Dispersion retrieval from multi-level ultra-deep reactive-ion-etched microstructures for terahertz slow-wave circuits

A multi-level microstructure is proposed for terahertz slow-wave circuits, with dispersion relation retrieved by scattering parameter measurements. The measured return loss shows strong resonances above the cutoff with negligible phase shifts compared with finite element analysis. Splitting the circuit into multi levels enables a low aspect ratio configuration that alleviates the loading effect of deep-reactive-ion etching on silicon wafers. This makes it easier to achieve flat-etched bottom and smooth sidewall profiles. The dispersion retrieved from the measurement, therefore, corresponds well to the theoretical estimation. The result provides a straightforward way to the precise determination of dispersions in terahertz vacuum electronics.</jats:p

Effect of substitution of K for Na on the ferroelectric stability and properties in (Bi0.5Na1/2)TiO3-BaTiO3-(K1/2N1/2)NbO3

The effect of an isovalent chemical variation in A site cations on the stability of ferroelectric order and consequent changes in the electrical properties of ferroelectric 0.93(Bi1/2Na1/2)TiO3-0.05BaTiO3-0.02(K0.5Na0.5)NbO3 (0.93BNT-0.05BT-0.02KNN) lead-free piezoceramic at the morphotropic phase boundary (MPB) was investigated by substituting K for Na. X-ray diffraction analysis reveals that all the studied compositions undergo an irreversible phase transition from a pseudocubic to a mixture of rhombohedral and tetragonal phases during poling. In spite of the absence of an obvious structural difference, both electric-field-induced strain and polarization hysteresis loops show a clear distinction. It was found that the effect of substitution is so drastic that about 0.5 at% substitution renders the material softer and more than 1.0 at% results in a significant destabilization of the ferroelectric order. However, no notable difference in the temperature dependent permittivity measurements was detected, which suggests that the depoling of these materials has some other origin than a symmetry-breaking phase transition

Long-Term Chemical Aging of Hybrid Halide Perovskites

Because the power conversion efficiency (PCE) of hybrid halide perovskite solar cells (PSCs) could exceed 24%, extensive research has been focused on improving their long-term stability for commercialization in the near future. In a previous study, we reported that the addition of a number of ionized iodide (triiodide: I-3(-)) ions during perovskite film formation significantly improved the efficiency of PSCs by reducing deep-level defects in the perovskite layer. Understanding the relationship between the concentration of these defects and the long-term chemical aging of PSCs is important not only for obtaining fundamental insight into the perovskite materials but also for studying the long-term chemical stability of PSCs. Herein we aim to identify the origin of the natural decay in PCE during long-term chemical aging of PSCs in the dark based on formamidinium lead triiodide by comparing the performance of control and low-defect (LD) devices. After aging for 200 days, the change in the PCE of the LD devices (1.3%) was found to be half that of the control devices (2.6%). We investigated this difference using grazing incidence wide-angle X-ray scattering, deep level transient spectroscopy, scanning photoelectron microscopy, and high-resolution photoemission spectroscopy. The addition of I-3(-) was found to reduce the amounts of hydroxide and O-x in the halide perovskites (HPs), affecting the migration of defects and the structural transformation of the HPs

Terahertz Field-Induced Reemergence of Quenched Photoluminescence in Quantum Dots

The continuous and concerted development of colloidal quantum dot light-emitting diodes over the past two decades has established them as a bedrock technology for the next generation of displays. However, a fundamental issue that limits the performance of these devices is the quenching of photoluminescence due to excess charges from conductive charge transport layers. Although device designs have leveraged various workarounds, doing so often comes at the cost of limiting efficient charge injection. Here we demonstrate that high-field terahertz (THz) pulses can dramatically brighten quenched QDs on metallic surfaces, an effect that persists for minutes after THz irradiation. This phenomenon is attributed to the ability of the THz field to remove excess charges, thereby reducing trion and nonradiative Auger recombination. Our findings show that THz technologies can be used to suppress and control such undesired nonradiative decay, potentially in a variety of luminescent materials for future device applications

Comparison of 7-day and 14-day proton pump inhibitor-containing triple therapy for Helicobacter pylori eradication: neither treatment duration provides acceptable eradication rate in Korea

BACKGROUND AND AIMS: Although triple combination therapy containing a proton pump inhibitor (PPI) and two antibiotics is considered as a standard regimen for the first-line anti-Helicobacter pylori treatment, there are still debates on the ideal duration of treatment. The aim of this study was to compare the efficacies of 7-day and 14-day PPI-containing triple therapy. MATERIALS AND METHODS: This study was performed in a randomized, multicenter, prospective manner. After upper gastrointestinal endoscopy, H. pylori-infected patients with a gastric ulcer and/or a duodenal ulcer were randomly assigned to a PAC7 group (omeprazole 20 mg or equivalent dose of other PPIs, amoxicillin 1000 mg, and clarithromycin 500 mg twice daily for 7 days) or to a PAC14 group (the same regimen as the PAC7 group but for 14 days). H. pylori status was evaluated by (13)C urea breath test 5 weeks after anti-ulcer treatment completion. RESULTS: A total of 598 patients were enrolled; 337 were randomized to the PAC7 group and 261 to the PAC14 group. The two groups were comparable in terms of baseline characteristics. The eradication rates of the PAC7 group were not inferior to those of the PAC14 group in both intention-to-treat analysis (71.2% vs. 75.5%) and per-protocol analysis (83.6% vs. 86.6%). Incidences of adverse events were comparable. CONCLUSIONS: Although the 7-day PPI-containing triple anti-H. pylori therapy is not inferior to the 14-day therapy, neither treatment duration provides acceptable eradication rate reaching 90% in per-protocol analysis. New combination regimen with higher efficacy should be developed as a first-line eradication therapy for H. pylori in Korea