Inside the pocket where that energy is trapped, a chemical reaction can take place, permanently altering the internal structure of the material. The process has previously been exploited for 2D and simple 3D metal nanofabrication.
"Normally, when people use femtosecond lasers in fabrication, they're creating a wood pile structure: something stacked on something else, being supported by something else," explains Mazur.
"If you want to make an array of silver dots, however, they can't float in space."
In the new process, Vora, Mazur, and their colleagues combine silver nitrate, water, and a polymer called PVP into a solution, which they bake onto a glass slide. The solid polymer then contains ions of silver, which are photoreduced by the tightly focused laser pulses to form nanocrystals of silver metal, supported by the polymer matrix.
The need for this particular combination of chemicals, at the right concentrations, was not obvious in prior work. Researchers sometimes combine silver nitrate with water in order to create silver nanostructures, but that process provides no structural support for a 3D pattern. Another process combines silver nitrate, water, PVP, and ethanol, but the samples darken and degrade very quickly by producing silver crystals throughout the polymer.
With ethanol, the reaction happens too quickly and uncontrollably. Mazur's team needed nanoscale crystals, precisely distributed and isolated in 3D.
"It was just a question of removing that reagent, and we got lucky," Vora says. "What was most surprising about it was how simple it is. It was a matter of using less."
|Contact: Caroline Perry|