Dayu Zhou

Motivated by recent EAST experiments showing that Li pellet injection from the high-field side triggers much smaller Edge localized modes (ELMs) than outer-midplane (OMP) injection, a BOUT++ three-field MHD model coupled with impurity effects has been employed to investigate how the poloidal injection angle affects the triggering and subsequent evolution of ELMs. To this end, two scenarios are considered, in which Li pellets are injected near the upper X -point from the low-field side (LFS-UP) and the high-field side (HFS-UP), respectively. The OMP simulation data obtained within the numerical framework established in our previous study are also included for comparison. The simulations show that the ELM-triggering threshold decreases as the poloidal injection angle shifts from the OMP toward the HFS; the trend is associated with the easier excitation of a low- n mode capable of reaching the amplitude required for ELM triggering. The subsequent ELM evolution also depends on the poloidal injection angle. In the LFS-UP scenario, the ELM undergoes phases of linear growth, fast crash, turbulent transport, and saturation, similar to that in the OMP scenario. In contrast, in the HFS-UP scenario, the nonlinear dominant mode is suppressed shortly after ELM onset by the stronger stabilizing effect of the pedestal E × B flow shear, leading to a negligible fast crash phase. Meanwhile, the inward spreading of the pressure perturbation is constrained near the pedestal top. The rapid mode suppression, together with the restricted inward spreading of the pressure perturbation, prevents the ELM from developing into a large crash. Accordingly, the HFS-UP scenario exhibits a parameter window for small pellets in which the triggered ELM causes a pedestal energy loss of about 0.1% or less. The present results provide a plausible physical explanation for the EAST observations.

The dielectric reliability of wurtzite ZnMgO thin-film capacitors is closely associated with intrinsic donor defects, such as singly ionized oxygen vacancies and zinc interstitials; however, the relationship between the evolution of point defects and dielectric reliability remains insufficiently understood. Here, ZnMgO films were independently deposited at different cumulative sputtering times while the other deposition parameters were maintained constant, enabling systematic investigation of the relationship between defect evolution and electrical performance. Photoluminescence and x-ray photoelectron spectroscopy analyses revealed a redistribution of defect-related components, progressive suppression of donor-type defect-related signals, and stabilization of the near-surface chemical environment with increasing cumulative sputtering time. These changes were accompanied by lower leakage currents and improved breakdown reliability, with the characteristic breakdown field increasing from 2.36 to 3.22 MV/cm. In addition, the EBD/EC ratio increased from below 1.0 to approximately 1.4, expanding the electric-field window available for polarization switching. Within this enlarged window, distinct polarization-switching current peaks were observed in the I–E curves, and a dynamic ferroelectric response was detected in the P–E and PUND measurements for the 48 h sample. These findings highlight a sample-level correlation among point-defect evolution, dielectric reliability, and ferroelectric response in wurtzite ZnMgO thin films.

The performance and reliability of wurtzite-type ferroelectric AlScN films are critically influenced by point defects, particularly nitrogen vacancies (VN·,(··),(···)), although a systematic understanding of their impact remains limited. This study demonstrates the effective modulation of point defects in AlScN films by controlling the Ar/N2 ratio during sputtering and employing successive depositions under a pure N2 atmosphere. We reveal that a high density of point defects induces domain pinning and leads to the split switching current peak. Furthermore, the reduction of point defects facilitates a transition in the switching kinetics from the nucleation-limited switching model to the Kolmogorov–Avrami–Ishibashi model, indicating a defect-mediated evolution from a multi-domain to a more uniform domain structure. Ultimately, this defect-engineering strategy enables an endurance of over 107 cycles in AlScN-based capacitors. These findings establish defect engineering as a viable pathway to optimize performance and endurance in AlScN-based memory devices.

本研究系统探讨了氧分压（40%-100%）对磁控溅射制备的Zn_0.6Mg_0.4O_(1-δ)薄膜结构、缺陷以及电学性能的调控规律与物理机制。结果表明，氧分压在80%以下时，薄膜呈现高结晶质量、强c轴择优取向的柱状晶结构。结合X射线光电子能谱和光致发光光谱结果分析发现，氧分压可以有效调控薄膜中的本征缺陷类型，高氧分压显著抑制薄膜内氧空位与金属间隙缺陷的形成。这类缺陷浓度的降低，使薄膜漏电流显著降低，介电可靠性大幅增强。铁电性能测试进一步表明，在60%-100%氧分压范围内薄膜均表现出清晰的翻转电流峰，验证了其铁电性；而剩余极化强度值随氧分压上升而下降的趋势，则揭示了高度一致的c轴择优取向是实现纤锌矿结构铁电薄膜高效极化翻转的关键结构基础。宽频介电谱有效区分了体极化与表面极化的贡献，证实低氧分压条件下表面极化贡献增强。本工作阐明了通过氧分压调控Zn_0.6Mg_0.4O_(1-δ)薄膜微观结构、缺陷类型与浓度以及宏观电学性能的协同机制，为其在高性能铁电存储器中的应用提供了重要依据。