Photo: Thorkild Amdi Christensen

Two new DTU doctors

Tuesday 21 Jun 16

Peter Munk

Photo: Thorkild Amdi Christensen
Larval fish ecology – adaptations and physical linkages.
When: Doctoral defence at 2 p.m. on 1 July in Building 101, Meeting Room 1.

Yunzhong Chen

Photo: Thorkild Amdi Christensen
Title: Emergent Material Science and Functionalities at Atomically-Engineered Oxide Interfaces
When: Doctoral defence at 2 p.m. on 8 July in Building 101, Meeting Room 1.

Two new doctoral theses from DTU are set to take us on a journey across the seven seas to examine fish larvae, and into the laboratory to push microscopic materials to their limits.

This summer, two DTU researchers will reach the pinnacle of academic achievement in the field of engineering and technical natural sciences research when they defend their doctoral theses prior to receiving their doctorates in technical science, along with the prestigious title of Doctor Technices (Dr. Techn.).

The ‘doctors in waiting’ are Senior Research Scientist Peter Munk from DTU Aqua, who has built up fully 35 years of research into fish larvae, and Senior Researcher Yunzhong Chen from DTU Energy, who is constantly challenging the limits of how far electronics can be miniaturized.

The ecology of fish larvae

Peter Munk has taken part in a great many voyages to destinations including Greenland, the North Sea and the Sargasso Sea, where he has examined the growing conditions for fish larvae, across fish species, physical conditions and climate zones.

The growing conditions for larvae are crucial to the future of fish populations. For example, the larvae have to have access to the right food in the right quantities, and the physical conditions must suit them from an evolutionary perspective. Changes to these conditions may have serious consequences for the entire fish population.

“At an early stage of my career, I realized that the physical conditions—the ‘hydrography’—for the larvae had to play a significant role in their growth and development, and were actually crucial in defining where the fish breeding areas were located. It is clear that fronts, where hot water meets cold water, for example, or where fresh water meets saltwater, provide the best conditions for the larvae,” relates Peter Munk, who has examined larvae both in huge populations in their natural marine surroundings, and at individual level in the laboratory, where it is possible to regulate aspects such as turbulence, light intensity and access to food.

“It is not one huge, mixed ‘soup’ out there in the seas. Even in the middle of the Sargasso Sea, where the eel grow up, there are clearly defined fronts that release energy, and where the larvae and the plankton they have to live off, are held back rather than allowed to spread freely. Finally, the fronts generate a specific current that leads the larvae to the places where they are to mature into adult fish,” he says, before going on to explain that the larvae are particularly well suited to these conditions and risk being adversely affected by the variations that arise.

Photo: Thorkild Amdi Christensen

This is not necessarily a problem for the various fish populations, which, during the slow grind of evolution, have proved time and time again that they can adapt. However, variations from one year to the next, which fishermen often experience, may become an issue —especially given that intensive fishing may amplify the effects of the variations, when fewer fish are given the opportunity to mature and breed.

Atom-thin film with a host of functions

Since Yunzhong Chen came to Denmark—and to DTU—seven years ago, he has been working to create materials that can be used, for example, to make electronic components even smaller than they are today. Oxides are the key.

We are familiar with such compounds in the form of water (hydrogen oxide), carbon dioxide (CO2) and rust on iron (iron oxide), for example. However, Yuzhong Chen primarily works with the synthetically created strontium titanate (SrTiO3)—the same material as is used to make artificial diamonds—and uses lasers to cultivate it in films so thin that it is almost possible to call them two-dimensional. The finished film is no more than 0.2 mm thick, i.e. the thickness of a single atom.

One of the applications of such films is as interfaces in computer systems. This is where information is exchanged, so the capacity of the film to conduct current, for instance, is crucial in determining how efficiently the system functions. That is why researchers have been working flat out for 40 years to identify new materials for interfaces to make them even better. 

It is most common to use semi-conductors today, but Yunzhong Chen is working to develop improved interfaces based on ceramics or super-conductors, where the current can flow freely, without any resistance at all.

Photo: Thorkild Amdi Christensen

“My research has to do with designing new materials and coming as close to the limits of their optimal performance as is possible,” says Yunzhong Chen, who explains that a gas of electrons forms in the interfaces between two oxides, where one may be strontium titanate, and that a number of phenomena—including magnetism, superconductivity, ionic conductivity and ferroelectricity—appear in this gas.

“Using oxides allows us to create much smaller components, while simultaneously having the opportunity to combine many more functions in a single unit. Depending on how you design them, the components can be used for transistors in quantum computers, as catalysts in fuel cells, in sensors, in solar cells, or in data storage units.