Lee, Gil Sik

Permanent URI for this collectionhttps://hdl.handle.net/10735.1/2906

Gil Lee is a professor and head of the Micro-device Research Laboratory (MdRL). Dr. Lee's research interests include semiconductor material properties, physics of semiconductor devices, device fabrication, and measurement and characterization of materials and devices. Recently his activities have involved:

  • Carbon nanotubes growing by atmospheric PECVD and spinning of CNT.
  • Lithium ion battery and lithium air battery using CNT sheet.
  • Transparent touch screen, transparent heat, and strain sensor applications using CNT sheet.
  • Solar cells.

Learn more about Gil Lee on his Home and Research Explorer pages

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Recent Submissions

Now showing 1 - 4 of 4
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    Thickness Modulated MoS2 Grown by Chemical Vapor Deposition for Transparent and Flexible Electronic Devices
    Park, Juhong; Choudhary, Nitin; Smith, Jesse; Lee, Gil Sik; Kim, Moonkyung; Choi, Wonbong; 0000 0001 3865 4673 (Lee, GS)
    Two-dimensional (2D) materials have been a great interest as high-performance transparent and flexible electronics due to their high crystallinity in atomic thickness and their potential for variety applications in electronics and optoelectronics. The present study explored the wafer scale production of MoS2 nanosheets with layer thickness modulation from single to multi-layer by using two-step method of metal deposition and CVD process. The formation of high-quality and layer thickness-modulated MoS2 film was confirmed by Raman spectroscopy, AFM, HRTEM, and photoluminescence analysis. The layer thickness was identified by employing a simple method of optical contrast value. The image contrast in green (G) channel shows the best fit as contrast increases with layer thickness, which can be utilized in identifying the layer thickness of MoS2. The presence of critical thickness of Mo for complete sulphurization, which is due to the diffusion limit of MoS2 transformation, changes the linearity of structural, electrical, and optical properties of MoS2. High optical transparency of > 90%, electrical mobility of to ~12.24 cm² V⁻¹ s⁻¹, and I-on/off of ~10⁶ characterized within the critical thickness make the MoS2 film suitable for transparent and flexible electronics as compared to conventional amorphous silicon (a-Si) or organic films. The layer thickness modulated large scale MoS2 growth method in conjunction with the layer thickness identification by the nondestructive optical contrast will definitely trigger development of scalable 2D MoS2 films for transparent and flexible electronics.
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    Flexible Transparent Conductive Heater Using Multiwalled Carbon Nanotube Sheet
    (AVS Science and Technology Society) Jung, Daewoong; Han, Maeum; Lee, Gil Sik; 0000 0001 3865 4673 (Lee, GS)
    This paper reports highly flexible, transparent, conducting heaters based on multiwalled carbon nanotube (MWCNT) sheets. The MWCNT sheets were spun directly from a well-aligned MWCNT forest. The fabrication of the MWCNT sheet heater was quite simple and suitable for mass production, requiring only a one-step transferring process, in which the MWCNT sheet is drawn onto the target substrates. This study examined the parameters that affect the heat generation of the MWCNT sheet-based heater; input power, surface area, and thermal conductivity of the substrate. In particular, more effort was focused on how to increase the surface area and contact points between the individual MWCNTs; simple acid treatment and added metal nanoparticles increased the heat performance of the heater dramatically. Moreover, the heaters exhibited durability and flexibility against many bending cycles. Therefore, the MWCNT sheet-based heater can be used for versatile applications requiring transparency, conduction, and flexibility.
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    Fabrication of a Microneedle/CNT Hierarchical Micro/Nano Surface Electrochemical Sensor and its In-Vitro Glucose Sensing Characterization
    Yoon, Youngsam; Lee, Gil Sik; Yoo, Koangki; Lee, Jeong-Bong; 0000 0001 3865 4673 (Lee, GS)
    We report fabrication of a microneedle-based three-electrode integrated electrochemical sensor and in-vitro characterization of this sensor for glucose sensing applications. A piece of silicon was sequentially dry and wet etched to form a 15 x 15 array of tall (approximately 380 μm) sharp silicon microneedles. Iron catalyst was deposited through a SU-8 shadow mask to form the working electrode and counter electrode. A multi-walled carbon nanotube forest was grown directly on the silicon microneedle array and platinum nano-particles were electrodeposited. Silver was deposited on the Si microneedle array through another shadow mask and chlorinated to form a Ag/AgCl reference electrode. The 3-electrode electrochemical sensor was tested for various glucose concentrations in the range of 3~20 mM in 0.01 M phosphate buffered saline (PBS) solution. The sensor's amperometric response to the glucose concentration is linear and its sensitivity was found to be 17.73 ± 3 μA/mM-cm². This microneedle-based sensor has a potential to be used for painless diabetes testing applications.;
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    Effect of Acetylene Concentration and Thermal Ramping Rate on the Growth of Spin-Capable Carbon Nanotube Forests
    Lee, Kyung Hwan; Jung, Daewoong; Burk, Dorothea; Overzet, Lawrence J.; Lee, Gil Sik; 0000 0001 3865 4673 (Lee, GS); 0000 0003 5379 4329 (Overzet, LJ)
    Spin-capable multiwalled carbon nanotube (MWCNT) forests that can form webs, sheets, and yarns provide a promising means for advancing various technologies. It is necessary to understand the critical factors to grow spin-capable carbon nanotubes (CNTs) in a repeatable fashion. Here we show how both the spinning capability and morphology of MWCNT forests are significantly changed by controlling the C2H2 concentration and ramp rate of temperature. The acetylene gas flow was varied in the range of 0.25-6.94% by volume. The MWCNTs grown at C2H2 concentrations between 1.47-3.37% are well-aligned and become spin-capable. The well-aligned forests have higher areal density and shorter distance between CNTs. The thermal ramp rate was also changed from 30 degrees C/min to 70 degrees C/min. A specific range of thermal ramp rate is also required to have the suitably sized nanoparticles with sufficient density resulting in higher CNT areal density for spinnable MWCNTs. A ramp rate of 50 degrees C/min forms suitable sized nanoparticles with sufficient density to produce CNT forests with a higher areal density and a shorter tube spacing.

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