Catalyst of Synergies

The new Nano-Institute will be officially opened today. When did the idea first appear?

Jochen Feldmann : The idea of integrating research efforts in the field of energy conversion was first proposed a decade ago. We had often discussed the possibility with colleagues in the nanosciences in the Munich area. We concluded that it would require new structures, new laboratories, recruitment of creative research groups and room to accommodate them – in our archi-tecturally attractive, but cramped and outdated buildings between Amalienstrasse and Schellingstrasse, space was already scarce. The idea really began to take shape when the LMU decided to create a new Chair in Energy Conversion. At around the same time, the Bavarian Government called for project proposals designed to promote the transition to sustainable energy sources. That initiative led to the establishment of a research network called Solar Technologies Go Hybrid (SolTech) in 2012. Since then, ‘key laboratories’ located in five Bavarian cities have collaborated with one another. In the context of the initiative, the funding needed for the construction of a new research center in Würzburg and the Nano-Institute at LMU was also made available.

So the SolTech Network provided the initial impulse for the Nano-Institute?

SolTech not only strengthened the research infrastructure, it also provided excellent opportunities for young scientists in the field. The collaboration between the key labs at LMU and the Technical University of Munich has resulted in an array of joint projects and a steady stream of publications. This then con-vinced the DFG’s review panel to fund the e-conversion Excellence Cluster in energy research. It is noteworthy that this Cluster consists largely of university-based research groups.

How would you describe the concept behind the new Institute?

There are essentially two ways to build nanostructures for the conversion of solar energy. The first involves chemical synthesis and exploits various modes of self-organization to assemble the functional structures. This ‘bottom-up approach’ is the one used in my group. The alternative, ‘top-down’, route is nanofabrication. Here, the functional structures are successively made on a substrate by means of lithography. This is the strategy adopted by my new colleague Stefan Maier, who holds the second aca-demic chair at the Nano-Institute. It basically mimics the mode of production of commercial semiconductor chips. At the interface between these methodologies, entirely new opportunities emerge for the control or enhancement of optical, electrical and catalytic processes. This is where the philosophy behind the Nano-Institute comes to the fore.

Your own research focuses on the use of solar radiation to split water into hydrogen and oxygen. What makes this photocatalyt-ic approach so attractive for sustainable energy production?

Electricity produced by wind turbines and solar cells can now be electrolytically converted into chemical energy, in the form of hydrogen or methane gas. This offers a CO₂-neutral route to an easily storable fuel. Photocatalysis enables us to produce hydrogen and methane directly – without having to generate electricity as an intermediate. We use light to split water or reduce CO₂.

Where does artificial photosynthesis as a technical process now stand?

It is often asserted that Mother Nature knows best, but in terms of efficiency this is not true. In order to survive, green plants do not need to convert radiant energy into biochemical energy with high efficiency. The efficiency of natural photosynthesis is less than 1%. Genetic modification of plants such as corn can increase this value to 5-8%. Systems based on simple solar cells and electrolysis now reach values of around 9%. The figure for photocatalysis is currently at 3%.

You are currently experimenting with catalysts based on semi-conductor nanoparticles. What are these particles made of?

We work with chemically synthesized semiconductor nanocrys-tals, which have a number of interesting features. By taking advantage of quantum effects, one can tune their spectral sensitivity. Moreover, in relation to their volumes, nanocrystals have very large surface areas, which is a tremendous advantage for catalytic processes. In addition, they are easy to modify, so that one can attach various chemical groups to alter their catalytic properties.

The interaction of nanosystems with light is the common thread that connects all of your research efforts. – What other applications do you envisage for these systems, apart from their use in energy conversion processes?

Tailormade nanosystems have a wide range of applications in areas such as data transmission, sensors and medical diagnostics.

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Novel optoelectronic components show great promise for applications like displays and lighting. Luminescent materials, such as thin films made of perovskite nanoparticles, are cheap and are well suited for use in LEDs. How long will it take to bring these devices onto the market?

Semiconductor nanoparticles are already used in modern dis-plays to maximize the range of colors available. But they contain toxic substances and are not fully integrated into electronic circuits, as they need to be stimulated optically. Developing nanocrystals that can be electronically controlled is a far more complicated undertaking. Much effort is being put into this task around the world, and we are working together with industrial partners on a related project funded by the Federal Ministry for Education and Research.

Your colleague Stefan Maier works on similar problems, using very different methods. How do the two strategies complement one another?

Stefan Maier’s research focuses on modifying the interactions of light with nanostructures. We, on the other hand, concentrate on controlling the temporal behavior of the electronic excitations generated by such interactions. In the case of solar energy conversion, both processes are eminently important. Indeed, this is a prime example of the synergies that the Nano-Institute allows us to exploit.

With this specific conceptual framework, can the Nano-Institute itself act as a catalyst for the field?

With its clear focus, the Nano-Institute can bring its own partic-ular brand of innovation to bear on crucial questions relating to sustainable energy conversion processes. And the fact that our groups can now work together in a very well equipped setting has already attracted international attention.

In addition to your work as a physicist, you took on the task of overseeing the construction of the new Institute. How did you prepare for this task?

Let me put it this way: Experimental physicists are constantly confronted with the deficiencies of the premises in which their laboratories are housed. And the available options are not always equally satisfactory for all the experiments that one would like to do. In comparison, supervising the construction of a new building was a liberating experience.

What particular challenges did the planners of the Nano-Institute face?

The building was explicitly intended to house an interdisciplinary group of researchers. So we needed a diverse set of facilities – laboratories for chemical syntheses, for modern electron microscopy and laser spectroscopy, and workstations for photocatalytic experiments. And a highly complex cleanroom for nanofabrication was a must. Finally, the unique architecture itself stimulates communication and promotes creative interactions.

What steps did you take acquire the necessary supervisory skills?

It probably helped that I had already overseen the building of my own house, and that I grew up in the Sauerland, in a family whose members not only designed but built the houses they lived in. When you are your own building supervisor, you keep a constant eye on how the work is going and check that everything conforms to the idea you originally had in mind. The scale was very different, but my own building experiences certainly sharpened my eye for possible problems.

What phase of the planning required the highest degree of foresight?

One major problem was that, when the shell of the building was completed, we did not yet know who would be appointed to the second academic chair. So concrete planning for the second department had to be restricted to what the architects and the Office of Public Works deemed absolutely necessary. But we did have a clear idea of the synergies the building was intended to facilitate.

Some of your experiments require the use of helium. Organizing a steady supply of the gas also turned out to pose a number of challenges. Can you explain why?

Liquid helium is used as a coolant when temperatures near absolute zero are required. Conventional helium-based cooling systems, such as those we had in the old building between Amalienstrasse and Schellingstrasse, are extremely expensive and require complex recycling apparati. For example, we had to capture as much as possible of the helium gas that is unavoidably formed in such experiments. This then had to be transported to the Walther Meissner Institute in Garching for liquidation, and was returned to us by truck. In the new Institute, we no longer have to worry about such complex logistics. We now have so-called cryostats with closed circulation systems, which in principle work like the cooling system in a freezer. During the planning phase, we chose a technology that was still under development. This method is now competitive and works with minimal amounts of helium.

How will the new building accelerate the pace of discovery?

It provides us with a range of novel technological capabilities, which allow us to test ideas that we could not otherwise put into practice. In addition, the installation of an existing experimental set-up in a new building provides a unique opportunity to improve the performance. So, essentially every apparatus undergoes a kind of rejuvenation under these conditions.

Prof. Dr. Jochen Feldmann holds the Chair in Photonics and Optoelectronics at LMU and supervised the construction of the Nano-Institute.