The world as we perceive it is a world of surfaces. We see the shimmering brightness of metal, the semi-transparent reflections on glass and the matt structure of plastic. The atomic and electronic structure of surfaces is responsible for many important effects. Nevertheless, there remains little knowledge about surfaces compared with the interior of materials. The reason for this is clear: "Surfaces are just more complex," says Professor Ulrike Diebold from TU Wien. In her laboratory, she investigates the processes, on an atomic scale, that take place on the surfaces of metal oxides and which often have an impact on the interior of the material. The European Research Council (ERC) has now awarded the TU researcher one of its prized "ERC Advanced Grants" – endowed with 2.5 million euros.
Metal and oxygen
Most metals oxidise in air, which is often a serious disadvantage for physical experiments. However, for Ulrike Diebold, metal oxides are not an unwanted by-product, but rather an exciting area of research. "When I started dealing with these materials more than twenty years ago, the research field was a rather exotic one. These days, everyone around the world is interested in it," she remarks. This is not only because metal oxides occur so frequently, but also because they are extremely useful for industrial applications.
One example of a frequently used material is titanium oxide (TiO2). It is non-toxic and cheap to produce. On account of its brilliant white colour, it is often used as a pigment (for example, in toothpaste) and, because it is highly compatible with biological tissue, it can be used to coat implants, such as hip joints. Titanium oxide is used frequently these days; however, this does not mean that we understand exactly which chemical and physical processes determine the properties of this substance: "Industry often relies on trial and error," says Ulrike Diebold. "However, we can investigate metal oxide surfaces atom by atom and find out exactly what's happening there."
High-tech surfaces for self-cleaning cotton jumpers?
Diebold's study group investigated how titanium oxide can be used as a photocatalyst. Catalysts are materials used to enable or facilitate chemical reactions between other substances. Photocatalysts only do this when they are irradiated with light - in other words, light can be used specifically to "switch on" their activity. This has made it possible to develop a coating for cotton fibres that break down dirt all by themselves in the presence of sunlight.
Metal oxides are also used as sensors for particular gases. If the surface is harbouring any noxious carbon monoxide (CO), this could result in atomic and electronic rearrangements in certain materials. "It changes the electrical conductivity of the material, so it is easy to construct a sensor, which, for example, emits a warning when the gas pipe is leaking and allowing carbon monoxide to escape into the kitchen," explains Ulrike Diebold.
Perfect surfaces are rare - and they are not very interesting either. "We are often more interested in the surface's defects," explains Diebold. "Small disturbances at atomic level can have a huge impact." A crucial tool of Diebold's trade is the scanning tunnel microscope. "We can use this to study individual defects, place molecules on the surface and observe directly what happens next."
Lucrative ERC grant for TU researcher
The ERC Advanced Grant "Oxide Surfaces" has been awarded by the European Research Council (ERC) – an institution that provides funding for fundamental research, established by the European Commission. "The ERC grant now enables us to significantly expand our research," says a delighted Ulrike Diebold. In the coming years, we shall be able to fund a number of additional posts in the research group. Diebold's specific research plans are ambitious: not only does she want to continue the pursuit of her previous work with metal oxides, she also wants to study ternary connections - these are connections that consist of three different elements, rather than just one metal plus oxygen. It should also be possible to study surface effects not only in a vacuum or in the air, but also to develop high-resolution microscopic images of surfaces in liquid solutions. "If we achieve that, surface research will open up some brand-new opportunities for us," of this, Diebold has no doubt.
Prof. Ulrike Diebold
Institute of Applied Physics
Wiedner Hauptstraße 8-10, 1040 Vienna
Phone: +43 1 58801 13425