How ETH Zurich’s Professor of Physics, Rachel Grange, makes use of the optical properties of materials and develops novel devices. A visit to her laboratory.

«Actually, I had chosen physics by sheer chance,» says Rachel Grange and laughs, as we meet with her at her office located at ETH Zurich Hönggerberg campus. The young scientist from the Swiss canton of Valais has been heading the research group for optical nanomaterials at ETH Zurich for the last four years. After her Swiss high school years, she had intended to study mathematics; however, she missed the concrete reference to real practice. So instead, she chose the study programme physics engineering at EPFL and discovered the world of optics and photonics. «I keep being fascinated by the possibility to control complex processes by light alone, without mechanical parts,» she explains her passion for optoelectronics, where optics bonds with semiconductor electronics. By light, which is conducted through materials with specific optical properties, data and energy can be transmitted in great quantities in a minimum of time.

«I keep being fascinated
by the possibility to control
complex processes by light alone.»

This physical finding opens up enormous possibilities of unprecedented technological applications. However, in order for them to function properly, cleverly designed constellations of materials and light must be complied with that are very difficult to produce. Together with her team, Rachel Grange analyses how to enhance both use and control of the optoelectronic properties of certain nanomaterials so as to fit them into smallest devices such as modulators. The suitable materials are known but their optoelectronic potential is by far not yet exhausted. This is the starting line for Rachel Grange and her team. The focus of her research and development work is currently on a group of metal-oxide nanocrystals produced by her team in intricate processes in the cleanroom and which are then placed on chips. Hereby, completely novel «devices» are developed.

The spectrometre on chip

From her office, Rachel Grange leads us down one floor to her laboratory where she wants to show us some of her developments. Marc Reig Escalé, who just finished his PhD thesis, is already expecting us. He brought along the prototype of the latest product of the «Grange workshop» – a spectrometre on a chip, only the size of a fingernail. It is capable of measuring spectra with a range of up to 500 nanometres in high resolution. The revolutionary aspect of this device compared to established spectrometres is that it functions without mechanical drives and parts. «We make use of the electro-optical effects to control the device,» Rachel Grange explains the trick. «We can apply an electric field and therewith control the path of the light. By changing the electric field, we also change the path of the light. Nothing mechanical is needed to adjust the spectrometre.» Spectrometres are often implemented in extremely inaccessible objects such as space telescopes. Most of these devices are still controlled by means of mechanical drives. A drive failure also means an interference with the measurements. The novel spectrometre on chip was partially funded by the Swiss Space Office. The joint pilot project with a company lasted one year. Afterwards, it took another two years to attain good results. «It takes an enormous amount of time and development work in the cleanroom in order to process the material in such a way that it is small and works as a low-loss waveguide,» Rachel Grange explains. Three PhD students were involved in creating the spectrometre. Marc Reig Escalé, one of the three, now works as a postdoc in Rachel Grange’s team and plans to make the prototype ready for the market.

«My three children say,
‹She is a teacher and tinkers
about with light, laser
and powder.›»

The fact that Rachel Grange and her team were able to develop this spectrometre is not least because of the ERC Starting Grant which was awarded to the scientist in 2016. It allowed her to analyse how the optoelectronic potential of nano-oxides could be exploited even more efficiently so that they can produce strong optical signals with little energy. To find the ideal structure of the nano-oxides turned out to be a great challenge. Rachel Grange and her team experimented at length and finally succeeded in producing such materials that ultimately were used in the construction of the spectrometre. It is not easy to explain this highly specialised research and development work to outsiders. Rachel Grange knows this rather well. «When adults ask my three children about their mother’s work at ETH Zurich, they would say, ‹She is a teacher and tinkers about with light, laser and powder.› This actually comes pretty close to what I do,» the researcher says with a wink while leading us to another device in her laboratory.

The automated microscope

We stand in front of a rectangular metal box about the size of a fruit box. «This is the prototype 1 of our microscope PolarNon,» Rachel Grange introduces the device as she lifts the lid off the box. We see an installation made from holdfasts and lenses across which laser light is being transferred and guided onto a slide behind which a camera is installed. «With this microscope we can analyse defects and compositions of metal oxides and semiconductors at a very high resolution. We conduct the light onto the test sample and capture the image with the digital camera. The entire process is automated. In this manner we can process hundreds of test samples in sequence over the course of several hours and look at every individual measurement result on the photos afterwards,» the scientist explains. For the development of PolarNon Rachel Grange and her team again utilised the specific optical properties of certain materials (especially metals, oxides and semiconductors). Successfully so. Their microscope opens up entirely novel possibilities in the quality control of materials used in the electronic, photonics, aviation and aerospace industries. What is more, the device can be applied in the building industry for the purpose of corrosion control. It has a spectacular advantage over the established instruments such as the electron microscope: The test samples can be measured quickly and easily. Unlike required for present devices, they do not need to be effortfully prepared, brought into a vacuum and cooled down to low temperatures in advance. What is more, the material survives the examination; measurements with conventional instruments destruct the material.

«We have the ability to redesign
materials that we use today.
This will result in entirely new
application possibilities.»

The great application potential of this innovative microscope also captured the attention of the EU Research Council. In 2019, Rachel Grange was awarded an ERC Proof of Concept Grant worth 150,000 euros, which allows her to develop a PolarNon prototype 2 ready for the market. The tasks are to find a suitable applicable design for the device, to simplify its operation and to enhance both software and automation. The plan is to found a spin-off company for the commercialisation of PolarNon. The spin-off will sell devices and software and offer a measurement service. Companies and research institutions will be able to have their test samples measured directly on site at the spin-off location.

Dedicated to teaching

Back in her office, we learn about yet another facet of the researcher and developer Rachel Grange – her dedication to teaching. In the autumn of 2019, she teaches the introductory course Physics 1 for first semester physics and mathematics students. «I find it important to get to know the new students right at the beginning und motivate them for physics. They have to overcome great hurdles in order to reach the second and third year.

«I find it important to show
the students the fascination
of physics.»

I find it interesting to prepare them for the challenges ahead and to show them the fascination of physics, even though mechanics and thermodynamics are very effortful and involve a great deal of calculation during the first semester. But I do hope that we will have a lot of fun together, the students and I.» The four hours of basic lectures and the two hours of tutorials per week will take up much of Rachel Grange’s time. But she will certainly make time to further advance her research and development projects with her team and to follow her vision. «We have the ability to completely redesign and change the structures of materials that we use today in our electronic devices as a matter of course. This will result in entirely new application possibilities with great potential for quantum computers and quantum engineering as well. Maybe, even certain semiconductors could be replaced. It will be exciting!» states Rachel Grange as we say goodbye; she, the young, enthusiastic Professor of Physics who actually chose physics by sheer chance all those years ago.