Physicists Control Reactions at the Nanoscale with a Laser

Nanoparticle Field Femtosecond Laser Pulse Tailored Waveform Polarization
A nanoparticle in the femtosecond laser pulse field with specific waveform and polarization. Controlled enhancement of the field in certain nanoscopic regions of the nanoparticle (yellow dots) induces field-selective photochemical reactions of molecules adsorbed on the surface. Imaging the molecular fragments emitted from these regions provides purely optical control of the reaction sites with nanometer resolution. Credits: RMT.Bergues.

Physicists at the Max Planck Institute for Quantum Optics and Ludwig-Maximilians-Universität Munich, in collaboration with Stanford University, have for the first time used laser light to control the location of light-dependent reactions on the surface of nanoparticles.

Controlling strong electromagnetic fields on nanoparticles is key to triggering targeted molecular reactions on their surface.

Such control over strong fields is achieved by laser light. Although the formation and breaking of laser-induced molecular bonds on nanoparticle surfaces has been observed in the past, nanoscopic optical control of surface reactions has not yet been achieved. Dr. Boris Berggues and Prof. Ludwig-Maximilians-Universität (LMU) and Matthias Kling of the Max Planck Institute for Quantum Optics (MPQ) in collaboration with Stanford University have now closed this gap. Physicists have for the first time pinpointed the location of light-induced molecular reactions on the surface of isolated silicon dioxide nanoparticles using ultrashort laser pulses.

There is a lot of activity on the surface of nanoparticles. It settles in molecules, dissolves and changes places. All these trigger chemical reactions, change matter and even cause new materials to appear. Electromagnetic fields can help control events in the nanocosm.

This is now Dr. Ultrafast Electronics and Nanophotonics Group's Dr. Boris Berggues and Prof. Demonstrated by a research team led by Matthias Kling.

To this end, the researchers used powerful, femtosecond laser pulses to create localized fields on the surfaces of the isolated nanoparticles.

A femtosecond is one millionth of a billionth of a second, or 10 of a second.-15 as much as i.

A new technique recently developed in the same group, called reaction nanoscopy, physicists were able to image the reaction site and formation site of molecular fragments on the surface of silica nanoparticles with a resolution of better than 20 nanometers.

Thus, they had to adjust the time delay between two pulses with attosecond accuracy. An attosecond is still a thousand times shorter than a femtosecond. When interacting with this adapted light, the surface of nanoparticles and the molecules adsorbed there were ionized at the targeted sites, causing the molecules to split into different fragments.

The nanoscopic spatial control achievable at even higher resolution was achieved by the scientists by superimposing the fields of two laser pulses with different colors and controlled waveform and polarization.

“Molecular surface reactions on nanoparticles play a fundamental role in nanocatalysis. In particular, they could be the key to clean energy generation through photocatalytic water splitting,” explains Matthias Kling. “Our results also pave the way to monitor photocatalytic reactions on nanoparticles with not only nanometer spatial resolution, but also femtosecond temporal resolution. This will provide detailed insights into surface processes on the natural spatial and temporal scales of their dynamics,” adds Boris Bergues.

source: scitechdaily

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