For all its hype, nanotechnology is still a lot of 'nano' and just a little 'technology' according to Dutch plasma physicist Erwin Kessels. That’s something he would like to change. And he is already making headway in the area of nanomanufacturing, focussing particularly on nanoelectronics and renewable technologies such as solar cells and batteries.
“You can often read articles in the newspaper about a new discovery in nanotechnology, such as a transistor made of nanotubes or graphene,” Erwin says. “A wonderful result, which researchers may be able to achieve in one of a hundred attempts. To produce something on an industrial scale, however, you need to succeed 99 out of 100 times. It requires a lot, both technically and economically, to do that.”
Implementing new innovations in a cost-effective manner – what he calls ‘the art of making’ – plays a big role in Erwin’s research at Eindhoven University of Technology (TU/e) in The Netherlands. As a professor at the Department of Applied Physics, he leads a group of almost 50 people working to translate discoveries in the lab into industrial processes – ‘from lab to fab’ (fabrication, that is). Techniques developed by the group have found their way into companies such as Roth & Rau, Q-Cells, Oxford Instruments and FEI Company.
Their innovations can be labelled by the term nanomanufacturing – the development, adjustment, manipulation and assembly of materials with dimensions at the nanoscale (one nanometre is one-billionth of a metre). To give this mind-bogglingly small magnitude some perspective: at 2.5 nanometres in diameter, a strand of your DNA is measured at the nanoscale, whereas a strand of your hair – 50,000 to 100,000 nanometres thick – is way off scale.
Working with atomic layers and plasmas
Erwin was always fascinated by the ‘infinitely’ small – how atoms build up matter and how technology depends on controlling matter at the atomic level. This led him to pursue a research degree in applied physics. After earning his PhD at TU/e, he worked for a couple of years at universities in the USA and Germany. Returning to TU/e in 2002, he spent the next few years pioneering technologies underpinning the synthesis and use of ultrathin material films, such as those used in electronic semiconductor devices and solar cells.
An important technique in Erwin’s toolbox is called atomic layer deposition (ALD). It involves building up thin films – atomic layer by atomic layer – through chemical reactions at the surface. The technique can create very precise, complex structures at the nanoscale.
About ten years ago, Erwin made a breakthrough in the field by combining ALD with plasma technology. Plasma – the fourth fundamental state of matter, besides solid, liquid and gas – has unique properties.
Erwin and members of his group demonstrated that this high-energy state offers great advantages in manufacturing. Plasma energy changes important surface properties of materials and – when applied to ALD – enables thin films to be layered at much lower temperatures, for example. This is important for temperature-sensitive materials.
“People now associate the term plasma-assisted ALD with Eindhoven,” Erwin says with pride. “It started with two PhD candidates, and now more than half of my group is working on this.”
Making solar cells more efficient
Being able to identify and take advantage of such opportunities is one of the group’s strengths, according to Erwin. Another is unravelling the underlying mechanisms of a technique – down to the atomic and molecular level.
“We don’t actually create devices, such as solar cells, ourselves. That’s very complex for a university research group, certainly if you want to remain at the leading edge,” Erwin says.
“Our strength lies in establishing the fundamental processes, and then we collaborate with others – the leaders in the field – to make devices. We are an ideal partner to work with.”
One of the group’s greatest successes is a good example of this. Back in 2006, they discovered that aluminium oxide – then mainly used in nanoelectronics – has material properties that are excellent for ‘passivation’ of solar cell surfaces. Passivation makes a surface passive, in other words resistant to reactions, for instance corrosion. For solar cells, surface passivation means lower electrical loss and greater efficiency.
At the time, the perfect candidate for passivation of solar cell surfaces appeared to be a thin layer of silicon oxide. But manufacturing of this material requires high temperatures and elaborate treatment – neither of which would suit commercial production of solar cells.
“We then coated solar cells (using ALD) with a layer of aluminium oxide, which increased the efficiency by as much as one per cent. That is really a lot,” Erwin enthuses. “This led to a great deal of interest from companies, including the Eindhoven OTB Solar (now Roth & Rau BV) and the German company Q-cells, which now use alumina films on their new solar cells.”
Exploring the future of nanoelectronics
For many years, Erwin has chipped away at the idea of using ALD to create nanocontacts for future nanoelectronics. “For example, the components of computer chips are currently made from silicon by etching away very fine pieces of material,” Erwin says. “But this is reaching its limits. The ideal thing would be to make nanoscale structures locally where we want, in a kind of ‘bottom-up’ process. The advantage is that you can make even more precise small patterns – and continue to develop ever better electronics.”
In collaboration with FEI, a company that makes electron microscopes, Erwin’s group has developed a technique to create very tiny patterns using an electron beam and then build up material on the pattern using ALD.
The aim is to use the technique for creating transistors of carbon nanotubes or 2D materials such as graphene – hailed for years as ‘wonder materials’ for many applications. “It’s very difficult and we’re still not there, but I think we can pull it off,” Erwin says.
Success through serendipity
While Erwin’s research benefits from a large number of industry collaborations, he is also experiencing some negative consequences of the new Dutch innovation policy to invest more in innovation within businesses and less in basic scientific research. As a result, many funding sources have started to disappear.
“Companies get tax benefits from investing in our research. But to get a tax benefit, they need to make a profit – meaning that small businesses often don’t benefit from the scheme. Funding has therefore become much harder to come by, and trying something new is very difficult,” Erwin explains.
“It means you can only harvest low-hanging fruit rather than invest in research where you have more freedom to discover something completely new,” he adds, stressing the importance of funding to maintain fundamental research at universities.
As his group has demonstrated, the greatest successes are sometimes achieved through serendipity – emerging from projects set out to investigate something completely different. Paraphrasing Picasso, he says: “The secret of art lies not in what you seek, but in what you find.”
– Adapted from TU/e blog