An Ultrafast Glimpse of Nanoscopic Aerosols

An intense laser pulse hits a nanoparticle made of glass and interacts with molecules on its surface. Subsequently, as depicted, hydrogen ions may be detached, and the yield of such reactions can be measured by reaction nanoscopy. (Source: A. Gelin)

Many natural phenomena begin with a minuscule shift in the states of atoms or molecules, triggered by radiation. One such process has now been elucidated by a team led by Matthias Kling and Boris Bergues at the Laboratory for Atto­second Physics (LAP), which is jointly run by Ludwig-Maximilians Univer­sität (LMU) and the Max Planck Institute of Quantum Optics (MPQ). The group studied how molecules that were attached to the surface of nano­particles responded to irra­diation with light. Light-induced molecular processes on nano­particles play an important role in atmo­spheric chemistry, and can ultimately influence our climate.

The nanocosmos is constantly in motion. All natural processes are ulti­mately determined by the interplay between radiation and matter. Light strikes particles and induces reactions. By altering the energy states of electrons, it reshuffles atoms and causes molecules to be reconfigured. These processes are signi­ficantly acce­lerated when the reactants are absorbed on the surface of nanoparticles in the atmosphere. This phenomenon is crucial for the photo­chemistry of the atmosphere and thus has an impact on our health and climate. One of the light-driven molecular processes that takes place on aerosols has now been inves­tigated in detail by researchers led by Matthias Kling and Boris Bergues at the Laboratory for Atto­second Physics. The group has developed a new method – reaction nanoscopy – which makes it possible to study elemental physico­chemical transitions on solid interfaces. They have now used it to charac­terize the reaction of ethanol with water molecules on the surface of glass nano­particles under the influence of high-intensity laser light.

The researchers irradiated the spherical particles with ultra­short laser pulses, each lasting for a few femto­seconds. With the aid of reaction nanoscopy, they were able to record this ultrashort interaction in three dimensions with nanometer resolution. “We have observed the detachment and acce­leration of hydrogen ions from molecules on the surface of nano­particles. The ability to do so forms the basis for the high spatial resolution of our imaging technique,” explains Boris Bergues. “Because the tech­nology enables us to determine the exact position on the nano­particle with the highest reaction yield, we can trace reactions of molecules adsorbed on the surface of aerosols with high spatial resolution“, adds Matthias Kling.

Such processes are ubi­quitous, especially in the fields of atmo­spheric physics and astro­chemistry. For example, light in our atmo­sphere interacts with aerosols and their attached molecules, trig­gering subsequent reactions that may be important for the development of our climate. In the universe, similar chemical processes occur on the tiniest dust grains under extreme conditions. Here, molecules are formed and undergo reactions – a process that could also contribute to the synthesis of biomolecules. In the short term, the results obtained with the new ana­lytical procedure by the Munich laser physicists may provide useful insights, especially in the field of atmo­spheric chemistry. Even­tually, they could lead to a better under­standing of reactions on aerosols, and might even point to ways of slowing the rate or mitigating the effects of climate change. (Source: MPQ)

Reference: P. Rupp et al.: Few-cycle laser driven reaction nanoscopy on aerosolized silica nanoparticles, Nat. Commun. 10, 4655 (2019); DOI: 10.1038/s41467-019-12580-0

Link: Ultrafast Imaging and Nanophotonics, Max-Planck-Institute for Quantum Optics, Munich, Germany

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