https://scholar.dgist.ac.kr/handle/20.500.11750/820 Fri, 24 Apr 2026 18:38:25 GMT 2026-04-24T18:38:25Z https://scholar.dgist.ac.kr/handle/20.500.11750/60218 Title: A Hidden Photoinduced Phase-Transition Pathway in Strain-Engineered VO2 Author(s): Park, Soon Hee; Park, Jaeku; Kim, Hyeong-Do; Choi, Songhee; Lee, Shinbuhm; Kim, Jong-Woo; Cho, Byeong-Gwan; Koo, Tae-Young; Eom, Intae; Kim, Minseok; Jang, Dogeun; Choi, Hyeongi; Park, Gwangryeol; Kim, Kyung Sook; Park, Sang-Youn; Shin, Hee Jun; Chae, Bok Nam; Park, Jaehun; Chun, Sae Hwan Abstract: Photoexcitation provides a versatile route to drive quantum materials into nonequilibrium states, opening opportunities for phase engineering beyond conventional tuning parameters such as temperature, magnetic field, pressure, or chemical doping/substitution. VO2, a prototypical correlated oxide, has long served as a model system for understanding photoinduced insulator-metal transitions, yet the sequence of structural and electronic transitions remains intensely debated. Here, we uncover a hidden photoinduced transition pathway in epitaxially strained VO2 thin films, in which the structural transition precedes the electronic insulator-metal transition, reversing the canonical temporal order. Femtosecond X-ray diffraction reveals a transient structural state characterized by the disappearance of vanadium dimers generating dynamic tensile strain, while time-resolved terahertz spectroscopy shows that the electronic gap closes only after the strain relaxation. This lattice-driven transition highlights the pivotal role of Mott correlations in dictating electronic properties under nonequilibrium conditions. Our findings establish strain-light coupling as a design principle for ultrafast control of phase transitions, offering new avenues for reconfigurable electronic and photonic devices based on correlated oxides. Sat, 31 Jan 2026 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/60218 2026-01-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60031 Title: Achieving wide-range steep slopes in SnS2 negative capacitance transistors through an isolated band structure and thermionic emission enhancement via Bi contacts Author(s): Song, Chong-Myeong; Park, Jaewoo; Lee, Shinbuhm; Kwon, Hyuk-Jun Abstract: Negative capacitance FETs aim for sub-60 mV dec-1 switching to curb power consumption, but often encounter instability and narrow steep-slope windows. We present a hysteresis-free NCFET that strategically utilizes a 2D SnS2 channel. The inherent isolated conduction band of SnS2, yielding a step-like density of states, is pivotal for sharp turn-on characteristics when effectively coupled with the negative capacitance effect. The SnS2 channel is integrated with an La:HfO2/HfO2 ferroelectric-dielectric gate stack and Bi contacts. This architecture shows an average subthreshold swing of 34 mV dec-1 across four current decades, maintaining sub-60 mV dec-1 operation over this wide range, and enabling sub-0.4 V operation. Bi contact is key, minimizing Fermi-level pinning at the SnS2/metal interface. This expands the thermionic emission region, allowing the negative capacitance to fully leverage the distinct properties of SnS2 for sustained wide-range steep-slope performance. This work demonstrates a novel approach to ultralow-power transistors by integrating an isolated-band semiconductor, optimized ferroelectric, and contact engineering. Sun, 30 Nov 2025 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/60031 2025-11-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/59910 Title: Tunable Hydrogen Dynamics Under Electrical Bias for Neuromorphic Memory Applications Author(s): Noh, Hee Yeon; Lee, Chan-Kang; Haripriya, Gopalakrishnan Nair Ramani; Lee, Shinbuhm; Lee, Myoung-Jae; Wee, Jiyong; Lee, Hyeon-Jun Abstract: A wide variety of materials and device architectures have been explored for memristor applications targeting neural network simulations, most of which rely on oxide-based structures that exhibit resistive switching driven by oxygen-vacancy-mediated memory effects. In this study, we present a novel approach for modulating resistive and nonvolatile memory behavior in oxide semiconductors through the controlled injection and extraction of hydrogen. The proposed two-terminal device incorporates a hydrogen source layer that facilitates the diffusion of hydrogen ions into the active oxide matrix, where they form hydroxide (OH) bonds and locally modulate the electron concentration. This process induces a stable and reversible memory effect under an applied electric field. Hydrogen exchange predominantly occurs at the interface between the active and insulating layers, with the latter serving as a buffer to maintain an optimal hydrogen concentration. Furthermore, neural network simulations were performed by utilizing the synaptic characteristics controlled via hydrogen modulation, achieving a recognition accuracy of 97.2% on the MNIST data set. The effects of input data resolution and weight quantization on recognition performance were also systematically investigated and discussed. Sat, 31 Jan 2026 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/59910 2026-01-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/59348 Title: High Oxygen Ion Conductivity in Hexagonal Perovskite Ba7Nb4MoO20 via Epitaxy-Assisted Orienting of Two-Dimensional Diffusion Pathways Author(s): Kim, Yunyeong; Kim, Dongha; Park, Jiseok; Chen, Aiping; MacManus-Driscoll, Judith L.; Lee, Shinbuhm Abstract: Oxygen ion conductors are a key component in solid-state ionic devices such as fuel cells, catalysts, sensors, and artificial intelligent devices. The recent discovery of undoped Ba7Nb4MoO20 hexagonal perovskites has attracted great attention due to the existence of two-dimensional oxygen diffusion pathways between NbO4 and MoO4 tetrahedra. However, there have been rare studies on the control parameters for hexagonal perovskites to further boost oxygen ion transport at lower temperatures. Here, we find significantly higher oxygen ion conductivity (5.6 x 10(-4) S cm(-1) at 340 degrees C, 3.2 x 10(-1) S cm(-1) at 600 degrees C) of (001)-oriented Ba7Nb4MoO20 epitaxial films by several orders of magnitude than that of sintered pellets. Our report is comparable to the oxygen ion conductivities of conventional doped conductors. X-ray diffraction and atomic-scale characterization with energy-dispersive X-ray spectroscopy reveal that this epitaxy-driven enhancement is attributed to the good alignment of two-dimensional pathways in an ion current direction. Our design principle of hexagonal perovskites will trigger an advanced understanding of the correlation between the crystal structure and ultrahigh oxygen ion conductivity Sun, 31 Aug 2025 15:00:00 GMT https://scholar.dgist.ac.kr/handle/20.500.11750/59348 2025-08-31T15:00:00Z