Phthalocyanine reactivity and interaction on the 6H-SiC(0001)-(3×3) surface by core-level experiments and simulations

The adsorption of phthalocyanine (H2Pc) on the 6H-SiC(0001)-(3×3) surface is investigated using X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption fine structure spectroscopy (NEXAFS), and density functional theory (DFT) calculations....

Molecular chemisorption on passivated and defective boron doped silicon surfaces: a "forced" dative bond

We investigate the adsorption mechanism of a single trans 4-pyridylazobenzene molecule (denoted by PAB) on a doped boron Si(111)√3×√3R30° surface (denoted by SiB) with or without boron-defects, by means of density functional theory calculations. The semiempirical approach proposed by Grimme allows us to take the dispersion correction into account. The role of the van der Waals correction in the adsorption geometries and energies is presented. In particular, two adsorption configurations are electronically studied. In the first one, the molecule is parallel to the surface and interacts with the SiB surface via the -N=N- bond. In the presence of a boron-defect, a Si-N chemical bond between the molecule and the surface is then formed, while electrostatic or/and van der Waals interactions are observed in the defectless surface. In the second adsorption configuration, the molecule presents different orientations with respect to the surface and interacts via the nitrogen atom of the pyridyl part of the PAB molecule. If the molecule is perpendicular to the perfect SiB surface, the lone-pair electrons associated with the heterocyclic nitrogen atom fill the empty dangling bond of a silicon adatom via a dative bond. Finally, in the presence of one boron-defect, the possibility of a "forced" dative bond, corresponding to a chemical bond formation between the PAB molecule and the silicon electron occupied dangling bond, is emphasized.

Non-local atomic manipulation on semiconductor surfaces in the STM: the case of chlorobenzene on Si(111)-7×7

Control over individual atoms with the scanning tunnelling microscope (STM) holds the tantalising prospect of atomic-scale construction, but is limited by its "one atom at a time" serial nature. "Remote control" through non-local STM manipulation-as we have demonstrated in the case of chlorobenzene on Si(111)-7×7-offers a new avenue for future "bottom-up" nanofabrication, since hundreds of chemical reactions may be carried out in parallel. Thus a good understanding of the non-local manipulation process, as provided by recent experiments, is important. Comparison of scanning tunnelling spectroscopy (STS) measurements of the bare Si(111)-7×7 surface and chemisorbed chlorobenzene molecules with the voltage dependence of the non-local STM-induced desorption of chlorobenzene proves particularly instructive. For example, the chlorobenzene LUMO appears at +0.9 V with respect to the Fermi level, whereas non-local manipulation thresholds are found at +2.1 V and +2.7 V. This difference supports a picture in which the voltage thresholds for non-local electron-induced desorption depend principally on the energies of the electronic states of the surface. Furthermore, the demonstration that the non-local process is largely insensitive to surface steps up to five layers in height suggests that either the electron transport in this process is subsurface in character or surface charge transport is responsible but is in some way unaffected by the steps.

A new assisted molecular cycloaddition on boron doped silicon surfaces: a predictive DFT-D study

In the framework of the Density Functional Theory (DFT-D), we investigate the phthalocyanine (H2Pc) molecule adsorption on SiC(0001)3 × 3 and Si(111)√3 × √3R30°-B (SiB) surfaces, and particularly compare the involved molecular adsorptions. In the H2Pc-SiC(0001)3 × 3 system, the molecular adsorption can be ascribed to a [10+2] cycloaddition. The H2Pc-SiB system is considered in three cases: defectless SiB surface (denoted SiB-0D) and SiB surfaces presenting one or two boron defects (denoted SiB-1D and SiB-2D respectively). The SiB-0D surface is passivated by a charge transfer from the Si adatoms to the boron atoms and therefore no chemical bond between the molecule and the substrate is observed. A similar molecular adsorption as already evidenced in the H2Pc-SiC(0001)3 × 3 system is involved in the SiB-2D case. In the case of the SiB-1D surface, two Si-N bonds (Si1-N1 and Si2-N2) are observed. One of them, Si1-N1, is nearly similar to that found in the H2Pc-SiB-2D system, but the Si2-N2 bond is unexpected. The Bader charge analysis suggests that, in the presence of the H2Pc molecule, the boron atoms behave like an electron reservoir whose availability varies following the involved molecular adsorption process. In the SiB-1D case, charges are transferred from the substrate to the molecule, allowing the Si2-N2 bond formation. Such a kind of molecular adsorption, not yet observed, could be designed by "assisted pseudo cycloaddition".

Self-assembly, photophysical and electrochemical properties and activation of the TiO2 photocatalyst by perylene bisimide

DPBI exists as highly fluorescent molecular wires and DPBI loaded TiO₂ is more efficient in RO4 photodegradation.