Maarten Nijland

Anisotropy in Patterned Perovskite Oxides

Promotion date: November 26.

Promotors: Prof. dr. ir. André ten Elshof and Prof. dr. ing. Guus Rijnders

Assistant Promotor: Dr. ir. Gert Jan Koster

Artificial patterning is catching up with nature, heading towards the ability to shape functional materials with control in the atomic limit. The intention of this thesis is to contribute to the ambitious objective to hold on to the unprecedented control of film growth that pulsed laser deposition offers, while at the same time reach for similar control in directions normal to that of growth.

Different routes are discussed to pattern epitaxial heterostructures on micrometer length scales and below. Sacrificial micro- and nanostructures are discussed to pattern thin films. These sacrificial patterns can be introduced either before or during PLD and selectively be removed afterwards.

In the second part an entirely new concepts is presented, to pattern the crystallographic orientation of a thin film rather than the material itself. Seed layers of inorganic nanosheets can be used to realize heteroepitaxial growth on substrates that do not allow for epitaxy by themselves. By patterning nanosheets with different lattice parameters, the strain, orientation, and properties of perovskite thin films can be locally tailored.

Was your PhD research fundamental in nature or was it also aimed towards applications in the future?

The intention of the research was fairly fundamental. Nevertheless, in the background, applications did certainly play an important role.

Combining PLD techniques with patterning techniques opens up new fabrication routes, which may possibly lead to new and robust functionalized materials. For example, we can now do without crystalline substrates to obtain controlled epitaxial growth, using inorganic nanosheets on silicon based substrates instead. The technique of patterning epitaxial perovskites, makes use of soft lithographic techniques. Here micro- and nanostructures form a new kind of starting point to fabricate epitaxial heterostructures.

It is interesting to explore these new routes and think of new combinations, with or without PLD, delivering high quality nanostructures which are widely available and preferably cheaper to fabricate.

Did you pass some distinctive milestones during your PhD project before reaching the final results at the end?

I think a PhD process is a series of little milestones and half-expected, sometimes unexpected, intermediate results.

For example, the growth on nanosheets requires extra treatment steps in order to control the process as a whole. While examining intermediate results some parts of the sample did show a much better quality than on other parts. One learns to cherish these moments as you are challenged highly by them, knowing some parameters might lead to qualitatively better results and better process control.

We also developed a method to pattern a structure on a single crystalline substrate, to protect parts of this substrate during pulsed laser deposition and be able to form epitaxial micro- and nanostructures. Because these substrates are expensive, we first tried this on much cheaper silicon substrates. When this was working, we tried to do the same trick on the expensive substrates, but that didn't work initially. Then, we decided to spin coat a thin polymer layer on all of our substrates. This led to a much better adhesion of the surface. This was an unexpected result we encountered during the process.

The most personal milestone was me publicizing in Advanced Functional Materials. This was one of the goals I set myself right from the start of the project. I am proud to have reached this goal, turning my PhD thesis work into a success. Also I published in ACS Applied Materials & Interfaces. Another article is still under preparation.

What skills have you developed over the last four years?

In order to come to good publications, it is essential to work on various levels at the same time. From experiments one can find data from which to extract relevant results later on. These findings you have to report for yourself carefully, in order to form a coherent story that is interesting for fellow researchers in the field.

In the beginning I was too much focused on studying literature as an isolated activity. New ideas didn’t come to my mind anymore. After starting first experiments new ideas enfolded leading to nice results.

What are your future plans?

I would like to go and work in industry as I am ready for new challenges now. Although the academic atmosphere does suit me well, I decided not to pursuit a career in academics. In that case I would have to choose a post-doc position abroad, as a logical next step. Having a family now, my hope is to find an interesting job in research at a regional company. As a chemical engineer with quite some experience now in physics as well, I think I have a reasonable chance to find one.

Which strengths are important for Mesa+ to preserve in the future?

I attended the Mesa+ colloquia quite regularly. These meetings were interesting in its own right and did lead to some fresh, new ideas on some occasions. Also the Mesa+ Day was inspiring. It is easy to make collaborations work from there, as the colleagues are literally to be found next-door. The Nanolab and the surrounding labs give access to a wide variety of techniques.

Also I enjoyed the informal working atmosphere throughout Mesa+. As a researcher and PhD you are free to run into the office of a colleague, be it a professor, fellow-student or cleanroom technician. I reckon Mesa+ should cherish this atmosphere into the far future.