On-Surface Synthesis and Characterization of Radical Spins in Kagome Graphene.

Flat bands in Kagome graphene might host strong electron correlations and frustrated magnetism upon electronic doping. However, the porous nature of Kagome graphene opens a semiconducting gap due to quantum confinement, preventing its fine-tuning by electrostatic gates. Here we induce zero-energy states into a semiconducting Kagome graphene by inserting π-radicals at selected locations.

Dissociation of N on a Si(111)-7x7 Surface at Room Temperature.

We demonstrate that the strong N bond can be efficiently dissociated at low pressure and ambient temperature on a Si(111)-7x7 surface. The reaction was experimentally investigated by scanning tunnelling microscopy and X-ray photoemission spectroscopy. Experimental and density functional theory results suggest that relatively low thermal energy collision of N with the surface can facilitate electron transfer from the Si(111)-7x7 surface to the π*-antibonding orbitals of N that significantly weaken the N bond.

[2+2] Cyclo-Addition Reactions for Efficient Polymerization on a HOPG Surface at Ambient Conditions.

Polymers obtained by on-surface chemistry have emerged as a class of promising materials. Here, we propose a new strategy to obtain self-assembled 1D polymers by using photochemical [2+2] cyclo-addition or by using a mild thermal annealing. All nanostructures are fully characterized by using scanning tunneling microscopy at ambient conditions on a graphite surface.

Degradation of Sub-Micrometer Sensitive Polymer Layers of Acoustic Sensors Exposed to Chlorpyrifos Water-Solution.

The detection of organophosphates, a wide class of pesticides, in water-solution has a huge impact in environmental monitoring. Acoustic transducers are used to design passive wireless sensors for the direct detection of pesticides in water-solution by using tailored polymers as sensitive layers. We demonstrate by combining analytical chemistry tools that organophosphate molecules strongly alter polymer layers widely used in acoustic sensors in the presence of water.

On-Surface Synthesis of Ligands to Elaborate Coordination Polymers on an Au(111) Surface.

On-surface metal-organic polymers have emerged as a class of promising 2D materials. Here, we propose a new strategy to obtain coordination polymers by transforming supramolecular networks into coordination polymers by surface-assisted cyclo-dehydrogenation of organic building blocks. All nanostructures are fully characterized by using scanning tunneling microscopy under ultra-high vacuum on a gold surface.

Unravelling the growth mechanism of (3,1) graphene nanoribbons on a Cu(111) surface.

The growth of graphene nanoribbons has been widely investigated on metal surfaces in an ultrahigh vacuum. Here, we re-investigate the growth of graphene nanoribbons obtained by thermal annealing of 9,9'-bianthryl derivatives on a Cu(111) surface by using scanning tunnelling microscopy. On the basis of our results, we propose to complete the reaction mechanism commonly accepted in the literature by adding an intramolecular hydrogen atom transfer from the 2,2'-positions to the 10,10'-positions as a key-step in the formation of (3,1)-graphene nanoribbons on a Cu(111) surface.

Nano-sheets of two-dimensional polymers with dinuclear (arene)ruthenium nodes, synthesised at a liquid/liquid interface.

We developed a new class of mono- or few-layered two-dimensional polymers based on dinuclear (arene)ruthenium nodes, obtained by combining the imine condensation with an interfacial chemistry process, and use a modified Langmuir-Schaefer method to transfer them onto solid surfaces. Robust nano-sheets of two-dimensional polymers including dinuclear complexes of heavy ruthenium atoms as nodes were synthesised. These nano-sheets, whose thickness is of a few tens of nanometers, were suspended onto solid porous membranes.

Collective radical oligomerisation induced by an STM tip on a silicon surface.

Over the past decade, on-surface fabrication of organic nanostructures has been widely investigated for the development of molecular electronic components, catalysts, and new materials. Here, we introduce a new strategy to obtain alkyl oligomers in a controlled manner using on-surface radical oligomerisations that are triggered by electrons between the tip of a scanning tunnelling microscope and the Si(111)√3 ×√3 R30°-B surface. This electron transfer event only occurs when the bias voltage is below -4.

Large-extended 2D supramolecular network of dipoles with parallel arrangement on a Si(111)-B surface.

We have investigated the self-assembly of a strong dipolar molecule (LDipCC) on the semiconducting Si(111)-B surface with scanning tunneling microscopy (STM), density functional theory (DFT) calculations and STM simulations. Although the formation of an extended two-dimensional network was clearly revealed by STM under ultra-high vacuum, the assignment of a specific STM signature to the different terminal groups from the LDipCC molecular unit required a complete analysis by numerical simulations. The overall observed assembly is explained in terms of STM contrasts associated with the molecular structure of LDipCC and the molecule-surface interactions.

Stable self-assembly of dipolar molecules on an Au(111) surface under UHV and an inert-atmosphere.

The growth of an extended supramolecular network using dipolar molecules as the building blocks is of great technological interest. We investigated the self-assembly of a dipolar molecule on an Au(111) surface. The formation of an extended two-dimensional network was demonstrated by scanning tunnelling microscopy under ultra-high vacuum and explained in terms of molecule-molecule interactions.

Photochemistry Highlights on On-Surface Synthesis.

On-surface chemistry is a promising way to achieve the bottom-up construction of covalently-bonded molecular precursors into extended atomically-precise polymers adsorbed on surfaces. These polymers exhibit unprecedented physical or chemical properties which are of great interest for various potential applications. These nanostructures were mainly obtained in ultra-high vacuum (UHV) on noble metal single-crystal surfaces by thermal annealing as stimulus to provoke the polymerization with a catalytic role of the surface adatoms.

Controlled growth of a bicomponent supramolecular network by the sergeants & soldiers principle.

The co-deposition of 1,4-di(4',4''-pyridyl)benzene and 1,4-di(4',4''-bromophenyl)benzene on Si(111)-B surface leads to the formation of a highly regular self-assembly. The formation of this network has been investigated by STM and has been elucidated in the light of sergeants & soldiers principle due to halogen bonding on a silicon surface.

Influence of Cu adatoms on the molecular assembly of 4,4'-bipyridine on Cu(111).

The formation of highly organized structures based on two ligands with pyridyl functionalities, 4,4'-bipyridine (BPY) and 1,4-di(4,4''-pyridyl) benzene (BPYB), and Cu adatoms on the Cu(111) surface has been studied with low temperature and variable temperature scanning tunneling microscopy (STM) and first-principles calculations. We show that the formation of a highly organized adlayer built from adatom-molecule and molecule-molecule units strongly depends on the number of mobile Cu atoms on the surface. While a high concentration of Cu adatoms (high adatom/BPY ratio, ≥1) leads systematically to the formation of organometallic nanolines, their absence (low adatom/BPY ratio, ≈0) gives a compact self-assembled molecular network, and more specifically hydrogen-bond networks (HBN) with BPY molecules organized in a T-shaped fashion.

Soluble Two-Dimensional Covalent Organometallic Polymers by (Arene)Ruthenium-Sulfur Chemistry.

A class of two-dimensional (2D) covalent organometallic polymers, with nanometer-scale crosslinking, was obtained by arene(ruthenium) sulfur chemistry. Their ambivalent nature, with positively charged crosslinks and lypophylic branches is the key to the often sought-for and usually hard-to-achieve solubility of 2D polymers in various kinds of solvents. Solubility is here controlled by the planarity of the polymer, which in turn controls Coulomb interactions between the polymer layers.

Extended monolayer of cyano-ended oligo(para-phenylenes) at the air/HOPG interface investigated by high-resolution AFM.

The formation of functional networks on surfaces is one of the main challenges in the field of nanotechnologies. In this paper, we shall propose a very simple process which can be used to achieve the formation of extended monolayer of functional oligo(para-phenylenes) molecules at the air/graphite interface. By developing a convergent strategy, we successfully achieved the synthesis of oligo(para-phenylenes) molecules with a tuneable length.

Towards 1D nanolines on a monolayered supramolecular network adsorbed on a silicon surface.

The growth of 3D extended periodic networks made up of π-conjugated molecules on semi-conductor surfaces is of interest for the integration of nano-components in the future generations of smart devices. In the work presented in this article, we successfully achieved the formation of bilayered networks on a silicon surface including 1D-isolated nanolines in the second layer. Firstly, we observed the formation of a 2D large-scale supramolecular network in the plane of a silicon surface through the deposition of tailored molecules.

Controlled Directional Motions of Molecular Vehicles, Rotors, and Motors: From Metallic to Silicon Surfaces, a Strategy to Operate at Higher Temperatures.

In the last decade, many nanomachines with controlled molecular motions have been studied, mainly on metallic surfaces, which are easy to obtain very clean, and are stable over months. However, the studies of mechanical properties of nanomachines are mainly performed at very low temperatures, usually between 5 and 80 K, which prevents any kind of applications. In this Minireview, we will present our strategy to operate at higher temperatures, in particular through the use of semiconducting silicon surfaces.

Surface-induced optimal packing of two-dimensional molecular networks.

High-density packing in organic crystals is usually associated with an increase of the coordination between molecules. Such a concept is not necessarily extended to two-dimensional molecular networks self-assembled on a solid surface, for which we demonstrate the key role of the surface in inducing the optimal packing. By a combination of scanning tunneling microscopy experiments and multiscale computer simulations, we study the phase transition between two polymorphs.

Supramolecular self-assembly of brominated molecules on a silicon surface.

Hydrogen and halogen bonds have been associated for the growth of 2D compact supramolecular networks on a silicon surface. These interactions have been elucidated in a complete monolayer of a 4,4''-dibromo-p-terphenyl (DBT) molecule on a Si(111)-B surface by combining scanning tunneling microscopy (STM) and density functional theory (DFT) calculations.

Anisotropic growth of the thiophene-based layer on Si(111)-B.

The formation of large assemblies on the Si(111)-B surface is discussed with the help of STM simulations and DFT calculations. Although highly regular assemblies of DTB10B along the Si row direction are observed, the existence of two herringbone isomers introduces a lower periodicity within the 2D molecular network. The formation of herringbone units is explained by weak intermolecular interactions while the 1D assembling depends mainly on the interactions of the C10 side chains with the Si(111)-B surface.

Seeding molecular rotators on a passivated silicon surface.

Thermally activated rotation of single molecules adsorbed on a silicon-based surface between 77 and 150 K has been successfully achieved. This remarkable phenomenon relies on a nanoporous supramolecular network, which acts as a template to seed periodic molecule rotors on the surface. Thermal activation of rotation has been demonstrated by STM experiments and confirmed by theoretical calculations.

Directional molecular sliding at room temperature on a silicon runway.

The design of working nanovehicles is a key challenge for the development of new devices. In this context, 1D controlled sliding of molecules on a silicon-based surface is successfully achieved by using an optimized molecule-substrate pair. Even though the molecule and surface are compatible, the molecule-substrate interaction provides a 1D template effect to guide molecular sliding along a preferential surface orientation.

Self-assembly of a halogenated molecule on oxide-passivated Cu(110).

The supramolecular self-assembly of brominated molecules was investigated and compared on Cu(110) and Cu(110)-O(2×1) surfaces under ultrahigh vacuum. By using scanning tunnelling microscopy, we show that brominated molecules form a disordered structure on Cu(110), whereas a well-ordered supramolecular network is observed on the Cu(110)-O(2×1) surface. The different adsorption behaviors of these two surfaces are described in terms of weakened molecule-substrate interactions on Cu(110)-O(2×1) as opposed to bare Cu(110).