LAURA LEAY: Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on the hot topics in materials research. My name is Laura Leay. 3D printing of ceramics is a hot topic right now. Also known as additive manufacturing, 3D printing allows for increasingly smaller or complex structures to be created as techniques improve. New research into the 3D printing of silica glass could pave the way for future advances in the printing of ceramics. Methods for 3D printing of such structures involve high temperatures, produced by using either a laser or a furnace to obtain temperatures of around 1000°C, often at high pressure. The latest research has shown that such high temperatures are not required; printing of silica glass is possible at around just 200°C if you introduce photochemistry.
JERRY QI: We use a kind of chemistry that actually exists for a while; people knew about it since back to maybe the 90s—1990s or early 2000s. It’s an interesting approach. So basically you can convert a polymer—a special elastomer—into a ceramic. And people had done a little bit of work on that but not really on the 3D printing. So we kind of utilized that approach, combine that with 3D printing, we can generate parts with complicated shapes.
LAURA LEAY: That was Professor Jerry Qi from Georgia Institute of Technology. After using two-photon polymerization to cross-link poly-dimethylsiloxane, his team then used deep UV to convert the polymer into silica glass. The deep UV irradiation is carried out in an oxygen-rich atmosphere. The UV light converts the oxygen to ozone which then goes on to react with the polymer, prompting the formation of silica glass. Structure of several tens of micrometers in size can be fabricated with a resolution of a few hundred nanometers. Using deep UV light, the process of converting the polymer to glass and removing the excess carbon takes around 5 hours, much shorter than the 20 to 50 hours required for traditional techniques.
JERRY QI: The property change is also dramatic because when we print the sample, the stiffness of the sample is like your skin: very, very soft. The modulus is about 100 kPa. But when we shine the light for about 3 or 4 hours, the modulus becomes like bone. So the modulus goes to about 30 GPa. So you can see the modulus changes almost five orders of magnitude, so it’s a really dramatic change yet we can also maintain the shape so it’s a kind of amazing process.
LAURA LEAY: Several structures were printed including lattices, the Georgia Tech Buzz mascot, and a smooth miniature lens with a diameter of 150 μm. The role that the ozone plays is intriguing. Dr. Mingzhe Li, who is a post-doc at Georgia Institute of Technology, explains that several factors have to be taken into account when using the deep UV, or DOE, photochemical reaction.
MINGZHE LI: Because we want to fully convert these 3D structures we need to facilitate this process. So we want to find out the optimal conditions for this DUV conversion process. We have done a lot of parameter studies: the flow rate of oxygen and also the environment, the experimental set-up, the distance between the DUV light and the sample so that we find this optimal condition for this conversion without proper structural design. Basically after the DUV conversion you will crack the samples because of the shrinkage, so we have to carefully design the structure to be printed on the substrate.
LAURA LEAY: The micro-lens could have uses in optical devices and the team also produced a structure with a hollow microfluidic channel with a diameter of 30 μm. Such tiny silica-based structures have applications in medical devices, optoelectronics, semiconductors, and more. To realize the full potential of this new fabrication technique, the team will continue to refine it and determine the exact role that the ozone plays. The structures they have made so far have a density below that of conventionally made glass components and a low modulus, properties that are not favorable for applications that involve load-carrying. The current achievement represents a significant learning curve that the team will build on.
JERRY QI: It took us two years almost. One big challenge is how you can actually retain the structure without damage of the structure. Initially when we started, we printed a thin film and just shine the light then you see promising results but you see lots of small pieces of glass on the floor. And then we gradually learned more: we know we need a substrate to support and then you can retain the structure.
MINGZHE LI: All the experiments are quite challenging because the samples are so small. I think the most exciting part is the low temperature we’ve achieved which is like, only 200°C which is far below the conventional method of about 1000°C.
LAURA LEAY: The low temperature is particularly beneficial for in situ printing of microelectronics where semiconductors cannot withstand the higher temperature of conventional methods. The team is working on printing larger structures and will use a light with higher intensity than the one they’re currently using as a first step to refine their new fabrication process. This work was published in a recent issue of Science Advances. My name is Laura Leay from the Materials Research Society. For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin. Don’t miss the next episode of MRS Bulletin Materials News – subscribe now. Thank you for listening.