https://scholar.dgist.ac.kr/handle/20.500.11750/11853 2026-08-23T22:44:55Z 2026-08-23T22:44:55Z Kim, Junil Cho, Kyungjune Lee, Jieun Lee, Takhee Chung, Seungjun Kwon, Hyuk-Jun https://scholar.dgist.ac.kr/handle/20.500.11750/60593 2026-08-04T09:10:11Z 2026-05-31T15:00:00Z

Title: High-Resolution Microlens-Assisted Tunable n-Type Optical Doping in Monolayer MoS2 Author(s): Kim, Junil; Cho, Kyungjune; Lee, Jieun; Lee, Takhee; Chung, Seungjun; Kwon, Hyuk-Jun Abstract: Atomically thin two-dimensional transition metal dichalcogenides (2D TMDCs), especially monolayer MoS2, have garnered considerable attention as promising materials for next-generation transistors. However, their large surface-to-volume ratio renders them highly sensitive to defects, underscoring the need for selective, localized, and precise control of their defect profiles. Here, we introduce a laser-assisted microlens array processing (LAMP) technique that enables highly localized n-type optical doping of monolayer MoS2 by utilizing self-assembled polystyrene microspheres as microlenses to focus a 532 nm continuous-wave laser below the diffraction limit. Under low laser powers (40-60 mW), sulfur vacancies are selectively generated without inducing global thermal damage, allowing systematic control of the vacancy concentration. Spectroscopic analyses reveal electron-donor-like defects and tunable vacancy density. MoS2 transistors treated by LAMP exhibit finely tunable doping, yielding up to a 51-fold increase in field-effect mobility and a 37-fold increase in carrier density, with the enhanced n-type characteristics remaining stable for several weeks. Unlike direct laser irradiation, LAMP offers high spatial resolution, low energy consumption, and reproducible vacancy engineering while minimizing thermal damage. This complementary metal-oxide-semiconductor-compatible strategy provides a robust post-fabrication approach for precise electronic property tuning in two-dimensional transition metal dichalcogenide devices.

2026-05-31T15:00:00Z Kim, Yunseo Kong, Daeyoung Park, Jeonghwan Jang, Bongho Kim, Taeyeon Kwon, Hyuk-Jun Cho, Jungwan Bin In, Jung Lee, Hyoungsoon https://scholar.dgist.ac.kr/handle/20.500.11750/60589 2026-08-03T01:40:18Z 2026-02-28T15:00:00Z

Title: Thermally induced structural evolution of diamond surface for pool boiling enhancement Author(s): Kim, Yunseo; Kong, Daeyoung; Park, Jeonghwan; Jang, Bongho; Kim, Taeyeon; Kwon, Hyuk-Jun; Cho, Jungwan; Bin In, Jung; Lee, Hyoungsoon Abstract: Effective thermal management in power devices is essential for energy-efficient operation. Pool boiling dissipates heat effectively through passive phase changes, eliminating the need for pumping power. However, these benefits remain unrealized in high-power-density devices owing to the risk of reaching Critical Heat Flux (CHF). The superior heat-spreading capabilities of diamond can help mitigate excessive heat flux in such devices. Consequently, pool boiling on diamond surfaces represents a promising cooling strategy for devices with high power densities. However, the inherent chemical inertness of diamond severely limits its surface modification, thereby posing significant challenges to the control of interfacial phenomena. This study investigated methods to modify Polycrystalline Diamond (PCD) surfaces to enhance their pool boiling performance. Thermal oxidation efficiently altered the PCD surface, exploiting its unique material properties. The enhanced surface enabled a 47.8% increase in the heat transfer coefficient and a 119.4% increase in the CHF. Additionally, an in-depth investigation clarified how structural and chemical modifications induced by high-temperature oxidation enhanced pool boiling performance.

2026-02-28T15:00:00Z Hong, Woongki Bissannagari, Murali Cho, Youngjae Jang, Jae Eun Kwon, Hyuk-Jun Kang, Hongki https://scholar.dgist.ac.kr/handle/20.500.11750/60546 2026-07-30T10:40:13Z 2026-05-31T15:00:00Z

Title: Inkjet-Printed BaTiO3 Nanoparticle-Embedded Capacitor Array for Physical Unclonable Function Author(s): Hong, Woongki; Bissannagari, Murali; Cho, Youngjae; Jang, Jae Eun; Kwon, Hyuk-Jun; Kang, Hongki Abstract: Nanoparticle (NP)-based physical unclonable functions (PUFs) have attracted attention as a digital fingerprint technology that alternates with microfabrication-based PUFs by utilizing natural randomness at the nanoscale. Mostly NP-based optical PUFs have been proposed due to the absence of nanomaterial fabrication method compatible with microelectronics, but the need for a bulky optical readout system makes it difficult to utilize them in microelectronics. In this work, we developed the NP-based capacitor PUF (CAP-PUF) technology that can be read electrically and integrated into microelectronics while utilizing the benefit of the natural physical randomness of NPs. We incorporated a high-k BaTiO3 NP inkjet printing micropatterning process for the fabrication of the NP-embedded CAP-PUF array. The inkjet-printing parameters have been optimized to maximize the natural randomness of the BaTiO3 NP micropatterns by increasing the intrinsic stochasticity, especially the fluid dynamics that occurring during the multilayer printing. The BaTiO3 NP-embedded CAP-PUF array shows high security performance, showing the inter-hamming distance of 0.52, uniformity of 0.44, entropy of 0.989, and intra-hamming distance up to 0.064. High-k NP inkjet-printing-based CAP-PUFs can provide highly unique digital fingerprints based on the intrinsic randomness in nanoscale for microelectronics.

2026-05-31T15:00:00Z Lee, Jieun Kim, Junil Sim, Young-Jun Lee, Byeongmoon Jang, Jae Eun Kwon, Hyuk-Jun https://scholar.dgist.ac.kr/handle/20.500.11750/60480 2026-08-12T08:40:13Z 2026-04-30T15:00:00Z

Title: Laser-Induced Oxygen Engineering for Localized Homojunction Formation in SnS2 Photodetectors Author(s): Lee, Jieun; Kim, Junil; Sim, Young-Jun; Lee, Byeongmoon; Jang, Jae Eun; Kwon, Hyuk-Jun Abstract: The development of high-performance optoelectronic devices based on 2D materials has attracted significant attention. However, conventional vertical stacking methods are limited by complex processes and interfacial defects. To overcome these challenges, we propose a simple and efficient one-step process to form an in-plane homojunction within a single n-type tin disulfide (SnS2) flake via direct laser irradiation. The core process, oxidative thinning, utilizes a focused 532 nm laser to locally convert a portion of SnS2 into tin oxide (SnOx). Consequently, an energy barrier arising from a work-function difference of approximately 0.7 eV is formed at the interface, promoting the separation of photogenerated electron-hole pairs. The fabricated photodetector demonstrates a fast response time (tau r/tau f = 474/299 ms), an improvement of several tens of times compared with the pristine SnS2 device. Furthermore, it exhibits a high responsivity (R) of 703 mA W-1, an external quantum efficiency (EQE) of 170%, and a remarkable specific detectivity (D*) of 2.35 x 1014 Jones, along with excellent operational stability. This laser-induced local conversion technique presented can provide a powerful and practical platform for developing next-generation flexible and wearable optoelectronic devices.

2026-04-30T15:00:00Z