https://scholarworks.unist.ac.kr/handle/201301/49 2026-04-18T16:24:33Z https://scholarworks.unist.ac.kr/handle/201301/91359 Title: Highly Enhanced Directional Emission from Emitter-Integrated Dielectric Metasurfaces: Role of the Emitter Layer Author(s): Han, Jungho; Jang, Heejoo; Kim, Yugyeong; Lee, Jeheon; Jun, Young Chul Abstract: Combining semiconductor quantum dots (QDs) with dielectric metasurfaces offers a promising platform for enhancing and controlling light emission properties. Highly enhanced directional and polarized emission is experimentally demonstrated from dielectric metasurfaces integrated with colloidal QDs. Specifically, emission enhancements from InP/ZnS QD- and CdSe/ZnS QD-integrated metasurfaces are directly compared. It is found that low absorption losses in the emitter layer can drastically increase the maximum achievable enhancement when different QDs are coated on the same metasurface. In particular, the lower intrinsic losses of the InP/ZnS QD layer enable dramatically enhanced vertical emission with narrow angular divergence, achieving a 140-fold enhancement in experiment. Our detailed experimental and theoretical investigations indicate the critical role of the emitter layer in the design of the emitter-integrated metasurface. Strong agreement between simulation and experiment confirms the critical-coupling behavior in maximized emission enhancement. Our study provides general guidelines for the development of directional light sources. Compact light sources with high directionality and controlled polarization hold strong potential for applications in displays, optical communications, sensing, and imaging. 2026-03-31T15:00:00Z https://scholarworks.unist.ac.kr/handle/201301/91352 Title: Processing and optimization of textured (Na0.5Bi0.5)TiO3-BaTiO3-SrTiO3 incipient piezoelectric ceramics by Templated Grain Growth using NaNbO3 templates Author(s): Ecebas, Nazim; Ayuningsih, Arum; Tran, Tran Thi Huyen; Fisher, John G.; Lee, Jong-Sook; Choi, Woo-Jin; Jo, Wook Abstract: Due to their large electric field-induced strains, (Na0.5Bi0.5)TiO3 (NBT)-based lead-free piezoceramics show promise to replace lead-containing piezoelectric materials in actuator applications. However, they have some disadvantages such as large strain hysteresis and a requirement for high electric driving fields. The combined effects of chemical modification and crystallographic orientation in specific directions are effective strategies for overcoming the drawbacks of NBT-based ceramics. Chemical modification of NBT-BaTiO3 by the addition of SrTiO3 can transform it into an incipient piezoelectric, characterized by large electric field-induced strains but accompanied by significant hysteresis. To overcome this limitation, in the present work strain hysteresis is reduced by enhancing ergodicity and boosting the electrostrictive effect through the incorporation of NaNbO3 templates. At the same time, maximum strain is improved by inducing {001} crystallographic orientation via the Templated Grain Growth (TGG) method. The combination of {001} crystallographic orientation with enhanced ergodicity has improved unipolar strain (S-uni = 0.203%) and electrostrictive coefficient (Q(33) = 0.0288 m(4)/C-2) while significantly reducing strain hysteresis (H = 21.6%) at an electric field of 3.5 kV/mm in the 3 wt% NaNbO3 textured sample, compared to an untextured counterpart (S-uni = 0.13%, Q(33) = 0.0136 m(4)/C-2 and H = 47.2%). These results demonstrate that combining Templated Grain Growth with increased ergodic and electrostrictive behavior is an effective approach to reduce hysteresis while enhancing strain. 2026-02-28T15:00:00Z https://scholarworks.unist.ac.kr/handle/201301/91348 Title: Polymer-scaffold-guided graphitization for high thermal conductivity in SWCNT-derived carbon fibers Author(s): Heo, So Jeong; Kim, Jiyeon; Jin, Jeong-Un; Jeon, Changbeom; Kim, Jungwon; You, Nam-Ho; Chae, Han Gi; Kim, Seo Gyun; Ku, Bon-Cheol Abstract: Carbon nanotube (CNT) fibers exhibit outstanding intrinsic properties, yet their macroscopic performance is often limited by structural disorder, void formation, and collapse during high-temperature processing. Here, we introduce a polymer-scaffold-guided graphitization strategy in which polyimide (PI) functions as a thermally stable scaffold to maintain CNT alignment, suppress collapse, and regulate structural evolution. Upon heat treatment up to 2900 degrees C, the PI-containing CNT fibers exhibited enhanced graphitic ordering, extended axial correlation length, and reduced interlayer spacing, as confirmed by Raman spectroscopy, small-angle and wideangle X-ray scattering (SAXS and WAXS). Notably, the CNT/PI fiber with 50% PI content achieved a correlation length of 13.7 nm, leading to exceptional thermal conductivity (534 + 91 W m- 1K- 1), electrical conductivity (0.64 + 0.02 MS m- 1), tensile strength (3.26 + 0.3 GPa) and modulus (870+ 138 GPa). These findings demonstrate that PI acts not only as a reinforcing polymer but also as a structural scaffold that guides graphitization and directional phonon transport, enabling the design of high-performance, anisotropic CNT-based fibers for thermal management and advanced structural applications. 2026-03-31T15:00:00Z https://scholarworks.unist.ac.kr/handle/201301/91340 Title: Anomalous Pressure-Temperature Ultrahigh Sensitivities in Atomically Engineered Carbonitride MXenes for Multifunctional Wearable Human-Machine Interfaces: Joint Computational-Experimental Elucidations Author(s): Mohapatra, Debananda; Han, Ju-Hyoung; Kang, Hyun Jin; Byun, Jeong Eun; Lee, Seonghun; Lee, Sanghyuk; Son, Yeseul; Park, Jaeeun; Shin, Tae Joo; Kang, Youngho; Lee, Jung Woo; Kwon, Soon-Yong; Kim, Soo-Hyun Abstract: In the era of autonomous systems and multifunctional devices, sensors serve as vital sensory components in our Internet of Things and technologically advanced society. At the end of the synthetic 2D nanomaterials research, MXenes are not just chemicals but materials, depending on how they are synthesized for targeted applications, such as dual-functional temperature and pressure-sensitive wearable sensing. The current findings introduce the potential strategic role of nitrogen atoms to the Ti-Carbonitride (Ti3CNTz) structure in a controlled compositional stoichiometry of Ti3C1.8N0.2Tz, Ti3C1.5N0.5Tz, Ti3CNTz, Ti3C2Tx to deliver an ultrahigh sensitivity (300%-400% temperature & pressure sensitivity enhancement) and durability in real-time human-machine sensing interface applications. These recorded outstanding dual-sensing performance outplays many other MXene stoichiometries, graphene-related 2D nanomaterials, and their associated composites. Synchrotron radiation-based X-ray absorption fine structure and density functional theory analysis reveal that incorporating low N content (e.g., Ti3C1.8N0.2Tz) enhances temperature sensitivity by boosting electrical conductivity, and an upshift in the vibrational spectrum with increased lattice deformability significantly improves pressure sensitivity. We provide valuable insights for developing advanced sensing materials, emphasizing the need to investigate the fundamental mechanisms that control the interactions among layered 2D MXene materials and the sensing device functions that bridge human and machine interfaces. 2026-03-31T15:00:00Z