Laser Process Allows Precision Design of Nanospheres

A laser-based technique for creating light-scattering silicon nanospheres could have applications in medicine and sensor technology.

Molten silicon forms nanoparticles which, due to surface tension, fly onto a receiver substrate. Images courtesy of Laser Zentrum Hannover.

The Nanophotonics Group of the Laser Zentrum Hannover (LZH) used femtosecond laser pulses to irradiate thin layers of silicon. The surface tension of the molten silicon created perfectly round, 165-nm particles, which were then captured on a substrate.

Silicon nanoparticles are particularly interesting, the researchers said, because they not only scatter visible light but also electrical and magnetic fields. Other materials interact almost exclusively with the electrical field.

After printing, the fabricated silicon particles are in an amorphous phase and can be transformed into the crystalline phase with a second laser pulse. In their work, the resonance-scattering spectrum of the crystalline silicon was blue shifted compared to the amorphous silicon, and exhibited a peak intensity that was three times greater, the researchers said.

Laser-printed silicon nanoparticles in amorphous (red) and crystalline (yellow) phases.

“This novel method is the first that allows for both fabricating and precisely depositing nanoparticles of a certain size,” said professor Dr. Boris Chichkov, head of the LZH Nanotechnology Department. “In this respect, our method is far superior to chemical processes which can produce large quantities of nanoparticles, but not place them at the desired position.”

The method can generate 2-D or 3-D particle structures, such as nanoantennas, nanolasers and metamaterials, the team noted.

The research was carried out under projects funded by the German Research Foundation. The work is published in Nature Communications (doi: 10.1038/ncomms4402).