Professor Dr Karl-Heinz Ernst, a distinguished Senior Researcher and Head of Molecular Surface Science at Empa – Swiss Federal Laboratories for Materials Science and Technology discusses how he manipulates single molecules and what technique has revolutionized surface science.
Q: What research projects are you and your group currently working on?
We’re interested in all types of molecular dynamics that are important in surface chemistry and heterogeneous catalysis. Our activities are manifold, but all located in the field of surface science. The main activities are 2D crystallization of chiral molecules on single-crystal surfaces, modification of surfaces with curved aromatic molecules and single-molecular surfaces dynamics triggered by inelastic electron tunneling. We use surface sensitive techniques, in particular scanning tunneling microscopy (STM) as a main research tool.
Molecular recognition among chiral molecules is very important in many processes. For example, crystallization is the most important way for separating chiral molecules into their left- and right-handed isomers, but it is not well understood. By means of well-defined model systems, that is, single crystalline surfaces in ultrahigh vacuum, we study the aggregation of chiral molecules. This allows us to use ultrasensitive methods with sub-molecular resolution.
A similar approach allows us to manipulate single molecules. At a very low temperature we tunnel electrons through them and watch how they react upon excitation. We let them jump, roll, flip or break apart.
Q: What motivated you to pursue this field of research?
Twenty years ago the Swiss National Science Foundation launched a priority program for Nanosciences. Working for a Materials Research Institute, I had the idea to synthesize new chiral materials. The reviewers liked the idea and granted support. We never really synthesized what we planned, because we got stuck looking at fascinating processes in chiral molecular monolayers before moving on. We came to manipulation of single molecules actually due to a part-time retirement of one of the world experts in the field, Karl-Heinz Rieder. He joined my group as post-prof, brought one of his old low-temperature STMs from Berlin with him, and we started ‘tickling’ single molecules with electrons.
Q: Where do you think the field is heading?
The ultimate dream is to use the acquired knowledge for creating new materials or useful processes. We found a new amplification process where a few dopant molecules switch very thin crystals into single handedness. This might be used one day for manipulation of crystallization in general. Crystal engineers still have little control of polymorphism of molecular crystals, a very important aspect in pharmaceutical science. A very promising new research tool of molecular physics is manipulating the charge of adsorbed molecules by gating graphene. By just turning a knob, we will be able push or pull electrons into or from molecules and study how they react or if thin layers become superconducting. This has been made possible by the progress in nanotechnology. Single molecule manipulation is now entering the field of artificial molecular motors. After we have shown that special motor molecules can ‘drive’ uni-directionally across a surface, the community needs to better understand how it actually works and how energy is dissipated in such process.
Q: What has been the most exciting development in physics during the course of your career?
The invention of the STM by Binnig, Gerber and Rohrer at IBM Rüschlikon in the beginning of the 1980s revolutionized surface science and became the founding tool of nanotechnology. I learned about it in a class that I took on surface science a couple of years after this invention. I was intrigued by this technique right away, and now it is the most important tool I am using in my research.
Equally exciting is what we have learned in astrophysics over the last decades. During astronomy classes that I took at the Free University in Berlin we were still discussing if black holes exist or if they will remain a theoretical construct. Nowadays we observe with ever bettering telescopes how they occupy centers of galaxies, eat up stars or direct them into extreme orbits.
But let’s leave physics, for a short moment. The highest potential of a substantial impact for society will be the future progress in the field of microbiology. If we understand entirely – and we will some day – how a cell works, how it runs as a molecular factory all the processes of life, this will have a tremendous impact on society. In that respect, I consider the really ground breaking achievements of Betzig and Hell, who received together with Moerner the Chemistry Nobel Prize in 2014, much more important for mankind than having thousands of physicists measuring the exact mass of an elementary particle on a huge single machine.
Q: What would you say to a student who wanted to shape her or his future with a career in science?
Concerning science: I would start with a quote of the ingenious Louis Pasteur: “Dans le champs de l’observation, l’hasard ne favorise que les esprits préparés.” (In the fields of observation, chance favors only the prepared mind.) My interpretation would be: ”Look for something unusual all day and explore it, when you encounter it.” Too often researchers overlook details that deserve to be investigated. Concerning career: “Stay focused on what you want to do, go straight for it and don’t get lost in administrational tasks or other services. Yourself is the most important person in your life.” Sounds pretty egoistic, but is a mere fact. Nevertheless, talk to people and listen to what they have to say.
Q: What do you find to be the most rewarding aspect of your job?
First of all, although not encountered on a daily basis, unraveling a phenomenon that is not understood. Let me explain by using the example of a little baby that starts to learn new aspects of life. Apparently, successful learning triggers a flush of hormones that makes it happy. An award installed by nature. This does apply to (old) researchers as well! Facing an unexpected observation (see the Pasteur quote above) is a challenge, mastering it, is the best reward you can get as a scientist. On a daily basis, I enjoy dealing with young, curious people and meeting colleagues from all over the world. A professional exchange may make me smarter and may help solve the problems I am working on, but it is the social interaction that comes with it, which I enjoy most.
You can read some of Professor Dr Ernst’s work, here. If you are interested in reading more on surface science you can also read the 2012 special issue on “From reciprocal space to real space in surface science“, which Ernst was Guest Editor of.
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Categories: Journal of Physics: Condensed Matter