MESA+ University of Twente
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Tim Tsarfati (promotion date: 26 June 2009)

Surface and interface dynamics in multilayered systems

Promotion date: 26. June 2009

Promotor: Prof.dr. F. Bijkerk

Assistant promotor: R.W.E. van de Kruijs


Reflective multilayer optics for next generation λ=13.5 nm photolithography, show more oxidation when protected by layers of a very noble metal like gold. Less noble metals actually work better.


Non-destructive surface cleaning has been studied and improved by the use of atomic O and H radicals,


Partial diffusion of the surface layer to subsurface interfaces, driven by chemistry.


Nitridation of the interfaces has greatly improved the reflective properties of La/B4C multilayers for λ=6.7 nm.

What were the highlights of your thesis project?

We discovered several chemically driven processes at the multilayer surface and interfaces that can be put to direct use in next generation photolithography. Together with Carl-Zeiss, MoBx was patented as a barrier material to limit the diffusion. We found that the use of different protective surface layers and/or treatment with atomic O and H radicals have the potential to significantly improve the optics lifetime. This also initiated collaboration with research groups abroad.

My invention to use N2+-ions to greatly improve chemical and optical properties of La/B4C multilayer optics for even shorter wavelengths has also been patented.

Were you actually part of Mesa+?

I worked at FOM Plasmaphysics Rijnhuizen at the nanolayer Surfaces and Interfaces (nSI) department. Here in Twente Fred Bijkerk was my supervisor. I visited Mesa+ for a tour and did some measurements there that were essential for my research.

I am really impressed by the apparatus available and the experts’ help for the researchers making use of the equipment.

Could you characterize your thesis project, and what you learned as a researcher?

It is fair to say my work was a steady process, without many abrupt changes but with important insights after long series of measurements. At some moments you have nice results to publish and you are highly motivated to carry on.

I learned that one should follow its intuition at some crucial moments. If you really expect results will arise, you should walk the crossroads. At the same time it is important to stay efficiently focused on the goal you have in mind. Apart from this it is important to really organize your research in detail and keep looking for the right leads and contacts, within the institute and outside, even internationally.

What are your plans for the near future?

A project of my promoter and me has been granted to improve the valorisation of research, institute-wide. This means that I’ll continue research on some promising topics, assist others to find applications for their research.

Along the way, I might get more involved in industry and politics. After many years of academic research, I might then feel the need to switch and broaden my scope of interest, using the skills I developed during my PhD research.