My field of research is commonly called Experimental Surface Science. Surface Science is a relatively broad field situated somewhere between physics, chemistry and material science. In the last years, it has undergone quite some changes due to the tremendous evolution of Nanotechnology, an area that is heavily depending on our progress in Surface Science. This is due to the fact that, the smaller things get, the more important become their surface-(2D)- compared to their volume-(3D)-properties. This poses some challenges, but opens as well up for some new and very exciting possibilities, e.g. to produce materials with custom-tailored properties, like new catalysts that might benefit the environment and the economy.
One of the areas, where we believe that nanotechnology quite soon will have a major impact on our daily life, is nanocatalysis. In a catalyst, only the very surface atoms are active. As catalysts are very often very expensive (like precious metals), typical challenges are to
In any case, we need to obtain an atomistic understanding of the catalyst's function in order to be able to rationally design better new catalysts.
Looking for a project in that area? PhD and PostDoc positions available! Check here.
In order to learn more about this fascinating 2D world and the surface properties that might be interesting from a fundamental as well as from a technological point of view, experimental Surface Scientists either prepare so-called model systems: well-defined surfaces and/or structures, e.g. nanostructures, on these surfaces, or they use available surfaces, e.g. the surface of an industrial catalyst. After careful preparation under very clean conditions, often in Ultra-High Vacuum (UHV), they typically investigate the physical / mechanical or chemical properties. But one can as well investigate biological properties, like how biocompatible a surface (e.g. that of an implant) is. Similarly, one can investigate the signatures of interesting bulk material structures (like dislocations, grain boundaries etc) at the surface and use them to learn more about these otherwise hidden structures.
Here at DTU, we are in the lucky situation that we both have theoretical and experimental surface scientists working on these nano properties in the same group, the Center for Atomic-scale Materials Design (CAMD) (formerly the Center for Atomic-scale Materials Physics or CAMP). My part in CAMD is concerned with atomic scale microscopy and to this end we use a very special instrument.
The STM is a quite unique instrument as it potentially allows true atomic resolution on surfaces. Thus, we can study the interesting surfaces with the necessary resolution to gain the atomistic understanding necessary to optimize our systems. In my current field, nanocatalysis, this means that we can study e.g. differences in reactivity on different sites on a nanocatalyst. Or, we can study the actual form of a nanoparticle before and after it has been used as a catalyst. The aim is of course then to use this insight to design better catalysts.
Together with my colleagues from CINF (another center here at the physics institute), we investigated nanoparticulate MoS2, a catalyst widely used in industry as a hydrodesulfurization (HDS) catalyst in order to e.g. get gasoline with low sulfur content. It is widely believed that a special electronic state only present at the edges of the MoS2 crystallites is doing this job (cf. images below that were taken with my STM). This has however never been proven.
In a paper we published recently in Science 6 July 07 (click the link to read the article online), we investigated this nanocatalyst as a possible substitute for the expensive Platinum normally used in electrolysis and we were for the first time able to prove that it is indeed this edge state that is active under catalytic conditions. The important step here was that we were able to go all the way from preparing the catalyst in different, well-defined forms, over imaging and characterizing these catalyst particles in my STM to doing reactivity measurements on the exact same particle investigated in STM! Moreover, from our measurements we could come up with some suggestions on how to improve this catalyst even more.
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