eV, comparable to the indirect band gap of 1.69(1) eV measured for BiI3 and smaller than that reported for other bismuth halides, suggesting that structures with a close-packed iodide sublattice may give narrower band gaps than those with perovskite structures. Band edge states closely resemble those of BiI3; however, the p-type nature of AgBiI4 with low carrier concentration is more similar to MAPbI3 than the n-type BiI3. AgBiI4 shows good stability toward the AM1.5 solar spectrum when kept in a sealed environment and is thermally stable below 90 °C.

The direct coupling of complex, functional organic molecules at a surface is one of the outstanding challenges in the road map to future molecular devices. Equally demanding is to meet this challenge without recourse to additional functionalization of the molecular building blocks and via clean surface reactions that leave no surface contamination. Here, we demonstrate the directional coupling of unfunctionalized porphyrin molecules--large aromatic multifunctional building blocks--on a single crystal copper surface, which generates highly oriented one-dimensional organometallic macromolecular nanostructures (wires) in a reaction which generates gaseous hydrogen as the only byproduct. In situ scanning tunneling microscopy and temperature programmed desorption, supported by theoretical modeling, reveal that the process is driven by C-H bond scission and the incorporation of copper atoms in between the organic components to form a very stable organocopper oligomer comprising organometallic edge-to-edge porphyrin-Cu-porphyrin connections on the surface that are unprecedented in solution chemistry. The hydrogen generated during the reaction leaves the surface and, therefore, produces no surface contamination. A remarkable feature of the wires is their stability at high temperatures (up to 670 K) and their preference for 1D growth along a prescribed crystallographic direction of the surface. The on-surface formation of directional organometallic wires that link highly functional porphyrin cores via direct C-Cu-C bonds in a single-step synthesis is a new development in surface-based molecular systems and provides a versatile approach to create functional organic nanostructures at surfaces.

Crystalline materials that combine electrical polarization and magnetization could be advantageous in applications such as information storage, but these properties are usually considered to have incompatible chemical bonding and electronic requirements. Recent theoretical work on perovskite materials suggested a route for combining both properties. We used crystal chemistry to engineer specific atomic displacements in a layered perovskite, (Ca(y)Sr(1- y))(1.15)Tb(1.85)Fe2O7, that change its symmetry and simultaneously generate electrical polarization and magnetization above room temperature. The two resulting properties are magnetoelectrically coupled as they arise from the same displacements.

We report on the formation of a metal-molecule complex that can be used as a molecular switch. Using a cryogenic scanning tunneling microscope, a covalent bond was formed reversibly between a gold atom and a perylene-3,4,9,10-tetracarboxylic dianhydride molecule supported by a thin insulating film. The bonded and the nonbonded state of the complex were found to be associated with different charge states, and the switching between the two states was accompanied by a considerable change in the tunneling current. Atomic force microscopy molecular imaging was employed to determine precisely the atomic structure of the complex, and the experimental results were corroborated by density functional theory calculations. DOI: 10.1103/PhysRevLett.105.266102 PACS numbers: 68.37.Ef, 68.37.Ps, 71.15.Mb, 82.37.Gk The concept of using single atoms and molecules as memory elements or switches in electronic devices was established long ago [1]. Scanning tunneling microscopy (STM) has been used to investigate and identify promising molecular switches [2][3][4][5][6][7], due to its capabilities to image and manipulate adsorbates on the atomic scale. Atomic manipulation was also performed with noncontact atomic force microscopy (AFM) a few years ago [8][9][10], and most recently it was shown that atomic resolution can be achieved on organic molecules by functionalizing an AFM tip with a suitable atomic termination [11]. STM has repeatedly been used for the making and breaking of single chemical bonds between metal atoms and molecules [12][13][14][15][16] and between molecules [17,18]. Those previous examples of bond formation, however, were not suited as molecular switches, because they required complex protocols of STM tip positioning, voltage pulses or current injection, involved various possible configurations of the constituents, or resulted in only a slight change of the tunneling current. Furthermore, in the examples mentioned it was not possible to switch between the bonded and the nonbonded state in a reliable and directed manner (meaning that the system can be switched with certainty to the desired state).In this Letter, we present a molecular switch that is based on the reversible bond formation between a Au adatom and an organic admolecule [perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA)] on a thin NaCl film supported by a Cu substrate. The switching between the bonded and the nonbonded configuration was accompanied by a change in the tunneling current of about 2 orders of magnitude. The bond making and breaking were controlled simply by applying voltage pulses of according polarity and did not require an exact tip movement or positioning over a particular part of the molecule. The operation and electronic characterization of the switch were performed with STM, whereas the exact geometry of the complex was deduced from atomically resolved AFM images. The experimental results were combined with density functional theory (DFT) calculations to gain further insight into the details of the bonding geometry and the el...