Thomas Chassé

Straightforward Generation of Pillared, Microporous Graphene Frameworks for Use in Supercapacitors

Microporous, pillared graphene-based frameworks are generated in a simple functionalization/coupling procedure starting from reduced graphene oxide. They are used for the fabrication of high-performance supercapacitor devices.

Buried interfacial layer of highly oriented molecules in copper phthalocyanine thin films on polycrystalline gold.

The growth of copper phthalocyanine thin films evaporated on polycrystalline gold is examined in detail using near edge x-ray absorption fine structure spectroscopy and surface sensitive x-ray photoemission spectroscopy. The combination of both methods allows distinguishing between the uppermost layers and buried interface layers in films up to approximately 3 nm thickness. An interfacial layer of approximately 3 ML of molecules with an orientation parallel to the substrate surface was found, whereas the subsequent molecules are perpendicular to the metal surface. It was shown that even if the preferred molecular orientation in thin films is perpendicular, the buried interfacial layer can be oriented differently.

B3N3 Borazine Substitution in Hexa-peri-Hexabenzocoronene: Computational Analysis and Scholl Reaction of Hexaphenylborazine

The doping of graphene molecules by borazine (B(3)N(3)) units may modify the electronic properties favorably. Therefore, the influence of the substitution of the central benzene ring of hexa-peri-hexabenzocoronene (HBC, C(42)H(18)) by an isoelectronic B(3)N(3) ring resulting in C(36)B(3)N(3)H(18) (B3N3HBC) is investigated by computational methods. For comparison, the isoelectronic and isosteric all-B/N molecule B(21)N(21)H(18) (termed BN) and its carbon derivative C(6)B(18)N(18)H(18) (C6BN), obtained by substitution of a central B(3)N(3) by a C(6) ring, are also studied. The substitution of C(6) in the HBC molecule by a B(3)N(3) unit results in a significant change of the computed IR vibrational spectrum between 1400 and 1600 cm(-1) due to the polarity of the borazine core. The properties of the BN molecule resemble those of hexagonal boron nitride, and substitution of the central B(3)N(3) ring by C(6) changes the computed IR vibrational spectrum only slightly. The allowed transitions to excited states associated with large oscillator strengths shift to higher energy upon going from HBC to B3N3HBC, but to lower energy upon going from BN to C6BN. The possibility of synthesis of B3N3HBC from hexaphenylborazine (HPB) using the Scholl reaction (CuCl(2)/AlCl(3) in CS(2)) is investigated. Rather than the desired B3N3HBC an insoluble and X-ray amorphous polymer P is obtained. Its analysis by IR and (11)B magic angle spinning NMR spectroscopy reveals the presence of borazine units. The changes in the (11)B quadrupolar coupling constant C(Q), asymmetry parameter η, and isotropic chemical shift δ(iso)((11)B) with respect to HPB are in agreement with a structural model that includes B3N3HBC-derived monomeric units in polymer P. This indicates that both intra- and intermolecular cyclodehydrogenation reactions take place during the Scholl reaction of HPB.

Locally resolved core-hole screening, molecular orientation and morphology in thin films of diindenoperylene deposited on Au(111) single crystals

Organic electronics has reached the market in a very short period of time, since the first organic light emitting device has been demonstrated.[1] Growth of organic thin films has been the focus of intensive investigations that in the recent years have gained knowledge about the involved mechanisms: substrate-molecule interaction versus molecule-molecule interaction, preparation parameters, substrate morphology (i.e., roughness, local defects, steps), and post growth treatment.[2–6] Here we investigate thin films of diindenoperylene deposited on Au(111) single crystals by using photoelectron emission microscopy (PEEM). We also discuss the effect of the growth on the film structure using the molecular orientation (i.e., the angle between the molecular axis and the substrate).

Tetra-t-butyl magnesium phthalocyanine on gold: Electronic structure and molecular orientation

In this work we have investigated the electronic structure and the molecular orientation of (t-Bu)(4)PcMg (tetra-t-butyl magnesium phthalocyanine) on polycrystalline and single crystalline gold substrates using photoemission spectroscopy and x-ray absorption spectroscopy, and we compare the results to the unsubstituted PcCu (copper phthalocyanine). The C 1s photoemission spectrum is described similar to unsubstituted relatives with an additional component for the aliphatic substituents. The variation of the excitation energy causes distinct differences in the shape of the C 1s spectrum, which is very useful for the analysis of the molecular orientation in the uppermost layer. It is shown that despite of the sterically demanding substituents, ordered sublimed films of (t-Bu)(4)PcMg are accessible, the orientation of the molecules, however, is different from the orientation of the unsubstituted relatives.

A unique ECR broad beam source for thin film processing

We present the special microwave excited ECR (electron cyclotron resonance) type broad beam ion source EC/A 125 together with first results in ion beam deposition. Our source concept overcomes different disadvantages of common broad beam ion sources. By means of a modular source design and an autotuning microwave power supply, an adaptation at different process requirements is possible. The efficiency of the source is demonstrated analysing the performance in inert and reactive environment. We analyse and discuss the resulting beam composition and draw important conclusions on the plasma-chemical processes occurring in the source from the measurement of the ion energy distributions. The source is operated at the CYBERITE ion beam equipment and results in deposition of magneto-resistive films and multilayer films are illustrated.

Molecular orientation in diindenoperylene thin films deposited on polycrystalline gold

We present x-ray photoemission spectroscopy (XPS) and near-edge x-ray absorption fine structure spectroscopy measurements taken on diindenoperylene (DIP) thin films of different thicknesses deposited on polycrystalline gold. Our investigations show that DIP films present flat lying molecules in the first layer, while the angle between the molecular axis and the surface increases with thickness. By using XPS, we find evidence for Stranski–Krastanov growth mode.

CoPc and CoPcF16 on gold: Site-specific charge-transfer processes

Summary Interface properties of cobalt(II) phthalocyanine (CoPc) and cobalt(II) hexadecafluoro-phthalocyanine (CoPcF16) to gold are investigated by photo-excited electron spectroscopies (X-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS) and X-ray excited Auger electron spectroscopy (XAES)). It is shown that a bidirectional charge transfer determines the interface energetics for CoPc and CoPcF16 on Au. Combined XPS and XAES measurements allow for the separation of chemical shifts based on different local charges at the considered atom caused by polarization effects. This facilitates a detailed discussion of energetic shifts of core level spectra. The data allow the discussion of site-specific charge-transfer processes.

Heptacene: Characterization in Solution, in the Solid State, and in Films

Acenes comprise an important class of organic semiconducting materials. As graphene nanoribbons of ultimate width, they are valuable atom-precise model systems for studying the properties of this form of nanoscale carbon materials. Heptacene is the smallest member of the acene series that could only be studied under matrix isolation conditions. Its existence in bulk had never been positively confirmed, despite efforts dating back more than 70 years. We report that the reduction of 7,16-heptacenequinone produces a mixture of two diheptacene molecules. The diheptacenes undergo thermal cleavage to heptacene at high temperatures in the solid state. Monitoring this cycloreversion by solid state 13C cross-polarized magic angle spinning NMR reveals that solid heptacene has a half-life time of several weeks at room temperature. The diheptacenes are valuable precursors for generating films of heptacene by vapor phase deposition that can be studied below or at room temperature.

Nanoscale Assembly of Paramagnetic Organic Radicals on Au(111) Single Crystals

The successful thin-film deposition of a pyrene-substituted nitronyl nitroxide radical under controlled conditions has been demonstrated. The electronic properties, chemical environment at the interface, and morphology of the thin films have been investigated by a multitechnique approach. Spectroscopic and morphological analyses indicate a Stranski-Krastanov growth mode and weak physisorption of molecules onto the metallic surface. Electron spin resonance (ESR) spectroscopy shows that evaporation processes and deposition do not affect the paramagnetic character of the molecules. Useful concepts for the engineering of new, purely organic-based magnets, which may open the way to fruitful exploitation of organic molecular-beam deposition for assembly on solid surfaces in view of future technological applications, are presented.