Sense Jan van der Molen
Professor of Physics of condensed matter
In the media
In the Van der Molen lab, we investigate the properties of low-dimensional materials, with an enthusiastic scientific team. We focus on two types of quantum systems: one-dimensional and two-dimensional.
First, we investigate charge transport (conductance) through molecules. You can consider molecules as quasi one-dimensional quantum systems, with properties that are tunable by chemical synthesis. We have a specific interest in functional molecules, e.g. photochromic switches and spin-crossover compounds.
Second, we study the electronic properties of and charge transport in quasi two-dimensional systems. The most famous of these is undoubtedly graphene--a carbon layer of exactly one atom thick. But there are many more, such as hexagonal BN and MoS2. Remarkably, such layers can be stacked to create novel materials--called Van der Waals materials--with properites that we may be able to tune! To reach that point one day, we are accurately studying the electronic interaction between different layers within Van der Waals materials. We have a unique way to do this, thanks to our low-energy electron microscope (LEEM), that we have adapted to our needs.
Our low-energy electron microscope (LEEM), is called ESCHER. Due to its aberration correction, it has a record lateral resolution of 1.4 nm. Still, our research program aims far beyond pure microscopy. One of our goals has been to make LEEM a key measurement system in condensed matter physics research as a whole and to use it for our research on Van der Waals materials, in particular thin oxides and molecular layers. Therefore we have recently introduced various new techniques:
- LEEM-based potentiometry, by Johannes Jobst
- Angle-resolved reflected-electron spectroscopy (ARRES)
- A novel form of transmission electron microscopy operating at very low energies (eV-TEM), by Daniël Geelen
As a result, 'LEEM' has become an umbrella term for a measurement system that incorporates a plethora of unique techniques that can be used in real-time (also including LEED, dark-field imaging and ARPES).
Sense Jan van der Molen, Full professor
I studied physics in Groningen, the Netherlands, following an exchange year in Olympia, Washington, USA. My Master project, carried out under the supervision of Prof. Teun Klapwijk, focussed on quantum mechanical interference effects in mesoscopic samples.
Next, I moved to the group of Prof. Ronald Griessen at the Vrije Universiteit Amsterdam to investigate so-called switchable mirrors. These metalhydrides, such as YHx, switch from perfect mirrors to transparent windows upon hydrogen uptake. My work focused on both the fundamentals of the metal-insulator transition and the possibility to manipulate the hydrogen concentration in these mirrors electrically (e.g. by electromigration).
In 2002, I joined the group of Prof. Bart van Wees in Groningen, the Netherlands, to start up a new research line in molecular transport. We put considerable effort in creating and optimizing new techniques to investigate single molecules. In a collaboration with Prof. Ben Feringa (Nobel prize in Chemistry, 2016), we focused on light-sensitive, switchable molecular devices (and somewhat on his motors). Furthermore, we explored the exciting field of spin transport through carbon nanotubes.
In 2005, I obtained an NWO talent grant to perform research in the group of Prof. Christian Schönenberger in Basel, Switzerland. After a pleasant and rewarding stay, I moved to Leiden in 2007.
Here, I took up the challenge of building up my own research group. At first my main research focus was on molecular properties, and specifically on molecular charge transport. In November 2009, I received a personal VIDI-grant for my research. Furthermore, I have been part of several national and European research programs.
Presently, my main focus is on the electronic properties of two-dimensional systems. These do include molecular layers, but there is a further emphasis on so-called van der Waals systems. These materials consist of weakly coupled atomic sheets (put) on top of each other. An example is twisted bilayer graphene which features two graphene layers at a small twist angle. Remarkably, at certain twists, this system becomes a superconductor. Quite exciting!
What makes us rather unique is that we study the electronic properties of such systems not only via conductance measurements, but mainly with an unconventional set of ‘eyes’. We make use of a low-energy electron microscope (LEEM) called 'ESCHER' (financed via a large NWO grant) with a lateral resolution of 1.4 nm. It allows us to apply a versatile set of different experiments on the same sample, including home-developed techniques such as LEEP, ARRES and eV-TEM. For this, I have fruitfully been collaborating with Prof. Ruud Tromp (Leiden and IBM Yorktown) and others.
In my opinion, outreach and science communication are important tasks for a scientist. Hence, I try to contribute to society by presenting physics in general and our research in particular. My biggest project here, is also the most unconventional one. Together with Ivo van Vulpen and the Stichting TEGEN-BEELD, I am responsible for the wall formulas in Leiden. The project recently won the NWO Science communication prize. With the money awarded, we will spread the concept to other university cities in the Netherlands and Europe.
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