Hongseok Youn - Academia.edu (original) (raw)

Papers by Hongseok Youn

ACS Applied Materials & Interfaces, Jun 22, 2022

ACS Applied Materials & Interfaces, Aug 11, 2021

The flashlight annealing process has been widely used in the field of flexible and printed electr... more The flashlight annealing process has been widely used in the field of flexible and printed electronics because it can instantly induce chemical and structural modifications over a large area on an electronic functional layer in a subsecond time range. In this study, for the first time, we explored a straightforward method to develop strong self-adhesion on a metal nanowire-based flexible and transparent conductive film via flashlight irradiation. Nanowire interlocking, for strong mechanical bonding at the interface between the nanowires and polyamide film, was achieved by simple hot pressing. Then, by irradiating the nanowire-impregnated film with a flashlight, several events such as interdiffusion and melting of surface polymers could be induced along with morphological changes leading to an increase in the film surface area. As a result, the surface of the fabricated film exhibited strong interfacial interactions while forming intimate contact with the heterogeneous surfaces of other objects, thereby becoming strongly self-adhesive. This readily achievable, self-attachable, flexible, and transparent electrode allowed the self-interconnection of a light-emitting diode chip, and it was also compatible for various applications, such as defogging windows and transparent organic light-emitting diodes.

The increasing demand for improved electronic devices in the wide area of information technology ... more The increasing demand for improved electronic devices in the wide area of information technology enforced the research for organic semiconductors, because they can be possible to use soluble and room temperature process and flexible substrates. If the transparent photodetector is located in front of the display unit, it can control electronic devices by measuring the position data of illuminated point source of light similar to the operating principle of a touch screen. For technical realization of such construction, photodetetcor should be transparent. Therefore the polymer photodetector has the structure of PEDOT:PSS/heterojunction photoactive layer/ITO, where heterojunction photoactive layer consists of PVK and PCBM and fabricated by spin coating and spray method. It generates 25 mV in 15mW 405nm laser and has high transmission of 84.3 % at 580 nm. To control electronic devices using electrical signal from polymer photodetector, the output voltage of polymer photodetector should be amplified and transmitted to electronic devices by electrical signal processing system which is composed of op-amp, multiplexer and microcontroller, etc. The electrical signal processing system converts electrical signal from polymer photodetector to the position data of illuminated ultraviolet ray and shows on monitor. This paper presents transparent polymer photodetector to control electronic devices by using organic semiconductor. It can solve limitations of the earlier controllers for electronic devices on convenience and accuracy. We suggest possibility of transparent polymer photodetector to control electronic devices by demonstration using 4 inch transparent polymer photodetector samples and electrical signal processing system.

Optics Express, Sep 21, 2021

This study aims to resolve the trade-off between the constraints and capabilities of ultra-precis... more This study aims to resolve the trade-off between the constraints and capabilities of ultra-precision machining to achieve ophthalmic Fresnel lenses. A general Fresnel lens pattern has a narrow variable pitch and curved grooves. However, we obviate the limitations of the tool nose radius constraint and the long tool path via ultra-precision machining of the modified Fresnel lens, ensuring a constant pitch of 0.1 mm and varying the height of straight grooves from 0 to 11 µm. Photorealistic raytracing visualization and MTF simulation verified the compatibility of the lens pattern with human perception sensitivity. Copper-coated mold was fabricated using a diamond tool with a tool nose radius of 5 µm. The replicated flexible Fresnel lens demonstrated a relative MTF imaging performance of 89.1% and was attached to the goggles for the qualitative assessment. The proposed Fresnel lens design and fabrication approach can be extended to applications in the visual and infrared ranges as well.

Nanoscale, 2017

This research reports fabrication of highly efficient polymer light-emitting diodes (PLEDs) by a ... more This research reports fabrication of highly efficient polymer light-emitting diodes (PLEDs) by a thermally activated multi-layer transfer and lamination (MTL) process. As the first stage of the fabrication process, multiple layers consisting of a light-emitting polymer, electron transport/electron injection layer and metal cathode were sequentially deposited onto a hydrophobic low-surface energy self-assembled monolayer (SAM)-coated glass substrate. Subsequently, a very rapid delamination of PLEDs multi-layers from the SAM-coated glass was achieved by applying a high-pressure air jet. The custom air jet system ensures the excellent multi-film quality and also prevents the occurrence of common buckling and cracks. In addition, the adhesiveness of polyamide (PA) onto polyethylene terephthalate (PET), which serves as a protective barrier from atmospheric water and oxygen, is thermally activated by heating PA above its glass transition temperature. Finally, once delaminated from the PA/PET, the multi-layer structure (light-emitting polymer/electron transport layer/electron injection layer/metal cathode) was successfully laminated onto the target glass (hole transport layer/transparent anode) with a soft roller under mild pressure for the realization of the PLED device. The maximum brightness of the device fabricated by a thermally activated lamination process was around 13 120 cd m(-2) at 8.4 V, whereas the maximum current efficiency and the power efficiency were 5.2 cd A(-1) and 4.0 lm W(-1), respectively.

International Journal of Precision Engineering and Manufacturing, Aug 1, 2017

Micro-machining has been widely used for manufacturing of micro molds for flat panel displays. Be... more Micro-machining has been widely used for manufacturing of micro molds for flat panel displays. Because the mold has a large area and heavy weight, the workpiece setup system with a high stiffness and ultraprecise positioning control is required to obtain a longterm manufacturing stability and precision. In this study, a novel ultra-precision tilting stage with 3-DOF motions (z-translation, pitch, and roll) has been developed to setup a heavy duty and large area workpiece. The structure is designed to realize a long motion range via an amplified guide mechanism of high stiffness flexure guide and the piezo-electric actuators are integrated to achieve the motion resolution of less than 100 nm. The guide mechanism has a large stiffness with long-term stability through the unique combination of a closed-lying bridge and a half-standing bridge, which can amplify the motion rage double and minimize the overall volume of tilting system. The static, dynamic, and thermal characteristic of the system was optimized by structural analysis using finite element modeling. Finally, the tilting stage provides 50 nm positioning repeatability for a workpiece of 150 kg within a vertical stroke of 160 µm and a machining area of 400×400 mm 2 .

Advanced Engineering Materials, Jun 18, 2020

Herein, a roll‐to‐roll (R2R) continuous reverse‐offset (RO) printing process combined with an int... more Herein, a roll‐to‐roll (R2R) continuous reverse‐offset (RO) printing process combined with an intense pulsed light (IPL) sintering technique for the mass production of Ag nanoparticles (NPs)‐based highly conductive, ultrafine patterns on the low‐cost, heat‐sensitive polyethylene terephthalate (PET) substrate is first explored. Variations in printing quality depending on the ink‐coating thickness and the applied pressure during the off process and printing times are observed. By these observations, their effects on pattern quality are identified, and the blanket swelling responsible for printing stability degradation is solved using infrared (IR) exposure. By analyzing the thermal behavior of RO ink, the microstructures of patterns as IPL irradiation conditions are investigated. Contrary to the case of high‐power light for a short time, a steady and gradual volume change is induced in the pattern irradiated by low‐power light for a long time so that cracks and pores are considerably suppressed. The R2R inline production of densely sintered mesh (less than ≈10 μm) transparent electrodes (Rs = 9.86 ± 0.36 Ω sq−1 at T ≈ 90%) is successfully demonstrated via successive IPL irradiations synchronized with printing velocity. Finally, the potential use of R2R‐produced electrodes is clearly proved by fabricating flexible organic light‐emitting diodes (OLEDs).

Energy technology, Feb 27, 2015

ACS Applied Materials & Interfaces, Oct 21, 2019

Applied Physics Letters, Dec 13, 2010

We studied the solution processed vanadium pentoxide (V 2 O 5) doping effect in PEDOT:PSS for use... more We studied the solution processed vanadium pentoxide (V 2 O 5) doping effect in PEDOT:PSS for use in hole injection layer (HIL), and as a result, V 2 O 5 doped PEDOT:PSS improved the performance of polymer light-emitting diode (PLED) significantly. The improvement is related to the increased conductivity of PEDOT:PSS by V 2 O 5 doping. This improvement enhances hole injection into the emission layer, and it will improve the charge balance. The PLED with PEDOT:PSS HIL and super yellow polymer has maximum current and power efficiencies of 12.01 cd A À1 and 9.67 lm W À1 , respectively. On the other hand, the device with V 2 O 5 (10:1) doped PEDOT:PSS indicates the maximum current and power efficiencies of 15.12 cd A À1 and 12.66 lm W À1 , respectively, indicating that the efficiencies increase over 20% compared to the control device. The leakage currents of the PLED decrease to $10% of the control PLED. Note also that V 2 O 5 suppressed the diffusion of indium from anode to PEDOT:PSS, and also prevented the acidic damage from sulfate ions of PEDOT:PSS to IZO and active layer.

IEEE Transactions on Antennas and Propagation, 2017

A novel optically transparent, flexible and mechanically reconfigurable zeroth-order resonant (ZO... more A novel optically transparent, flexible and mechanically reconfigurable zeroth-order resonant (ZOR) antenna using stretchable micromesh structure is presented in this paper. The size reduction of the antenna is achieved by using the ZOR property, and the uniform metallic patches of the antenna are replaced with the tortuous micromesh. The tortuous micromesh structures provide a high degree of freedom for stretching when encapsulated in elastomeric polymers with added feature of semi-transparency. Accordingly, the structure can undergo mechanical deformation such as stretching (up to 40%), folding, or twisting without breakage. The resonant frequency of the antennas is linearly reconfigurable from 2.94 GHz to 2.46 GHz upon stretching.

한국생산제조학회 학술발표대회 논문집, Oct 1, 2005

In this research, CNC tool grinding system has been developed with open architectural PC-NC kerne... more In this research, CNC tool grinding system has been developed with open architectural PC-NC kernel. The developed 4 axis tool grinding system is motion-controlled by PC-based controller. To reduce the machining error, machine vision system is adopted. By using the various image processing algorithms, alignment and auto-setaup processes are achieved between grinding wheel and workpiece. Also, the resolution of machine vision system is improved 10-15 times with the process of image enhancement and noise reduction. In grinding mechanism, there exist numerous parameters especially in machining conditions and processes. It is a very hard work to decide the optimal machining parameters. In this work, to optimize the grinding conditions, the grinding force has monitored using hall sensor. Since the hall sensor signal from the spindle current represents the grinding force, the excessive grinding force occurred at comer could be stabilized by feed rate control. In grinding process, as the wheel wear is natural phenomenon with its self-sharpening action, it is exceedingly difficult to measure the wear width during grinding process. The tracking method was developed with machine vision system. This algorithm enables the system to measure the wear width during grinding process. It is very useful to compensate the wheel wear in real-time.

Organic Electronics, Aug 1, 2012

This paper reports that large-scale, all-solution processed, polymer, light-emitting diodes can b... more This paper reports that large-scale, all-solution processed, polymer, light-emitting diodes can be fabricated by a new blade-slit coating method under ambient conditions. It is practical to use an ionic solution and a ZnO nanoparticle solution as electron injection and electron transport materials, respectively, through a blade-slit coating system, and reduce the deviation of the layer thickness to less than one-third compared to the result of a conventional blade-only coating system. The standard deviations of the layer thickness coated by the blade-slit process were only 0.68 nm in the hole injection layer (PEDOT:PSS), and 2.3 nm in the polymer light-emitting layer (Super Yellow). In the case of blade-only coating, the standard deviations were 5.7 nm and 5.7 nm, respectively. The film non-uniformities of PEDOT:PSS and the Super Yellow layers fabricated by the blade-slit method were only 2.1% and 2.2%. In the case of blade-only coating, those were 7.9% and 9.1%, respectively. The application area was 80 mm Â 70 mm. Moreover, because the devices do not contain any alkali or alkaline earth metals in the electron injection layer, they can be fabricated by an all-solution process in a normal air conditioned environment. The maximum luminous efficiency of allsolution blade-slit coated devices was as high as 5.26 cd/A without alkali metals, and the maximum luminance reached was 14 120 cd/m 2 at 7.8 V. These results are comparable to the performance of spin-coated devices.

Energy and Environmental Science, 2014

A multi-layer roll transferring (MRT) approach is reported, in which a highly conductive solution... more A multi-layer roll transferring (MRT) approach is reported, in which a highly conductive solution processed Ag electrode is prepared separately from the rest of the organic layers, and the fully solution-processed device is completed by a final roll-transferring process.