https://scholar.dgist.ac.kr/handle/20.500.11750/10159 2026-10-27T05:17:40Z https://scholar.dgist.ac.kr/handle/20.500.11750/60998 Title: Ferroelectric polarization and bandgap engineering in perovskite oxide via sulfur diffusion Author(s): Ahmad, Munir; Duong, Nguyen Xuan; Yun, Won Seok; Ullah, Asif; Kim, Hwan Min; Ullah, Aman; Khan, Raj Wali; Suleman, Muhammad; Kim, Ill Won; Yun, Seok Joon; Shin, Young-Han; Sheeraz, Muhammad; Bae, Jong-Seong; Ahn, Chang Won Abstract: Surface and interface conditions strongly influence the ferroelectric properties of oxide films because such regions significantly affect the output performance by controlling the internal physics of ferroelectric capacitors. In this work, we recover the dead layer, probably formed due to oxygen vacancies, at the ferroelectric film surface using sulfur-diffusion-based surface modification. For this purpose, Pb(Zr,Ti)O3 (PZT) thin films are deposited via chemical solution deposition, with subsequent sulfur incorporation for surface chemical modification. Specifically, an as-deposited PZT film on Pt(111)/TiO2/SiO2/Si(100) is spin-coated with a thiourea (CH4N2S) solution, with sulfur atoms incorporated into the oxygen-deficient dead surface layer through thermal diffusion. This sulfur diffusion substantially enhances the ferroelectric polarization and dielectric characteristics of the films. Such enhancements are associated with an increase in the tetragonality of the PZT crystal structure, as confirmed by X-ray diffraction analysis. Furthermore, X-ray photoelectron spectroscopy depth profiling reveals efficient sulfur diffusion within the dead layer to depths around 150 nm. The chemical incorporation of sulfur atoms at oxygen vacancies is responsible for enhancing ferroelectric and dielectric properties and reducing the bandgap. This study provides an approach for surface defect engineering in oxide ferroelectrics, offering new insights into the restoration of dead layers and their role in enhancing ferroelectric-photovoltaic performance. 2026-08-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60997 Title: Reversal of interlayer exchange coupling through post-annealing process accompanying asymmetric crystallization in Ta/Co2Fe6B2/MgO/Co2Fe6B2/ MgO heterostructures Author(s): Kim, Tae-Hwan; Cho, Jaehun; Kim, Soojung; Hong, Jung-Il; Kim, June-Seo Abstract: The effect of the post-annealing process accompanying asymmetric crystallization on interlayer exchange coupling in the Ta/Co2Fe6B2/MgO/Co2Fe6B2/MgO heterostructure is systematically investigated using ferromagnetic resonance. To induce structural asymmetry, the bottom Co2Fe6B2 layer is in contact with a Ta buffer, which acts as a boron absorber, while the top Co2Fe6B2 layer is encapsulated between two MgO layers. Structural analysis and magnetization measurements confirm that the selective crystallization of the bottom Co2Fe6B2 layer is well established upon a thermal annealing process, while the top Co2Fe6B2 layer is remained as a disordered state. The ferromagnetic resonance spectra reveal distinct coupling regimes depending on the annealing state. In as-grown samples, an antiferromagnetic (AFM)-like coupling is observed for MgO thicknesses, tMgO above 2.0 nm. In particular, the post-annealing process can trigger a sign reversal of the interlayer exchange coupling to a ferromagnetic (FM)-like state in the thick spacer regime (tMgO ≥2.6 nm). 2026-08-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60993 Title: Gate-Reconfigurable Single- and Double-Dot Transport in Trilayer MoSe2 Author(s): Lee, Seungwoo; Park, Minjun; Noh, Yunsang; An, Sung Jin; Kim, Soyun; Cho, Minseo; Kim, Dohun; Taniguchi, Takashi; Watanabe, Kenji; Jung, Minkyung; Kim, Youngwook Abstract: We report gate-controlled quantum-dot transport in a trilayer MoSe2 device that combines a graphite back gate beneath the active region, a separate global gate for conductive access regions, and local top finger gates. In the low-backgate regime, bias spectroscopy shows regular Coulomb-blockade diamonds characteristic of single-dot transport. As backgate is increased, additional low-bias structure develops beyond a simple single-dot pattern, indicating that the electrostatic landscape is reshaped and that a second dot becomes active in transport. In the higher-backgate regime, plunger-gate tuning and two-gate measurements establish a gate-reconfigurable double-dot configuration with two non-equivalent dots whose relative alignment and interdot coupling evolve with gate voltage. These results indicate that trilayer MoSe2 supports electrically reconfigurable single- and double-dot transport in the present device architecture. 2026-08-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60964 Title: Interface engineering of IGZO/TiO2 heterostructure for UV driven analog memristive dynamics in in-sensor reservoir computing Author(s): Ghafoor, Faisal; Patil, Harshada; Kim, Honggyun; Gao, Lili; Li, Zhenting; Lee, Myoung-jae; Shi, Tuo; Kim, Deok-kee Abstract: Conventional machine vision systems face critical limitations, including substantial data latency and elevated energy consumption, due to the physical separation of memory, sensing, and processing units. In contrast, in-sensor computing, particularly using optoelectronic synapses, offers a promising paradigm shift by enabling direct sensing and processing of optical signals, thereby enhancing efficiency. Light-sensitive photodetectors exhibiting history-dependent dynamic responses further advance this field by facilitating temporal vision processing and time-series prediction without complex circuitry or excessive power demands. Recent approaches aim to emulate biologically inspired vision using light-modulated memristive behaviors. However, accurate realtime analog optical signal processing remains a significant challenge, necessitating the development of a photonic analog to electrically driven memristors. In this study, we introduce an optoelectronic synaptic device based on a TiO2/IGZO heterostructure, where ultraviolet (UV) photon flux triggers memristive behavior. We analyze photoexcited oxygen-vacancy (VO-) related defect states and activation energies to elucidate the correlation between photocarrier relaxation dynamics and optical synaptic behavior. The device demonstrates high recognition accuracy 98.01% (MNIST), 88.07% (FMNIST), and 96.10% (Weizmann dataset) within a 4-bit reservoir computing framework, highlighting its potential as an energy-efficient, cost-effective solution for real-time spatiotemporal optical signal processing in next-generation machine vision systems. 2026-07-31T15:00:00Z