A stable room-temperature molecular assembly of zwitterionic organic dipoles guided by a Si(111)-7x7 template effect.
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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
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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
© Wiley-VCH 2007
69451 Weinheim, Germany
Stable room temperature molecular assembly of zwitterionic
organic dipoles guided by Si(111)-7x7 template effect **
Younes Makoudi, Madjid Arab, Frank Palmino, Eric Duverger, Christophe Ramseyer,
Fabien Picaud, and Frédéric Chérioux*
Synthesis of MSPS
[∗] Y. Makoudi, Dr. M. Arab, Dr. F. Palmino, Dr. E. Duverger
and Dr. F. Chérioux
Institut FEMTO-ST/LPMO UMR CNRS 6174
32, Avenue de l’Observatoire, F-25044 Besancon cedex,
Fax: (+) 33 8185 3998
Homepage ((optional)): www.femto-st.fr
Dr. F. Picaud and Prof. Dr. C. Ramseyer
Laboratoire de Physique Moléculaire, UMR CNRS 6624
16 Route de Gray, F-25030 Besancon cedex, FRANCE
[∗∗] This work was supported by the Communauté
d’Agglomération du Pays de Montbéliard. Authors thank Dr.
C. Joachim (CEMES, FRANCE) for fruitful discussions
Supporting information for this article is available on the
WWW under http://www.angewandte.org or from the
MSPS molecules have been synthesised in accordance with the method previously described by Nicoud et al.i
The procedure is based on two steps:
1) formation on the zwitterion
2) building of the large dipole
EtOH, Reflux, 10h
4-Picoline was treated at 0 °C with one equivalent of propylsultone, leading to crystalline 4-methyl-(n-
sulfonatopropyl)pyridinium, which was used for the subsequent reaction without further purification. To a
solution of 4-methyl-(n-sulfonatopropyl)pyridinium in 15 mL of anhydrous ethanol was added one equivalent of
the 4-methoxybenzaldehyde and a catalytic amount of pyrrolidine. The mixture was heated under reflux for 10 h
and then cooled to 0 °C. The precipitated product was filtered and washed with ether. The pale yellow solid was
purified by column chromatography (Silica gel, acetone, Rf close to 0.5). The pure MSPS was isolated as an
intense yellow powder after evaporation of the solvent.
1H NMR (300 MHz, CDCl3, 25°C): δ = 1.96 (quint., 3J = 7.3 Hz, 2H), 2.45 (t, 3J = 7.3 Hz,
2H), 3.76 (s, 3H), 4.62 (t, 3J = 7.3 Hz, 2H), 6.85 (d, 3J = 8.7 Hz, 2H), 7.06 (d, 3J = 16.2 Hz,
1H), 7.59 (d, 3J = 8.7 Hz, 2H), 7.69 (d, 3J = 16.2 Hz, 1H), 8.03 (d, 3J = 6.7 Hz, 2H), 8.99 (d,
3J = 6.7 Hz, 2H). MS (ESI): m/z : 333 [M+]; elemental analysis (%) calcd for C17H19NO4S
(333.10): C 61.24, H 5.74, N 4.20; found: C 61.17, H 5.81, N 4.09.
All properties of the isolated molecules are obtained by using the Vienna Ab Initio Simulation Package
(VASP),ii which is a density functional theory (DFT) code with plane wave basis set. Electron–ion interactions
were described using the projector-augmented wave (PAW) method, which was expanded within a plane wave
basis set up to a cutoff energy of 400 eV. Electron exchange and correlation effects were described by the
Perdew–Burke–Ernzerhof (PBE) GGA type exchange-correlation functional.
In order to investigate the molecule-substrate interactions, two pictures showing the DOS isolines evolution for
the entire system at different cut planes centered on the MSPS have been described in the following figures. We
have used Xcrysdeniii for the isolines dos representation.
In this top view, the methoxy group/Si(111)-7x7 interactions are proved by the DOS isolines (bias voltage +2V).
In this top view, the sulfonato/Si(111)-7x7 interactions are proved by the DOS isolines (bias voltage -2V).
These two figures show the template effect of the surface which induces a change conformation of MSPS in
order to lead to the supramolecular self-assembly of three MSPS in a Si(111)-7x7 half-cell.
i Serbutoviez, C.; Nicoud, J.-F.; Fisher, J.; Ledoux, I. & Zyss, J. Chem. Mater. 1994, 6, 1358-1368.
ii (a) Kresse, G. & Furthmüller, J. Phys. Rev. B 1996, 54, 11169-11186. (b) Blöchl, P. E. Phys. Rev. B 1994, 50,
iii (a) Kokalj, A. J. Mol. Graphics Modelling 1999, 17, 176. (b) Kokalj, A. Comput. Mater. 2003, 28, 155.