High-Uniformity Threshold Switching HfO2-Based Selectors with Patterned Ag Nanodots.

High-performance selector devices are essential for emerging nonvolatile memories to implement high-density memory storage and large-scale neuromorphic computing. Device uniformity is one of the key challenges which limit the practical applications of threshold switching selectors. Here, high-uniformity threshold switching HfO2-based selectors are fabricated by using e-beam lithography to pattern controllable Ag nanodots (NDs) with high order and uniform size in the cross-point region. The selectors exhibit excellent bidirectional threshold switching performance, including low leakage current (<1 pA), high on/off ratio (>108), high endurance (>108 cycles), and fast switching speed (≈75 ns). The patterned Ag NDs in the selector help control the number of Ag atoms diffusing into HfO2 and confine the positions to form reproducible filaments. According to the statistical analysis, the Ag NDs selectors show much smaller cycle-to-cycle and device-to-device variations (C V < 10%) compared to control samples with nonpatterned Ag thin film. Furthermore, when integrating the Ag NDs selector with resistive switching memory in one-selector-one-resistor (1S1R) structure, the reduced selector variation helps significantly reduce the bit error rate in 1S1R crossbar array. The high-uniformity Ag NDs selectors offer great potential in the fabrication of large-scale 1S1R crossbar arrays for future memory and neuromorphic computing applications.

Amylase-Protected Ag Nanodots for in vivo Fluorescence Imaging and Photodynamic Therapy of Tumors.

BACKGROUND: Fluorescent metallic nanodots (NDs) have become a promising nanoprobe for a wide range of biomedical applications. Because Ag NDs have a high tendency to be oxidized, their synthesis and storage are a big challenge. Thus, the method for preparing stable Ag NDs is urgently needed. Surface modification and functionalization can enrich the capability of Ag NDs. METHODS: In this work, fluorescent Ag NDs were synthesized in deoxygenated water by using porcine pancreatic α-amylase (PPA) as the stabilizing/capping agent. The absorption and fluorescence of PPA-protected Ag NDs (PPA@AgNDs) were measured with a spectrophotometer and a spectrofluorometer, respectively. The morphology of PPA@AgNDs was characterized by high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM). The biocompatibility of PPA@AgNDs was evaluated by tetrazolium (MTT)-based assay. PolyLys-Cys-SH (sequence: KKKKKKC) peptides were conjugated to PPA@AgNDs via heterobifunctional crosslinkers. PolyLys-Cys-linked PPA@AgNDs absorbed 5-aminolevulinic acid (ALA) by electrostatic interaction at physiological pH. The capability of tumor targeting was evaluated by intravenously injecting PPA@AgND-ALA into 4T1 breast cancer xenograft mouse models. Photodynamic therapy (PDT) against tumors was performed under 635 nm laser irradiation. RESULTS: PPA@AgNDs emitted at 640 nm with quantum yield of 2.1%. The Ag NDs exhibited strong photostability over a long period and a fluorescence lifetime of 5.1 ns. PPA@AgNDs easily entered the cells to stain the nuclei, showing the capabilities of living cell imaging with negligible cytotoxicity. ALA-loaded PPA@AgNDs (PPA@AgND-ALA) presented the superiority of passive tumor targeting via the enhanced permeability and retention (EPR) effect. Tumors were visualized in the near-infrared (NIR) region with reduced background noise. ALA molecules released from PPA@AgND-ALA was converted into the photosensitizer (PS) of protoporphyrin IX (PpIX) intracellularly and intratumorally, which greatly improved the PDT efficacy. CONCLUSION: Our approach opens a new way to design a novel theranostic nanoplatform of PPA@AgND-ALA for effective tumor targeting and fluorescence image-guided PDT.

Interfacial engineering of Ag nanodots/MoSe2 nanoflakes/Cu(OH)2 hybrid-electrode for lithium-ion battery.

Although the Lithium ion batteries (LIBs) have attracted remarkable attentions, their practical development is hindered by the low rate performance and poor unit area capacity, which is significantly caused by the low conductivity of the active electrode materials. Herein, a three-dimensional (3D) architecture consisting of Ag nanodots embedded MoSe2 sheets wrapping Cu(OH)2 nanorods (Cu(OH)2/MoSe2/Ag) hybrids were in-situ synthesized on self-standing Cu- foam collector for LIBs application. The 2D MoSe2 nanoflakes supported on 1D highly conductive Cu nanowires provides efficient pathways for both electrons and ions. The embedded Ag nanodots in the MoSe2 as the internal-plane active sites not only improves the intrinsic conductivity but also allows the reversible formation and decompose of Ag-Li alloy, and thus leading to the promotion of Li+ ion storage. As a result, the Cu(OH)2/MoSe2/Ag electrode exhibits a high reversible discharge capacity of 1285.5 mAh g-1 (current density of 0.2 C), good rate performance (discharge-specific capacity remained 544.8 mAh g-1 at 5.0C), and excellent cycling stability (with almost no decay after 500 cycles). Significantly, the 3D Cu(OH)2/MoSe2/Ag electrode exhibits a high areal capacity of 2.50 mAh cm-2 at a high current density of 1.82 mA cm-2. This work provides the new insight into interfaces engineering for 3D architecture toward advanced self-standing LIB electrodes.

A Threshold Switching Selector Based on Highly Ordered Ag Nanodots for X-Point Memory Applications.

Leakage interference between memory cells is the primary obstacle for enlarging X-point memory arrays. Metal-filament threshold switches, possessing excellent selectivity and low leakage current, are developed in series with memory cells to reduce sneak path current and lower power consumption. However, these selectors typically have limited on-state currents (≤10 µA), which are insufficient for memory RESET operations. Here, a strategy is proposed to achieve sufficiently large RESET current (≈2.3 mA) by introducing highly ordered Ag nanodots to the threshold switch. Compared to the Ag thin film case, Ag nanodots as active electrode could avoid excessive Ag atoms migration into solid electrolyte during operations, which causes stable conductive filament growth. Furthermore, Ag nanodots with rapid thermal processing contribute to forming multiple weak Ag filaments at a lower voltage and then spontaneous rupture as the applied voltage reduced, according to quantized conductance and simulation analysis. Impressively, the Ag nanodots based threshold switch, which is bidirectional and truly electroforming-free, demonstrates extremely high selectivity >109, ultralow leakage current <1 pA, very steep slope of 0.65 mV dec-1, and good thermal stability up to 200 °C, and further represents significant suppression of leakage currents and excellent performances for SET/RESET operations in the one-selector-one-resistor configuration.