Since it takes me a little longer sometimes to post something new here, I have decided to explain you what I am doing when I am not blogging. I do science. I assume the readers of this blog knew that already pretty much. But actually I am doing pretty science. What does that mean? It means I do measurements that generate very pretty images. But let's start from the top.I am a chemist, holding the degree of Diplomchemiker from TU Kaiserslautern. I finished my undergraduate studies with a diploma thesis, which is roughly equivalent to a Master's thesis. The Diplom used to be the one and only degree to finish undergraduate studies, while now Bachelor's and Master's degrees can be obtained all across Europe. In the course of this so-called Bologna process the German Diplom has been as good as abandonned. Yet I have such a degree, and since I got it only in 2004, you can tell that I am one of the last students to get one. - The Diplomarbeit, as the final thesis is called in German, was meant to be the project in which the student specializes on one of the sub-fields of chemistry, such as Organic Chemistry, Inorganic Chemistry, or Physical Chemistry, to name but a few. As for myself, I chose Physical Chemistry, because I enjoy doing measurements more than synthesis. A physical chemist is, generally speaking, someone who measures the physical properties of a chemical compound (and of atoms and molecules), or follows chemical reactions by physical means. Let me explain that a little further. In chemical reactions we have reactants and products. The reaction converts the former into the latter. Since they are different molecules, they must differ in some physical property. By following this property (if possible) over time, we can determine conversion rates and other important quantities.
After graduating from TU Kaiserslautern, scarse funding (and poor scientific advising) drove me out of town - which ended up being one of the most fortunate things that have happened so far in my life. I was accepted to become a doctoral student at the famous Fritz Haber Institute in Berlin. It turned out to be a great opportunity for me, as not only I learned an incredible lot about science, but I can now also state that a Nobel prize was awarded to someone while I was actually working at the same institution and in the same field. - It is that field that I would like to introduce now.
As mentioned above, I am a physical chemist. However, this describes my approach to science rather than a field of expertise. When I joined the Fritz Haber Institute (more precisely: the Department of Chemical Physics), I began to specialize in the field of catalysis. That is ironic, as catalysis was the genuine topic of Technical Chemistry at TU Kaiserslautern, and I had never taken any classes related to that. That is because I like fundamental research better than the applied one - but that is exactly how research is done in that place in Berlin.
If you think of a catalyst, you might actually think of an automotive catalyst in the first place. While this is certainly an important and interesting system, catalysts can be applied to vastly more than just cars. By definition a catalyst modifies the energy barrier between the reactants and the products in a chemical reaction, which it does by offering an alternative route. Thus you do not need to spend ("waste") as much energy to surpass the barrier, if you choose the proper catalyst. (If the barrier is even higher than without the catalyst, then that is a so-called 'inhibitor".) - However, and now we finally plunge into my actual work, industral catalysts are highly complex systems that are difficult to study by means of fundamental research. In order to tweak and improve catalysts, we need to understand them as deeply as possible. In terms of fundamental research, this is called "at the atomic level"; i.e., we would like to know the exact location and function of all atoms involved in a catalyzed reaction.
To that end it is beneficial to replace the indusrial catalyst of interest by an appropriate model with reduced complexity. That model should image key features of the structure found in an idustrial catalyst (typically so-called "nanoparticles" dispersed on a "support"), while at the same time it facilitates fundamental studies. The trick is of course that we use the same materials in the models as can be found in a real system (yet often not all of them, again for the sake of simplicity).
While I would like to spare you from outlining the preparation of the models, I would like to dwell on their investigation now. Intrinsically physical chemists will use physical means for their studies. There is more than a handful of different methods, but I deem Scanning Tunneling Microscopy (STM) to be the most demonstrative. One thing I have not mentioned thus far is that the model catalysts I focus on are "heterogeneous". That means they are solids, while the reactans and products are gaseous. Therefore, for a reaction to take place, all parties involved have to come close to each other in the first place. "Close" in this case means that the gas or gases will have to adsorb on the surface of the catalyst. As a doctoral student I (mostly) studied the fate of adsorbates by a technique called Reflection Adsorption InfraRed Spectroscopy (RAIRS), but in order to obtain a complete picture, one has of course to investigate the catalytically active surface as well. That is what STM is there for. Given that surface fulfills certain conditions, STM will image it "on the atomic level", which we postulated to be desirable at the outset of this entry. In simple words, it means that images obtained by STM ideally possess a magnification large enough to even make atoms visible. In that case we can also see the structure of the arrangement of the atoms with respect to each other (the so-called lattice), and the size and relative position of nanoparticles, if they should be present. This structural information can then be correlated to observed reactivity phenomena, and hopefully we can learn how modifying the surface structure will improve the reactivity.
It should also be mentioned that STM is not only good for catalytic studies; it is also capable of moving so-called adatoms (atoms sitting on top of the surface) around. This has been impressively demonstrated by some scientists that have formed Chinese characters from atoms. This is possible because STM is on one hand a "microscope", but on the other hand it does not rely on a combination of magnifying glasses, as traditional microscopes do. Instead, it exploits the so-called "tunneling effect", which belongs to the realm of quantum mechanics. Again I would like to spare you from the details, but essentially it means that we get a current going from a very sharp and thin tip to the surface (or vice versa), even though the two are not touching each other, and hence the electric circuit seems to be interrupted. Yet the tunneling effect allows for closing it despite the lack of direct contact. - Some additional electronic devices make sure that this tunneling current remains the same. Should the tip, which is moving across the surface as indicated in the figure above, encounter a protrusion (or any other change in the local surface), it will compensate for that by backing off accordingly, as the protrusion will lead to a higher current. Hence, the electronics act as a feedback control for the tip, and the compensation motions of the tip are recorded and combined to give an image of the surface. - On the other hand, the tip can also be used to push adatoms around and reposition them as outlined above.
This may sound very complicated, but in most cases I do not touch the physical basis of STM, but I just use it to get some nice images, which will hopefully allow me to better understand the structure/reactivity of a given catalyst. Learning the ropes of using my current machine is most likely much easier than it seems.
