PhD in the Spotlight: Wieteke de Boer
On 30 January, Wieteke de Boer (1983) will defend her doctoral thesis at the UvA, presenting the finding that silicon nanocrystals are capable of emitting visible light. De Boer did her research at the Institute of Physics. Her discovery has various applications, including the production of more efficient solar panels.
What was your most important finding?
‘We discovered that very small particles of silicon emit visible light. In our study, we cut silicon into smaller and smaller pieces until we were left with nanocrystals. A nanocrystal is tiny, with a diameter of around one-thousandth the thickness of a hair. It was already known that bulk silicon – that is, larger pieces of silicon – emit infrared radiation, but that light is so weak that it’s undetectable by the human eye. Our experiments showed that silicon nanocrystals radiate stronger and, moreover, visible light. This has to do with what we call quantum effects, which are absent in larger pieces of silicon. Another property of these nanocrystals is that they can “cut” single high energy (typically UV) photons, (i.e. “light particles”), to produce two (or more) lower-energy photons.’
What’s so great about that?
‘Using this technology, you can make solar panels more efficient. Solar panels are made of silicon and convert light into electricity. But in this conversion a lot of excessive heat is generated, which you don’t want. We found that silicon nanocrystals generate less heat than bulk silicon when they absorb a photon. So if you were to implement silicon nanocrystals into solar panels, less heat will be produced and more electricity. On top of that, nanocrystals are simple and inexpensive to make. Hopefully we’ll be able use them to produce LED light bulbs and lasers before too long. At the moment, we cannot produce nanocrystals that are uniform in size. When you have nanocrystals of different sizes, however, they all emit a different colour of light. You couldn’t use that in lasers.’
What was the most interesting aspect of your doctoral research?
‘What I liked best was the diversity of the work. I love retreating to the lab on my own for a week and conducting experiments. And supervising and teaching students was also great. Perhaps the thing I most enjoyed was how quickly I could join in the discussion at conferences. I could just walk up to another researcher and say, “what you’re saying isn’t quite right” and then discuss it with them. I’m sure it helped that my supervisor, Tom Gregorkiewizc, is a well-known and respected physicist. Plus the fact that I was able to publish an article in Nature Nanotechnology midway through my doctorate. Naturally there were some downsides, too. I had a hard time with the total absence of deadlines. When you work for a company, you have to deliver your product to the client at a set time. Here it was up to me when I delivered my work.’
Are you going to continue researching silicon nanocrystals?
‘I think it’s time for a different subject. I found this research to be very worthy because it has to do with solar panels, but I’d like to shift my focus now to biomedicine. Another doctoral student is going to pick up my silicon research. I’ve been offered a postdoc position in New York, where I’d be studying the molecular transport of medicines. I might do that, but I’d consider working at a company as well.’
Author: Carin Röst