Sublime Designs: Discovery of 3D nanostructures that occur in liquid crystal sublimation
With the funding from National Research Foundation’s General Researcher Support Program’s for outstanding young researchers, Korean researchers became the first in the world to develop sublimation and recombination phenomena of liquid crystal materials.The research team led by Professor Dong Ki Yoon (Graduate School of Nanoscience & Technology, KAIST) developed a method that can sketch nanostructures inside liquid crystals by using the process of sublimation (solid to vapor). This method enables precision 3D nanopatterning by simple temperature control and is expected to contribute in developing next-generation devices.
Until now, the only method to directly observe the interior of a nanostructure was to break up the sample itself. Samples of liquid crystals have been observed by transmission electron microscope after instantaneously breaking them up at -150℃, lower than the water-crystallizing temperature, coating with platinum sideways, and using a carbon film as support. However, because a liquid crystal material can actually flow like rubber dispersion, it was difficult to watch by freezing and breaking up its internal structure and was known to be virtually impossible to observe at the nanometer level.
To solve this problem, Professor Yoon used molecular recombination in accompanying sublimation.
Inspiration from the process of sublimation
Before this study, the researchers measured by heat analysis (DSC) the temperature at which liquid crystal melts, and at which change to liquid crystal occurs, and confirmed by observing mass change according to temperatures that sublimation occurs at 120℃, much lower than 190℃ at which liquid crystal melts. Also, when liquid crystals drop forming a toric focal conic structure are placed on a certain substrate, the surface is holed like dimples if observed from above and its cross section shows a tangent structure at nano-size level because of the phenomenon that floor side molecules lie flat and air side molecules stand upright.
The team conducted full-fledged research by using such defect structures, recognizing that sublimation peels out toric focal conic structure one layer at a time, and found that at a certain pressure, part of the flying molecules return and combine with the original, toric focal conic structure molecules. This enabled them to peel out the toric focal conic structure of liquid crystals one layer at a time and at the same time to observe the internal structure formed by soft materials (e.g., liquid crystal) through the new 3D nanostructure formed.
Possible groundbreaking development in photo-electronic materials
The result of this study is significant in that it enables 3D nano-patterning through nanostructure, shaped in 3D, instead of simply observing the internal structure of various soft materials. The reason is that use of 3D nano-patterning decisively reduces process stages and time in the manufacture of nano devices currently required by the semiconductor industry (e.g., vertical transistors.)
Existing nano device manufacturing mainly uses 2-D etching processes and thus requires more processes, but 3D nano-patterning technique enables single-process manufacturingfor some devices. Professor Dong Ki Yoon explained, “Generally, the reason why liquid crystals are used a lot in displays such as mobile phones, tablet PCs, and TVs, is that they are very sensitive to electromagnetic fields… If such characteristics of liquid crystals are combined with our results, groundbreaking, new photo-electronic materials can be developed.”
Devoted to conquering defect liquid crystal’s structures
Professor Yoon, who first began to research liquid crystals when attracted by their beautiful structure and strong practicality, plans to focus on solving defect structures, considered by both liquid crystal-related academics and industry as a future task.
Professor Yoon said, “There is little research in Korea whatsoever going on to solve liquid crystal’s defects, so in-depth convergence research of related fields is a must.” He went on, “Failure to solve liquid crystal defects means that future display applications will be just a daydream.”
Professor Yoon, the first Korean recipient of the International Liquid Crystal Society’s “Michi Nakata Award,” presented a new method based on his research (3D nano-patterning technique utilizing a new method) focusing on researching the platforms and systems that can conquer the defective structure, a fundamental problem in liquid crystal application, based on his achievement.