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, Associate professor
I studied physics in Groningen, the Netherlands, following an exchange year in Olympia, Washington, USA. My Master project, carried out under Prof. Teun Klapwijk, focused 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, we focused on light-sensitive, switchable molecular devices. 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 successful and pleasant stay, I moved to Leiden in 2007.
In Leiden, I took up the challenge of building up my own research group. My research has since concentrated on molecular properties, and specifically on molecular charge transport. My fascination for this field stems from both my deep interest in quantum charge transport phenomena and my affection with chemistry. I am convinced that our science efforts can reach the highest levels if we are able to effectively combine both these fields. Hence, I am actively participating in collaborations and am organizing workshops to bridge ‘cultural’ differences between both fields. In November 2009, I received a personal VIDI-grant for research in this direction. Furthermore, I am excited to be part of a FOM-program on quantum interference in molecular charge transport, and of the Delft-Leiden Nanofront program, which both kicked off in 2013.
To also study layer growth, molecular assembly and transport with a different set of ‘eyes’, we make use of a low-energy electron microscope (LEEM). I am the project leader of 'ESCHER' for which we obtained a large 'NWO-groot onderzoek' grant. We have optimized aberration-corrected LEEM/PEEM to a world-record value of 1.4 nm laterally. To see if we can go even further, we are also investigating the theoretical limits of LEEM and electron microscopy in general. Within this ESCHER project, I collaborate with Prof. Ruud Tromp (Leiden and IBM Yorktown) and others.