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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. We utilize the on-surface reaction of tribromotrioxoazatriangulene molecules to synthesize carbonyl-functionalized Kagome graphene on Au(111), thereafter modified in situ by exposure to atomic hydrogen. Atomic force microscopy and tunneling spectroscopy unveil the stepwise chemical transformation of the carbonyl groups into radicals, which creates local magnetic defects of spin state S = 1/2 and zero-energy states as confirmed by density functional theory. The ability to imprint local magnetic moments opens up prospects to study the interplay between topology, magnetism, and electron correlation in Kagome graphene.

The controlled growth of self-assembled networks on surfaces based on viologen salts is a major scientific challenge due to their unique electronic properties. The combination of solid-state NMR spectroscopy and atomic force microscopy at ambient conditions can unravel the fine organization of the supramolecular network on a graphitic surface by positioning the counter-ions relative to the viologen cation.

The design of supramolecular networks based on organic molecules deposited on surfaces, is highly attractive for various applications. One of the remaining challenges is the expansion of monolayers to well-ordered multilayers in order to enhance the functionality and complexity of self-assemblies. In this study, we present an assessment of molecular conformation from 2D to 3D supramolecular networks adsorbed onto a HOPG surface under ambient conditions utilizing a combination of scanning probe microscopies and atomic force microscopy- infrared (AFM-IR). We have observed that the infrared (IR) spectra of the designed molecules vary from layer to layer due to the modifications in the dihedral angle between the C=O group and the neighboring phenyl ring, especially in the case of a 3D supramolecular network consisting of multiple layers of molecules., (© 2023. The Author(s).)

We demonstrate that the strong N 2 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 2 with the surface can facilitate electron transfer from the Si(111)-7x7 surface to the π*-antibonding orbitals of N 2 that significantly weaken the N 2 bond. This activated N 2 triple bond dissociation on the surface leads to the formation of a Si 3 N interface., (© 2023 Wiley-VCH GmbH.)

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. We demonstrated that nature of the stimulus strongly alters the overall quality of the resulting polymers in terms of length and number of defects. This new way is an efficient method to elaborate on-surface self-assembled 1D polymers.

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. This chemical degradation can limit the use of these polymers in detection of organophosphates in water-solution.

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. We demonstrated that the balance between molecule-molecule interaction and molecule-substrate interaction can be drastically modified by a strong modification of the geometry of the molecules thanks to a thermal annealing. This new way is an efficient method to elaborate on-surface coordination polymers.

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.

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. Then, they were thoroughly characterised with a combination of local probes, including Raman spectroscopy, Fourier transform infrared spectroscopy and transmission electron microscopy in imaging and diffraction mode., (© 2021 IOP Publishing Ltd.)

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 -4.5 V and allows access to reactive radical species under exceptionally mild conditions. This transfer can effectively 'switch on' a sequence leading to the formation of oligomers of defined size distribution thanks to the on-surface confinement of the reactive species. Our approach enables new ways to initiate and control radical oligomerisations with tunnelling electrons, leading to molecularly precise nanofabrication.

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. To distinguish the relative arrangement of the dipolar molecules within the assembly, a rational combination of experimental results and electronic structure calculations allows us to identify a single adsorbed LDipCC phase in which the molecular dipoles are homogeneously arranged into a parallel fashion on the Si(111)-B surface.

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. This 2D-network is still stable under the pressure of one atmosphere of nitrogen, which demonstrated its interest for the development of submolecular-precisely polyfunctional smart surfaces.

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. Nevertheless, photons are also a powerful source of energy to induce the formation of covalent architectures, even if it is less-used on surfaces than in solution. In this minireview, we discuss the photo-induced on-surface polymerization from the basic mechanisms of photochemistry to the formation of extended polymers on different kinds of surfaces, which are characterized by scanning probe microscopies., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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.

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. Alternatively, an intermediate concentration of Cu adatoms (0 < adatom/BPY < 1) allows the formation of a well-organized and compact structure where both organometallic and HBN components coexist. Although STM images cannot clearly reveal the presence of Cu adatoms within the organometallic moiety, the bonding of BPY to a single or two Cu adatoms can be clearly identified by scanning tunneling spectroscopy (STS), and is supported by Density Functional Theory (DFT) results. Additional STM simulations suggest that the relative position of the Cu adatom with respect to the organic ligands just above has a significant impact on its detection by STM. This study exemplifies the prominent role of metallic adatoms on the formation of a complex organometallic network and should open more rational practices to optimize the formation of these supramolecular networks.

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. High planarity is achieved for high symmetry crosslinks and short, rigid branches. Owing to their solubility, the polymers are easily processable, and can be handled as powder, deposited on surfaces by mere spin-coating, or suspended across membranes by drop-casting. The novel 2D materials are potential candidates as flexible membranes for catalysis, cancer therapy, and electronics., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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. The photophysical properties of these new oligomers were characterized by UV-vis absorption and fluorescence spectroscopy. Deposition of these molecules by a simple spin-coating process on a highly oriented pyrolytic graphite (HOPG) surface leads to the formation of extended monolayered 2D networks. These networks were characterized by atomic force microscopy experiments under ambient conditions with submolecular resolution thus providing the adsorption model of these molecules on an HOPG surface.

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. We also review our best achievements in the field through some examples of rotating molecular machines that have been designed, synthesized, and studied in our groups. On metallic surfaces, the nanovehicles are molecules with two or four triptycenes as wheels and the molecular motor is built around a ruthenium organometallic center with a piano-stool geometry and peripheric ferrocenyl groups. On semiconducting silicon surfaces, vehicles are also made from triptycene fragments and the rotor is a pentaphenylbenzene molecule., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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. Then using the same molecules, a second-layer, based on 1D nanolines, grew above the first layer, thanks to a template effect. Mono- or bi-layered networks were found to be stable from 100 K up to room temperature. These networks were investigated by scanning tunnel microscopy imaging under an ultra-high vacuum (UHV-STM).

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. We find that, contrary to intuition, the structure with the lowest packing fraction corresponds to the highest molecular coordination number, due to the competition between surface and intermolecular forces. Having the lowest free energy, this structure spreads out as the most stable polymorph over a wide range of molecular concentrations.

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.

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.

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., (Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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. Molecular motion is monitored by STM experiments under ultra-high vacuum at room temperature. Molecule-surface interactions are elucidated by semi-empirical calculations.

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). The effect of oxygen-passivation is to suppress debromination and it can be a convenient approach for investigating other self-assembly processes on copper-based substrates., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Two-dimensional supramolecular multicomponent networks on surfaces are of major interest for the building of highly ordered functional materials with nanometer-sized features especially designed for applications in nanoelectronics, energy storage, sensors, etc. If such molecular edifices have been previously built on noble metals or HOPG surfaces, we have successfully realized a 2D open supramolecular framework on a silicon adatom-based surface under ultrahigh vacuum with thermal stability up to 400 K by combining molecule-molecule and molecule-silicon substrate interactions. One of these robust open networks was further used to control both the growth and the periodicity of the first bicomponent arrays without forming any covalent bond with a silicon surface. Our strategy allows the formation of a well-controlled long-range periodic array of single fullerenes by site-specificity inclusion into a bicomponent supramolecular network.

We investigated the adsorption of 4-methoxy-4'-(3-sulfonatopropyl)stilbazolium (MSPS) on different ionic (001) crystal surfaces by means of noncontact atomic force microscopy. MSPS is a zwitterionic molecule with a strong electric dipole moment. When deposited onto the substrates at room temperature, MSPS diffuses to step edges and defect sites and forms disordered assemblies of molecules. Subsequent annealing induces two different processes: First, at high coverage, the molecules assemble into a well-organized quadratic lattice, which is perfectly aligned with the <110> directions of the substrate surface (i.e., rows of equal charges) and which produces a Moiré pattern due to coincidences with the substrate lattice constant. Second, at low coverage, we observe step edges decorated with MSPS molecules that run along the <110> direction. These polar steps most probably minimize the surface energy as they counterbalance the molecular dipole by presenting oppositely charged ions on the rearranged step edge.

The formation of a large scale pattern on Si(111)-7 × 7 reconstruction is still a challenge. We report herein a new solution to achieve this type of nanostructuration by using of zwitterionic molecules. The formation of a large-scale pattern is successfully obtained due to the perfect match between the molecular geometry and the surface topology and to electrostatic interactions between molecules and surface. The adsorption is described by high-resolution scanning tunneling microscopy (STM) images and supported by density functional theory and STM calculations.

A single 4-pyridylazobenzene molecule is observed at room temperature on a Si(111)-B surface by using scanning tunnel microscopy. The reversible conformational switching of this molecule is induced by tunneling electrons and observed at room temperature. This process is based on an intramolecular rotation of a single phenyl group without isomerization of the N=N double bond.

The formation of compact and large-scale self-assembled monolayers (SAMs) adsorbed on a mica surface has been achieved by insertion of alkyl chains on azobenzene derivatives, leading to strong intermolecular van der Waals interactions and hydrogen bonding. The reversible photoswitching of monolayers was investigated by monitoring the variation of the thickness of the SAMs during the cis-trans isomerization of the azobenzene cores with an atomic force microscope (AFM). The absence of covalent bonds between molecules and substrate induces a molecular diffusion which leads to the complete isomerization of the molecules constituting the SAMs.

This work describes an innovative concept for the development of organized molecular systems based on the template effect of the pre-structured semi-conductive SmSi(111) interface. This substrate is selected because Sm deposition in the submonolayer range leads to a 8x2-reconstruction, which is a well-defined one-dimensional semi-metallic structure. Adsorption of aromatic molecules [1,4-di-(9-ethynyltriptycenyl)-benzene] on SmSi(111)- 8x2 and Si(111)-7x7 interfaces is investigated by scanning tunneling microscopy (STM) at room temperature. Density functional theory (DFT) and semi-empirical (ASED+) calculations define the nature of the molecular adsorption sites of the target molecule on SmSi as well as their self-alignment on this interface. Experimental data and theoretical results are in good agreement.

The engineering of a complete adlayer of organic nanolines by supramolecular self-assembly has been achieved for the first time on a silicon-based surface at room temperature and has been studied by scanning tunneling microscopy. This complete adlayer has been successfully obtained thanks to the combination of a specific Si(111)-B square root 3x square root 3R30 degrees semiconductive surface and of strong hydrogen bonds between a pair of dipolar molecules.

Organic nanostructures on semiconductors are currently investigated but the surfaces are known to interact strongly with molecules. To reduce the molecule-surface interaction, we used the Si(111)-B square root 3 x square root 3R30 degrees . Deposition of isolated 2,4,6-tri(2'-thienyl)-1,3,5-triazine, was achieved at room temperature without modification of their pi skeleton. This fascinating arrangement, observed by STM, has been validated by full density functional theory computations onto the entire system. The theoretical results give a clear explanation for the specific adsorption sites of molecules on the substrate.