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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. | |
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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 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. | |
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| NanoMesh |
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Surface supported molecular self-assemblies with the goal to realize highly ordered, functional supramolecular nanostructures have become a field of very intense research. In most of the cases the control of the assembly process is achieved by designing and exploiting specific molecule-molecule interactions. | |
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A complementary ordering mechanism can be added by nanopatterned surfaces, which exhibit long range - ideally periodic - modulations of the molecule adsorption properties. Regardless the importance of such template surfaces, the physical origin of their site specific adsorption properties is in most cases poorly understood. We approached this topic by combining STM investigations with molecular dynamics (MD) simulations on adsorbed xenon on our model system, which is hexagonal boron nitride (h-BN) on Rh(111), representing a nanotemplate surface with a 3.2 nm lattice constant, the so-called nanomesh. The insight into the interplay of van der Waals and polarization interaction potentials, where both effects contribute in a similar magnitude should pave the way to gain a more general knowledge on such site specific adsorption processes. | |
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| Template Surfaces |
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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. | |
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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 of in the range 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 therefore required. | |
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