Liquid Crystals



 Bi-directional dielectrophoresis (BDEP)

Usually, dielectrophoresis can actuate particles along one direction. However, it is possible to achieve bidirectional dielectrophoresis using anisotropic property of liquid crystallines without using a complicated cell structure. In addition, we can control the shape, size, position and volume of liquid droplets using biphasic liquid crystals. We also try to implement display devices using the bidirectional DEP.





  -S. D. Kim, B. Lee, S. W. Kang, J. K. Song*, "Dielectrophoretic manipulation of the mixture of isotropic and nematic liquid", Nature Communications, 6, 7936 (2015)



 Cholesteric liquid crystals (CLCs)

Selective molecular transfer among living cells or organs is involved in all vital processes. However, the artificial molecule transfer technology, an innovative tool in optical devices and materials science, is still at an early stage of development. We can control in situ molecular transfer between the heterogeneous liquid crystal (LC) microdroplets in an LC emulsion. In addition, chiral dopants can be transferred between nematic and cholesteric LC droplets, which are the receiver and supplier of chiral molecules, respectively, and a continuous phase with tunable solubility acts as the switchable transfer channel. These enable the topological evolution and structural color.



2D Materials



 Liquid crystal of 2D materials

Graphene Oxides (GO) have an extremely high Kerr coefficient, and one can control the GO alignment with extremely low electric fields. Using this property, we aim to develop an extremely low power display device using graphene-oxide dispersions.





  -T. Z. Shen, S. H. Hong, and J. K. Song *, “Electro-optical switching of graphene-oxide liquid crystals with an extremely large Kerr coefficient” , Nature Materials, 13 394-399 (2014)



 Photonic crystal of 2D materials

A few lyotropic 2D materials exhibits Bragg reflection due to periodic arrangement within solvent. By controlling the 2D material concentration and alignment, one can obtain colorful drawings.





  -T. Z. Shen, S. H. Hong, B. Lee and J. K. Song*, "Bottom-up and top-down manipulations for multi-order photonic crystallinity in a graphene-oxide colloid.", NPG Asia Materials, 8, e296 (2016)




Quantum-Dot LED (QD-LED) 



 Colour-tuneable QD-LED

Most colour display devices are composed of R/G/B sub-pixels spatially separated in a 'side-by-side' geometry. This layout of sub-pixels is an essential technology in display devices to reproduce a wide range of colours, but it has clear limitations such as the reductions in resolution and optical efficiency. An innovative approach to overcome these limitations is to implement colour-tuneable pixel technology. We research unique device structures that can reproduce various colours in a single pixel.





   -S. H. Song, S. J. Park, T. J. Bae, K. M. Jung, W. H. Park, Y. S. Kim, Q. Yan, S. S. Kim*, and J. K. Song*, "All-solution-processed colour-tuneable quantum-dot light-emitting diode driven by AC signal", Nanoscale, 12(32), 17020 (2020)



 Performance Improvement

Quantum dot is a promising material, in which bandgap depends on its size. It emits highly pure color, which is one of the most important factors in display devices. However, it remains several critical drawbacks such as quantum efficiency and lifetime. We research new device structures, materials, and fabrication process that can improve the efficiency and lifetime of QD-LED.





   -D. H. Song, S. H. Song, T. Z. Shen, J. S. Lee, W. H. Park, J. M. Kim, Y. S. Kim, W. J. Yu, S. S. Kim*, and J. K. Song*, "Reduced Graphene Oxide as Efficient Hole Injection Layer for Quantum-Dot Light-Emitting Diodes", Physica Status Solidi A, 215(23), 1800517 (2018)




Energy Harvesting



 Triboelectric Nanogenerator (TENG)

We are facing increasing challenges of diminishing fossil fuels and increasing the energy demand. There is an increasing interest in seeking new methods of energy generation not only large scale energy but also in micro scale energy. We are investigating new methods of harvesting micro scale energy by mainly using colloid and water.





  -K. R. Wijewardhana, T. Z. Shen, E. N. Jayaweera, A. Shahzad, and J. K. Song*, "Hybrid nanogenerator and enhancement of water-solid contact electrification using triboelectric charge supplier", Nano Energy, 52, 402-407, (2018)