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General description


I am chargé de recherche (permanent researcher) in the French CNRS (Institut de Physique, Section 05, condensed matter) and work in the CINaM institut, which is located on the Campus of Luminy in Marseille, in the south of France. My work deals with the fundamental research of insulating ionic surfaces (oxide surfaces and related bulk ionic crystal surfaces, thin insulating oxide films on metal surfaces) and of supported metal nanoparticles (NPs) and small functionalized molecules, which I characterzie by noncontact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM).
Some of my results are summarized in a review in Advanced Materials 23 (2011) 477 and in recent 3 book chapters (Link 1, Link 2, Link 3). The main keywords are:

Surfaces



Metal nanoparticles (NPs)


Molecules


The main part of my research is located in heterogeneous model catalysis. In particular, I focus on the morphology, atomic structure, defects and charge state of oxide surfaces (MgO [paper1,paper2, book chapter], Al2O3 [paper1, paper2] and since recently also cerium oxide (ceria)). Furthermore, I characterize  supported gold (AuNPs) and palladium nanoparticles (PdNPs), their morphology and structure  [paper1, paper2] but also charge related phenomena [paper1, paper2] at such NPs. Recently, I started to characterize the reactivity of metal NPs by using the Kelvin microscope via monitoring work function changes of the NPs. For instance, we could observe strong WF changes upon carbon contamination of PdNPs [paper].
Although alkali halides are not relevant in heterogeneous catalysis, they are nevertheless very interesting for me because they are somewhat similar to oxide surfaces. One advantage by using alkali halide surfaces is that they are accessible for high resoultion nc-AFM and KPFM imaging. Furthermore, because the number of surface defects can be narrowed down to only a few the identification of defects is relatively easy to accomplish. For instance, thanks to the Kelvin microscope I could directly evidence the Debye-Frankel layer and with it, I could identify cation vacancies at the steps [paper]. A real key advantage of alkal ihalides is that they can be doped with divalent metal impurities (Cd, Mg), which may produce new phases in the crystals, like the Suzuki phase [paper1, paper2, paper3]. Doping of alkali halides leads to nanostructured insulating surfaces, on which the growth of metal NPs can be confined inside specific surface regions at the nanometer scale. With this, metal NPs with a narrow size distribution can be created, with interesting potential applications in heterogeneous model catalysis [paper].

The second, smaller part of my research is located in the self-assembly of molecules on insulating surfaces. On the alkali halide surfaces I'm interested in the mechanisms of adsorption and desorption of functionalized molecules. Functionalization of molecules with polar substituents and the charge matching principle, i.e. the electrostatic interaction between polar functional groups of molecules and the ionic sublattices of the surface, are of key interest. Furthermore, phenomena of self-assembly and chirality within molecular films are part of my research. In recent years, I focused on pentahelicene molecules ([5]helicene), functionalized with one or two bromine or cyano substituents (MonoBromo, DiBromo, MonoCyano, DiCyano [5]helicene). The detailed adsorption and self-assembly mechanisms could be described in great detail on the Suzuki NaCl surface [paper1, paper2].


Atomic Force Microscopy
The local morphological, structural and electrostatic properties of surfaces are studied at the nanometer and atomic scale with help of local scanning probe techniques in ultra-high vacuum and mostly at room temperature. Because of the insulating character of the materials I use frequency modulated nc-AFM (dynamic SFM), which permits obtaining the true atomic resolution. Furthermore, the Kelvin microscope (KPFM) supports the characterization of surfaces and supported nano-objects by detecting the electrostatics of the surface, e.g. the surface work function (WF) and charge and polarization related phenomena. Apart from standard nc-AFM and KPFM imaging, I also have a large interest in the manipulation of nano-objects, like in the lateral manipulation of nanometer sized metal NPs [paper] and in charge manipulation experiments conducted at metal NPs [paper] and molecular islands [paper]. Keywords:

nc-AFM

Kelvin microscopy






Key words (German, French)
Kraftmikroskopie, Nichtkontakt Kraftmikroskopie, Dynamische Kraftmikroskopie, Biegebalken, Steinsalz, Aluminiumoxid, Magnesiumoxid, Kalziumfluorid -- Microscopie à force atomique, AFM noncontact, AFM dynamique, AFM harmonique, cantilever, pointe, halogénures alcalins, hauteur constante, nanosonde de Kelvin, travail de sortie, injection des charges

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