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Herein, we employed lead-free Cs 3 Cu 2 I 5 perovskite films as the functional layers to construct Al/Cs 3 Cu 2 I 5 /ITO memory devices and systematically investigated the impact on the corresponding resistive switching (RS) performance via adding different amounts of hydroiodic acid (HI) in Cs 3 Cu 2 I 5 precursor solution. The results demonstrated that the crystallinity and morphology of the Cs 3 Cu 2 I 5 films can be improved and the resistive switching performance can be modulated by adding an appropriate amount of HI. The obtained Cs 3 Cu 2 I 5 films by adding 5 μL HI exhibit the fewest lattice defects and flattest surface (RMS = 13.3 nm). Besides, the memory device, utilizing the optimized films, has a low electroforming voltage (1.44 V), a large on/off ratio (∼65), and a long retention time (10 4 s). The RS performance impacted by adding HI, providing a scientific strategy for improving the RS performance of iodine halide perovskite-based memories.

Recently, several types of lead halide perovskites have been demonstrated as active layers in resistive switching memory or artificial synaptic devices for neuromorphic computing applications. However, the thermal instability and toxicity of lead halide perovskites severely restricted their further practical applications. Herein, the environmentally friendly and uniform Cs 3 Cu 2 I 5 perovskite films are introduced to act as the active layer in the Ag/Cs 3 Cu 2 I 5 /ITO memristor. Generally, the Ag ions could react with iodide ions and form AgI x compounds easily, so the Ag/PMMA/Cs 3 Cu 2 I 5 /ITO memristor was designed by employing the ultrathin polymethylmethacrylate (PMMA) layer to avoid the direct contact between the top Ag electrode and Cs 3 Cu 2 I 5 perovskite films. After optimization, the obtained memristor demonstrated bipolar resistive switching with low operating voltage (< ±1 V), large on/off ratio (10 2 ), stable endurance (100 cycles), and long retention (>10 4 s). Additionally, biological synaptic behaviors including long-term potentiation and long-term depression have been investigated. By using the MNIST handwritten recognition data set, the handwritten recognition rate based on experimental data could reach 94%. In conclusion, our work provides the opportunity of exploring the novel application for the development of next-generation neuromorphic computing based on lead-free halide perovskites.

Objective: To screen and identify a bacterium capable of converting daidzein to S-equol., Methods: We used antibiotics to limit unrelated bacterial growth and enrich the target bacteria, and isolated the aim bacterial strain from rat intestine. The metabolite of daidzein was tested by HPLC, MS and NMR. The taxonomic group of the strain was identified by 16S rDNA sequence analysis and phylogenetic tree; the strain's morphological and physiological biochemical characters were also tested., Results: A gram-negative facultative bacterial strain LH-52 (JN861767) capable of transforming daidzein to S-equol was isolated. Basic Local Alignment Search Tool (BLAST) search of LH-52's 16S rDNA sequence on GenBank suggested that this strain has 99% similarity to that of Proteus mirabilis, the morphological and physiological biochemical characteristics of LH-52 also showed highly similarity to P. mirabilis. Based on these data, we identified LH-52 as P. mirabilis, and named it as P. mirabilis LH-52. The results of HPLC, MS and NMR suggested that the metabolite of daidzien was S-equol., Conclusions: Bacteria strain P. mirabilis LH-52 was the first reported facultative bacteria strain capable of converting daidzein to S-equol, and might be more suitable in industrial application than obligate anareobic bacterial strains.