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

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

Atomically Precise Incorporation of BN-Doped Rubicene into Graphene Nanoribbons.

Substituting heteroatoms and non-benzenoid carbons into nanographene structure offers a unique opportunity for atomic engineering of electronic properties. Here we show the bottom-up synthesis of graphene nanoribbons (GNRs) with embedded fused BN-doped rubicene components on a Au(111) surface using on-surface chemistry. Structural and electronic properties of the BN-GNRs are characterized by scanning tunneling microscopy (STM) and atomic force microscopy (AFM) with CO-terminated tips supported by numerical calculations.

Electrostatic patterning on graphene with dipolar self-assembly.

We have investigated the influence of electric dipole moment in different periodic two-dimensional network on the electronic structure properties of graphene. Although the control of doping level in graphene within a van der Waals heterostructure constitutes a difficult task, the dipolar nature of the different molecular stacks can be used to control its electrostatic properties. First, we demonstrate that the orientation and magnitude of the adsorbed molecular dipole moments allow to control the electrical behaviour of graphene, and acts as an electrostatic gate that shifts neutrality point of graphene to behave as n- or p-doped materials.

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

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

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

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

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

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

States modulation in graphene nanoribbons through metal contacts.

We are reporting the results of density functional calculations of the electronic structure of finite graphene nanoribbons adsorbed on Au, Pd, and Ti electrodes. While the interaction of nanoribbons with the Au contact is more characteristic of a physisorbed state, the adsorption of Pd and Ti involves much stronger state mixing as in chemisorption. Metal-induced gap states, which can potentially short-circuit the device, are clearly revealed for the first time, allowing us to evaluate their penetration length.

Noncovalent bicomponent self-assemblies on a silicon surface.

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

Large-scale patterning of zwitterionic molecules on a Si(111)-7 × 7 surface.

The formation of a large scale pattern on Si(111)-7 × 7 reconstruction is still a challenge. We report herein a new solution to achieve this type of nanostructuration by using of zwitterionic molecules. The formation of a large-scale pattern is successfully obtained due to the perfect match between the molecular geometry and the surface topology and to electrostatic interactions between molecules and surface.

A single molecule Kondo switch: multistability of tetracyanoethylene on Cu(111).

Single tetracyanoethyelene (TCNE) molecules on Cu(111) are reversibly switched among five states by applying voltage pulses with the tip of a scanning tunneling microscope. A pronounced Kondo resonance in tunneling spectroscopy indicates that one of the states is magnetic. Side bands of the Kondo resonance appear at energies which correspond to inter- and intramolecular vibrational modes.

Strong adsorption of aminotriazines on graphene.

DFT calculations reveal that aminotriazines have a strong affinity for graphite and suggest that part of the driving force for adsorption is a specific attractive interaction of NR(2) groups with the underlying surface.

High on-off conductance switching ratio in optically-driven self-assembled conjugated molecular systems.

A new azobenzene-thiophene molecular switch is designed, synthesized, and used to form self-assembled monolayers (SAM) on gold. An "on/off" conductance ratio up to 7 x 10(3) (with an average value of 1.5 x 10(3)) is reported.

Hexaphenylbenzenes as potential acetylene sponges.

Acetylene sponges can be created by taking advantage of the nonplanar geometry of hexaphenylbenzenes and the special capacity of the central aromatic ring to engage in C(sp)-H...

Tailoring the photoluminescence properties of ionic iridium complexes.

Density functional theory/time-dependent density functional theory (DFT/TD-DFT) calculations were performed to investigate the structural, electronic, and optical properties of ionic Ir complexes with several different substituents on the cyclometalated ligand. Geometric parameters, highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap, and Mulliken charge on different parts of the molecule were obtained and correlated to the calculated emission and absorption energies. We also discuss the influence of the position of fluoro-substituent on the spectroscopic properties of Ir complexes.

Strongly reshaped organic-metal interfaces: tetracyanoethylene on Cu(100).

The interaction of the strong electron-acceptor tetracyanoethylene with the Cu(100) surface is studied with scanning tunneling microscopy experiments and first-principles density functional theory calculations. We compare two different adsorption models with the experimental results and show that the molecular self-assembly is caused by a strong structural modification of the Cu(100) surface rather than the formation of a coordination network by diffusing Cu adatoms. Surface atoms become highly buckled, and the chemisorption of tetracyanoethylene is accompanied by a partial charge transfer.

Interaction of substituted aromatic compounds with graphene.

We have modeled the adsorption of various substituted derivatives of benzene on a graphene sheet, using a first-principles density functional theory-local density approximation method. The presence of functional groups can significantly alter the overall magnitude of pi-pi interactions between the adsorbed molecules and graphene by giving rise to strong medium-range interactions involving pi-orbitals of the substituents. When the substituents can simultaneously permit the formation of hydrogen bonds between adsorbed molecules, it is possible to evaluate the relative contributions of hydrogen bonding and pi-based interactions to the overall adsorption.