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Mark Huijben (promotion date: 28 April 2006)

Interface engineering for oxide electronics;
tuning electronic properties by atomically controlled growth.

Promotion Date: 28 April 2006

Mark Huijben

The main part of my thesis involved the growth of materials. Using pulsed laser deposition we ‘grow’ extremely thin layers of a few nanometres on a crystalline substrate.
If you can control this process, you can control the electronic properties of the layers you are making, tuning them from insulating to conducting or semiconducting or even superconducting. In this process we use a piece of material with the right properties, called ‘target’, in our case containing an oxide, and ablate it with a laser inside a controllable vacuum system. Since the temperature in the material is locally increased above 20.000
oC you get an explosion of material (a plasma) that eventually deposits in a very thin layer on a prepared substrate.
We can make materials with either various conducting or magnetic properties, and with a precision on the atomic scale.

What was your thesis about?

The main part of my thesis involved the growth of materials. Using pulsed laser deposition we ‘grow’ extremely thin layers of a few nanometres on a crystalline substrate. If you can control this process, you can control the electronic properties of the layers you are making, tuning them from insulating to conducting or semiconducting or even superconducting. In this process we use a piece of material with the right properties, called ‘target’, in our case containing an oxide, and ablate it with a laser inside a controllable vacuum system. Since the temperature in the material is locally increased above 20.000 oC you get an explosion of material (a plasma) that eventually deposits in a very thin layer on a prepared substrate. We can make materials with either various conducting or magnetic properties, and with a precision on the atomic scale. This growth technology is very useful to investigate material properties. However, it is not used in industry, because the deposited ultrathin layers are only homogeneous in an area of 5 mm x 5 mm.In our group we can build these layers with atomic precision and we can check what we are doing by a direct analysis.

So the precision of the process is the subject of your thesis ?

No, I investigated a variety of thin films that you can make, changing them from hardly conducting to superconducting by adding just a few atoms or varying the thickness of the layer. Philips and FOM, participants in the ‘Laboratorium zonder muren’ project, were interested in the development of new materials that vary from insulating to conducting (a switching property) on a very small scale.

And did you find the ultimate material?

In the second part of my thesis I concentrated on materials that have a possible strong switching capacity. So both parts are comprehensive studies into these materials, but they cannot be applied in industry as yet. It is still very fundamental, with extremely interesting phenomena at the interface of two thin films. Hopefully there will be a publication on the subject shortly.

In what journal?

Perhaps in Nature Materials. They were very positive about our experiments and the results.

What did you like best of your research?

Being involved in the entire process; I enjoyed both the making of the layers and studying them. You also have the control on the smallest scale possible and that is absolutely fascinating. I found that when I attended conferences people who have worked longer in this field than I have done, were also very interested.

Where have you been?

Thiox (Thin Films for Novel Oxide Devices) organizes a lot of meetings where people in this field meet, mainly PhD’s. Outside Europe there is the WOE conference, either in Europe, USA or Japan. I have been to the US twice.

What didn’t you like?

I can’t say that there was anything I didn’t like. I could do my own research and follow my own ideas, I had good contacts with my supervisors and they kept me on the track, I could go to conferences, had good contacts with other groups, no, on the whole the going was good.

What are you going to do next?

I am not completely sure yet, but 1,5 months ago I got a job offer from Berkeley, California.

It is a postdoc position for two years with a professor working in the field of this oxide thin layers. That is fantastic of course, and I would jump at the chance, but I am only going if my girlfriend can come as well and if she can do some work there. But there is a fair chance of that as well.

For the summary of the thesis, click here.

Voor de samenvatting van het proefschrift, click hier.