Relaxation frequencies for flip-flop rotation of three- and four-ring compounds and dual frequency addressing mixtures with high birefringence

Relaxation frequencies f_r characterising the molecular rotation around the short axes (flip-flop movement) of 45 three- and four-ring polar compounds with high birefringence (mainly cyclohexyl, phenyl and biphenyl tolanes and quaterphenyls terminated with F, OCF₃, NCS group) have been measured. These compounds exhibit a large positive dielectric anisotropy Δε = ε_║ ? ε_⊥ in the nematic phase and relatively low f_r values (in the range of dozens kHz). The dependence of f_r upon molecular structures and physical properties of systems (molecular rigid core length, polarity and viscosity) is discussed. Mixtures for dual frequencies addressing display with the crossover frequency f_co of the order of ~1 kHz have been prepared by joining the above compounds with a mixture consisted of two, three and four fluoro-substituted in the lateral position tolanes and phenyltolanes showing negative dielectric anisotropy. It was stated that relaxation frequency is correlated mainly with their length and polarity.     

基于微分几何的平面天线阵列测向精度研究

利用阵列流形的微分几何作为分析工具,构造了实际使用中常见的平面天线阵的几何结构,并对这些阵列结构的测向精度进行了研究和全面仿真。通过比较各种天线阵几何结构的优劣,可以从中选择一种合适的、最优的阵列结构,避免设计的盲目性和随意性。这为超分辨阵列结构的选择和设计提供了一条有效的途径,在实际应用中将具有十分重要的参考价值。     

氟化氘激光大气传输的定标规律

 利用激光大气传输4维程序,结合均方和半径分析方法,对氟化氘（DF）激光大气传输的定标规律进行了数值分析。得到了焦平面处63.2%环围能量半径的光斑扩展规律以及在焦平面上不同环围能量半径内的平均功率密度定标关系式。此定标关系不仅适用于大菲涅耳数、弱传输效应条件下,同时也适用于小菲涅耳数、强传输效应条件下DF高能激光大气传输,从而能够对激光大气传输的效果做出快速地预测和有效地评估。     

In Operando Optical Tracking of Oxygen Vacancy Migration and Phase Change in few Nanometers Ferroelectric HZO Memories

Ferroelectric materials offer a low-energy, high-speed alternative to conventional logic and memory circuitry. Hafnia-based films have achieved single-digit nm ferroelectricity, enabling further device miniaturization. However, they can exhibit nonideal behavior, specifically wake-up and fatigue effects, leading to unpredictable performance variation over consecutive electronic switching cycles, preventing large-scale commercialization. The origins are still under debate. Using plasmon-enhanced spectroscopy, a non-destructive technique sensitive to <1% oxygen vacancy variation, phase changes, and single switching cycle resolution, the first real-time in operando nanoscale direct tracking of oxygen vacancy migration in 5 nm hafnium zirconium oxide during a pre-wake-up stage is provided. It is shown that the pre-wake-up leads to a structural phase change from monoclinic to orthorhombic phase, which further determines the device wake-up. Further migration of oxygen ions in the phase changed material is then observed, producing device fatigue. These results provide a comprehensive explanation for the wake-up and fatigue with Raman, photoluminescence and darkfield spectroscopy, combined with density functional theory and finite-difference time-domain simulations.