Kyung Tae Kang

Silver inkjet printing with control of surface energy and substrate temperature

The characteristics of silver inkjet printing were intensively investigated with control of surface energy and substrate temperature. A fluorocarbon (FC) film was spincoated on a silicon (Si) substrate to obtain a hydrophobic surface, and an ultraviolet (UV)/ozone (O3) treatment was performed to control the surface wettability of the FC film surface. To characterize the surface changes, we performed measurements of the static and dynamic contact angles and calculated the surface energy by Wus harmonic mean model. The surface energy of the FC film increased with the UV/O3 treatment time, while the contact angles decreased. In silver inkjet printing, the hydrophobic FC film could reduce the diameter of the printed droplets. Merging of deposited droplets was observed when the substrate was kept at room temperature. Substrate heating was effective in preventing the merging phenomenon among the deposited droplets, and in reducing the width of printed lines. The merging phenomenon of deposited droplets was also prevented by increasing the UV/O3 treatment time. Continuous silver lines in the width range of 48.04–139.21 µm were successfully achieved by inkjet printing on the UV/O3-treated hydrophobic FC films at substrate temperatures below 90 °C.

Fabrication of large-area periodic nanostructures using two-mirror laser interference lithography

This study demonstrates laser interference lithography (LIL) using two rotatable mirrors located at a height of 20–50 cm in order for reflected coherent beams with a controlled incident angle to interfere on a substrate placed horizontally. The periods of the nanostructures are adjusted by the height of the mirrors from the substrate and the distance between the two mirrors without any significant change of the optical alignment. The periodic nanostructures are fabricated on a 6 inch Si substrate using the horizontal substrate LIL setup incorporated with an X-Y translation stage. For large area nano-patterning, a multi-step process is employed which repeats exposure- and-translation to expose small areas one by one.

Design and analysis of a rotor type magneto-rheological fluid brake and clutch

This study focuses on the design and analysis of a Rotor type magneto-rheological fluid (MR Fluid) brake and clutch. The brakes braking torque and the clutchs torque output can be easily controlled by adjusting the MR fluid and the configuration of Rotor. Electromagnetic finite element analysis(FEA) is performed, using FEMLAB software of the COMSOL Group, to find out the optimization conditions for the design of the Rotor type MR Fluid clutch and brake. In this paper, the design method of the Rotor type MR Fluid brake and clutch is investigated theoretically. The equation of the torque transmitted by the MR fluid within the Rotor type brake and clutch is derived to provide the theoretical foundation in the rotor design of the brake and clutch. The output torque values are recorded for different input velocities and applied magnetic fields, and the experimental results are compared with the theoretical results. Theoretical and experimental analyses have illustrated that this Rotor type MR fluid brake and clutch can transfer high controllable torques with a very fast time response. It was demonstrated that the Rotor type MR fluid clutch and brake have a strong capability of transmitting and isolating the high torque.