Group name: Energy Materials Group, Thin Film Physics Division, Linköping University

Group leader: Associate Professor Per Eklund

Location: Department of Physics, Chemistry and Biology, Linköping University, Sweden


Thin films, big potential

Thin films of oxide and nitride materials are finding use in a wide range of energy technologies from ionic conductors in fuel cells to photovoltaics, thermoelectrics, and capacitors. By their very nature, the chemistry, substrate, and environmental conditions of thin films are influential on their properties and behavior.

The challenge of thin films is to understand their chemistry and interactions with the environment and substrate material during synthesis and application.  New thin-film materials are now being synthesized and tailored to a range of energy-related applications.

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Per Eklund
Per Eklund

Materials Today spoke to Group leader Professor Per Eklund, to find out more about his group...

How long has the group been running?

Research into thin films has been a core activity at Linköping University under the direction of the Thin Film Physics Division since the 1970s. Per Eklund joined the faculty at Linköping University as an assistant professor in 2008 and has been running the Energy Materials Group since 2009.

How large is your group?

The Thin Film Physics Division as a whole comprises around 65 members organized into six groups. Eklund’s Energy Materials Group typically comprises 8-10 members, with a mixture of postdocs, PhD and MSc students. Team members are predominantly experimental materials scientists.

What are the major themes of research in your lab?

Hard coatings have been the focus of research activities within the Thin Film Physics Division at Linköping University since the 1970s, especially in relation to cutting tools, where Sweden has a number of key industrial players. “There was and still is a major need to understand how thin-film coatings are grown and behave in these kinds of applications,” explains Eklund. “But now we are taking thin-film hard coatings to a new level.”

Eklund’s group is primarily focused on thin-film materials for energy applications. One of those interests is MAX phases, a class of ternary carbide and nitride ceramics that naturally form layered or ‘nano-laminated’ structures. The unusual structure of MAX phases gives them peculiar properties: resistance to oxidation and corrosion, elastically stiff but able to deform plastically, and high thermal and electrical conductivity. This unique combination of properties makes MAX phases interesting as structural materials for nuclear applications or as thin-film contacts in high-power electronics.

Thermoelectric thin films for energy harvesting and heat conversion applications make up another strand of the Energy Materials Group’s activities. The group’s interests also encompass thin films based on stabilized zirconia and ceria, which have potential in solid oxide fuel cells.

“Energy is one of the biggest challenges facing our society,” explains Eklund, “and one of the most crucial issues within that area is the quality and abundance of materials used. It is an industrial problem that hinges on improved materials.”

While the emphasis of the group is on fundamental and application-related aspects of thin-film energy materials, material synthesis using a wide range of sputter-deposition techniques and theoretical studies is integral to the effort. The group’s work is inspired by applications, often working on materials that are of interest to industry, says Eklund. 

How and why did you come to work in these areas?

Eklund became interested in materials science during his masters’ degree, which led him to pursue a PhD in thin-film physics (2007). He followed his PhD with a postdoc at the Interdisciplinary Nanoscience Center (iNano) at the University of Arhus in Denmark. Before rejoining Linköping University, Eklund was a visiting researcher at CNRS in Paris and he is now also a visiting professor at the University of Poitiers in France.

SEM images and EDX mapping of 4H-SiC substrates coated with Ti at 960 °C: (a) 10 min deposition, showing plate-like Ti3SiC2 grains; (b) 10 min deposition, showing a faceted Ti5Si3 grain; and (c) 10 min deposition, showing the EDX data of the C Ka peak. Surface morphology of samples deposited for (d) 10 min, (e) 30 min and (f) 150 min.
SEM images and EDX mapping of 4H-SiC substrates coated with Ti at 960 °C: (a) 10 min deposition, showing plate-like Ti3SiC2 grains; (b) 10 min deposition, showing a faceted Ti5Si3 grain; and (c) 10 min deposition, showing the EDX data of the C Ka peak. Surface morphology of samples deposited for (d) 10 min, (e) 30 min and (f) 150 min.

What are the highlights of your most recent work?

This year Eklund’s group demonstrated a novel two-step sputtering/annealing method for the growth of highly textured thermoelectric Ca3Co4O9 thin films. CaO-CoO thin films can be deposited by reactive rf-magnetron co-sputtering from Ca and Co targets. The underlying growth mechanism, which is a thermally activated phase transformation from CaO-CoO into Ca3Co4O9, was revealed using a combination of synchrotron-based 2D X-ray diffraction, ex-situ annealing experiments, and standard lab-based X-ray diffraction analyses.

The lab has also recently developed a single-step process for growing ohmic Ti3SiC2 on 4H-SiC using sputter-deposition of Ti at 960°C, based on the Ti-SiC solid-state reaction. In an improvement on multistep-processes with deposition followed by rapid thermal annealing, the as-deposited contacts using the new process are ohmic. The new process offers the possibility of direct synthesis of oxygen-barrier capping layers before exposure to air, which could improve contact stability in high-temperature and high-power devices.

What facilities and equipment does your lab have?

Linköping University has some of the best chemical and structural characterization facilities for thin films. There are also large sputter and arc deposition facilities, some adapted for research-scale as well as industrial-scale work.

Do you have a favorite piece of kit/equipment?

“My favorite sputter deposition chamber is called Laura!” says Eklund. “We have a naming system for all our equipment from the Macahan family in the 1970s TV series How the West Was Won or characters from Nordic mythology,” he explains.

What is your key to running a successful lab?

“I believe that the key is to grasp that running a successful lab is more than just doing science,” says Eklund. “It is like running a small business, you have to be aware of everything from team management to financing to the legal aspects of research. But science is at the heart of it all.”

How do you plan to develop the lab in the future?

“My group has had a major expansion over the last few years and it is now key to consolidate,” says Eklund. “In scientific terms, we want to build on our knowledge of thermoelectric thin films and apply it in other areas.”

Eklund adds that is for his coworkers to come up with the ‘next big thing’. “We don’t know what it is now,” he says, but he strives to create and nurture an environment in which his group members have the space and confidence to explore the possibilities.

“As a materials research lab as a whole, the Thin Film Physics Division has been instrumental in setting the standard for undertaking really ground-breaking work,” he says. “We now have to drive each other forward through collaboration and competition.”

Key publications

  • B. Paul, J. L. Schroeder, S. Kerdsongpanya, N. Van Nong, N. Schell, D. Ostach, J. Lu, J. Birch, P. Eklund. Mechanism of formation of the thermoelectric layered cobaltate Ca3Co4O9 by annealing CaO-CoO thin films. Advanced Electronic Materials (2015) 1 (3), DOI: 10.1002/aelm.201400022
  • S. Kerdsongpanya, N. Van Nong, N. Pryds, A. Žukauskaite, J. Jensen, J. Birch, J. Lu, L. Hultman, G. Wingqvist, P. Eklund. Anomalously high thermoelectric power factor in epitaxial ScN thin films.  Applied Physics Letters (2011) 99, 232113,
  • H. Fashandi, M. Andersson, J. Eriksson, J. Lu, K. Smedfors, C.-M. Zetterling, A. Lloyd Spetz, P. Eklund. Single-step synthesis of Ti3SiC2 ohmic contacts on 4H-SiC by sputter deposition of Ti. Scripta Materialia (2015) 99, 53-56, DOI: 10.1016/j.scriptamat.2014.11.025
  • P. Eklund, M. Beckers, U. Jansson, H. Högsberg, L. Hultman. The Mn+1AXn phases: materials science and thin-film processing. Thin Solid Films (2010) 518, 1851-1878, DOI: 10.1016/j.tsf.2009.07.184
  • S. SØnderby, P. L. Popa, J. Lu, B. H. Christensen, K. P. Almtoft, L. P. Nielsen, P. Eklund. Strontium diffusion in magnetron sputtered gadolinia-doped ceria thin film barrier coatings for solid oxide fuel cells. Advanced Energy Materials (2013), DOI: 10.1002/aenm.201300003
  • J. Halim, M. R. Lukatskaya, K. M. Cook, J. Lu, C. R. Smith, L.-A. Näslund, S. J. May, L. Hultman, Y. Gogotsi, P. Eklund, M. W. Barsoum. Transparent conductive two-dimensional titanium carbide epitaxial thin films. Chem. Mater. (2014) 26, 2374-2381, DOI: 10.1021/cm500641a

Further information