Controlling the strong electromagnetic field on nanoparticles is the key to trigger the reaction of target molecules on their surfaces. This control of strong field is realized by laser. Although scientists have observed the formation and fracture of molecular bonds on the surface of nanoparticles induced by laser in the past, the nano optical control of surface reaction has not been realized. An international team of scientists led by Dr Boris Bergues of the University of Munich (LMU) and Professor Matthias Kling, working with Stanford University, has now filled this gap. For the first time, physicists have used ultrashort laser pulses to determine the location of light induced molecular reactions on the surface of isolated silica nanoparticles.
There are many activities on the surface of nanoparticles. Molecules dock, dissolve, and change their position. All these have promoted chemical reactions, changed substances, and even produced new materials. Electromagnetic fields can help control events in the nano universe. The ultrafast electronics and nanophotonics research group led by Dr. Boris Bergues and Professor Matthias Kling has now proved this. To this end, researchers use powerful femtosecond laser pulses to generate local fields on the surface of isolated nanoparticles.
Using the so-called reactive nano mirror, a new technology recently developed by the same team, physicists can image the reaction sites on the surface of silica nanoparticles and the birthplace of molecular fragments - with a resolution better than 20 nm. By superimposing two laser pulse fields with different colors and controlling the waveform and polarization, scientists have realized nano spatial control, even at higher resolution. Therefore, they must set the time delay between the two pulses with attosecond accuracy. When interacting with this customized light, the surface of nanoparticles and the molecules adsorbed there are ionized at the target position, resulting in the dissociation of molecules into different fragments.
"Molecular surface reactions on nanoparticles play a fundamental role in nano catalysis. They may be a key to clean energy production, especially through photocatalytic water separation," Matthias Kling explained. "Our results also pave the way for tracking photocatalytic reactions on nanoparticles, with not only nanoscale spatial resolution, but also femtosecond time resolution." Boris Bergues added: "this will provide detailed insights into its dynamic surface processes on natural spatial and temporal scales."
Scientists predict that this promising new method can be applied to many complex and isolated nanostructured materials.