[Show abstract][Hide abstract] ABSTRACT: High-density packing in organic crystals is usually associated with an increase of the coordination between molecules. Such a concept is not necessarily extended to two-dimensional molecular networks self-assembled on a solid surface, for which we demonstrate the key role of the surface in inducing the optimal packing. By a combination of scanning tunneling microscopy experiments and multiscale computer simulations, we study the phase transition between two polymorphs. We find that, contrary to intuition, the structure with the lowest packing fraction corresponds to the highest molecular coordination number, due to the competition between surface and intermolecular forces. Having the lowest free energy, this structure spreads out as the most stable polymorph over a wide range of molecular concentrations.
[Show abstract][Hide abstract] ABSTRACT: The development of nanomachines is a key challenge for the future electronics, energy conversion, biology, and medicine. Semiconductor surfaces have been one of the basic elements of many technologies for 40 years. However, despite their promising interest, semiconductor-based nanomachines are almost unstudied. In this work, a panel of single nanomachines-based semiconductor surfaces is described. The role of molecule–surface interaction for the development of nanomachines is highlighted.
[Show abstract][Hide abstract] ABSTRACT: We report a convergent surface polymerization reaction scheme on Au(111),
based on a triple aldol condensation, yielding a carbon-rich, covalent
nanoporous two-dimensional network. The reaction is not self-poisoning and
proceeds up to a full surface coverage. The deposited precursor molecules
1,3,5-tri(4'-acetylphenyl) first form supramolecular assemblies that are
converted to the porous covalent network upon heating. The formation and
structure of the network and of the intermediate steps are studied with
scanning tunneling microscopy, Raman spectroscopy and density functional
[Show abstract][Hide abstract] ABSTRACT: Achieving control over formation of molecular films on insulating substrates is important for designing novel 2D functional materials and devices. To study the main factors governing successful control, organic molecules with interchangeable polar functional groups, a variable length aromatic body, and flexible hydrocarbon chains are designed, synthesized and then deposited on the (001) surfaces of bulk sodium chloride, potassium chloride, and rubidium chloride. The deposited structures are imaged using noncontact atomic force microscopy and modeled using density functional theory. The results show that it is possible to form large-scale, highly ordered, 2D, porous molecular domains (>104 pores), which are stable at room temperature, and to control the size of the 2D pores. Alternatively, it is possible to form line structures or droplets (through molecular dewetting) by altering the molecular structure or changing the substrate lattice constant. Theoretical calculations explain the balance of the molecule–molecule and molecule–surface interactions and the structure and thermodynamic stability of the grown films.
[Show abstract][Hide abstract] ABSTRACT: The self-assembly of two-dimensional (2D) molecular structures on a solid surface relies on the subtle balance between noncovalent intermolecular and molecule–surface forces. The energetics of 2D molecular lattices forming different patterns on a passivated semiconductor surface are here investigated by a combination of atomistic simulation methods. Density-functional theory provides structure and charges of the molecules, while metadynamics with empirical forces provides a best guess for the lowest-energy adsorption sites of single molecules and dimers. Subsequently, molecular dynamics simulations of extended molecular assemblies with empirical forces yield the most favorable lattice structures at finite temperature and pressure. The theoretical results are in good agreement with scanning tunneling microscopy observations of self-assembled molecular monolayers on a B-doped Si(111) surface, thus allowing to rationalize the competition of long-range dispersion forces between the molecules and the surface. Such a result demonstrates the interest of this predictive approach for further progress in supramolecular chemistry on semiconductor surfaces.
The Journal of Physical Chemistry C 06/2014; 118(24):12817–12825. DOI:10.1021/jp501955v · 4.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hydrogen and halogen bonds have been associated for the growth of 2D compact supramolecular networks on a silicon surface. These interactions have been elucidated in a complete monolayer of a 4,4''-dibromo-p-terphenyl (DBT) molecule on a Si(111)-B surface by combining scanning tunneling microscopy (STM) and density functional theory (DFT) calculations.
Chemical Communications 04/2014; 50(43). DOI:10.1039/c4cc01158a · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The formation of large assemblies on the Si(111)-B surface is discussed with the help of STM simulations and DFT calculations. Although highly regular assemblies of DTB10B along the Si row direction are observed, the existence of two herringbone isomers introduces a lower periodicity within the 2D molecular network. The formation of herringbone units is explained by weak intermolecular interactions while the 1D assembling depends mainly on the interactions of the C10 side chains with the Si(111)-B surface.
Chemical Communications 04/2014; 50(41). DOI:10.1039/c4cc01674b · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Thermally activated rotation of single molecules adsorbed on a silicon-based surface between 77 and 150 K has been successfully achieved. This remarkable phenomenon relies on a nanoporous supramolecular network, which acts as a template to seed periodic molecule rotors on the surface. Thermal activation of rotation has been demonstrated by STM experiments and confirmed by theoretical calculations. Round the roundabout: Thermally activated rotation of single molecules adsorbed on a silicon-based surface between 77 and 150 K is successfully achieved. This phenomenon relies on a nanoporous supramolecular network, acting as a template to seed periodic molecule rotors on the surface.
[Show abstract][Hide abstract] ABSTRACT: The design of working nanovehicles is a key challenge for the development of new devices. In this context, 1D controlled sliding of molecules on a silicon-based surface is successfully achieved by using an optimized molecule-substrate pair. Even though the molecule and surface are compatible, the molecule-substrate interaction provides a 1D template effect to guide molecular sliding along a preferential surface orientation. Molecular motion is monitored by STM experiments under ultra-high vacuum at room temperature. Molecule-surface interactions are elucidated by semi-empirical calculations.
[Show abstract][Hide abstract] ABSTRACT: The supramolecular self-assembly of brominated molecules was investigated and compared on Cu(110) and Cu(110)O(2×1) surfaces under ultrahigh vacuum. By using scanning tunnelling microscopy, we show that brominated molecules form a disordered structure on Cu(110), whereas a well-ordered supramolecular network is observed on the Cu(110)O(2×1) surface. The different adsorption behaviors of these two surfaces are described in terms of weakened molecule-substrate interactions on Cu(110)O(2×1) as opposed to bare Cu(110). The effect of oxygen-passivation is to suppress debromination and it can be a convenient approach for investigating other self-assembly processes on copper-based substrates.
Chemistry - An Asian Journal 06/2013; 8(8). DOI:10.1002/asia.201300283 · 4.59 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An open-and-shut case: By using tailored molecules, the formation of open or close-packed supramolecular network can be achieved on a silicon-based surface. The role of molecule-molecule interactions and molecule-substrate interactions to control the geometry of organic network on semi-conductor surface is investigated.