The darling element of electronic devices, silicon can be found in all mobile phones and computers in the form of thin wafers. However, when fabricated into nanoparticles, it has a new set of applications that range from photonics to magnetic resonance imaging.
“The typical method of producing nanoparticles in solution, or nanoparticle colloids as we call them, is by chemical synthesis. However, this method isn't yet well developed for silicon nanoparticles of the required nanoparticle dimensions of a few hundred nanometers,” said Arseniy Kuznetsov, Head of the Advanced Optical Technologies department at A*STAR’s Institute of Materials Research and Engineering (IMRE).
Currently, laser ablation is how most laboratories produce silicon nanoparticle colloids, but a major drawback is poor control over the resultant nanoparticle sizes. To overcome this challenge, Kuznetsov's team, in collaboration with scientists at the Chalmers University of Technology, Sweden, devised a multistep process combining two techniques—hole-mask colloidal lithography (HCL) and laser-induced transfer.
Put simply, HCL allows for nanodisks of very uniform size and shape to be formed. This step serves as a size control mechanism. The nanodisks are then melted with a laser over a droplet of water, forming spherical nanoparticles due to the surface tension as liquid silicon contacts the water droplet. Using their technique, the researchers were able to fabricate nanoparticles with a mean diameter of 137 nm and standard deviation of less than three percent.
Next, using a low energy laser as an ‘optical tweezer,’ they were able to trap and position individual silicon nanoparticles within a ten-microliter droplet near a solid surface. When the laser power was abruptly increased, the nanoparticles were printed onto the solid surface.
“Our work represents one of the first demonstrations of controllable manipulation of silicon nanoparticles in solution, applied to the printing of controllable structures onto a substrate. It demonstrates how optical forces can be used to create functional 3D silicon nanoparticle structures,” he said.
Kuznetsov does not rule out exploring the use of silicon nanoparticles in biomedical applications. “Silicon nanoparticles are known for their strong fluorescence and biocompatibility, which means they could be used in bioimaging, drug delivery and cancer treatment,” he added.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering (IMRE).