KTH Royal Institute of Technology
A team of Swedish researchers has developed a new 3D-printing method for silica glasses that simplifies an energy-intensive, complex process. As a proof of concept, they 3D-printed the world’s smallest wineglass (made of actual glass) with a rim smaller than the width of one human hair, as well as an optical resonator for fiber optic telecommunications systems—one of several potential applications for 3D-printed silica glass components. The researchers described their method in a paper published in Nature Communications.
“The backbone of the Internet is based on optical fibers made of glass,” said co-author Kristinn Gylfason of the KTH Royal Institute of Technology in Stockholm. In these systems, filters and couplers of all types are required. Our technique can 3D print them. This opens many new possibilities.”
The authors state that silica (amorphous silicon oxide) is proving to be incredibly challenging to 3D-print, especially on the microscale. However, several methods have been developed to help overcome this problem, including stereolithography. Direct ink writing and digital light processing. Even these methods have been limited to feature sizes of a few tens micrometers. One study from 2021 reported nanoscale resolution.
All of these processes use silica-nanoparticle-loaded organic mixtures. The printed structures, therefore, are composites containing many organic materials. They lack the desirable properties of silica glasses (i.e. chemical and thermal stability, hardness, transparency across a broad spectrum of wavelengths). It requires an extra sintering step at high temperatures of around 1,200° Celsius (2,192° F) for several hours to remove the organic residues and achieve those properties. The energy-intensive additional step severely limits possible applications because only substrates that can tolerate such high temperatures can used. Some methods require that 3D structures be assembled into a finished form. This is difficult at the micrometer level.
Gylfason developed a new technique to 3D print silica glasses. et all. Hydrogen silsesquioxane, an inorganic substance similar to silica, can be patterned using electron beams and ion lasers. The method is able to achieve a high level of precision because it doesn’t rely on organic molecules as photoinitiators, binders or other materials that remain on the surface like stereolithography. The method relies upon the direct crosslinking of inorganic HSQ.
The process consists of three steps. They first drop-cast the HSQ in organic solvents onto a substrate. Then, using a sub-picosecond focused laser beam, they trace a 3D design. The HSQ that has not been exposed is then dissolved using a potassium hydroxide. Raman spectroscopy revealed all the features of silica in the microstructures.
There were also traces left of carbon and hydrogen. For applications requiring a more pure silica glass, the residual organics can be removed by annealing the structures at 900° Celsius (1,652° F)—an extra step, granted, but at a much lower temperature than the usual extra sintering step. The spectrum of the structures then matched a commercially available fused silica substrate. Although annealing 3D microstructures may cause them shrink or distort the authors found the maximum shrinkage of their silica glasses structures to be around 6 %, compared with between 16 % and 56 % for glass objects created using stereolithography or direct ink writing.
They also created a proof-of concept tiny wine glass, an optical resonator and a KTH logo. The authors believe their method can be used to create customized lenses for micro-robots and medical devices. The coating of 3D-printed structures with nanodiamonds and ferrous nanoparticles can be used to further tailor the properties of the microstructures for hybrid quantum photonics, or magnetically remove the motion control.
“The concerns when integrating 3D printing methods are usually different for different applications,” said co-author Po-Han Huang, a graduate student at KTH. “Even though optimization of our method is still required for different applications, we believe our method presents an important and necessary breakthrough for 3D glass printing to be used in practical scenarios.”
Nature Communications 2023. 10.1038/s41467-023-38996-3 (About DOIs).