Forschung  
Kohlenstoff Nanomaterialien
Molekulares Engineering
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Atomistische Simulationen
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Functional Nanostructured Surfaces

 

Intermetallic PdGa Catalysts

With its highest technological and economical importance, catalysis is an extremely active research area, which yields in a great impact on the development of new catalyst systems with the aim to produce more efficient and selective chemical processes.

Recently, intermetallic Pd-Ga compounds are presented to play an essential role as catalysts in the semi-hydrogenation of acetylene in the polyethylene production, which is attributed to the surface stability and site-isolated Pd atoms. However, within a technological context, it is clear that the application of these compounds is critically dependent on establishing a fundamental understanding of all relevant chemical and physical processes underlying the catalytic processes. Our research is based on the determination of the surface physical properties with all surface sensitive techniques such as STM, STS, XPS, UPS, XPD, ARPES, aso.

Complex Metallic Alloys (CMA) and Quasicrystals (QC)

Quasicrystals discovered by Shechtman (1984) et al., show particular physical properties. For instance the electrical resistivity decreases with increasing structural disorder in the crystal and is unusually high with a negative temperature coefficient.

The relation between the aperiodic atomic structure and these peculiar properties is still not understood. With the aim to get a better understanding on the interplay between the aperiodic crystal structure and the resulting valence electronic structure we use low-temperature scanning tunneling microscopy and spectroscopy to simultaneously measure the topography and local density of states of quasicrystal (QC) and approximant surfaces. Our investigations show a multitude of electron states near the Fermi level resembling the "spiky" density of states theoretically predicted for aperiodic crystals, consistent with the concept of critical states. As the investigated QC surfaces are very complex, we extend our research to approximant phases, being the periodic counterparts to Quasicrystals and in general to complex metallic alloys possesing similar building blocks as the QC.

Metal-insulator-organic hybrid structures

A prominent goal of molecular surface science is to realize ultrathin organic layers with promising structural, electronic or magnetic properties. This thriving field of surface science has seen tremendous progress in the last 15 years regarding the control, complexity and functionality of the fabricated organic thin films.

Much of the work in this field has been devoted to metallic substrates. Recent developments in organic photovoltaics and the general lessons learned from the CMOS semiconductor industry however point to the importance of incorporating insulating layers to achieve a successful technology. To this end, we study key processes in molecular surfaces science such as self-assembly, surface induced templating, covalent coupling, charging and charge transfer of molecular thin films on ultra-thin insulators. At the moment much of our work is carried out on a single layer of hexagonal boron nitride (h-BN) on metal single crystals where the choice of the metal allows to tune the functionality of the h-BN layer. A prominent example is the 3.2 nm periodic h-BN “nanomesh” on Rh(111), which not only provides an electronic decoupling of adsorbed molecular layers from the underlying metal but also a strong templating effect for single molecules which allows detailed investigations of isolated single molecules.

Template Surfaces

The future of molecular electronics will be crucially depending on the ability to control the assembly of molecular species into complex supramolecular structures. This is true for molecular assembly not only in solutions, but especially also on substrate surfaces.

On substrates, there are two major mechanisms which control the self-assembly of molecules. The first mechanism is based on specific and non-specific molecule-molecule interactions, which can be controlled by an appropriate functionalization of the molecules. The second mechanism to control the molecular assembly is based on the use of specific molecule-substrate interaction, in other words on the use of template surfaces. However, this approach is by no means trivial because the template lattice parameter should be in the order of the molecule dimensions which typically are in the range of 1-2 nm. It is evident that this length scale is still not available to the most advanced micro or even nano-pattering of semiconductor fabrication like deep UV or electron beam lithography. To obtain substrates structured at the nano-meter scale, new approaches are required.

ADDRESS

nanotech@surfaces Laboratory

Empa, Swiss Federal Laboratories for

Materials Science & Technology

Ueberlandstrasse 129

8600 Duebendorf

Switzerland

How to find us :

printable map, interactive map

 

CONTACT

Prof. Dr. Roman Fasel, Head of Laboratory

Dr. Oliver Gröning, Deputy head

Ms. Christine Tran, Head assistant

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