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A great stir around light

Whether solar cells, sensors or storage elements: materials with completely new properties could push forward future areas from renewable energies to life sciences and quantum computers. Physicist Nahid Talebi wants to develop the special microscopes needed for this.

© Nahid Talebi

Nahid Talebi has designed and fabricated complex hole patterns (a) to create tiny nano sieves of gold foil. When electrons hit it, fascinating light vortices (b, simulation) are created that can improve the performance of electron microscopes.

With conventional light microscopes, like those we know from biology lessons, surfaces and structures of a few micrometres can be examined quite well. However they cannot show how atoms and electrons move inside materials at the nanoscale. Yet these nanoscale processes are central to fundamentally understanding the properties of materials and defining them in a targeted manner. Scientists can use special electron microscopes to observe the ultra-short processes "live" and thus gain direct insights into quantum physics. To do this, they bundle electrons into a beam, accelerate them and direct them at a material sample. The way the electrons pass through the sample or are reflected by it allows conclusions to be drawn about the processes in the material and its properties. "Due to the quantum effects, a moving electron is a wave and its wavelength is much shorter than that of visible light. This means that a much better resolution can be achieved than with a conventional light microscope," says Nahid Talebi, Professor of Nanooptics at the Institute of Experimental and Applied Physics. As part of her "NanoBeam" project, funded by the European Union, she wants to develop electron microscopy even further by combining theoretical and practical approaches.

"About ten years ago, the late Nobel laureate Ahmed Zewail evolved electron-beam science into another stage when he combined its electron beam with a laser light beam," Talebi explains. This combination is so interesting because the electrons interact with the photons. Among other things, this leads to an exchange of energy between electrons and photons and thus to a higher temporal resolution of the microscope to show ultra-short processes of a few femtoseconds. "But we are still at the beginning here; especially when it comes to designing materials with highly specialised properties," explains Talebi. This is because the complex interactions of electrons and light are not fully understood yet. Theoretical simulations could help, but they are very time-consuming, which is why only rough approximations are often used.

On the one hand, Talebi has developed a simulation method to describe the interaction processes as precisely as possible by showing them as a film in real time. On the other hand, she is working on components with a special nanostructure to further improve the electron microscopes. In doing so, she makes use of the fact that the interactions not only change the behaviour of the electrons, but also of the light. The light particles can form vortices that could further improve the time resolution of electron microscopes.

In order to generate these light vortices in a targeted manner, Talebi, together with colleagues from Stuttgart and Amsterdam, developed a tiny "photon sieve" that can be inserted into the microscopes. They drilled tiny holes of 50 to 200 nanometres in a thin metallic film of gold. Talebi calculated their sizes and distances exactly, because the desired light vortices only occur with a certain hole pattern. "When the electron beam hits the photon sieve, it excites free electrons inside to vibrate, which spread out in waves on the gold surface, so-called plasmons. When they hit the holes, the desired vortices are created," says the Iranian-born physicist. After completing her doctorate at the University of Tehran in 2011, Talebi worked as an Alexander von Humboldt Fellow in Stuttgart before coming to Kiel in 2019. Here, she appreciates the maritime atmosphere and that it is easy to travel by bike and enjoy the landscape. “For my work, one of the things that appeals to me is the proximity to DESY." At the Deutsche Elektronen-Synchrotron in Hamburg, which is considered the leading accelerator centre in Germany, she wants to characterize the structures she is planning to design and has fabricated special x-ray photon sources to further pursue the combination of electron and laser light and to make advances in electron microscopy.

Author: Julia Siekmann

Supporting research talents for Europe

With the "ERC Starting Grant" funding measure, the European Research Council (ERC) supports projects by talented young scientists so that they can build up their own research group. Nahid Talebi's project "NanoBeam" has been funded with 1.5 million euros since 2019. The aim is to further develop microscopy methods in order to better investigate ultra-short processes inside materials. (jus)