Some of the most important developments marking advances in the 3D printing industry are in the realm of material science, notes 3d Printing Industry. "The more materials we can print, the more useful the technology becomes." As an example, researchers exploring possibilities with strength-to-weight material ratio are coming up with surprisingly strong yet lightweight composites for industries such as aerospace. In February, The Conversation reported that scientists were exploring a bone-like material lighter than water yet as strong as steel. 3D Printing Industry also reported last year of a project funded by the U.S. Army, where researchers at MIT 3D-printed a material that they said was fracture-resistant and resembled human bone. One of the major goals of the study was to develop a meta-material that could be used for engineering purposes. Now a Princeton University team's study has been published in Nano Letters, "3D Printed Quantum Dot Light-Emitting Diodes" which further challenges the limits of 3D printing, taking the technology beyond its plastics and a few biological materials.
"Achieving seamless integration of diverse materials with 3D printing is a significant challenge," Princeton Prof. Michael McAlpine and others on the team wrote, and they sought to take on the challenge with interesting results. They demonstrated seamless interweaving of five different materials: emissive semiconducting inorganic nanoparticles; an elastomeric matrix; organic polymers as charge transport layers; solid and liquid metal leads; and a UV-adhesive transparent substrate layer. They 3D-printed a 2 × 2 × 2 cube of encapsulated LEDs, in which every component of the cube and electronics were 3D printed. The scientists performed feats which suggest that 3D printing "is more versatile than has been demonstrated to date and is capable of integrating many distinct classes of materials."
Their paper reflects ambitious tasks set out by the McAlpine Research Group at Princeton, to focus on 3D-printed bionic nanomaterials. "The ability to three-dimensionally interweave biology with nanomaterials could enable the creation of bionic devices possessing unique geometries, properties, and functionalities, for a variety of fundamental and applied research directions. We focus on developing novel strategies for 3D printing bio- and nanomaterials to enable this vision," according to the group's web site.
Ryan Whitwam, writing in ExtremeTech on Wednesday, went into more detail about their methods and materials. They used a custom 3D printer, as "no off-the-shelf printer was going to do the job," said Whitwam. It took more than six months. The resulting LED printer was fully functional. The bottom layer of each quantum dot LED is composed of silver nanoparticles; on top are two polymer layers that push electrical current up toward the next layer. The top layer is a comparatively ordinary gallium indium that directs the electrons away from the LED, said Whitwam, The printer goes to work; it lays down a single layer of the LED, then moves up to add the next one composed of a different material. When the five-layer stack is complete, it's a functional quantum dot LED.
Commenting on the findings, Sarah Fecht of Popular Science wrote that "the printed LEDs performed on par with the kinds of LEDs that are used in iPhone screens, though they didn't come close to beating the really fancy LEDs that are out there. But by controlling thickness and uniformity of the quantum dots, and by experimenting with different ink formulations, the performance of the printed LEDs could get better."
McAlpine looks forward to making more headway. Up next, McAlpine's team wants to try printing transistors, said Fecht.