A stable room-temperature molecular assembly of zwitterionic organic dipoles guided by a Si(111)-7x7 template effect.

Institut FEMTO-ST/LPMO, UMR CNRS 6174, 32, Avenue de l'Observatoire, 25044 Besancon cedex, France.
Angewandte Chemie International Edition (Impact Factor: 11.34). 02/2007; 46(48):9287-90. DOI: 10.1002/anie.200702794
Source: PubMed
  • [Show abstract] [Hide abstract]
    ABSTRACT: We demonstrate that the Si(111)-7×7 surface reconstruction can be used to template an ordered array of 1,3,5-methyl benzene molecules that are uniformly distributed over both the faulted and the unfaulted halves of the 7×7 unit cell by covalent attachment in vacuo. An intermolecular steric interaction, which hinders nearest-neighbor adsorption, is shown to play an important role in the formation of the ordered array. The stable equilibrium structure is shown to be one where the molecules are located at the corner of the half unit cells maximizing the intermolecular separation. In addition to the intermolecular steric interaction, there is an interaction between the molecule and the surface that plays a important role in reducing disorder in the array. Moreover, as the coverage is increased, there is a switch in site preference, from edge to corner, that mitigates the effect of the intermolecular interaction. To investigate this system we used scanning tunneling microscopy to study site occupancy as a function of coverage, ab initio total energy calculation to study the stability of the attachment sites, and Monte Carlo modeling to examine the emergence of translational order in the overlayer. The switch in site preference from edge to corner is faithfully reproduced by the kinetic Monte Carlo model when an interaction term is included.
    Physical review. B, Condensed matter 10/2011; 84(16). · 3.66 Impact Factor
  • physica status solidi (a) 04/2012; 209(4):647-652. · 1.21 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We explore the limits of modifying metal work functions with large molecular dipoles by systematically increasing the dipole moment of archetype donor-acceptor molecules in self-assembled monolayers on gold. Contrary to intuition, we find that enhancing the dipoles leads to a reduction of the adsorption-induced change of the work function. Using atomistic simulations, we show that large dipoles imply electronic localization and level shifts that drive the interface into a thermodynamically unstable situation and trigger compensating charge reorganizations working against the molecular dipoles. Under certain circumstances, these are even found to overcompensate the effect that increasing the dipoles has for the work function.
    Journal of Physical Chemistry Letters 10/2013; 4(20):3521-3526. · 6.59 Impact Factor

Full-text (2 Sources)

Available from
Jun 5, 2014