Leiden physicist Rudolf Tromp has been awarded the 2017 Distinguished Lectureship on the Applications of Physics by the American Physical Society. As part of his lectureship, Tromp will deliver a lecture series on his career as a physicist in industry. More info
Since 1983 he has worked as a scientific researcher at IBM T.J. Watson Research Labs in Yorktown Heights, New York, in areas of both basic and applied science. As of 2006 he is also a professor at Leiden University. In his lectures for young scientists, Tromp will elaborate on the possibilities and opportunities of working in industry as a physicist.
The APS Distinguished Lectureship comes with a $5,000 cash prize.
Synthetic fuel is cleaner than natural oil, but its production process needs to be more efficient. Now for the first time, physicists have directly observed the molecules produced in the chemical process. This paves the way for designing more efficient More info
To date, natural oil still serves as our primary source of fuel, even though a much cleaner alternative exists in the form of synthetic fuel. This contains much less sulfur and doesn’t require oil as the starting material. At the moment, only five percent of the world production of diesel fuel makes use of this process, because it is cheaper for companies to use more polluting substances. If researchers have a better understanding of the production process of synthetic fuel, the balance could tip the other way.
Now, physicists from Leiden University have seen for the first time how this chemical process unfolds in the early stages. It was already known that the necessary chemical reaction between carbon monoxide and hydrogen takes place on the surface of small cobalt particles. These serve as the catalyst for the reaction. It is however very difficult to verify the exact working mechanism in experiments. Researchers have to deal with pressures of several atmospheres and temperatures of several hundred degrees Celsius. These are far from ideal circumstances to observe molecules. Group leader Joost Frenken and his team developed a special type of Scanning Tunneling Microscope—a so-called Reactor-STM—to bypass this problem.
To their surprise, they observed that in the first stages of the process, the surface covers itself up progressively in a single layer of hydrocarbon molecules with a highly ordered regular pattern. The molecules accumulate on the cobalt surface all with the same, surprisingly long length. The Leiden physicists were able to explain these findings with a simple theory, in which the catalyst constructs the molecules step-by-step at the atomic steps on the cobalt surface. Most molecules spend some time on the surface and then evaporate, but the longer ones stick more strongly and fill the surface. The most efficient way to do that is to fill the surface with a regular pattern, similar to cars in a parking lot.
Currently, catalysts are being developed mostly by trial and error. With the new discovery, first author Violeta Navarro and her colleagues pave the way for future generations of genuine ‘designer’ catalysts, with fully optimized efficiency and selectivity for the desired products. Frenken: ‘The ultimate goal is that of true “designer catalysts”. We’re absolutely not there yet, but understanding the early stages of synthetic fuel production forms an essential component of unraveling the entire, complex reaction mechanism. We have introduced a new way of looking at an active catalyst with the ultimate resolution.’
This research was supported by a Veni grant from STW.
Physics Outreach Officer, Leiden University
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Top: Artist impression of the reactants carbon monoxide and hydrogen and the produced hydrocarbon molecules of different lengths on the cobalt catalyst (carbon atoms are represented in green, oxygen atoms in red and hydrogen atoms in blue).
Bottom left: Topographic image of a region (3840 nm2) of the surface of a cobalt catalyst during reaction, obtained with a scanning tunneling microscope. The height in the image is represented in a color scale where the darker colors are lower than the lighter ones, and the total height is 1.4 nm. The image was taken after 40 minutes of reaction at 221 °C and a pressure of 4 atmospheres in a mixture of the gases carbon monoxide, hydrogen and argon in the ratio 1:2:2 respectively. The cobalt surface is covered by a stripped pattern which results from the organization of the molecules produced during the reaction, that align next to each other in a regular pattern, similar to cars in a parking lot. The magnifying glass shows an impression of how the molecules are organized within the stripes.
Bottom right: Graphic representation of the concentration of the molecules produced during the reaction on the cobalt catalyst surface as a function of the reaction time, depending on their length. All lengths are produced during the reaction, but the shorter molecules are very volatile and leave the surface fast. Longer molecules reach higher concentrations on the surface of the catalysts. The molecules with 15 carbon atoms are the first ones that reach a concentration on the surface which is high enough to organize themselves in a striped regular pattern.
For the first time, physicists have visualized the ‘melting’ of electrons inside a special class of insulators. It allows electrons to move freely and turns the insulator into a metal and possibly later into a superconductor. Publication on September 19th More info
Some materials carry an electrical current more easily than others. Metals are for example world class conductors. Inside them, the electrons form an electronic liquid that flows through the atomic lattice. In specific insulators on the other hand, electrons are stuck to their place in the lattice; the electronic liquid is frozen (see image below). In these so-called Mott insulators, you can replace some atoms with different ones. Physicists call this ‘doping’. It is known that doping leads to a melting of the frozen electronic liquid, but nobody knows how this process works.
Now, Leiden physicist Milan Allan together with lead authors Irene Battisti and Koen Bastiaans have, for the first time, visualized this melting process in a family of materials called iridates. They discovered that the melting process is very inhomogeneous, with puddles forming in between frozen areas. These puddles are only a few nanometers in size (see image below). The research group, in collaboration with theoretical physicist Jan Zaanen, publishes their results in Nature Physics.
Apart from getting insight in a very fundamental process, the discovery also shines light on the mystery of superconductivity—a phenomenon where electrons move without resistance. Superconductivity is important because it allows transportation of electricity with zero energy loss. ‘We came to believe that this kind of melting is a universal prerequisite of superconductivity,’ says Allan. ‘If we would manage to melt the electronic liquid in all parts of the sample, it would likely become a new superconductor.’
The melting of electrons. In the blue areas, the electrons (red dots) are stuck to the atoms in the lattice (green circles), meaning that there is no current. In the red areas, dopant atoms (black circles) are added, giving the electrons room to move and making them behave like a liquid. The researchers expect that once the whole area is molten, the material is a high-temperature superconductor.
Left: Actual measurement. Right: Illustration of concept.
Header: Image produced based on data from a Scanning Tunneling Microscope (STM). Red ‘mountains’ are molten electrons. The blue parts represent frozen electronic liquid.
PhD student Rik Mom has been awarded the Michel Cantarel grant by the French Vacuum Society (SFV). At the European Conference on Surface Science he gave a prize-winning talk on the subject of his PhD research, making him More info
one of five award winners. During his PhD research, Mom images catalysts at the atomic scale while they are operating in chemical reactions. Performing such studies under realistic conditions is essential. ‘Atomic scale studies on catalysts are often done in ultrahigh-vacuum and at low temperatures,’ he says. ‘This is not representative of real-life processes, which happen under pressures of 1 to 100 bar and at temperatures between 100 and 400 °C.’
To obtain results that are useful for real applications, Mom studies nanoparticle catalysts in chemical reactions at 1 bar and 250 °C, as he explained in his talk. In an effort to also improve the realism in the model catalyst that is used in the studies, he published a paper in The Journal of Physical Chemistry C on his successful attempt to control the preparation of complex, realistic model catalysts.
Casper van der Wel, Afshin Vahid, Anđela Šarić, Timon Idema, Doris Heinrich &
Daniela J. Kraft (2016) Lipid membrane-mediated attraction between curvature inducing objects, Scientific Reports , 6, 32825. [DOI]
S. Voltan, C. Cirillo, H.J. Snijders, K. Lahabi, A. García-Santiago, J.M. Hernández, C. Attanasio, and J. Aarts (2016) Emergence of the stripe-domain phase in patterned permalloy films, Physical Review B, 94, 094406. [DOI]
28 Sept, 10:00, HL 207
Extra BSM Seminar Jennifer Mathies (MIT): Having Fun with Unpaired Electrons: Enhancing the Sensitivity of NMR & Radicals Essential for Life
29 Sept, 13:45, Academy building, Rapenburg 73
Thesis Defense Stefano Voltan - QMO: Inducing Spin Triplet Superconductivity in a Ferromagnet Promotor: Prof.dr. J. Aarts