Scanning probe frontiers in molecular 2D-architecture world

Resume : Adsorption, diffusion, structure formation and reactions of molecules on surfaces are most fundamental processes in a wide range of natural and technological fields. For example, the interaction of organic molecules with inorganic surfaces governs biomineralization and biomimetic crystallization. The subtle balance between molecule-surface and molecule-molecule interactions as well as covalent coupling on the surface are explored as versatile strategies to tailor functionality and to arrive at stable structures, e.g., for future molecular electronics applications. Last but not least, fundamental reactions at the solid-liquid interface are at the heart of many processes, e.g., in catalysis and corrosion protection as well as in geochemistry and environmental science. Understanding, controlling and predicting these processes requires detailed insights into the surface and interfacial structure. In this respect, atomic force microscopy operated in the dynamic mode has developed into a most powerful tool for investigating the interfacial structure and reactivity in real space with utmost spatial resolution. Here, recent advances in the AFM instrumentation will be presented that allow for atomic-resolution imaging of mineral-water interfaces as well as hydration layer mapping. AFM sheds light onto pH-induced chages in the adsorption structure as well as molecule-induced surface restructuring. Three-dimensional mapping allows for resolving the hydration structure above mineral surfaces and even enables chemical identification of interfacial cations.

Resume : Simulations have played a key role in understanding the AFM contrast mechanisms responsible for the unprecedented resolution obtained with metal tips functionalized with nonreactive closed-shell molecules like CO or atoms (e.g. Xe). So far, most of the theoretical work has been based on simple and efficient models that rely on pair-wise potentials for the calculation of the total tip-sample interaction [1]. A more fundamental approach can be developed from information extracted from first-principles calculations [2]. This model separates the total tip-sample interaction into an electrostatic (ES), short-range (SR), and van der Waals (vdW) components, and accounts for the CO molecule tilt through an angular spring. The ES interaction is determined from the charge density of the CO-metal tip and the electrostatic potential of the sample (obtained from independent first-principles calculations), while the SR interaction is modelled as a sum of pairwise Morse potentials with species-dependent parameters fitted to reproduce our DFT force calculations. This approach, originally applied to reproduce the complex evolution of the contrast between the cation and anion sites and the positively charged vacancy in NaCl as a function of tip height, can be extended to describe both the intra- and intermolecular contrast observed in a hydrogen-bonded monolayer of triazine molecules [3]. Here, we go a step further and demonstrate that the SR interaction with CO-metal tips can be accurately computed as a power of the overlap of the tip and the sample charge densities [4]. This approach only requires two non-species dependent parameters (a prefactor and the exponent of the power law). It avoids the growing number of parameters needed when pair-wise potentials are used for the calculation of the SR interaction in molecules with a large number of different chemical species [3], and retains DFT accuracy for the range of tip-sample distances that are relevant for imaging. Our model captures the subtle effects introduced by the stoichiometry and bonding environment in the image contrast of a given chemical specie in different molecules, reproduces the contrast associated with different bond orders, and provides a fundamental insight into the highly controversial role of charge redistribution in the imaging of Hydrogen bonds. [1] Hapala, P. et al PRB 90 (2014) 85421. [2] M. Ellner, et al, Nano Lett. 16 (2016) 1974-1980. [3] M. Ellner, et al, Phys. Rev. B 96 (2017) 075418. [4] M. Ellner, et al, submitted (2018).

Resume : Controlled manipulation processes of single-molecules with an atomic force microscope (AFM) provide valuable information about their interactions with surfaces, leading to fundamental insights into adhesion and friction properties. To understand such phenomena at the molecular level, tuning-fork based AFM operated at low temperature and in ultra-high vacuum is an appropriate tool since complex manipulations of a single molecule are possible. With such approach however, the measured frequency shifts are related to normal force gradients, and thus the interpretation of friction phenomena is not fully straightforward. To overcome this issue, we combined original experiments with appropriate analytical models in order to determine adhesive energy and nanoscale friction of those single molecules at surfaces. In this presentation, few examples of single-molecule manipulation experiments [1-2] will be shown consisting in either their vertical pulling or lateral manipulations of synthetic molecules obtained by on-surface reaction [3-4] or spray-deposited biological samples [5]. The forces gradient variations experimentally observed that way were found to be related to the interplay between intra-molecular mechanics, adhesion and friction properties and is supported by the analytical models as well as numerical calculations. [1] R. Pawlak, S. Kawai, T. Glatzel, E. Meyer. Single Molecule Force Spectroscopy (ncAFM, vol. 3, Springer, Japan 2015). [2] R. Pawlak et al., Single-Molecule Manipulation Experiments to Explore Friction and Adhesion, Topical Review in J. Phys. Cond. Matt. D, accepted (2017). [3] S. Kawai et al., Quantifying the atomic-level mechanics of single long physisorbed molecular chains, Proc. Natl. Acad. Sci., 111, 3968?3972 (2014). [4] R. Pawlak et al. Single Molecule Tribology: Force Microscopy Manipulation of a Porphyrin Derivative on a Copper Surface ACS Nano, 10, (2016), 713-722. [5] A. Hinaut et al. Electrospray deposition of structurally complex molecules revealed by atomic force microscopy Nanoscale,(2017).

Resume : The ultimate spatial resolution of scanning tunnelling microscopy (STM) has allowed to gain an exceptional insight into the structure and the intra- and inter-molecular bonding of a huge number of adsorbed molecular system. Unfortunately, these remarkable analytical capabilities are achieved only under ultrahigh vacuum (UHV) conditions and therefore cannot be directly applied to more interesting systems composed of functional (bio)molecules or complex synthetic compounds. In fact, thermal sublimation is the strategy of choice for preparing ultrathin films of small and heat-resistant molecules in UHV but larger, complex (bio)molecules are not compatible with this process. This challenge has been overcome in recent years by adapting soft-ionisation techniques developed in mass spectrometry (mainly electrospray ionisation, ESI) to transfer intact fragile molecules into the gas phase and to soft-land them onto atomically flat and clean substrates. When combined with advanced scanning probe microscopes operating under UHV conditions, these novel set-ups allow the surface deposition and high-resolution characterisation of a wide range of functional organic molecules and inorganic nanoparticles. This talk will present recent advances in the development of ESI-deposition techniques and their combination with UHV-STM to analyse complex (bio)molecule-surface systems. It will start by reviewing the limits that standard molecular deposition imposes on the size of (bio)molecules that can by studied in surface science. It will continue by presenting a recently developed ESI-deposition setup based on a simple, efficient and modular design with a high intensity and mass selectivity. The discussion will then proceed to the application of ESI-STM to the characterisation of adsorbed polypeptides and polymers. In particular, it will be shown that this technique allows the imaging of individual macromolecules with unprecedented detail, thereby unravelling structural and self-assembly characteristics that have so far been impossible to determine.

Resume : We use low temperature scanning tunneling microscopy (STM), spectroscopy, and molecular manipulation schemes to investigate complex molecular systems on metal and 2-D materials surfaces [1,2,3]. A recent emergent research direction is the development of complex molecular machines suitable to operate on solid surfaces. Unlike biological counterparts, the synthetic molecular machines may tolerate a more diverse range of conditions, and thus be advantageous for the complex functions with low power consumption suitable to operate in solid state devices. In this talk, operations of individual molecular motors on materials surfaces using STM tip will be presented. For the manipulation and spectroscopy of molecular systems on 2-D materials, we will present our resent results of anomalous Kondo resonance discovered in vertically stacked heterostructures formed by magnetic molecules-graphene nanoribbons (GNRs)-gold surface. Unlike graphene, atomically precise semiconducting GNRs grown on a Au(111) surface do not have free electrons due to their large bandgap. Although GNRs would be expected to effectively decouple the electronic molecular orbitals from the metal substrate, the strengths of Kondo resonances for the molecules on GNRs appear nearly identical to those molecules directly adsorbed on the top, bridge, and three-fold hollow sites of Au(111). This GNR induced anomalous spin-coupling effect is confirmed by density functional calculations that reveal no spin electron interactions if the molecule is left at the same height from the Au(111) surface without the mediation of the GNRs. These findings suggest GNRs mediate effective spin-coupling while electronically isolating the molecules from the substrate, opening a way for potential applications in spintronics. This talk will also discussed mechanical properties of magnetic molecules on graphene surfaces. [1] Y. Zhang, H. Kersell, R. Stefak, J. Echeverria, V. Iancu, U.G.E. Perera. Y. Li, A. Deshpande, K.-F. Braun, G. Rapenne, C. Joachim, and S.-W. Hla. Simultaneous and Coordinated Rotational Switching of all Molecular Rotors in a Network. Nature Nanotechnology 11, 706-711 (2016). [2] U.G.E. Perera. F. Ample, H. Kersell, Y. Zhang, G. Vives, J. Echeverria, M. Grisolia, G. Rapenne, C. Joachim, and S.-W. Hla. Controlled Clockwise and Anticlockwise Rotational Switching of a Molecular Motor. Nature Nanotechnology 8, 46-51 (2013). [3] Y. Li, A. Ngo, A. DiLullo, K.Z. Latt, H. Kersell, B. Fisher, P. Zapol, S.E. Ulloa, and S.-W. Hla. Anomalous Kondo resonance mediated by semiconducting graphene nanoribbons in a molecular heterostructure. Nature Communications 8, 946 (2017).

Resume : Weak interlayer coupling in 2-dimensional layered materials such as graphite gives rise to rich mechanical and electronic properties in particular in the case where the two atomic lattices at the interface are rotated with respect to one another. A lack of crystal symmetry leads to anti-correlations and cancellations of the pz orbital interactions across the twisted interface, which gives rise to low friction behavior and low interlayer electrical transport. Using our AFM based manipulation technology1 we studied the interlayer electrical conductivity as a function of twist angle between two misoriented graphene layers with unprecedented angular resolution of ~ 0.1º. The angular dependence indicates that the electrical transport across the interface is dominated by a phonon assisted channel which conserve the momentum of conduction band electrons, tunnelling across the twisted Dirac bands. Most intriguingly, the conduction is significantly enhanced within a narrow angular range of less than 0.5º at pseudo-commensurate angles of 21.8º and 38.2º. This provides the first experimental evidence for the existence of a 2-dimensional interface state originating from the coherent coupling of electronic states in the twisted sheets due to commensurate superlattices2. Turning to the mechanical properties, we investigated the shear forces of a twisted graphene flake sliding on a graphene substrate using both experimental and numerical methods. We found that the sliding force is dominated by so called rim forces originating from a symmetry breaking of the force field in the Moiré supercells which in turn gives rise to uncompensated force contributions from incomplete tiles covering a 2-dimensional annulus at the periphery of the flake. This mechanism is distinctively different from the so-called edge effect due to lattice relaxations of the edge atoms. Moreover, we show that the friction force originates from a genuine lattice interaction between the rotated sliding surfaces, hall mark signatures being the scaling of the friction force with the cross-section area to the power of 0.35 and the observation of lattice peaks in the power spectrum of the friction force. From an analysis of the friction force statistics we show that sliding friction is essentially a stochastic process. An interesting case results at a twist angle of 30º at which a quasi-crystalline interface structure is formed leading to virtually vanishing sliding forces for the fundamental dodeconal tiling units independent of their size3. References [1] E. Koren et al., Science, 6235 (2015) 679. [2] E. Koren et al., Nature Nanotech., 9 (2016) 752. [3] E. Koren et al., Physical Review B, 20 (2016) 201404.

Resume : Metallic atoms are known to play a vital role in several cellular environments through interacting with nucleobases. However, it still remains a great challenge in delicately controlling the balance between the interactions of nucleobases and metallic atoms within the biological system. Thus, a fundamental insight to understand the interactions between metal and nucleobases and further to rationally design ligands for novel biomedical applications is necessarily needed. Here, in this talk, on the basis of DNA/RNA bases, we studied the interactions between metallic atoms like alkali metal (Na, K) and transition metal (Ni, Fe) and different base molecules. Also, we introduce water into UHV conditions, and we surprisingly find that water molecules can interact with base molecules in several different ways, which will also be discussed in this talk. We hope these results would provide new insights into the basic physicochemical nature of biologically relevant systems.

Resume : Sublimed C60 films have been grown on hBN at a range of substrate temperatures and coverages and studied using AFM. For films of 0.4 ML coverage, monolayer C60 islands are observed at room temperature, with a transition from dendritic monolayer islands to faceted bi-layers above 178°C. By comparing the island density of C60 grown at a series of temperatures, the diffusion barrier for C60 on hBN was extracted [1]. Sublimed films of perylene tetracarboxylic diimide (PTCDI) were also grown on hBN and found to form monolayers. By sequential deposition of 0.4 ML of PTCDI and C60, molecular heterostructures were formed. For C60 deposited on PTCDI at room temperature, monolayers were observed while C60 bi-layers were observed at temperatures of 139 °C, suggesting a lower Ehrlich-Schwoebel barrier for C60 on PTCDI than hBN. Finally, the fluorescence of PTCDI/C60 heterostructures was investigated with increasing coverage of C60. C60 was found to quench the fluorescence of the underlying monolayer PTCDI, which was also blue shifted by approximately 30 meV upon the initial deposition of a sub-monolayer coverage of C60. The growth of molecular heterostructures is a promising area, both in the study of molecular fluorescence at interfaces and in molecular electronics [2,3], such structures could be incorporated into conventional device architectures and novel van der Waals heterostructures. [1] F. Loske et al. Phys. Rev. B. 82, 155428 (2010) [2] T. Schmitz-Hübsch et al. Surface Science. 445 358?367 (2000) [3] V.V. Korolkov et al. Nature Chemistry. 9, 1191-1197 (2017)

Resume : The fact that light is emitted when a current is injected through a tunnel junction was first found in the 70?s by Lambert and McCarthy, and is currently exploited to analyze the light arising from the local junctions created between the tip and the sample in Scanning Tunneling Microscopes (STM). Different studies on STM induced luminescence of organic molecules directly adsorbed on top of nobel metal substrates report a plasmonic origin of the emmited light which originates from the underliying substrate. In order to study the intrinsic light emission from organic molecules a deocupling layer between the molecules and the metal electrode is necessary to avoid radiationless energy transfer from a molecular energy level to the metallic substrate. In these studies the most commonly proposed mechanism for light emission is that of radiative recombination of an electron and a hole located in two different molecular energy states. In this contribution we study the light emitted from C60 nanocrystals grown on top of NaCl on Ag(111). We have observed that depending on the concrete tunneling parameters, when injecting electrons onto a C60 nanocrystal, we are able to reversibly switch from a broad plasmonic spectrum to a very sharp molecular resonance of 10meV width. While previous studies have shown a continuous transition from plasmonic to molecular emission as a function of the tip position, here we control the emission type and monochromaticity on a single spot with the tunneling parameters. Our results may be of great importance for applications such as single photon emitters or quantum computing since future devices may need to be able to switch monochromaticity in a controlled fashion.

Resume : Cross-linking of functionalized monomers on solid surfaces was demonstrated to be a versatile synthetic route for the bottom-up fabrication of unique low dimensional covalent nanostructures. However, the covalent interlinks are typically irreversible, resulting in a kinetically controlled polymerization, yielding low structural quality especially for 2D polymers. Surface-assisted Ullmann coupling is the most widespread coupling reaction, due to its predictability and controllability, as well as the large availability and high stability of halogenated precursors. Upon dehalogenation, on Au(111) mostly direct covalent coupling is observed, whereas metastable organometallic intermediates emerge on Ag(111). Interestingly, the C-Ag-C linkages become reversible at elevated temperatures, facilitating structural equilibration by ?organometallic self-assembly?. The isostructural conversion of this ordered state into covalent networks is feasible, and was shown to improve the structural quality. In this contribution, we present experiments that aim to shed more light onto fundamental processes and reaction steps, concerning the kinetics of dehalogenation and organometallic network formation as well as the role of steric hindrance and perfluorination. Lastly, intercalation of iodine monolayers is introduced as straightforward method for post-synthetic decoupling, in order to alleviate the influence of the strongly interacting, but synthetically inevitable metal supports.

Resume : Synthetic organic materials have gained an irrevocable presence in our daily lives. The variety of their applications is continuously growing, including highly refined functionalities as for example in optoelectronic devices, catalysts, filters or batteries. In the frame of their synthesis, on-surface chemistry is rapidly attracting increasing attention. On the one hand it is expected to allow the synthesis of materials not achievable by other means, while on the other hand it overcomes potential problems in the transfer of complex molecular compounds synthesized by conventional wet-chemistry onto solid device structures. Besides, running the reactions under ultra-high vacuum and on well-defined surfaces allows the use of a variety of sophisticated surface-science techniques for their characterization. We have followed an on-surface chemistry approach for the synthesis and characterization of a variety of organic materials, including molecular structures displaying magnetism, atomically precise graphene nanoribbons, as well as a variety of their heterojunctions.

Resume : A major objective in modern surface and nanoscale science relates to complex interfaces and the development of protocols for their control, both in the static and dynamic regime. Notably two-dimensional molecular architectures promise special properties related to their nontrivial structure. Interfacial molecular engineering employing optimized assembly procedures and carefully selected molecular building blocks represents a powerful tool for constructing a variety of intriguing materials. Herein we report advances towards surface-confined complex networks using different fabricaton schemes. Specifically, we realized networks and tesselations via (i) supramolecular organization of organic tectons, (ii) metal-directed assembly, notably exploiting rare-earth centers, (iii) flexible molecular units, and (iv) multi-step convergent synthesis where sequential chemical conversions of a simple organic species mediate the expression of a semiregular archimedean tiling. Our approach illustrates novel avenues to construct complex materials via specific interactions and interfacial adaptation or transformations of adsorbed molecular tectons. Moreover, the findings and employed methodology contributes to the general understanding of the emergence of complexity and hierarchic systems in chemistry and biology. Key papers include: JACS 130, 11778 (2008); ACS Nano. 6 (2012) 4258; Proc. Nat. Acad. Sci. 110, 6678 (2013); Angew. Chem. Int. Ed. 54 (2015); Nano letters 16, 4274 (2016); Nano Lett 16, 1884 (2016); Nature Chemistry 8, 657 (2016); 6163, Nature Chemistry 10.1038/NCHEM.2924 (2018).

Resume : Confinement effects are omnipresent in science and nanotechnology. Electrons experiencing quantum confinement generate emergent electronic and electromagnetic material properties. At the molecular scale, confinement inside encapsulation complexes can alter the kinetics and thermodynamics of chemical reactions and crystallization. Here, we investigate how nanoscale confinement impacts the spontaneous assembly of molecules at a solution surface interface. Confinement is achieved using in situ nanoshaving on a densely grafted graphite surface using scanning tunneling microscopy (STM). Upon local exposure of the bare graphite surface, molecules dissolved in an organic liquid above the surface undergo supramolecular self-assembly selectively within these void spaces, called ?corrals?. The gradual surface revelation necessarily places geometric as well as temporal constraints on the self-assembly processes. It will be discussed how these constraints affect the observed assemblies for a selected number of molecules. Finally, on-surface reactivity under confinement conditions will be presented.

Resume : Advancing the time resolution of AFM has been a primary pursuit of multiple research groups [1-3]. In particular, the idea to observe ultrafast events in the femtosecond range combined with nanometer spatial resolution is of great interest. Here the research focus ranges from measuring photocarriers to the molecule motion and beyond [4]. Recently, we demonstrated picosecond time resolution with nc-AFM and ultrafast laser pulses in low temperature grown GaAs [2]. Our most recent advances in ultrafast time resolution AFM will be presented. We developed an autocorrelation measurement for ultrashort laser pulses by force detection using nc-AFM. A non-linear crystal is used to generate an electric field which follows the intensity of the impinging ultrashort laser pulse; we directly trace the emitted electric field with attosecond temporal, and nanometer spatial, resolution using our nc-AFM setup. As such, we are able to demonstrate that the lower limit of time resolution in AFM is solely given by the minimal time delay achievable by the optical setup and the thermal noise of the nc-AFM. We are currently applying this technique to 2D materials as well as organic AD structures. [1] M. Takihara, T. Takahashi, T. Ujihara ? Appl. Phys. Lett. 93 (2008) 021902. [2] Z. Schumacher, A. Spielhofer, Y. Miyahara, P. Grutter, Appl. Phys. Lett. 110 (2017) 053111. [3] G. Shao, M. S. Glaz, F. Ma, H. Ju, D. S. Ginger, ACS Nano, 8 (2014) 10799 [4] M. Peplow, Nature 544 (2017) 408?410.

Resume : Recent advances in addressing and controlling the spin states of a surface-supported object (atom or molecule) have further accredited the prospect of quantum computing and of an ultimate data-storage capacity. Scanning probe techniques have shown that inelastic electron tunneling spectroscopy (IETS) within the junction of a scanning tunneling microscope (STM) is a good starting point to study the stability of these spin states. We present here a novel approach based on the molecular functionalization of a STM tip. We study the surface magnetism of a simple double-decker molecule, nickelocene [Ni(C5H5)2], which is adsorbed directly on a copper surface. By means of X-ray magnetic circular dichroism and density functional theory calculations, we show that nickelocene on the surface is magnetic (Spin = 1) and possesses a uniaxial magnetic anisotropy, while IETS reveals an exceptionally efficient spin-flip excitation occurring in the molecule. Interestingly, nickelocene preserves its magnetic moment and magnetic anisotropy not only on the surface, but also in different metallic environments. Taking advantage of this robustness, we are able to functionalize the STM tip with a nickelocene, which can then be employed as a portable source of inelastic excitations. As we will show during the talk, IETS can then be used to probe the interaction between a surface-supported object and the nickelocene tip, including a magnetic interaction.

Resume : Graphene is a remarkable material for many electronic applications. Recent advances in devices involve the transport of magnetic spin, which heralds the development of a spin-field effect transistor. A molecular layer on graphene containing heavy transition metal atoms would be an optimal prototype for spin-transport.1 In this presentation, I will discuss atomic-scale studies of the adsorption of two different molecules; Ni-phthalocyanine (NiPc) and Pt-tetraphenyl-porphyrin, on monolayer graphene (MG) grown epitaxially on 6H-SiC(0001).2 These molecular layers were studied using room temperature scanning tunneling microscopy (STM). Both molecules adsorb to from self-assembled layers on the graphene with a square lattice. In the case of NiPc, the molecular layers produce six equivalent uniform domains due to three-fold symmetry of graphene, similar to perylene derivatives on graphene.3 Tunneling spectroscopy reveals the energies of the molecular orbitals of the NiPc molecules, while Density Functional Theory (DFT) calculations will provide information on their localization. A comparison will made with the adsorption of PtTPP on graphene with several similarities and a few striking differences.4 These studies will deepen our understanding of the influence of metal-organic molecules on the electronic properties of graphene. 1. Chuan Li, K. Komatsu, S. Bertrand, G. Clavé, S. Campidelli, A. Filoramo, S. Guéron, and H. Bouchiat, Phys. Rev. B, 2016, 93, 045403. 2. M. Zhao, Ph. Sonnet, E. Duverger, G. Dujardin, and A. J. Mayne, submitted. 3. H. Yang, A.J. Mayne, G. Comtet, G. Dujardin, Y. Kuk, Ph. Sonnet, L. Stauffer, S. Nagarajan, A. Gourdon, Phys. Chem. Chem. Phys., 2013, 15, 4939-4946. 4. M. Zhao, S. Campidelli, H. Bouchiat, S. Guéron, Ph. Sonnet, E. Duverger, Y. Dappe, G. Dujardin, and A. J. Mayne, in preparation.

Resume : We present a study that reveals how the combination of chemical functionalization and surface templating can be exploited to obtain different types of self-assembled structures graphene nanoribbons (GNR) of varying length. We synthesize (-H, -F, -OCH3)-functionalized Chevron-type GNRs on Au(111), where the functional group is used to tune the balance between GNR-surface and inter-GNR interaction. In the diluted regime this can lead to a periodic superstructure of individual GNRs of narrow size distribution, where the herringbone reconstruction imposes their size and position by constraining the growth to the fcc domains. In the saturated regime close-packed domains of longer GNRs are obtained. A different molecule-surface interaction for aryl-functionalized DBBA precursors leads to periodic superlattices of parallel, ultralong (>100nm) GNRs. Here the interaction with the reconstruction is only exploited for the alignment but not for size limitation. The results show the potential to exploit the combined molecular and surface interactions to control GNR morphology and order.

Resume : There is increasing industrial demand for high performance thermoplastic polymer which is often achieved by blending polymers and adding rubbers to improve the impact properties. Understanding the contribution of the different phases to the mechanical properties is a pre-requirement to accelerate material improvement. Here, we present a new methodology based on AFM-QNM for the characterization of NORYLTM resin product, a multiphase polymer blend containing nano-size poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) rubber as an impact modifier. The nanomechanical properties of this multiphase system are characterized by AFM-QNM modulus mapping followed by data analysis to discriminate the modulus distribution of the different phases. The first results show that the contribution of the hard polymer matrix on the apparent SEBS modulus values increases significantly for small SEBS domains (< 100 nm). A model was developed to derive the intrinsic SEBS modulus from the measured value taking into account the indentation depth and rubber thickness. The nano-domains of the PS and EB blocks in SEBS are further distinguished by optimizing the indentation force and the deformation depth. The derived stiffness of PS and EB blocks is then correlated to the SEBS molecular structure to allow the detection of potential rubber degradation. This characterization greatly enhances our understanding of the relationship between the nano-structure of polymer blends and their impact properties.

Resume : In recent years, Tip Enhanced Raman Scattering (TERS) imaging made a dramatic progress from ?once in a lifetime experience? to a routine everyday characterization tool for nanoscale Raman imaging of various materials. This progress was mainly determined by the advent of new generation of TERS instrumentation, development of advanced TERS imaging modes and availability of highly reproducible commercially available TERS probes with high enhancement factors. Since TERS is intrinsically a hyperspectral imaging tool, it does not rely on apriori knowledge of the spectral properties of the investigated materials and therefore allows discovery of unexpected Raman peaks and mapping the distribution of their intensities. Cross-correlating the nano-Raman maps with other channels provides by scanning probe microscopy (SPM) such as the topography, surface potential, conductivity, photocurrent, friction etc, is another powerful tool allowing comprehensive characterization of novel materials at nanoscale. We?ll illustrate usefulness of TERS imaging and cross-correlation of nano-Raman with other SPM channels by probing the distribution of structural defects and chemical groups on a graphene oxide surface. We demonstrate mapping of chemical groups on carboxyl graphene oxide (GO-COOH) surface with an unprecedented spatial resolution of ? 10 nm using TERS. Furthermore, we extend the capability of TERS by in-situ measurement of local electronic properties in addition to the topography and chemical composition at the sample surface. In-situ topographical, electronic and chemical nanoscopy of the GO-COOH surface reveals that the Fermi level on GO-COOH surface increases with increasing Id/Ig ratio, enabling correlation of the local defect density to Fermi level at nanometre length-scales for the first time.

Resume : Miniaturization being a sought after criteria, a large body of work has been devoted over the last twenty years on confinement effects in polymer thin films. Besides the well-known deviation of the glass transition temperature, Tg with respect to the bulk value, polymer thin films in a confined state (thickness< 100nm) show-up many peculiar properties in their viscosity, physical aging, surface mobility and density, compared to their bulk counterpart. It has been shown that the interfaces (polymer/substrate and polymer/air) impact strongly these properties. In this presentation the influence of the interfaces will be illustrated through our contribution to the the study of the glass transition temperature, the stability and the density of thin polymer films. In spite of a wealth of experimental and theoretical studies on this topic, there is still an intense controversy over the role played by interfaces on the occurrence of Tg. We will show that by performing Atomic Force Microscopy measurements of pull-off force measurement as a function of the temperature, we were able to probe the dynamic of supported thin polystyrene (PS) thin films. We demonstrated the existence of two transition temperatures that can be associated to the relaxation of polymer chains located at different depth regions within the polymer film. Independently of the film thickness, we have confirmed the presence of a region of high mobility for the polymer chains at the free interface. We claim here that our results demonstrate, in agreement with other techniques, the stratification of thin polymer film depth profile in term of relaxation behavior. Stability of thin polymer films is of paramount importance for a variety of applications. In a second part of our presentation, by adopting a simple top-down method based on good solvent rinsing, we were able to prepare flat polystyrene films with a controlled thickness ranging from 1.3 nm to 7.0 nm.7 Their stability was scrutinized using AFM after a classical annealing procedure above the glass transition temperature. The Lifshitz van der Waals intermolecular theory that predicts the domains of stability as a function of the film thickness is in accordance with our experimental observations. We surmise that it is due to the solvent rinsing procedure that removes the residual stress and/or the density variation of the polystyrene films inhibiting thermodynamically the dewetting.

Resume : Conjugated two-dimensional (2D) materials are ultimately thin species, in which the hoping of charge carriers between neighboring atomic sites governs conduction. Graphene, which may be regarded as a giant conjugated molecule, is a typical example. Rich electronic, magnetic, and optical properties are expected in 2D materials with more complex structure and composition than graphene. Here, a new class of two-dimensional (2D) covalent organometallic polymers, with nanometer-scale crosslinking, is 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 straightforwardly processable, and can be handled as powders, deposited on surfaces by spin-coating, or suspended across membranes by drop-casting (1). The novel 2D materials are potential candidates as flexible membranes for catalysis, cancer therapy, and electronics. (1) F. Cherioux, J. Coraux, V. L. Muller, L. Magaud, N. Bendiab, M. den Hertog, O. Leynaud, W. Hourani, S. Lamare, D. Kamaruddin, F. Palmino, R. Salut, Chem. Eur. J. 2017, 23, 10969.

Resume : The fabrication of robust and conjugated organic nano-architectures deposited on surfaces is a key-challenge in order to build smart components. Most of covalent nano-architectures are obtained by thermally-induced on surface chemistry with an effective catalytic role of surfces (Ulmann cross-coupling, Glaser cross-coupling, etc.). Nevertheless, as molecular diffusion is also promoted by an increasing of the temperature, it is very difficult to achieve well-ordered covalently-bounded nano-architectures by these on-surface reactions. Photopolymerization of molecules is a powerful method to obtain organic polymers, because photopolymerization is not thermally-induced and does not require any catalytic role of the surface. Nevertheless, this strategy is still rare on surfaces despite of its interests. Here, we investigate the photopolymerization of supramolecular networks adsorbed on different surfaces (Si(111)-B, Cu(111), HOPG) by illumination with an ultra-violet (UV) light. All experiments were monitored by Ultra-High Vaccum Scanning Tunneling Microscopy (UHV-STM). We observe the formation of covalently-bounded nano-architectures, like nanowires, depending of geometry of the starting supramolecular networks. The properties of obtained polymers (air-stability, charge transport abilities, etc.) are currently under investigation with Atomic Force Microscopy (AFM) under ambient conditions.

Resume : The remarkable physical properties of two dimensional transition metal dichalcogenides (2D TMDs) such as transparency, flexibility and high carrier mobility proves potential of their device application. Especially, controllable band gap of semiconducting TMDs is the great advantage in various electronics such as nonvolatile memory devices. In this study, we investigate the resistive switching phenomena of heterojunction of MoS2 or WSe2 with (001)-oriented Nb doped SrTiO3 (Nb:STO) crystal. To improve interfacial properties, we treated Nb:STO with etchant and followed by annealing process. All processes were conducted in N2 atmosphere to hinder re-oxidation of oxygen vacancies. Conductive-atomic force microscopy (c-AFM) measurement with Pt/Ir coated tip, which acts as top electrode was used to induce different resistive state and analyze vertical charge transport behavior in each sample. Oxide trap and intrinsic 2D TMDs trap model were used to understand resistive switching behavior. Intrinsic 2D TMDs trapped charges tend to increase as the number of layer increases. Additionally, laser illumination was also used in c-AFM measurement. To minimize the effect of photo-generated charges from Nb:STO, we used low energy laser. Photo-generated carriers in MoS2 and WSe2 layers assist to achieve high ON/OFF current ratio and large I-V hysteresis, which is particularly desirable in memory application. Kelvin Prove Force Microscopy (KPFM) measurement was also conducted to draw band profile of different resistive state in dark and illumination. Comparison between pristine state and after poling with biased tip utilizes to figure out the mechanism of bipolar resistive switching in our samples as well. Therefore, our study suggests the controllable SET/RESET voltage memory device with the presence of illumination.

Resume : We have investigated the adsorption of metal-free phthalocyanine (H2Pc) thin films on hexagonal boron nitride (hBN) using high resolution atomic force microscopy under ambient conditions. The Pc molecules are sublimed onto hBN under vacuum conditions. A set of samples were grown at room temperature with wide range of film thickness (0.2nm-32nm) and the effect of temperature variation of the substrate was also investigated. At low coverage, H2Pc forms needle-like islands in which the molecules are coplanar with the substrate. With increasing thickness in the range 4nm to 32nm the morphology of the islands changed to form dendritic-like disordered islands which are attributed to cofacial stacking of molecules. At growth temperatures close ~100 oC we observe the formation of large monolayer islands and we are able to obtain AFM images with molecular resolution from which we can identify the packing and ordering of the molecules. The photoluminescence of the Pc films was measured with a fluorescence microscope and we find a very intense red-shifted zero-phonon peak for the monolayers with additional peaks for multilayer samples which appear at lower energy and are close to those observed for Pc powder. We discuss these red shifts in relation to substrate and intermolecular interactions.

Resume : The investigation of the interplay between the nanostructure and carrier dynamics is of crucial importance for the development of many emerging photovoltaic technologies. In this context, Kelvin probe force microscopy under frequency-modulated excitation (FMI-KPFM) has emerged as a useful technique for probing photo-carrier dynamics at the nanoscale in a wide range of photovoltaic materials. In short, FMI-KPFM allows the acquisition of spectroscopic curves of the average surface photo-voltage (SPVAV) as a function of the frequency-modulated illumination, providing access to the recombination dynamics. However, some aspects about FMI-KPFM data interpretation are still the subject of debate. The plausible presence of capacitance artifacts, the mathematical model used in the data-fitting process, the time needed to reach the equilibrium state of charge during each modulation cycle, are some of the hot topics that are still under research. Here, we take a different approach to tackle these enquiries by proposing and demonstrating an automatic numerical simulation routine that enables to predict the behavior of spectroscopy curves of SPVAV as a function of a frequency-modulated excitation source, constituting a way to check FMI-KPFM experiments self-consistency. We describe the general aspects of this simulation routine and we compare it against experimental results obtained using single-point FMI-KPFM over a silicon nanocrystal solar cell. Furthermore, we show how this simulation routine can complement experimental results as additional information about the samples photo-carriers dynamics can be gained via the numerical analysis.

Resume : 2D self-assembly of DBA in confined spaces: structural transition and selective adsorption in nanocorrals Yi Hu,1 Ana M. Braganca,1 Brandon E. Hirsch,1 Lander Verstraete,1 Kazukuni Tahara,2,3 Yoshito Tobe,3 and Steven De Feyter*1 1Department of Chemistry, Division of Molecular Imaging and Photonics, KU Leuven-University of Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium 2Department of Applied Chemistry, School of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, 214-8571, Japan 3Division of Frontier Materials Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan Two dimensional self-assemblies of dehydrobenzo[12]annulene (DBA) derivatives are explored in confined spaces using scanning tunneling microscopy (STM) as the visualization tool. Nanocorrals with different sizes and shapes are created on grafted highly oriented pyrolytic graphite (HOPG) surface via a nanoshaving approach.1, 2 The confinement effect has a strong influence on the self-assembly behavior by inducing i) structural transition and ii) selective adsorption. On the open terraces of unconfined HOPG, DBA molecules display a phase transition from porous at low concentration to non-porous structures at high concentration.3 We demonstrate how corrals give rise to a shift in the concentration range at which this phase transition occurs. Moreover, as the corral size becomes smaller, the confinement effects on the phase transition becomes stronger. Alternatively, enlarging the corrals results in disappearance of the confinement effect. For the mixtures, every component self-assembles into separated domains on bare HOPG. However, in confined area, only the molecule with longer alkyl chains adsorbs in the corral. In general, this work establishes fundamental relationships involved in confined self-assembly in supramolecular chemistry. References: [1] J. Greenwood, T. H. Phan, Y. Fujita, Z. Li, O. Ivasenko, W. Vanderlinden, H. Van Gorp, W. Frederickx, G. Lu, K. Tahara, Y. Tobe, H. Uji-i, S. F. L. Mertens and S. De Feyter, ACS Nano, 2015, 9, 5520-5535. [2] L. Verstraete, J. Greenwood, B. E. Hirsch and S. De Feyter, ACS Nano, 2016, 10, 10706-10715. [3] S. Lei, K. Tahara, F. C. De Schryver, M. Van der Auweraer, Y. Tobe and S. De Feyter, Angew. Chem., 2008, 120, 3006-3010.

Resume : Here we report about the synthesis and 2D supramolecular self-assembly of shape persistent arylene/alkinylene macrocycles with flexible alkyl/alkoxy side chains at the liquid/solid interface on graphite. Scanning tunneling microscopy is used to obtain a submoleculary resolved insight into the nanopatterns. In particular we investigate the influence of different corner units on the shapes of the backbones with otherwise identical symmetry and substitution pattern. The investigation aims at detailed understanding on how the pattern structures and lattice constants depend on the exact shape of the backbone as an effect of the corners and the strain induced by them. References: [1] P. Wilhelm, J. Vogelsang, G. Poluektov, N. Schönefelder, T. J. Keller, S.-S. Jester, S. Höger, J. M. Lupton, Angew. Chem. Int. Ed. 2017, 56, 1234-1238.

Resume : Transition metal dichalcogenides (TMDs) are a new class of layered materials developed1 following the discovery of novel physical properties of graphene. Based on their composition and crystal structure TMDs can exhibit a wide range of electronic behavior from semiconducting to semimetallic, metallic and sometimes superconducting2. Tunability of the electronic bandstructure in these materials thus becomes important. Functionalization by covalent and non-covalent approach is a promising approach to effectively modify the electronic band gap, Fermi level position and induce doping in these materials3. In this work we will discuss about visualization of functionalized TMDs with scanning probe microscopy (SPM) techniques. We have carried out covalent functionalization of TMDs by aryl diazonium chemistry which results in the formation of covalent bonds between for instance MoS2 and diazonium compounds. The grafted molecules on the TMDs are visualized using STM and AFM in ambient conditions. In an alternative approach, non-covalent functionalization of TMDs is carried out using supramolecular self-assembly, thereby passivating the surface in ambient conditions. References 1. Ruitao Lv et.al. Acc. Chem. Res. 2015, 48, 56?64 2. Sajedeh Manzeli, et al Nature review materials 2, 17033, 2017 3. Stanislav Presolski and Martin Pumera Materials Today 19, No 3 2016

Resume : Molecular assemblies driven by non-covalent interactions have sparked enormous interests in the last decade, due to the high versatility, flexibility and recoverability. To figure out the interplay of the non-covalent interactions intensive attention has been lately focused on the sophisticated systems composed of multiple components and balanced by multiple non-covalent interactions. However, given the complexity and difficulty, the underlying mutual effects of involved interactions remain unexplored or elusive in most cases. Molecular Landers are a distinctive family of molecules, with bulky functional groups acting as the legs to lift up the aromatic molecular board. When the compounds are adsorbed on surfaces, only the legs are in contact with the surface while the molecular board is decoupled from the substrate, which has endowed the Landers a special function as nanoscale molds by trapping metal atoms in the molecular cavity, holding great promise in molecular electronics. Another extraordinary advantage of Landers is that the lifted boards allow the attached functional groups to rotate or/and bend in a way that is otherwise strictly prohibited for legless molecules adsorbed on surfaces. Here, Lander molecules have been aligned in the matrix of PTCDI molecules and metal atoms (Ni) into a mixed network on Au(111). Importantly, facilitated by the electrostatic interactions with Ni, three-dimensional hydrogen bonding between the landers and legless molecules is enabled. Such a multi-component system with synergistic non-covalent interactions may have introduced a fresh strategy for design and engineering sophisticated nanostructures on surfaces.

Resume : On-surface synthesis is a versatile strategy to fabricate graphene-based nanoribbons from the bottom-up with high precision. Here, we demonstrate the on-surface synthesis of porous carbon nanoribbons on Ag(111) via a preprogrammed isomerization of conformationally flexible polymer chains followed by dehydrogenation reactions after thermal annealing.[1] The polymer chains are fabricated by polymerization of prochiral 1,3,5-tris(3-bromophenyl)benzene (mTBPB) directly on the surface using an Ullmann-type reaction. We unveil the reaction mechanism in a low-temperature scanning tunneling microscopy study and demonstrate that the rotation of m-phenylene units is a powerful design tool to promote structural control in the synthesis of porous covalent organic nanostructures on metal surfaces. We further discuss the influence of the molecule-surface interaction by comparing the on-surface synthesis on different substrates. [1] M. Ammon, T. Sander, S. Maier, J. Am. Chem. Soc., 2017, 139 (37), pp 12976?12984

Resume : Understanding the stability of the self-assembly of halogenated aromatic hydrocarbons on liquid-graphitic interfaces is relevant in areas such as pollutant removal, non-covalent doping for nanodevice creation, and organic building block design. However, calculating free energies of formation of organic self-assembled adlayers at the liquid-solid interface is challenging.[1,2] Factors such as large system sizes, polymorphism, and incommensurability can sky-rocket the computational cost. In this study we have computed the free energies of formation from solvation of self-asssembled layers of 1,3,5-trichlorobenzene (TCB) and hexachlorobenzene (HCB) on graphene. Periodic, dispersion-corrected DFT results have been benchmarked against coupled-cluster interaction energies. Free energies of formation including entropic and solvation effects predict the (lack of) spontaneity of (TCB) HCB self-assembly. Molecule-surface interactions play the main role in stabilizing the molecular adlayer. Intermolecular interactions are anticooperative. While halogen bonding is relevant in TCB interactions, HCB layers seem to lack type II halogen-halogen contacts. Scanning Tunnelling Microscopy and Raman experimental results support the computational predictions regarding adlayer geometry, electronic structure, and stability of TCB and HCB self-assembly. References: [1] (a) J R Reimers et al., Proc Natl Acad Sci USA, 2015, 112, E6101, (b) J R Reimers et al., J Phys Chem C, 2016, 120, 1739. [2] S Conti, M Cecchini, Phys.Chem.Chem.Phys., 2016, 18, 31480?3149.

Resume : One of the ongoing challenges in the field of piezoresponse force microscopy (PFM) is the accurate quantification of the piezoelectric coefficients. Conventional PFM systems almost exclusively use an optical beam deflection (OBD) system where a laser is focused on the back of the cantilever and the angle of the reflected light is used to deduce the cantilever normal and lateral tip motion. However, non-desirable buckling and torsion of the cantilever may be misinterpreted as cantilever tip motion. This is a shortcoming of the OBD method which measures the angle of the cantilever, rather than the displacement of the tip. Here, we describe results on highly sensitive PFM imaging and spectroscopic studies of ferroelectrics (LiNbO3 crystals and Pb(Zr,Ti)O3 and BaTiO3 thin films) performed with an interferometric AFM. This AFM is based on a commercial Cypher S AFM and combines the existing OBD system with a separate quantitative interferometric Laser Doppler Vibrometer (LDV) system to enable accurate measurements of the displacement and velocity of the cantilever tip [1]. This combined instrument allows a host of quantitative measurements to be performed including measuring a variety of in-situ PFM cantilever oscillation modes, as well as accurately measuring the cantilever spring constant prior to making contact with the surface. Importantly, the piezoelectric coefficients extracted from several LDV measurements showed an order of magnitude less variability compared to the error-prone OBD measurements acquired simultaneously. By performing simultaneous LDV and OBD measurements, we were able to conclude that most of the measurement error and variability in PFM measurements thus far can be attributed to the shortcoming of the OBD method. We present a systematic methodology for accurate PFM measurement of d33 and d15 coefficients. In this context, the notable differences between the OBD and LDV results are demonstrated and discussed. Even though the interferometer provides an intrinsically quantitative measurement of the cantilever motion, there are additional requirements for quantification of the tip-sample electromechanical response that prevent cantilever dynamics and stray electrostatic interactions from overwhelming the PFM signal. Further considerations about the effects of finite loading forces that may reduce the apparent piezoelectric sensitivity are also discussed. In addition, quantitative lateral PFM results, determined from sequential LDV measurements at various LDV spot positions, are also presented. [1] A. Labuda and R. Proksch, Appl. Phys. Lett. 106, 253103 (2015)

Resume : Advances in the precision and the temperature range of experiments at surfaces and interfaces have led to a wealth of new science over the past few years. In particular the ability to use the whole breadth of organic synthesis for the creation of specific molecules and molecular epitaxy as well as surface engineering to modify the physical properties of the molecular systems practically at will have expanded the range of results dramatically. This development, it turns out, leads to a huge variety of experimental results which is sometimes hard to assign to a particular effect or property. Here, theoretical simulations, which have also substantially improved over the last years, turn out to be essential. We shall, on a number of model systems and for a number of effects like Kondo resonances, vibrations, chiral adsorption, and molecular rotations show that this variety and precision make it possible today to use molecular interfaces like lab benches and to perform detailed experiments on individual electrons and spins.

Resume : Molecules at surfaces are ideal building blocks to investigate many-body quantum phenomena at the atomic scale such as the so-called Kondo effect. One and two-dimensional arrays of spins can be created through molecular self-assembly in order to investigate the largely unexplored Kondo physics in low-dimensional structures. In this work, we use single and double-decker macrocyles (phthalocyanine and/or porphyrin) molecules adsorbed on noble metals (111) surfaces to investigate the Kondo effect by means of scanning tunneling spectroscopy. These two systems were specially chosen based on the origin of their single unpaired spin. In the first case, it comes from charge transfer upon adsorption on the surface whereas it comes from the lanthanide ion center sandwiched between the two macrocycles, in the other case. For each molecular compound, we study the influence of molecule-molecule and molecule-substrate interactions on the occurence of a Kondo spectroscopic signature. We show that the many-body properties are preserved upon self-assembly for the charge-transfer induced Kondo system although they are strongly affected by the chemical environment for the cerium-based double decker molecules. This work provides insight into the design of molecular devices.

Resume : Nanodot molecular junctions (NMJ) fabricated on a large array of sub-10 nm single crystal Au nanodot electrodes, each junction containing less than 100 molecules, contacted by C-AFM [1] are powerful test-beds to assess new properties : effects of mechanical strain [2], demonstration of a molecular diode working up to 17 GHz [3] with a scanning microwave microscope. Here, [4] we report a study of ?-? intermolecular interactions from electrochemical and conductance measurements (C-AFM) on ferrocene-thiolated NMJs. We confirm the theoretical prediction [5] that t, the electronic coupling energy parameter, can be assessed from a statistical analysis of current histograms for thousands of nanocrystals. The extracted value of t ? 35 meV is in agreement with our density functional theory analysis. Furthermore, the t distribution is not necessarily Gaussian and could be used as an ultrasensitive technique to assess intermolecular distance fluctuation at the sub-angström level. The present work establishes a direct bridge between quantum chemistry, electrochemistry, organic electronics, and mesoscopic physics, all of which were used to discuss results and perspectives in a quantitative manner. [1] N. Clément et al. Small 2011, 7, 2607; K. Smaali et al. ACS Nano 2012, 6, 4639?. [2] K. Smaali et al. Nanoscale 2015, 7, 1809-1819. ?[3] J. Trasobares et al., Nature Communications 2016, 7, 12850. [4] J. Trasobares et al., Nano Lett. 2017, 17, 3215. [5] M. Reuter et al., Nano Lett. 2011, 11, 4693.

Resume : The electric current traversing the junction of a scanning tunneling microscope (STM) may generate a local emission of light. During the last years, we have used this method to study the intrinsic luminescence properties of individual molecules. This work has progressed in two directions. On one side we have used the ability of the STM to manipulate matter with atomic-scale precision to form single-molecule light emitting devices [1]. Composed by individual molecular wires suspended between the tip and the sample of the STM (see figure), these devices generate an emission of light whose color, intensity and bandwidth can be controlled with high precision [2,3]. On the other side, we used the intrinsic resolution of the STM to performed sub-molecularly resolved vibronic spectroscopy of molecules separated from a metallic surfaces by a thin insulating layers [4]. These results open the way to a new type of microscopy, called hyper-resolved fluorescence microscopy, where optical information may be recorded with atomic-scale accuracy. [1] G. Reecht et al., Phys. Rev. Lett. 112, 047403 (2014) [2] M.C. Chong et al., Phys. Rev. Lett. 116, 036802 (2016) [3] M.C. Chong et al., Nanoletters 16, 6480 (2016) [4] B. Doppagne et al., Phys. Rev. Lett. 118, 127401 (2017)

Resume : Graphene is a zero band-gap semiconductor, which confers to it many remarkable and potentially exploitable optoelectronic properties. The modulation of these properties, which can be obtained by molecular functionalization, is an important current issue for such applications. We have recently developed original molecular-engineering concepts for designing molecular building blocks spontaneously adsorbing on graphene according to various preprogrammed patterns.[1] We have realized and probed the photonic responses of several self-assembled molecular or polymeric structures grown onto graphene. The STM images permit an accurate structural analysis of molecular organization induced by the atomic-scale template of graphene. The organized self-assembly has a clear influence on optical properties, as observed by transmission and fluorescence spectroscopy.[2,3] We also report the first fluorescent molecular self-assembly on graphene.[4] The inherent quenching of dye?s excited-state by the adjacent graphene is hindered at the molecular scale based on a spacer approach, through specifically designed dual-functionalized self-assembling building blocks. [1] G. Schull et al, Nanolett, 6, 1360-1373 (2006). [2] T. Sghaier et al, Beilstein J. Nanotechnol. 7, 862?868 (2016) [3] S. Le Liepvre et al, Mol. Cryst. Liq. Cryst. 65, 5-15 (2017) [4] S. Le Liepvre et al, ACS Photonics 3, 2291-2296 (2016)

Resume : Imaging the bonding structure of organic molecules by noncontact atomic force microscopy (NC-AFM) has been a major breakthrough for a fundamental understanding of chemical processes in specific local environments. The methodology involves the atomic scale control of the tip termination by attaching single atoms or molecules (e.g. CO or Xe) to the metallic apex [1-3]. However, these probe particles are only weakly connected at the tip, which results in a considerable dynamic deflection in the experiments. As a consequence, such NC-AFM data show pronounced image distortions, a systematic overestimation of bond lengths, and artificial bond-like contrast features [3-5]. By combining NC-AFM- and scanning tunneling microscopy experiments with density functional theory, an alternative approach of tip functionalization was developed. By slightly indenting the probe tip into oxidized copper substrates and subsequent contrast analysis, allows for the verification of an O-terminated Cu tip (CuOx tip). This tip is chemically passivated and shows a high structural stability due to the tetrahedral configuration of the covalently bound terminal O atom [6,7]. It is shown that the rigidity of the CuOx tip allows to quantitatively determine bond lengths and to access bond order effects in molecular systems. Furthermore, artificial bond-like contrast features, as observed for flexible probe particles, can be neglected for the CuOx tip. This establishes this methodology as a valuable tool for investigations of intermolecular coupling in on-surface synthesis and molecular self-assembly. References: [1] L. Gross et al., Science 325, 1110 (2009); [2] F. Mohn et al., Appl. Phys. Lett. 102, 073109 (2013); [3] L. Gross et al., Science 337, 1326 (2012); [4] P. Hapala et al., Phys. Rev. B 90, 085421 (2014); [5] S. K. Hämäläinen et al., Phys. Rev. Lett. 113, 186102 (2014); [6] H. Mönig et al., ACS Nano 7, 10233 (2013); [7] H. Mönig et al., ACS Nano 10, 1201 (2016).

Resume : We present a new concept for the fabrication of up to 1?m long polymer fibres on insulating alkali-halide substrates. The novelty of our approach is that first, the chosen dimaleimide molecules perform a chain-like (and not a step-like) growth via a radical polymerization, second, that the polymerization is initiated from a two-dimensional gas phase rather than from an intermediate self-assembled structure, and third, that the cations of the chosen alkali-halide substrate interact with the molecule?s oxygen atoms and facilitate a defect-free propagation of the polymer fibres along a preferred axis of the substrate. We discuss the different initiation mechanisms of the polymer reaction at room-temperature that can either be spontaneous, most probably assisted by the molecule-substrate electrostatic interaction and the molecule?s conformation on the substrate, or induced by UV-light. Once initiated, the chain-like polymerization proceeds easily and is only stopped by either defects on the surface or exhaustion of the precursor molecules. The propagation of this reaction on the surface as well as the structure and stability of the formed 1D polymer fibres are discussed by means of Density Functional Theory calculations and noncontact Atomic Force Microscopy imaging and manipulation at room temperature.

Resume : Atomically precise graphene nanoribbons (GNRs) are at the forefront of nanocarbon research and hold great promise for electronic and optoelectronic applications. Theoretical studies have shown that narrow GNRs possess interesting electronic and magnetic properties that strongly depend on the nanoribbon?s width and edge structure. GNRs with different structures can be synthesized with atomic precision and fine-tuned properties by coupling properly designed molecular precursors and planarization of the resulting polymers. In this talk, I will describe our efforts to design and synthesize new atomically precise GNRs for electronic applications. First, I will discuss pristine and nitrogen-doped GNRs with the chevron structure that could be synthesized on surfaces [1-3] as well as in solution [3-5]. Then, I will demonstrate that the electrical conductivity of atomically precise chevron GNRs can be improved by their lateral extension [6]. The new laterally extended chevron GNRs were characterized by a number of microscopic and spectroscopic techniques and employed in gas sensors that showed very high responsivity to low molecular weight alcohols [6]. Overall, this talk will demonstrate the entire path from designing new atomically precise GNRs with improved properties to their bottom-up synthesis, characterization, processing and implementation in electronic devices. [1] J. D. Teeter, et al. Chem. Commun. 2017, 53, 8463. [2] J. D. Teeter, et al. Nanoscale 2017, 9, 18835. [3] T. H. Vo, et al. Nano Lett. 2015, 15, 5770. [4] T. H. Vo, et al. Chem. Commun. 2014, 50, 4172. [5] T. H. Vo, et al. Nat. Commun. 2014, 5, 3189. [6] M. Mehdi Pour, et al. Nat. Commun. 2017, 8, 820.

Resume : The fabrication of long-range ordered two-dimensional covalently-linked networks via on-surface synthesis in ultra-high vacuum is still a major challenge despite the use of various surface reactions. Here, we report on the atomic structure and electronic properties of porous covalently-linked 2D networks [1,2], which were fabricated in a bottom-up approach via Ullman-type reactions, using low-temperature scanning tunneling microscopy/spectroscopy in combination with density-functional theory. In the hierarchical synthesis of 2D networks on Au(111) using triphenylamine derivatives, we present a reduction of the electronic band gap from the monomer to the covalently-linked 2D structures, which confirms an effective conjugation along the building blocks. However, only small networks can be fabricated due to the irreversibility of the C-C bonds. In contrast, the reversible nature of the organometallic bond allows for the formation of extended networks with the drawback that those are often not fully covalently-bonded. We demonstrate that surface-supported organometallic networks with Ag-bis-acetylide bonds, which are intermediate products in the bottom-up synthesis of graphdiyne-like networks, are covalently-bonded. Scanning tunneling spectroscopy on Ag(111) reveals a frontier, unoccupied electronic state that is delocalized along the entire organometallic networks and proves the covalent nature of the Ag-bis-acetylide bonds. [1] C. Steiner et al. Nature Communications, 8, 14765 (2017) [2] Z. Yang et al. submitted (2018)

Resume : The interest in studying organic nanostructures on surfaces emerges from their prospective usage as nanoscale functional materials in applications ranging from electronics to spintronics and catalysis. By making use of molecular recognition processes based on non-covalent interactions, well-ordered 1D and 2D molecular structures can be formed on surfaces. Understanding the interplay of the underlying intermolecular and molecule-substrate interactions is the key for being able to deliberately tune the functional properties of organic nanostructures. However, since the intermolecular interactions for such structures can be rather weak, on-surface covalent coupling has emerged as a viable alternative for obtaining structures with improved stability and conductivity. In my presentation I will focus on the one side on the influence of the substrate on molecular self-assembly. For this purpose, we adsorbed the same molecule (1,3,5-benzenetribenzoic acid = BTB) on Cu(111), Au(111) and graphene/Cu(111) [1] and observed a decreasing molecule-substrate interaction (when keeping the order of the substrates). In particular, for Au(111) we observed a modification of the electronic surface properties based on confinement of the Au surface state in the pores of the molecular BTB network. Due to leaky confinement of the BTB network, the confined states can couple what results in the formation of an artificial 2D band structure. On the other side, I will show two examples where we made use of Ullmann-type coupling for the formation of covalently coupled molecular structures. For a biphenyl functionalized with an alkenyl gem-dibromide we observed the formation of cumulene units [2]. Moreover, a hydrogen dosing treatment employed during the on-surface reaction was proven successful for the removal of the halogen atoms which are split off during the reaction and which often stay chemisorbed on the surface [3]. [1] S. Gottardi et al., Nano Lett. 15 (2015) 917; J. Li et al., J. Phys. Chem. C 120 (2016) 18093. [2] Q. Sun et al., Angew. Chem. Int. Ed. 56 (2017) 12165. [3] B.V. Tran et al., Nanoscale 9 (2017) 18305.

Resume : When multiple binding modes are present simultaneously in the metal-organic coordination self-assembly, the outcome becomes less predictable and novel phases may emerge. Here I discuss two examples. The first system is co-existing twofold and threefold pyridyl?Cu coordination modes results in a demi-regular lattice which features local dodecagonal symmetry on a Cu(111) surface. This structure is thermodynamically robust and emerges solely when the molecular density is at a critical value. The second system involves Eu-carbonitrile coordination. Depending on ligand/metal stoichiometry, three-fold, four-fold, five-fold and six-fold coordination motifs can be formed on a Au(111) surface, resulting in various structures exhibiting irregular pores, square lattice, five-fold snub-square nodes structures, and hexagonal lattice. At a specific stoichiometry, the prevailing expression of five-fold and six-fold coordination nodes yields quasicrystalline tessellation. I will also discuss our recent efforts of synthesizing a ?-conjugated metal-organic system exhibiting a non-trivial topological band structure.

Resume : Self-assembled functionalized nanoparticle networks are at the focus of a number of potential applications, in particular for molecular scale electronics devices. An important unifying feature of several widely different physical-chemical systems of this kind, is that such networks are held together by a subtle competition between weak, long-ranged, non-covalent interactions, including electrostatics, dispersion forces, charge transfer, and in some cases hydrogen bonding. Theoretical understanding of the properties of these novel meta-materials cannot ignore the link between the finite-temperature dynamics and mechanics of the self-assembled network structure and their transport properties, such as thermal and electronic conductivity [1]. To this purpose, a combination of simulation techniques is needed, ranging from first-principle electronic structure calculations, to semi-empirical molecular dynamics, to large-scale Monte Carlo and statistical mechanics methods. I will present several examples of the interplay between the structural dynamics and the apparent transport properties of such structures, starting from the simpler case of fullerene [2] or planar polycyclic molecules [3,4] adsorbed at low temperature on doped-Si surfaces, to faceted Au nanoparticles functionalized with different alkene-based molecules and structured into 2D or 3D networks [5,6], to end up with semiconductor nanoparticles assembled into random 2D pseudo-lattices [7]. [1] F. Cleri, P. Keblinski, Phys. Rev. B69 (2004) 184201 [2] F. Cleri, Phys. Rev. B80 (2009) 235406 [3] B. Grandidier G. Copie, F. Cleri, Y. Makoudi, C. Krzeminski, M. Berthe, F. Cherioux, F. Palmino, Phys. Rev. Lett. 114 (2015) 66101 [4] Y. Makoudi, J. Jeannoutot, F. Palmino, F. Chérioux, G. Copie, C. Krzeminski, F. Cleri, B. Grandidier, Surf. Sci. Rep. 72 (2017) 316 [5] Y. Viero, G. Copie, D. Guerin, C. Krzeminski, D. Vuillaume, S. Lenfant, F. Cleri, J. Phys. Chem. C119 (2015) 21173 [6] G. Copie, M. Biaye, H. Diesinger, T. Melin, C. Krzeminski, F. Cleri, Langmuir 33 (2017) 2677 [7] F. Cleri, Phys. Rev. B92 (2015) 214203

Resume : Metallation of surface confined porphyrinoid architectures have emerged as an important research topic due to its importance for biological phenomena and potential applications including optoelectronics, nanomagnetism, sensing and catalysis. Hereby, the in-situ design of mutant porphyrinoids, either by selection of unconventional metal centers like lanthanides or by choosing expanded backbones, is attracting great attention. In this talk we report our latest research regarding the metallation by dysprosium, an archetype lanthanide metal, of porphyrinoid species of distinct cavity size. On one hand, the deposition of Dy on top a submonolayer of fluorinated 2HTPP species on Au(111) affords the expression of four different compounds, which are identified as physisorbed Dy-2H-TPP, Dy-1H-TPP, Dy-0H-TPP and 2HTPP species. Importantly, the Dy-2H-TPP complexes exhibit a zero bias resonance at Fermi level that is assigned to a molecular Kondo resonance and which can be switched off by voltage pulses transforming Dy-2H-TPP into Dy-1H-TPP species. On the other hand, the self-assembly on Au(111) of an expanded aza-porphyrin, namely, an ?expanded hemiporphyrazine?, through a unique growth mechanism gives rise to a long-range orientational self-assembly. Furthermore, a spatially controlled ?writing? protocol on such self-assembled architecture is presented based on the STM tip-induced deprotonation of the inner protons of individual macrocycles. Finally, the capability of these surface-confined macrocycles to host lanthanide elements is assessed, introducing a novel off-centered coordination motif. The presented findings represent a milestone in the fields of porphyrinoid chemistry and surface science, revealing a great potential for novel surface patterning, opening new avenues for molecular level information storage, and boosting the emerging field of surface-confined coordination chemistry involving f-block elements.

Resume : Multinuclear heterometallic nanoclusters with controllable stoichiometry and structure are anticipated to possess promising catalytic, magnetic, and optical properties. Here we demonstrate that heterometallic nanoclusters with precise stoichiometry of Bi3Cu4 and Bi7Cu12 can be stabilized in the scaffold of two-dimensional metal-organic networks on a Cu(111) surface through on-surface metallosupramolecular self-assembly processes. The atomic structures of the nanoclusters were resolved using scanning tunneling microscopy and density functional theory calculations. The nanoclusters feature highly symmetric planar hexagonal shapes and core-shell charge modulation. The clusters are arranged as triangular lattices with a periodicity that can be tuned by choosing molecules of different size. This work shows that on-surface metallosupramolecular self-assembly creates unique possibilities for the design and synthesis of multinuclear heterometallic nanoclusters.

Resume : Chemical functionalization of graphite using aryl radicals generated by electrochemical reduction of aryl diazonium salts has been used to introduce functionality on various surface. The grafted surfaces hold potential as scaffolds of new metal-organic frameworks, catalytic centers which function cooperatively, and possibly resists that can be removed to allow for molecular scale patterning (i.e. mold or stamp for nanocontact printing). However, because the addition of aryl radical takes place randomly, precise positional control over surface functionality remains a great challenge. Here I will present periodic chemical functionalization of graphite surface using porous self-assembled monolayers as templating masks using porous honeycomb type self-assembled monolayers formed at the solvent/graphite interfaces. As masking molecules, we used alkyl-substituted dehydrobenzo[12]annulenes (DBAs) and 1,3,5-benzenetribenzoic acid (BTB) which form regular porous networks via intermolecular van der Waals interactions and hydrogen bonds, respectively. The electrochemical functionalization by an aryl diazonium salt was performed on the graphite surface covered by the networks. Scanning tunneling microscopy (STM) showed quasi-regular alignment of bright dots due to grafted aryl groups on the surface. Fast Fourier transform (FFT) images together with analysis of the bright dots indicate the presence of hexagonal periodicity in the alignment of aryl groups.

Resume : This presentation will review our recent studies of the role of hydrogen bonding and other supramolecular interactions in controlling self-assembly of functional semiconducting molecules. Using a combination of STM, AFM, X-ray crystallography and DFT calculations, we explore the complex interplay of intramolecular, molecule-molecule and molecules-surface interactions in defining the supramolecular structure at the interface. The discussed case studies will include an unusual interplay between inter- and intramolecular interactions in self-assembly of diketopyrrolopyrrole oligomers, assembly of fullerenes on SAMs, investigations of the structure of 1D and 2D conjugated polymers

Resume : Arylene-alkynylenes with sufficiently long alkyl/alkoxy side chains form self-assembled monolayers at the solid/liquid interface on graphite (HOPG). 2D crystal engineering relates the size and shape of the molecules with the lattice constants and symmetries of these supramolecular nanopatterns. Scanning tunneling microscopy provides a submolecularly resolved insight. Tesselation concepts can be applied to design cocrystals (e.g., of triangles and hexagons), and the symmetry mismatch between molecule and the substrate lattice leads to complex superstructures (e.g., observed for pentagons).[1] The hierarchical formation of frustrated superstructures is observed for C3v symmetric molecules, but still difficult to predict.[2] Thereby, not only the number of alkoxy side chains per molecule, but also the substitution pattern is crucial for the periodic pattern formation, as we show for molecular spoked wheels.[3] References: [1] S.-S. Jester, E. Sigmund, S. Höger J. Am. Chem. Soc. 2011, 133, 11062; [2] S.-S. Jester, E. Sigmund, L. Röck, S. Höger Angew. Chem. Int. Ed. 2012, 51, 8555; [3] A. Idelson, C. Sterzenbach, S.-S. Jester, C. Tschierske, U. Baumeister, S. Höger J. Am. Chem. Soc. 2017, 139, 4429.

Resume : While spectacular molecular networks have been assembled on metal surfaces and then observed with scanning tunneling microscopy, there have been fewer studies of supramolecular networks on semiconductor surfaces, due to the high reactivity of their dangling bonds with organics. However, the saturation of the dangling bonds is known to make them inert and offers a unique way for the engineering of molecular patterns on these surfaces. In this talk, I will review a few examples of supramolecular networks on the passivated B-Si(111) (sqrt(3) x sqrt(3)) R30° surface as a function of the molecule geometries and moieties. With the help of theoretical simulations, I will insist on the relative importance of the molecule-substrate and molecule-molecule interactions that give rise to several types of arrangements depending on the growth conditions. Based on the different packings that can be obtained, I will provide directions for the potential utility of these molecular-semiconductor interfaces.

Resume : Two-dimensional (2D) chirality in molecular self-assembly on solid surfaces has gained wide interests because of its fundamental significance and application potentials. Through the adsorption of chiral molecules, 2D chirality can be endowed to achiral solid surfaces. Besides, self-assembly of achiral molecules on achiral surfaces could induce 2D chirality due to reduced freedom and the constraint of substrate lattice. However, the spontaneous resolution of achiral molecules into 2D enantiomorphous assemblies shows no chiral bias and typically leads to globally racemic surfaces. We report the induction of global homochirality in 2D enantiomorphous networks of achiral molecules via co-assembly with chiral co-adsorber. We further show that the global homochirality of the network assembly depends nonlinearly on the enantiomeric excess of chiral co-adsorber in the solution phase, demonstrating the validation of the ?majority-rules? for the homochirality control of achiral molecules at liquid/solid interface. In compared to the chirality induction by covalently introducing chiral center, the supramolecular induced chirality can be more flexible. Finally, the competition between the supramolecular chirality induction by co-adsorber and the chirality expression of chiral center in supramolecular assembly will be discussed. References: (1) Chen, T.; Yang, W. H.; Wang, D.; Wan, L.-J. Nature Commun. 2013, 4, 1389 (2) Chen, T.; Li, S.-Y.; Wang, D.; Yao M.; Wan, L.-J. Angew. Chem. Int. Ed. 2015, 54, 4309 (3) Li, S. Y.; Chen, T.; Yue, J. Y.; Wang, D.; Wan, L.-J. Chem. Comm. 2017, 53, 11095-11098. (4) Chen, T.; Li, S. Y.; Wang, D.; Wan, L.-J. Sci. Adv. 2017, 3, e1701208.

Resume : Over the past decade, on-surface fabrication of organic nanostructures has been widely investigated for the development of molecular electronic devices, nanomachines, and new materials. Here, we introduce a new strategy to obtain alkyl oligomers in a controlled manner using on-surface radical tandem reactions that are triggered by the electrons between the sample surface and the tip of a scanning tunnelling microscope. This radical-mediated mechanism is substantiated by a detailed theoretical study, which highlights the adsorbat induced resonance state as a key-parameter of the initiation step. This single-electron transfer event allows access to reactive radical species under exceptionally mild conditions and can effectively ?switch on? a tandem sequence leading to formation of oligomers of defined size distribution due to the on-surface confinement of reactive species. Our approach enables new ways to initiate and control radical oligomerisations, leading to molecularly precise nanofabrication.

Resume : Understanding how the constitutional dynamics of a dynamic combinatorial library (DCL) adapts to surface (compared to bulk solution) is of fundamental importance to the design of adaptive materials. Submolecularly resolved scanning tunneling microscopy (STM) allows us to get detailed insights into the imine and olefin metathesis at the interface. By analysing the distribution of products, we have revealed the important role of substituent effects and environmental pressure, reaction temperature etc. in the surface confined imine and olefin metathesis. We also report unprecedented preferred deposition and assembly of linear polymers and some specific oligomers on the surface that are hard to obtain otherwise.

Resume : Silylation and desilylation are important functional group manipulations in solution phase organic chemistry that are heavily used to protect/deprotect different functionalities. Herein we disclose first examples of sigma-bond metathesis of silylated alkynes with aromatic carboxylic acids on the Ag(111) and Au(111) surface to give the corresponding terminal alkynes and silyl esters, which is supported by DFT calculations and further confirmed by XPS analysis. Such a protecting group strategy applied to on-surface chemistry allows for generating self-assembly structures from molecules that are inherently unstable in solution and in the solid state. This is shown by successful formation of self-assembled hexaethynylbenzene at Ag(111). Further, it is also shown that on the Au(111) surface this sigma-bond metathesis can be combined with Glaser coupling to fabricate covalent polymers via a cascade process.

Resume : DBBA (10, 10?-dibromo-9,9?-bianthryl, whose molecule structure is shown in Figure 1 ), has drawn great attention due to its ability to fabricate graphene nanoribbons (GNRs) with atomically precise edges on coinage substrates. The initial growth of DBBA on metal surfaces is considered to play a key role in the formation of GNRs.[1] In this lecture, I will present the effect of Au(111), Ag(111) and Cu(111) on the self-assembly of DBBA. The two anthracene groups in one DBBA molecule are connected by a C-C bond, making the nonplanar DBBA molecule rotatable. Thus, the competition between intermolecular interactions and molecule-substrate interactions would lead to the molecular configuration change and result in different molecular packing. On Au(111), DBBA self assembles into two kinds of arrangements dependent on the coverage: zigzag molecular chains at low coverage and double-molecule chain at high coverage. On Ag(111), DBBA self assembles into three kinds of chiral superstructures: monomer, dimer, windmill-like tetramer and hexamer. Due to the more reactivity of Cu(111), DBBA self assembles into organic glass accompanied by debromination at room temperature. These findings may give deep insight to understand the difference in the formation of GNRs.

Resume : Achieving a molecular precision in the positioning molecules in 2D to form highly ordered architectures is not only a complicated chemical exercise, but it is also key to tune the physico-chemical properties of a material. In the present lecture I will provide some recent results obtained in our lab on the use of physisorption or weak thus reversible chemisorption to form adaptive and responsive 2D architectures. The structure and dynamics of such architectures have been unraveled, with a sub-molecular resolution, by Scanning Tunneling Microscopy studies. This will include : 1- The monitoring of the reversible on-surface reactivity under thermodynamic control by making use of Dynamic Covalent Chemistry.[1] 2- The visualization of the first dynamer operating at the solid-liquid interface, which is driven via metal complexation and release using pH as a remote control.[2] 3- The imaging of the reversible light induced molecular isomerization within a physisorbed monolayer of photochromic systems such as azobenzenes and diarylethenes at the solid-liquid interface.[3] 4- The development of artificial heterostructure devices with a variety of different electronic and optical properties by self-assembly of atomically precise supramolecular lattices on CVD graphene. This strategy made it possible to generate controllable 1D periodic potentials in the resulting organic?inorganic hybrid heterostructures.[4] Our approaches provide a glimpse on the chemist?s toolbox to generate responsive interfaces with ad-hoc properties, which can be of importance for applications in electronics and sensing. [1] Nat. Chem. 2014, 6, 1017. [2] Angew. Chem. Int. Ed. 2010, 49, 1963. [3] Angew. Chem. Int. Ed. 2015, 54, 4865. [4] Nat. Commun. 2017, 8, 14767

Resume : Side-selective functionalization of only one of two identical chemical groups within one molecule is challenging and hinders the production of complex macromolecules as well as 2D molecular architectures. We demonstrate that dissymmetric activation of 4,4''-Diamino-p-terphenyl (DATP) is possible on a metal surface. Our low temperature atomic force microscopy images, using CO-tip functionalization, reveal dissymmetric adsorption geometries of DATP on Cu(111), while on Au(111) the symmetry is fully retained. This symmetry breaking on Cu(111) is caused by a lattice mismatch and interactions with the subsurface atomic layer. The surface induced dissymmetry results in a side-selective activation of one of the amine groups leading to a non-stationary behavior under the influence of the scanning tip. Finally, we exploit this dissymmetric activation of DATP for side-preferential attachment of 2-triphenylenecarbaldehyde (TPCA). These findings are underpinned by dispersion corrected DFT D2 computations and show the potential of submolecular AFM imaging to explore new routes for controlling reaction pathways on surfaces.

Resume : 2D materials are often functionalized noncovalently with lying-down phases of molecules (e.g. diynoic acids) to avoid disrupting electronic structure within the 2D basal plane. The precise chemical functional patterns created in such monolayers (e.g. 1-nm-wide rows of functional groups with a ~5 nm pitch, for long-chain diynoic acids) represent a potential foundation for designing dimensionally controlled nanostructures at length scales very difficult to access using traditional lithographic techniques. A central requirement for this type of structural design is the ability to characterize and control interactions between functional groups in the monolayer and their environment. Recently, we have shown that relatively small changes in headgroup and chain structure in functional diynes (including the use of diynoic phospholipids) produce polymerized monolayers with substantial differences in interfacial wetting and functional group ionization, as measured by contact angle titrations using aqueous buffers. Monolayers with molecular architectures predicted to increase steric availability of the functional headgroup not only increase wetting, but also facilitate synthesis of organic and inorganic nanostructures using the monolayer as a template. We demonstrate synthesis of high-density arrays of ligand-capped gold nanowires with precisely controlled diameters, which appear to grow along individual rows of headgroups. Additionally, we demonstrate assembly of epitaxially aligned nanorods and plates of functional organic molecules, which appear to bridge rows of headgroups, and can exhibit topographic heights up to tens of nm. These findings illustrate the capability noncovalent monolayers on 2D materials to act as effective nanoscopic templates in both organic and aqueous solution environments.

Resume : The energy-related environmental challenges induce an intense research in the field of photovoltaic (PV) technologies. The new generation of PV devices includes organic and hybrid cells, the latter generally benefiting from the good stability of inorganic materials, combined with the low cost, large surface and flexibility of organic materials. The development of these hybrid devices is dependent on a fundamental understanding of the (photo)-physical processes occurring at the nanoscale, since the cell performance is directly related to the nanoscale phase separation between the electron donor and acceptor materials. Metallic diselenides (MSe2), such as MoSe2 or WSe2 have recently emerged as a new category of promising acceptor materials for third generation photovoltaic devices. In this work, 2D mono-crystals of MoSe2 (intrinsic or Nb doped (n-type)) synthetized using chemical vapor transport and 0D onion-like (Re:)MoS2 nanoparticles will be considered as well as their blends with an organic conjugated polymer as electron donor: the poly(3-hexylthiophene). By means of Scanning Probe Microscopy (SPM) based techniques, we will correlate the morphology of the samples with their photo-electrical properties. We will establish experimental protocols and subsequent interpretations of the measurements, both in terms of photocurrent (as measured with Photo-Conductive-AFM (pc-AFM)) and photo-voltage (as measured with Photo-Kelvin Probe Force Microscopy (p-KPFM)) under in situ illumination. In fine, in this growing field, hybrid organic-inorganic perovskite solar cells became also more and more popular in the last decades thanks to their ease to fabricate by solution process and their lower cost, environmental impact, energy payback time compared to today?s silicon panels. However, there are remaining unanswered questions, not only about the long-term stability of the device but also about its excitonic behavior, tolerance to defects or hysteresis among others. In this work, the perovskite stability is also addressed by the local study of morphological and electronical properties of methylammonium lead iodide (CH3NH3PbI3 (MAPI)) using various SPM techniques. Hence, provided better understandings of the degradation mechanisms in 3D perovskites, we shall compare MAPI to layered 2D perovskites in which cation combination is expected to improve their stability.

Resume : SPM tools have been extensively used in recent years to prepare, characterize and test the structural and functional properties of self-assembled molecular networks on surfaces. In many cases the molecular positional and conformational degrees of freedom determine a complex interfacial energy landscape, where subtle equilibria lead to the formation of various 2D ordered phases, often related to each other by phase transitions able to trigger the molecular reactivity, which therefore depends on subtle interrelations between local adsorption sites, intramolecular structure and long range supramolecular order. This talk will address some aspects of the structure-reactivity relationships in several surface-supported molecular networks, studied by means of STM complemented by other surface science and computational tools: e.g. the dependence of the catalytic activity toward oxygen reduction and of the magnetic properties of an Ag-supported iron phthalocyanine monolayer on the supramolecular arrangement of the molecules [1]; the requirements for either thermal [2] or photo-excited [3] covalent stabilization of single- and bicomponent supramolecular networks containing functionalized porphyrins on Ag low-index surfaces; the bottom up synthesis of long range ordered 1D poly-para-phenylene nanowires and 2D graphene nanoribbons on gold substrates [4]. [1] Casarin et al., J. Phys. Chem. C, 2010 ,114, 2144; Sedona, F. et al. Nat. Mater, 2012, 11, 970, Bartolomé et al. J. Phys. Chem. C, 2015 ,119, 12488. [2] Di Marino et al., Langmuir, 2010, 26, 2466; Sedona et al., ACS Nano, 2010, 4, 5147; Sedona et al. J. Phys. Chem. C, 2014 ,118, 1587. [3] Basagni et al., Chem. Eur. J. 2014, 20, 14296. [4] Basagni et al., J. Am. Chem. Soc. 2015, 137, 1802; Basagni et al., ACS Nano 2016, 10, 2644.

Resume : Carbenes are a promising alternative to thiols for self-assembled monolayers, metal-molecule junctions and metal nanoparticle stabilizers. In particular N-heterocyclic carbenes (NHC) are persistent carbenes applied in surface coordination, organometallic materials, metallopharmaceuticals, homogeneous catalysis. Our study targeted a clear picture of NHC adsorption at the interface of a metal surface. Our methodology encompasses experimental techniques for ultrahigh vacuum surface science: scanning tunnelling microscopy addresses single molecule behaviour, while soft X-ray photoelectron spectroscopy scrutinizes the chemical and electronic nature of molecular ensembles. We complement these methods with theoretical considerations. We employed an NHC with substituents imposing minimum steric hindrance towards planar adsorption and investigated it on group 11 metals. We deduce that on Cu(111), Ag(111), and Au(111) surfaces, the planar bis-carbene metal adatom mode is preferential in the monolayer. We thus stimulate a re-consideration of the current understanding of how NHC can coordinate and stabilize metallic surfaces and nanoparticles. Finally, we further explore the out-of-plane ligation with particular regard to its stability and binding nature. We achieve the formation of surface pillars with potential for extending supported two-dimensional to thin films of metal-organic frameworks.

Resume : We show that rutile TiO2(110) is a suitable substrate for the on-surface chemical and conformational modification of a homogeneous layer of free-base tetra-phenyl porphyrins, 2H-TPP. We followed by STM the morphological and structural evolution of the overlayer across different chemical reactions, depending on coverage and temperature. We achieved a full chemical and structural characterization by complementary X-ray spectroscopy measurements and DFT simulations. The key aspect behind the rich phase diagram is the chemical bonding of 2H-TPP atop the protruding rows of oxygen atoms, O. According to simulation, the chemisorption is driven by hydrogen bonding of the two pyrrolic nitrogens of the macrocycle to the two O atoms underneath. The remaining two iminic nitrogens can capture additional hydrogen from the surface and nearby layers forming 4H-TPP species at room temperature. A mild annealing triggers the incorporation in the macrocycle of one Ti atom that establishes two bonds with the O atoms underneath (previously bound to pyrrolic nitrogen), TiO2-TPP. At low coverage, the metalated molecule can capture O atoms diffusing on adjacent Ti rows, thus moving on top a Ti, TiO-TPP. At higher temperature, the dynamical vibrations of the phenyls trigger their partial cyclo-dehydrogenation leading to a flattening of the molecule, which remains bound to the original site, either O-bridge or Ti-top. G. Lovat et al. J. Phys. Chem. C 121 (2017) 13738; Nanoscale 9 (2017) 11694.

Resume : Porphyrins are stable, naturally occurring compounds that can accommodate most metal ions into their cavity by using the four nitrogen atoms as electron-pair donors and with substituents in their periphery, they easily assemble into a variety of functional well-defined supramolecular architectures. The recent progress of the design, fabrication and characterization of surface confined nanoarchitectures by employing porphyrins promises great potential in advanced applications in the field of nanotechnology. Here, we targeted the on-surface Os functionalisation, which is of interest as a single site catalyst in fine chemical synthesis. We investigated the interaction of free base tetraphenylporphyrin molecules with the metal precursor of triosmium dodecacarbonyl [Os3(CO)12] as function of annealing temperature on Ag(111) under ultra high vacuum conditions by means of scanning tunneling microscopy. We found metallation to Os porphyrins of a very limited percentage (1%-3%), when applying our earlier protocol of metallation with the corresponding Ru precursor [Ru3(CO)12]. To increase the efficiency of Os metallation, we needed to thermally decompose the Os3(CO)12 precursor prior to the deposition of the porphyrin molecules. Followed by moderate annealing, the yield increased to approximately 81%. Finally, we discovered that the presence of Os on Ag(111) catalyzes both, tetraphenylporphyrin intramolecular cyclodehydrogenations and intermolecular polymerisation.