Equipe Nanostructuration |
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| Address : IM2NP Faculté des Sciences et Techniques Avenue Escadrille Normandie Niemen Aile 1 - niveau 5, service 151 13397 Marseille Cedex 20 France |
IM2NP Université du Sud Toulon-Var BP 32 83957 La Garde Cedex France |
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Research subjects:
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Hydrogen-bonded
supramolecular networks
Supramolecular chemistry is
dedicated to the study and use of noncovalent interactions to build highly
organized molecular arrangements, aiming ultimately at creating systems with
tailored properties and useful functions. The adaptation of its powerful
principles to fabricate molecular systems at surfaces is very promising: the
extended possibilities for the choice of on the one hand molecules with defined
size, shape, symmetry and function, and on the other hand substrates with
controlled composition, symmetry and patterning allow for a quasi-infinite
tuning of the structure and properties of the respective assemblies.
Our approach is based on a detailed
understanding of the microscopic pathways of surface diffusion, nucleation and
aggregation. The hierarchy in the migration barriers as well as the non-uniform
strain fields induced by mismatched lattice parameters can be translated into
geometric order and well defined shapes and length scales of the resulting
aggregates.
In order to develop a rationale for
molecular engineering in two dimensions, we need a comprehensive
characterization of the coupling schemes of adsorbed complex molecules mediated
by their functional groups, their bonding to the employed solid substrates, and
the organization principles resulting from the balance of these interactions.
Our objectives are the development
of novel and efficient approaches for combining molecular building blocks into
desired functional architectures at well defined surfaces and the exploration
of their fundamental interactions and properties.
A scanning tunneling microscope is
used in ultra high vacuum environment to obtain experimental data on the
topography and the chemical properties of the arrangements. For the analysis,
theoretical support is provided by density functional theory (DFT)
calculations, in collaboration with the Theory Team.
In this example, functionalized
phthalocyanine molecules self-assemble in dense domains on Ag(111) surface. We
observe a sequential evolution with time that changes the molecular
organization and increases the packing density and the intermolecular bond
number.
Selected
publications:
Robust
supramolecular network on Ag(111): hydrogen bond enhancement through partial
alcohol dehydrogenation
Pawlak R.,
Clair S., Oison V., Abel M., Ourdjini O., Zwaneveld N. A. A., Gigmes D., Bertin
D., Nony L., Porte L.
ChemPhysChem 10, 1032 (2009)
http://dx.doi.org/10.1002/cphc.200900055
Mesoscopic
Arrays from Supramolecular Self-Assembly
Clair S.;
Abel M.; Porte L.
Angewandte Chemie International Edition 49, 8237 (2010)
http://dx.doi.org/10.1002/anie.201003335
We demonstrated the first example of
surface covalent organic frameworks (SCOFs) extended to near-complete monolayer
coverage with a tunable nanoporous structure. To accomplish this, we used a
boronate-based chemistry applied to two-dimensional network formation on
metallic surfaces that has previously been shown to be effective for the synthesis
of highly ordered three-dimensional covalent organic frameworks (COF). The
versatility of SCOFs was demonstrated by the production of two boronate-based
covalently bonded nanoporous surface networks.
SCOF-1 is obtained by the molecular
dehydration of 1,4-benzenediboronic acid (BDBA), with three boronic acid
molecules reacting to form a six-membered B3O3 (boroxine)
ring with the elimination of water.
We have developed a method to
synthesize a fully 2D-conjugated organometallic sheet. The combined approach is
based on a metal-directed surface reaction: polymeric arrays are obtained by
co-evaporation of Fe atoms and 1,2,4,5-tetracyanobenzene (TCNB, a basic
molecular unit commonly used for the synthesis of phthalocyanine derivatives) in
ultrahigh vacuum (UHV) conditions onto atomically clean and well-defined
surfaces.
The reaction between TCNB molecules
and iron atoms in 4:1 stoichiometry leads to the formation of individual
phthalocyanine molecules, that is cyano-functionalized Fe-Pc (FePc(CN)8). The
as-formed molecules then self-assemble in square superlattices with a unit cell
size of 1.55±0.1 nm as usually observed for this class of molecules. In 2:1
stoichiometry, polymeric Fe-phthalocyanine sheets are formed, on metal surfaces
but also on thin insulating NaCl islands. The film network has a square
structure with a measured periodicity of 1.15±0.1 nm in both directions.
Remarkably, the growth demonstrated on a metal
surface can be extended onto a thin insulating film. We thus expect the
intrinsic properties to be preserved, and the system should be easily transferable
to real devices.
Selected
publications:
Organized
formation of 2D extended covalent organic frameworks at surfaces.
Zwaneveld
N., Pawlak R., Abel M., Catalin D., Gigmes D., BertinD., Porte L.
Journal of the American Chemical Society, vol.130, p. 6678, 2008
http://dx.doi.org/10.1021/ja800906f
Single
Layer of Polymeric Fe-Phthalocyanine: An Organometallic Sheet on Metal and Thin
Insulating Film
Abel, M.;
Clair, S.; Ourdjini, O.; Mossoyan M.; Porte, L.
Journal of the American Chemical Society 133, 1203 (2011)
http://dx.doi.org/10.1021/ja108628r
Tip- or
electron beam-induced surface polymerization
Clair, S.;
Ourdjini, O.; Abel, M.; Porte, L.
Chemical Communications 47, 8028 (2011)
http://dx.doi.org/10.1039/c1cc12065d
Substrate-mediated
ordering and defect analysis of a surface covalent organic framework
Ourdjini,
O.; Pawlak, R.; Abel, M.; Clair, S.; Chen, L.; Bergeon, N.; Sassi, M.; Oison,
V.; Debierre, J.M.; Coratger, R.; Porte, L.
Physical Review B 84, 125421 (2011)
http://dx.doi.org/10.1103/PhysRevB.84.125421
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Electronic
properties of organic/inorganic interfaces
Electron spectroscopies like direct and inverse photoemission are powerful tools to explore the electronic properties of materials. One of the main aspects is their surface sensitivity making them particularly suited for the study of the interface between a thin organic film and an inorganic substrate. In the near ultra-violet range (UPS and IPES) the valence and conduction band are effectively probed. This can give valuable information about density of states of a thin film or the interface and on the adlayer/substrate energy level alignment. Such features are used in our group to study the interface bonding mechanisms and the charge injection barriers in organic/inorganic interfaces. Particularly, combining IPES and UPS the transport gap can be measured (see figure below, left panel).
XPS uses higher energy radiation and
enables one to probe deeper electronic levels with elemental sensitivity.
Moreover, since their binding energy depends on the valence charge distribution
around an atom, energy shifts are used to probe the chemical environment of a
given specie. Different oxidation states for –say- carbon within a given
molecule can be detected by XPS, (see figure below, right panel) which can also
shed light on the nature of the molecule-substrate interactions. Weaker
interactions as intermolecular hydrogen bonds can also be detected.
Electron spectroscopies are
performed in our group in two separate experimental set-up : the IPES and
the STM apparatus. In the first one, inverse (IPES) photoemission is available
together with LEED, Auger, and standard preparation techniques. In the second
UPS and XPS photoemission can be performed in parallel with in situ imaging by STM (LEED and
preparation chambers also available). Moreover we regularly access to different
synchrotron radiation facilities to perform high-resolution photoemission and
photo-absorption experiments.
Left panel:
Combination of UPS and IPES can measure the transport gap of the organic layer.
Right panel: high resolution XPS is able to discern different atomic sites (C1
and C2) within a phthalocyanine molecule. The fit analysis shows the
importance of the shake-up structure.
Charge
transfer at the ZnPcCl8/Ag(111) interface
When ZnPcCl8 are adsorbed
on Ag(111) they form an ordered layer of molecules whose structure evolves as a
function of time or annealing temperature. UPS performed at increasing
thickness (left panel) shows a feature close to the Fermi level at low coverage
(~ 1 ML). This feature is absent at higher coverage and is interpreted as a
filling of the LUMO through a charge transfer from the silver substrate to the
adsorbed molecules. Accordingly the NEXAFS spectra show a reduction of the LUMO
resonance for the molecules in direct contact with the substrate. The fact that
the partial filling of the LUMO does not lead to a metallic interface indicates
that electron correlations are important in this kind of systems. (L.
Giovanelli et al. J. Phys. Chem. C 112 (2008) 8654)
Molecules on semiconductors
Silicon Carbide (SiC) is a promising
material for high-voltage, high-temperature and high-frequency electronic
devices because of its wide bad-gap (~3eV), extreme hardness and thermal
stability. Moreover, the diversity of its surface reconstructions triggers high
interests in both the fundamental understanding of its surface electronic
structure and possible applications. The interaction of organic molecules with
SiC surfaces is of particular interest since it may lead to e.g. biosensors or
optoelectronic devices. Besides, studying the electronic structure of organic
molecules adsorbed on reconstructed semi-conducting surfaces may improve our
understanding of organic thin film growth and molecular self-assembly
mechanisms on semiconductor surfaces.
Selected
publications:
Evolution
of the electronic structure at the interface between a thin film of halogenated
phthalocyanine and the Ag(111) surface.
Giovanelli
L., Amsalem P., Themlin J. M., Ksari Y., Abel M., Nony L., Koudia M., Bondino
F., Magnano E., Mossoyan-Deneux M., Porte L.
Journal of Physical Chemistry C, vol. 112, p. 8654, 2008
http://dx.doi.org/10.1021/jp800116j
Interface
formation and growth of a thin film of ZnPcCl8/Ag(111) studied by photoelectron
spectroscopy.
Amsalem P.,
Giovanelli L., Themlin J.M., Koudia M., M. Abel M., Oison V., Ksari Y.,
Mossoyan M., Porte L.
Surface Science, vol. 601, p. 4185, 2007
http://dx.doi.org/10.1016/j.susc.2007.04.080
Final-state
diffraction effects in angle-resolved photoemission at an organic-metal
interface
F. C.
Bocquet, L. Giovanelli, P. Amsalem, L. Petaccia, D. Topwal, S. Gorovikov, M.
Abel, N. Koch,
L.
Porte, A. Goldoni and J.-M. Themlin
Physical Review B 84, R241407 (2011)
http://dx.doi.org/10.1103/PhysRevB.84.241407
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Molecules on
wide-gap surfaces
Our
research activities are focused at the investigation on the atomic-scale of the
structural and electrical properties of adsorbed molecules on wide-gap surfaces
by non-contact Atomic Force Microscopy combined with Kelvin microscopy
(nc-AFM/KPFM) in ultra-high vacuum (UHV). The motivations for that work rely on
the understanding of the fundamental processes driving the self-assembly of
molecules when deposited on a surface.
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Fig.2 a-
(35x25)nm2 nc-AFM image of BDBA molecules on KCl(001). The
molecular layer is visible on the left-hand of the figure and the atomic
resolution on KCl is visible on the right-hand side. b- nc-AFM image of the
supramolecular phase of BDBA showing dense rows of molecules. The unit cell
is rectangular and consists of one molecule developing four H-bonds with the
neighboring molecules. c- Structural model of the supramolecular phase
showing the rectangular unit cell with the four H-bonds engaged by each
molecule. It must be noticed that such a phase is allowed to the rotation of
the benzene ring w.r.t. the plane of B(OH)2 groups. |
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More
details on this research activity:
Selected
publications:
Understanding
the Atomic-Scale Contrast in Kelvin Probe Force Microscopy
Nony L.,
Foster A.S., Bocquet F., Loppacher C.
Physical Review Letter 103, 036802 (2009) <pdf>
http://dx.doi.org/10.1103/PhysRevLett.103.036802
Bocquet F.,
Nony N., Loppacher C., Glatzel T.
Analytical
approach to the local contact potential
difference on (100) ionic surfaces : implications for Kelvin probe force
microscopy.
Physical Review B, vol. 78, no 3, p 035410, 2008 <pdf>
http://dx.doi.org/10.1103/PhysRevB.78.035410
Supramolecular
Assemblies of 1,4-Benzene Diboronic Acid on KCl(001)
Pawlak, R.;
Nony, L.; Bocquet, F.; Olson, V.; Sassi, M.; Debierre, J.M.; Loppacher, C.;
Porte, L.
Journal of Physical Chemistry C 114, 9290 (2010)
http://dx.doi.org/10.1021/jp102044u
Polarization
effects in noncontact atomic force microscopy: A key to model the tip-sample
interaction above charged adatoms
Bocquet F.;
Nony L.; Loppacher C.
Physical Review B 83, 035411 (2011)
http://dx.doi.org/10.1103/PhysRevB.83.035411
La diffusion Raman met en jeu
l’interaction d’un faisceau laser avec les modes de vibration atomiques d’un
matériau. Elle fournit des informations diverses sur le matériau sondé :
structure, état de contrainte, composition chimique….. L’un des grands
avantages de la spectroscopie Raman est qu’elle ne nécessite aucune préparation
de l’échantillon.
Exemple 1 :
Exemple d’analyse par diffusion
Raman : mesures sur une boucle d’oreille
L’analyse immédiate du spectre
montre qu’elle n’est pas en diamant, il s’agit en fait d’oxyde de zircone
cubique
Exemple 2 :
Exemple d’analyse par maping Raman
In Situ : mesures sur des mémoires moléculaires (Cu-TCNQ) pour différents états
de polarisation
Le mécanisme de transfert de charge
est clairement visible sur les spectres Raman.
More information :
Selected
publications:
Turquat et al., IEEE Proceedings of NVMTS, p. 44–47, 2007
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Self-Assembled
Monolayers (SAM) on silicon surfaces
Selected
publications: