A groundbreaking study by a Swedish-German team has tracked ultrafast electron dynamics with unparalleled precision, opening new avenues for nanomaterials and solar cell research. When electrons move through molecules or semiconductors, their time scales are incredibly short. A Swedish-German research team, including physicist Dr. Jan Vogelsang of the University of Oldenburg, has made significant progress in better understanding these ultrafast processes: The researchers used laser pulses to track the dynamics of electrons released from the surface of zinc oxide crystals with a spatial resolution of nanometers and a temporal resolution that was previously unattainable.

Schematic of the experimental setup: Attosecond pulses (purple) eject electrons (green) from the crystal surface. A photoemission electron microscope (the tapered instrument at the top) examines the rapid movement of electrons. Image source: Edited by Jan Vogelsang

Through these experiments, the team demonstrated the applicability of this method to better understand electron behavior in nanomaterials and new solar cells, among other applications. Researchers at Lund University, including Professor Anne Lehuillier, one of last year's three Nobel Prize winners in physics, participated in the study, which was published in the scientific journal Advanced Physics Research.

Looking inside the vacuum chamber of a Lund light emission electron microscope: The research team used similar equipment to study electrons released from samples using laser pulses. Image source: Jan Vogelsang

In the experiment, the team combined a special type of electron microscope called light emission electron microscopy (PEEM) with attosecond physics techniques. The scientists used very short-duration light pulses to excite the electrons and record their subsequent behavior. "The process is much like a flash in photography capturing fast motion. Attoseconds are very short, only a billionth of a second," explains Vogelsang.

As the team reports, similar experiments so far have not been able to achieve the temporal precision required to track the electrons' movement. These tiny elementary particles move much faster than the much larger and heavier nuclei of atoms. However, in this study, the scientists were able to combine two technically demanding techniques, photoemission electron microscopy and attosecond microscopy, without compromising spatial or temporal resolution. "We can now finally use attosecond pulses to study the interaction of light and matter at the atomic level and in nanostructures in detail," Vogelsang said.

Technological Breakthroughs and Future Research

One factor in this progress was the use of a light source capable of producing a large number of attosecond pulse flashes per second - in this case, 200,000 light pulses per second. Each flash releases an average of one electron from the crystal surface, allowing researchers to study their behavior without affecting each other. The more pulses generated per second, the easier it is to extract small measurement signals from the data set.

Anne L'Huillier's laboratory at Lund University in Sweden, where the experiments for this study were conducted, is one of the few research laboratories in the world that has the technical equipment necessary for such experiments. Vogelsang, who worked as a postdoctoral researcher at Lund University from 2017 to 2020, is currently establishing a similar experimental laboratory at the University of Oldenburg. In the future, the two teams plan to continue research exploring the behavior of electrons in a variety of materials and nanostructures.

Compiled source: ScitechDaily