1/20/2014 Julia Cation
Written by Julia Cation
The use of standardized units—say, the bricks we use to construct our homes or even the LEGOs® children use to build toy ships and space shuttles—is considered, well, standard in the macro world of ordinary manufacturing and assembly. Standardization is one method we use to accomplish flexible manufacturing: Make a brick in one location, transport it to the construction site, and bind the bricks together using mortar. The ability to do this kind of assembly relies on the mass or gravity of units that allow us to pick up and place each unit onto another. At the scientific level, this is achieved because the unit’s body force is more dominant than its surface force in the macro world.
As manufacturing scales down to the micro and nano level, however, body force becomes negligible, and our inability to control the contact adhesion—one example of the surface force—introduces challenges in micro and nano assembly.
MechSE assistant professor Seok Kim has developed a process—what he’s termed “micro masonry,” inspired by both LEGOs® and traditional masonry—to overcome the challenge of controlling the surface adhesion. His solution involves transfer printing, which is the transfer of solid micro and nano materials from one substrate where they are generated to another substrate where they can be used to build something. He uses transfer printing with a polymer stamp, along with material bonding techniques, to manipulate and assemble small-scale materials. The materials, or microobjects, in this case are silicon, silicon dioxide, or gold—typical examples of semiconductors, dielectrics, and metals.
“We designed a polymer stamp that shows both very high adhesion and very low adhesion to be able to pick up and place our units on the substrate. So we can control the adhesion on this polymer stamp very efficiently,” Kim said. After transfer printing, the materials can be bonded together using rapid thermal annealing.
Kim’s innovative work caught the attention of the National Science Foundation, and he was recently honored with their prestigious Faculty Early Career Development (CAREER) Program award. The NSF CAREER includes a grant for Kim to continue his research for the next five years, through January 2019.
“Through our process, we can build more complex 3D micro and nano devices and structures that cannot be accomplished by traditional monolithic microfabrication techniques. And another advantage is that this manufacturing approach is very additive and flexible. We can build whatever shape we want using a standard unit. That is unique, and I think is what NSF appreciated about our research,” Kim said.
Interestingly, the other aspect of Kim’s research at Illinois focuses on bio-inspired engineering, or biomimetics, which underlies his innovations in adhesion control for micro and nano manufacturing.
“Biomimetics can be used for adhesion control, which is something that can be learned from nature. Gecko and aphid feet in particular have very unique adhesion control strategies, and we’re learning something from them in terms of smart adhesion and multi-scale manipulation. The two areas of my research are definitely interrelated. Without the adhesion control developed through my biomimetics research, we cannot have the micro and nano masonry,” Kim said.
Outside the lab, Kim hopes to transfer the experience and excitement of adhesion science and micro-scale engineering to underrepresented audiences. During the fall semester, he spoke to a group of minority students at Urbana High School about biomimetics. He also plans to build K-12 teaching modules in adhesion science; invite teachers to his lab for research experience; develop courses and curriculums in transfer printing-based microassembly for both undergraduate and graduate levels; and train and mentor underrepresented students at Illinois.
Kim found his interaction with the Urbana High School students extremely rewarding. “I discovered how curious and attentive they are to learn complex engineering concepts when they are explained in terms of ordinary and tangible principles, objects, or creatures. I believe science and engineering education can be more attractive to students when it is taught in such a way that they can see the connections between the course material and their everyday lives,” he said.
Kim’s micro-masonry research was also featured in the October 2013 issue of Nanowerk and in many peer-reviewed journal articles, including the Journal of Micromechanics and Microengineering, Applied Physics Letters, Optics Express, ACS Applied Materials and Interfaces, and the Journal of Microelectromechanical Systems.