https://scholarworks.unist.ac.kr/handle/201301/62 2026-04-08T21:35:22Z https://scholarworks.unist.ac.kr/handle/201301/91302 Title: A universal approach to understanding cryogenic quenching in pool boiling Author(s): Koo, Heeyeong; Lee, Jongbin; Jeong, Minsub; Lee, Kyungwon; Yoon, Aejung Abstract: This study experimentally and theoretically investigated the effects of material properties and geometric dimensions on quenching process of a flat plate in a liquid nitrogen pool. Quenching experiments were performed using stainless steel, aluminum, and copper plates with thicknesses ranging from 0.3 to 5.0 mm. Experimental results showed that the minimum heat flux (MHF) temperature increased as the plate heat capacity per unit area decreased. A theoretical model was developed to predict the MHF temperature and regime transition time, defined as the time required to reach the MHF point, and agreed well with experimental data, with MAPEs of 7.1% and 14.9%, respectively. The theoretical model identified three parameters governing quenching: (1) lumped capacitance time scale associated with transient heat conduction, (2) excess MHF temperature, and (3) local temperature drop resulting from liquid-solid contact. According to the first parameter, the regime transition time is linearly proportional to the heat capacity. The second one describes the dependence of MHF temperature on heat capacity, with smaller heat capacity leading to higher MHF temperature and shorter regime transition time. The third one accounts for thermal effusivity and diffusivity effects on regime transition, which are negligible when these properties are sufficiently high. Finally, a universal approach to understanding quenching is proposed: the contribution of transient conduction can first be isolated, as evidenced by the collapse of quenching curves onto a single curve independent of material and geometric parameters. This, in turn, enables a systematic analysis of the effects of individual parameters on regime transition. 2026-08-31T15:00:00Z https://scholarworks.unist.ac.kr/handle/201301/91251 Title: Structural characterization and bonding energy analysis for plasma-activated bonding of SiCN films: A reactive molecular dynamics study Author(s): Kim, Juheon; Jang, Minki; Choi, Won Hong; Park, Junhyeok; Kim, Byungjo; Kim, Sunghyup; Chung, Hayoung Abstract: Plasma-activated bonding of SiCN films enables high interfacial bonding strength, which is essential for the mechanical reliability of hybrid bonding technologies. While experimental studies have shown that the interfacial bonding properties of SiCN films depend on both film composition and plasma treatment conditions, the underlying atomistic correlations have not yet been established. In this work, we present an atomistic investigation of SiCN-SiCN plasma-activated bonding using reactive molecular dynamics simulations, focusing on the effects of SiCN composition and plasma fluence. The simulation model includes O2 plasma surface activation, surface hydroxylation, direct bonding, post-bonding annealing, and interfacial debonding. Structural analysis of plasma-activated SiCN surfaces reveals composition- and plasma fluence-dependent chemical and morphological modifications, characterized by changes in specific covalent bond density and surface roughness. Bonding energy, evaluated from traction-separation responses during debonding simulations, exhibits a positive correlation with the density of interfacial Si-O-Si linkages. As the interfacial Si-O-Si density reflects the combined effects of chemical activation and surface morphology, the dependence of bonding energy on both composition and plasma fluence can be interpreted at the atomic scale. These findings establish an atomic-level material-process-property relationship and provide practical guidance for selecting SiCN composition and plasma treatment conditions to enhance plasma-activated SiCN-SiCN bonding. 2026-06-30T15:00:00Z https://scholarworks.unist.ac.kr/handle/201301/91209 Title: Controlling the electron-hole separation in photo-assisted C-C coupling reactions catalysed by a RuO2-ZnO heterojunction loaded with ultra trace palladium Author(s): Bora, Tonmoy J.; Kim, Donguk; Park, Young-Bin; Phukan, Gaurisankar; Islam, Shamim; Devi, Arpita; Bania, Kusum K. Abstract: Zinc-oxide (ZnO) in combination with ruthenium-oxide (RuO2) appeared to be an effective light harvesting heterojunction, controlling the electron (e-) and hole (h+) recombination rate. An ultra-trace amount of palladium (Pd) loaded into this RuO2-ZnO hybrid heterojunction enabled a new, sustainable, cost-effective yet highly efficient non-free radical photocatalytic pathway for the Suzuki-Miyaura cross-coupling (SMCC) reaction, achieving superior selectivity and biaryl product yields over existing methods. Although research has aimed at improving photocatalysts' performance in SMCC, no study has yet been performed to understand such heterojunctions in the photocatalytic SMCC reaction. In the catalyst, ZnO retained its original role by absorbing UV-light, while RuO2, on the other hand, played a crucial role as a quasi-metallic co-catalyst favouring charge-carrier transportation. This cooperative charge-management strategy resulted in prolonged charge separation, enhanced redox-activity, and maximized the utilization of Pd centres. The reaction proceeded with 100% selectivity and provided excellent yields (up to 98%) within a very short reaction time of 70 min in a greener methanol/water (MeOH/H2O) solvent system. Some of the resulting SMCC keto-derivative products were reduced to synthesize a new range of important alcohol derivatives, further expanding the study. An in-depth kinetic study provided deeper insight into the reaction dynamics, while a systematic mechanistic analysis elucidated the charge carriers involved. Density functional theory (DFT) analysis was also performed to examine and compare the interactions involved in the photocatalysts. This work thus demonstrated a photostable, heterogeneous, recyclable, cost-effective, non-free radical and greener photocatalytic pathway for the SMCC reaction, highlighting the potential of multi-component semiconductor-metal architectures in the selective SMCC reaction with significantly low Pd loading. 2026-01-31T15:00:00Z https://scholarworks.unist.ac.kr/handle/201301/91208 Title: Topology optimization of thermoelectric generator for maximum power efficiency Author(s): Lee, Jungsoo; Yang, Seong Eun; Choo, Seungjun; Li, Haiyang; Han, Hyunjin; Kim, Keonkuk; Park, Yae Eun; Lee, Ho Hyeong; Suh, Dong-Woo; Chung, Hayoung; Son, Jae Sung Abstract: Thermoelectric generators offer a promising approach for harvesting waste heat from both natural and human-made sources, enabling sustainable electricity generation. While geometric design plays a crucial role in optimizing device performance, conventional approaches remain confined to simple configurations, limiting efficiency improvements. This constraint arises from the complex interplay of multiphysical interactions and diverse thermal environments, which complicates structural optimization. Here, we introduce a universal design framework that integrates topology optimization (TO) with additive manufacturing to systematically derive high-efficiency thermoelectric 3D architectures. By formulating an optimization problem to maximize power generation efficiency, our approach explores an unprecedentedly large design space, optimizing the geometries of thermoelectric materials across diverse thermal boundary conditions and material properties. The resulting TO-derived geometries consistently outperform conventional cuboids, demonstrating significant efficiency gains. Beyond in-silico studies, we provide theoretical insights and experimental validation, confirming the feasibility of our design approach. Our study offers a transformative way for enhancing thermoelectric power generation, with broad implications for next-generation sustainable energy technologies. 2026-01-31T15:00:00Z