Unveiling Defect-Mediated Carrier Dynamics in Monolayer Semiconductors by Spatiotemporal Microwave Imaging

The optoelectronic properties of atomically thin transition-metal dichalcogenides are strongly correlated with the presence of defects in the materials, which are not necessarily detrimental for certain applications. For instance, defects can lead to an enhanced photoconduction, a complicated process involving charge generation and recombination in the time domain and carrier transport in the spatial domain. Here, we report the simultaneous spatial and temporal photoconductivity imaging in two types of WS2 monolayers by laser-illuminated microwave impedance microscopy. The diffusion length and carrier lifetime were directly extracted from the spatial profile and temporal relaxation of microwave signals respectively. Time-resolved experiments indicate that the critical process for photo-excited carriers is the escape of holes from trap states, which prolongs the apparent lifetime of mobile electrons in the conduction band. As a result, counterintuitively, the photoconductivity is stronger in CVD samples than exfoliated monolayers with a lower defect density. Our work reveals the intrinsic time and length scales of electrical response to photo-excitation in van der Waals materials, which is essential for their applications in novel optoelectronic devices.Comment: 21 pages, 4 figure

Field-free switching of magnetization in oxide superlattice by engineering the interfacial reconstruction

Spin-orbit torque resulting from non-magnetic materials with strong spin-orbit coupling enables electrically controlled magnetization switching, offering potential applications in ultralow-power memory and logic devices. However, such switching of perpendicular magnetization usually requires an in-plane magnetic field along the applied current direction, which limits its use. To address this challenge, an all-oxide superlattice is designed and fabricated that show both the perpendicular magneto-crystalline anisotropy and in-plane magnetic anisotropies induced by interfacial engineering. The results demonstrate that the coexistence of perpendicular and in plane magnetic anisotropy breaks the symmetry and thus enables the pure electrical switching of perpendicular magnetization.This work was supported by the King Abdullah University of Science and Technology (KAUST), Office of Sponsored Research (OSR), under award Nos. ORA-CRG10-2021-4665 and ORA-CRG11-2022-5031.Peer reviewe

Current-driven magnetization switching in a van der Waals ferromagnet Fe3GeTe2

The recent discovery of ferromagnetism in two-dimensional (2D) van der Waals (vdW) materials holds promises for novel spintronic devices with exceptional performances. However, in order to utilize 2D vdW magnets for building spintronic nanodevices such as magnetic memories, key challenges remain in terms of effectively switching the magnetization from one state to the other electrically. Here, we devise a bilayer structure of Fe3GeTe2/Pt, in which the magnetization of few-layered Fe3GeTe2 can be effectively switched by the spin-orbit torques (SOTs) originated from the current flowing in the Pt layer. The effective magnetic fields corresponding to the SOTs are further quantitatively characterized using harmonic measurements. Our demonstration of the SOT-driven magnetization switching in a 2D vdW magnet could pave the way for implementing low-dimensional materials in the next-generation spintronic applications

Biocontrol potential of two deep-sea microorganisms against gray blight disease of tea

Abstract Background Gray blight is among the most destructive diseases that affect tea plants worldwide. In this study, microorganisms from deep-sea sediment samples for those with antagonistic effects were screened against gray blight caused by Pestalotiopsis theae. Results Thirty-two and twenty-eight morphologically different deep-sea bacteria and fungi were isolated, respectively. Isolates B5 and A65 clearly inhibited the pathogens in vitro and were prepared as wettable agent powders for evaluation in micro-plot field trials. Foliar application of the 48-h culture of B5 (1 × 108, 2 × 107, 1 × 107 colony-forming units (CFU)/ml) significantly reduced the incidence of gray blight disease. Compared to the untreated control, spraying with B5 inhibited gray blight disease by 78.57%. Isolate B5 was identified as Bacillus subtilis B5 in morphological and 16S rDNA sequence analyses. The foliar application of 7-day cultures of A65 (1 × 108, 2 × 107, 1 × 107 CFU/ml) significantly reduced the incidence of gray blight disease. A65 (108 CFU/ml) inhibited gray blight disease by 75.46% and was identified as Paecilomyces lilacinus A65 in morphologically and internally transcribed spacer sequence analyses. Conclusions These candidate microbial pesticides may inhibit gray wilt in tea, replace chemical pesticides’ use without causing environmental pollution, and promote the development of green agriculture