Journal of the Korean Society for Precision Engineering

Dual-laser-assisted Defect Engineering and Chlorination for Enhanced Photoluminescence in MoS₂: Yoonsoo Rho; J. Korean Soc. Precis. Eng. 2025;42(10):783-787.
Published online October 1, 2025; DOI: https://doi.org/10.7736/JKSPE.D.25.00002

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In this study, we demonstrate a synergistic enhancement of photoluminescence (PL) in an atomically thin molybdenum disulfide (MoS₂) monolayer using a dual-laser-beam-assisted chemical modification method. A continuous-wave (CW) green laser, directed perpendicularly at the MoS₂, locally raises the temperature and induces the formation of sulfur (S) vacancies, resulting in a significant increase in PL intensity. Subsequently, a UV nanosecond laser beam laterally illuminates the area above the MoS₂ layer, breaking chlorine molecules and introducing chlorine radicals without damaging the sample. This process further enhances the PL in the region previously affected by S vacancies. The binding energy of chlorine atoms to S-vacancy sites is greater than that to the pristine MoS₂ surface, facilitating more effective p-type doping. The stronger interaction at the defect sites created by the CW laser contributes to the observed synergistic PL enhancement. Our approach presents a novel method for precise and spatially selective chemical doping in two-dimensional (2D) van der Waals (vdW) materials.

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Laser Ablation Patterning of Metal Thin Films for On-demand of Shadow Mask Patterning in Vacuum Deposition: Beomsun Do, Seunghun Lee, Hyunho Lee, Hoon Jeong, Joel Ndikumana, Kunsik An; J. Korean Soc. Precis. Eng. 2025;42(10):775-782.
Published online October 1, 2025; DOI: https://doi.org/10.7736/JKSPE.D.25.00001

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This study explores the use of laser ablation technology for creating on-demand shadow masks, which are essential in the fabrication of thin film transistor (TFT) devices. Traditional methods for producing shadow masks often encounter significant challenges, such as high costs, lengthy production times, and difficulties in achieving fine, high-resolution patterns. To address these issues, this study introduces a method for manufacturing shadow masks using fiber laser-based laser ablation. Key laser parameters, including frequency and power, were optimized throughout the research. Systematic experimentation revealed that a frequency of 20 kHz and a power output of 14 W enabled the precise and uniform creation of patterns with a 50 μm channel spacing. When these custom shadow masks were employed in the TFT fabrication process, the resulting devices exhibited stable and reliable electrical performance. The findings suggest that laser ablation-based on-demand shadow mask technology offers a cost-effective and flexible solution for producing large-area, high-resolution TFTs. Additionally, this approach significantly reduces the prototyping cycle, making it ideal for rapid development and iterative testing in research and development environments.

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Bayesian Optimization of Process Parameters for Enhanced Overhang Structure Quality in L-PBF: Kyung Lim Oh, Ju Chan Yuk, Suk Hee Park; J. Korean Soc. Precis. Eng. 2025;42(7):555-564.
Published online July 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.075

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Overhang structures are essential geometries in metal additive manufacturing for realizing complex shapes. However, achieving stable, support-free overhang structures requires precise control of process parameters, and securing shape fidelity becomes particularly challenging as overhang length increases due to thermal deformation. To address this challenge, this study proposed a Bayesian optimization framework for efficiently identifying optimal process parameters to fabricate high-difficulty overhang structures. An image-based scoring method was developed to quantitatively evaluate shape defects. Experimental data were collected by fabricating 3, 6, and 9 mm overhang structures with various process parameters. Based on collected data, Gaussian Process Regression (GPR) models were trained. A physics-informed soft penalty term based on energy density was incorporated to construct a surrogate model capable of making physically plausible predictions even in extrapolated regions. Using this model, Bayesian optimization was applied to overhang lengths of 12, 15, and 18 mm, for which no prior experimental data existed. Recommended parameters enabled stable, support-free fabrication of overhang structures. This study demonstrates that reliable optimization of process parameters for complex geometries can be achieved by combining minimal experimental data with physics-informed modeling, highlighting the framework’s potential extension to a wider range of geometries and processes

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Laser-Induced Graphene Direct Writing on Textile for Smart Textile: Dongwook Yang, Young-Jin Kim; J. Korean Soc. Precis. Eng. 2025;42(7):543-554.
Published online July 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.074

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Laser-induced graphene (LIG) presents a promising route toward next-generation smart textiles by enabling direct patterning of conductive materials onto textiles through a single-step laser writing process. In particular, femtosecond laser-based fabrication offers high-resolution processing without damaging substrates. This review summarizes LIG formation mechanisms, laser manufacturing parameters, physical/chemical characteristics, electrical, thermal, and optical properties of LIG. Furthermore, it categorizes representative applications including biosignal monitoring, energy storage, thermal regulation, optical absorber, and extraterrestrial adaptability, all based on textile-integrated LIG. With its porous morphology, high conductivity, and structural versatility, LIG offers outstanding multifunctionality for smart textile applications. Future research should explore precise functional tuning of LIG through laser parameter optimization, accurate characterization of LIG, and advanced smart textile applications.

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Analysis of the Laser Ablation Threshold of Aluminum Foil under Varying Relative Humidity Conditions: Myeongho Park, Dongkyoung Lee; J. Korean Soc. Precis. Eng. 2025;42(7):537-542.
Published online July 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.064

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To reduce the use of fossil fuels, the adoption of battery electric vehicles (BEVs) using lithium-ion batteries has been increasing in internal combustion engine alternatives. Accordingly, significant efforts have been made to improve the manufacturing process of lithium-ion batteries within electric vehicles. In particular, the cutting process of lithium-ion batteries has been actively discussed as it is closely related to battery performance. Laser-based cutting enables a more precise and sustainable manufacturing process. The laser ablation threshold has been investigated in many studies to achieve high-precision laser processing. While laser parameters and ambient conditions have been examined to determine the laser ablation threshold, studies focusing on the effect of relative humidity remain insufficient. Thus, this study investigated the laser ablation threshold of aluminum foil under varying relative humidity conditions. First, a laser interaction chamber was fabricated to control the relative humidity during experiments. A scanning electron microscope (SEM) was then used to observe laser ablation craters and analyze the threshold. The variation of the laser ablation threshold with relative humidity revealed changes in the interaction between the laser and aluminum foil depending on the humidity level.

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Optimization of Angle of Incidence of the Laser Beam in Laser-FIB Hybrid Processing and Design of an Integrated System: Jeonghong Ha, Kyu Song, Hyun Choi, Chung-Soo Kim, Jong Wan Ko, Dong-Young Jang; J. Korean Soc. Precis. Eng. 2025;42(7):529-536.
Published online July 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.063

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The need for large-area cross-sectional analysis with nanometer precision is rapidly growing in various advanced manufacturing sectors. Traditional focused ion beam (FIB) techniques are too slow for milling millimeter-scale volumes. They often introduce ion implantation, redeposition, and curtaining effect, which ultimately prevent effective large-area processing and analysis. To overcome these limitations, we developed a hybrid machining process integrating femtosecond laser micromachining for rapid roughing with FIB milling for precision finishing. Angle of incidence (AOI) control during laser machining was employed to minimize the taper angle of laser-ablated sidewalls, thereby significantly reducing subsequent FIB milling volume. Using a 1030 nm, 350 fs laser, we achieved nearly vertical sidewalls (taper angle: ~2.5° vs. ~28° without AOI control) in silicon. Raman spectroscopy revealed a laser-affected zone extending about 2 μm perpendicular to the sidewall, indicating the need for further FIB milling besides laser-tapered regions to remove laser-induced damage. On multilayer ceramic capacitors and micropillar fabrication, the hybrid laser-FIB method achieved efficient large-area cross sections with preserved microscale details. We present the development of an integrated triple-beam system combining laser, plasma FIB, and SEM, capable of fast volume removal and nanoscale imaging in one equipment. This approach can markedly improve throughput for large-area cross-sectional analysis.

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Analysis of TGV Formation on Glass Substrates according to SLM Image: Jonghyeok Kim, Byungjoo Kim, Sanghoon Ahn; J. Korean Soc. Precis. Eng. 2025;42(7):521-527.
Published online July 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.062

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The demand for high-speed processing and big data has accelerated the adoption of three-dimensional integrated circuits (3D ICs), where interposers serve as essential components for chip-to-chip connectivity. However, silicon interposers using the through-silicon via (TSV) technology have structural limitations. As alternatives, glass-based interposers employing the through-glass via (TGV) technology are gaining attention. This study explored the fabrication of via holes in glass substrates using the selective laser etching (SLE) process. A spatial light modulator (SLM) was used to generate donut- shaped bessel beams by inserting an image pattern without relying on phase modulation. The machinability of via holes fabricated with these beams was compared to that of holes formed using phase-modulated beams. Effect of pulse energy on taper angle was also investigated. Hourglass-shaped holes were observed at lower pulse energies. However, taper angles approaching 90° were observed at higher energies, indicating an improved verticality.

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Femtosecond Laser Micro-drilling on Stainless Steel 316 L at Sub 90 µm Hole Diameter: Samuel Crankson, Dongkyu Kim, Dongkyoung Lee; J. Korean Soc. Precis. Eng. 2025;42(7):505-512.
Published online July 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.059

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Micro-hole perforation on stainless steel is essential for various industrial applications. However, achieving precise hole geometry, high aspect ratio, and excellent surface quality remains challenging with conventional drilling methods. In this study, we employed a single circular path trepanning technique using a femtosecond laser to drill micro-holes in 316L stainless steel with diameters less than 90 µm. Process parameters, including pulse energy, repetition rate, scan speed, and number of scans, were systematically varied. Resulting hole morphology and cross-sectional profiles were characterized using a confocal microscope and a scanning electron microscope. Our findings demonstrated that optimized femtosecond laser drilling could minimize recast layers, sputter deposition, and heat-affected zones, thereby achieving high-quality micro-holes suitable for demanding industrial applications.

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Laser-induced Process for Fabrication of Silicon Microstructure: Sung Jin Park, Bongchul Kang; J. Korean Soc. Precis. Eng. 2025;42(7):499-503.
Published online July 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.053

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Silicon is a key material in advanced technologies due to its thermal stability, appropriate bandgap, and wide applicability for advanced devices. Si microstructures offer enhanced surface area, thus improving performances for energy storage and biosensing applications. However, conventional top-down fabrication methods are complex, costly, and environmentally unfriendly as they rely on cleanroom facilities and toxic chemicals. This study proposed a simplified, eco-friendly bottom-up laser-based process to fabricate silicon microstructures. By controlling laser parameters during the interaction with silicon nanoparticles, diverse Si structures can be fabricated by Si nanoparticle coating and laser irradiation.

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Analysis of Nano Pattern Uniformity based on Elliptical Fourier Descriptor Method: June Sik Hwang, Ha Seong Joo, Huseung Lee; J. Korean Soc. Precis. Eng. 2025;42(6):477-482.
Published online June 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.046

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Due to their structural properties, nanopatterns are actively used in various fields. In the semiconductor industry, the importance of analyzing the uniformity of nanopatterns is becoming increasingly important. New analysis methods are needed. The elliptical Fourier descriptor (EFD) method can quantify the shape information into frequency components by Fourier transforming contours. In this study, shape analysis of nanopatterns was performed using EFD. Nanopatterns with a period of about 400 nm were formed using laser interference lithography. EFD coefficients were then compared. Results of the analysis showed that the variation between coefficients of poorly shaped patterns was larger than that of normal patterns, confirming the possibility of quantitative comparison. However, further research is needed to establish a clear correlation between coefficient changes and quality changes. In the absence of a standard for geometrical changes in nanopatterns, it is expected that EFD can be applied as a methodology to provide new quantitative indicator.

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Characteristics of Lamb Wave Propagation on a Nanoscale Membrane Induced by a Laser Ultrasonic Technique: Yun Young Kim; J. Korean Soc. Precis. Eng. 2025;42(5):355-360.
Published online May 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.007

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A lamb wave propagation behavior on a freestanding nanoscale membrane was investigated using a laser ultrasonic technique in the present study. A 110-nm thick aluminum (Al) layer was deposited on a rectangular 200-nm thick silicon nitride (SiN) membrane and the Lamb wave was launched using a pulsed laser. The transfer matrix technique was employed to obtain a theoretical dispersion curve so that material properties of the SiN membrane could be estimated through curve-fitting. In addition, picosecond ultrasonic measurement was used to characterize the Al film. Results showed that the dispersive behavior of Lamb wave in the fundamental antisymmetric mode could be clearly observed on the membrane. However, comparison of dispersion curves indicated that the effect of residual stress of the film became more influential at a low dimensional scale.

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Laser Pointing Control System based on Deep Reinforcement Learning Algorithm: Geemin Lee, Youngsu Park, Wonho Choi, Dae Gyu Choi, Chikyung Ahn, Yongeun Yoon; J. Korean Soc. Precis. Eng. 2024;41(12):949-955.
Published online December 1, 2024; DOI: https://doi.org/10.7736/JKSPE.024.088

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In the field of optical engineering, the laser position control system has important role in many applications, such as measurement, communication, fabrication. Traditional methods to solve laser position control system often face the problems of insufficient generalization, such as configuration or singular solution. In this study we proposed a novel model- free reinforcement learning approach based Proximal Policy Optimization (PPO) for laser position control system. To control the position of laser, we develop an efficient representation of environmental inputs and outputs. Position error of Position Sensing Detector (PSD), and three kinds of distance parameters are applied our environmental parameters. To overcome the challenges associated with training in real worlds, we developed training environment in simulation. The simulation to evaluate performance of our approach, we perform several times of experiments in both simulated and real world system.

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Improving Micro-hole Laser Drilling Performance Using an AOM: Young Hoon Kim, Sang Hwan Choi, Se Kyung Chun, Ji Won Lee, Doo Hyun Cho, Myung Woon Kim; J. Korean Soc. Precis. Eng. 2024;41(6):423-428.
Published online June 1, 2024; DOI: https://doi.org/10.7736/JKSPE.024.005

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PCBs (Printed circuit boards) have been widely used in electronic products such as wearables, smartphones, and table computers. Recent trends of miniaturizing electric components require improvement of component density and electronic functionality by decreasing the size of micro via holes (50-110 μm), which interconnect electric signals between adjacent layers in high density interconnection (HDI) PCBs. To generate micro via holes, we studied CO₂ laser drilling with the help of pulse shape controlling using acousto-optic modulator (AOM). Pulse shape controlling is one of the key factors to reduce heat effect during the laser drilling process. To increase laser absorption, the substrate was subjected to black oxidation prior to CO₂ laser drilling. We designed a diffractive optical system using a circular aperture. Micro via holes were obtained by optimizing the optical distance. The laser drilled via hole was studied both experimentally and theoretically.

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Characterization of a Copper Thin Film Using the Surface Acoustic Wave Measurement Technique: Taehyung Kim, Yun Young Kim; J. Korean Soc. Precis. Eng. 2024;41(3):183-189.
Published online March 1, 2024; DOI: https://doi.org/10.7736/JKSPE.023.125

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The elastic property of a copper (Cu) thin film was investigated using the surface acoustic wave (SAW) measurement technique. The Cu film was deposited on a quartz substrate using a direct current magnetron sputter and its surface morphology was inspected using atomic force microscopy. Time-domain waveforms of the SAW on the film were acquired at different propagation distances to estimate the Young’s modulus of Cu such that the experimentally-obtained dispersion curve can be compared to the analytical result calculated using the Transfer Matrix method for curve-fitting. Results showed that the film’s elastic property value decreased by 18.5% compared to that of the bulk state, and the scale effect was not significant in the thickness range of 150-300 nm, showing good agreement with those by the nanoindentation technique. The property, however, increased by 15.5% with the grain coarsening.

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Study on Automated Heat Treatment for Car-body Mold Using an Articulated Robot System: Kee Jin Park, Sung Ho Yoon; J. Korean Soc. Precis. Eng. 2023;40(12):1011-1018.
Published online December 1, 2023; DOI: https://doi.org/10.7736/JKSPE.023.111

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The quality and quantity of heat treatment in mold processing can vary depending on the skill level of the equipment operator. Therefore, study on ways to overcome these disadvantages are essential. This study aimed to increase the antiwear properties of molds through high-frequency induction heat treatment and laser heat treatment processes. The heat treatment was applied to the surfaces of molds used in car body production using an articulated robot, to achieve long-term use and quality maintenance. Additionally, an articulated robot system based on redundant degrees of freedom suitable for mold heat treatment processes was designed, and its operational efficiency was verified through virtual environment simulations. Furthermore, heat treatment was validated through on-site testing of the robot system. Its effects were analyzed according to mold materials and shape conditions, ultimately deriving the optimal robot heat treatment conditions. Finally, off-line programming (OLP) in virtual processes was proposed to minimize robot setup time and maximize production efficiency. The conditions for articulated robot automated heat treatment obtained in this study can be preapplied in simulation environments when generating heat treatment robot programs based on OLP. They can be utilized for optimizing the quality of mold heat treatment in car body production.