Extrusion-based additive manufacturing is the most fundamental form of 3D printing, relying entirely on the rheological properties of the printing ink. Therefore, the formulation of inks with tailored rheological behavior and functional performance is essential for fabricating architectured materials that exhibit high electrical, thermal, and mechanical properties. To address this need, our research focuses on the development of organic-free, inorganic particle-based colloidal inks, alongside the optimization of compatible extrusion-based printing processes.

Viscoelastic ink formulation
For the dispensing printing method, the ink must exhibit non-Newtonian and viscoelastic behavior, which facilitates reliable extrusion flow through the nozzle to prevent clogging, and high elasticity to avoid the collapse of the 3D structure. These inks are often paired with polymer-based organic binders to give rise to viscoelastic behavior. However, functional properties of these composite-type inks with polymer additives are strictly limited due to the intrinsically limited electrical properties of organic binders. To overcome this limitation, we have developed molecular chalcogenidometallate-based (ChaM) ions, anions containing metal atoms ligated with chalcogens. We design the rheological properties of TE ink through surface engineering such as ChaM ion addition, doping, etc.

Extrusion-based 3D printing process
Our group developed an extrusion-based 3D printing process for viscoelastic inks that enables the fabrication of functional materials into 3D shapes. In this printing process, ink is dispensed out of the nozzle directly to the substrate by pneumatic control. The printing process enables precise micro-scale 3D printing by reducing the particle size in the ink or the nozzle size while controlling the process parameters. This developed 3D printing process allows for increased freedom in designing materials and devices.

The design and optimization of 3D architectures are critical for enhancing structure-induced functionalities, thereby improving performance in real-world applications. Such strategies enable engineers to maximize energy efficiency, minimize losses, and tailor thermoelectric systems to accommodate diverse boundary conditions. To this end, we employ finite element modeling (FEM) to design materials and devices with target-specific properties for applications in thermoelectrics and electronics. This effort is complemented by topology and geometric optimization techniques. Furthermore, we are establishing new design principles grounded in fundamental multiphysics, which not only deepen scientific understanding but also enable transformative, real-world solutions for clean and efficient energy technologies.

Solution-based processing has attracted huge attention for its advantages of large-scale and cost-effective fabrication of various applications. We are synthesizing novel all-inorganic inks comprising soluble inorganic precursors or nanocrystals for the fabrication of thin films with tailored composition, structure, and properties. The materials of interest include semiconducting metal chalcogenides and phosphorus, metallic Ag, Cu, and 2D MXenes, applied to semiconductor and memory devices.

Nano 3D printing is a technology included in the world’s 50 innovation technology in Frost & Sullivan 2017 report. Nano 3D printing could play an important role in micro-, and nano- scale 3D fabrication such as MEMS. We are developing novel nanocrystal inks and processing for designing nano-scale 3D architecture with tailored structure and properties. We design stimuli-responsive, assembly-programmable nanocrystal building blocks through chemical engineering of surfaces and interfaces. To this end, we are exploring fundamental chemistry and physics governing the assembly of nanocrystal building blocks under various external stimuli. Architectured 3D matters will find potential applications of 3D electronics, sensors, catalysts as well as a platform of lithography.