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In this study, we investigate the coexistence of short- and long-term memory effects owing to the programmable retention characteristics of a two-dimensional Au/MoS2/Au atomristor device and determine the impact of these effects on synaptic properties. This device is constructed using bilayer MoS2 in a crossbar structure. The presence of both short- and long-term memory characteristics is proposed by using a filament model within the bilayer transition-metal dichalcogenide. Short- and long-term properties are validated based on programmable multilevel retention tests. Moreover, we confirm various synaptic characteristics of the device, demonstrating its potential use as a synaptic device in a neuromorphic system. Excitatory postsynaptic current, paired-pulse facilitation, spike-rate-dependent plasticity, and spike-number-dependent plasticity synaptic applications are implemented by operating the device at a low-conductance level. Furthermore, long-term potentiation and depression exhibit symmetrical properties at high-conductance levels. Synaptic learning and forgetting characteristics are emulated using programmable retention properties and composite synaptic plasticity. The learning process of artificial neural networks is used to achieve high pattern recognition accuracy, thereby demonstrating the suitability of the use of the device in a neuromorphic system. Finally, the device is used as a physical reservoir with time-dependent inputs to realize reservoir computing by using short-term memory properties. Our study reveals that the proposed device can be applied in artificial intelligence-based computing applications by utilizing its programmable retention properties.

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Recently, we demonstrated the nonvolatile resistive switching effects of metal-insulator-metal (MIM) atomristor structures based on two-dimensional (2D) monolayers. However, there are many remaining combinations between 2D monolayers and metal electrodes; hence, there is a need to further explore 2D resistance switching devices from material selections to future perspectives. This study investigated the volatile and nonvolatile switching coexistence of monolayer hexagonal boron nitride (h-BN) atomristors using top and bottom silver (Ag) metal electrodes. Utilizing an h-BN monolayer and Ag electrodes, we found that the transition between volatile and nonvolatile switching is attributed to the thickness/stiffness of chain-like conductive bridges between h-BN and Ag surfaces based on the current compliance and atomristor area. Computations indicate a "weak" bridge is responsible for volatile switching, while a "strong" bridge is formed for nonvolatile switching. The current compliance determines the number of Ag atoms that undergo dissociation at the electrode, while the atomristor area determines the degree of electric field localization that forms more stable conductive bridges. The findings of this study suggest that the h-BN atomristor using Ag electrodes shows promise as a potential solution to integrate both volatile neurons and nonvolatile synapses in a single neuromorphic crossbar array structure through electrical and dimensional designs.

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Two-dimensional (2D) materials have been studied as an emerging class of nanomaterials owing to their attractive properties in nearly every field of science and technology. Molybdenum disulfide (MoS2) is one of the more promising candidates of these atomically thin 2D materials for its technological potential. The facile synthesis of MoS2 remains a matter of broad interest. In this study, MoS2 was synthesized by chemical vapor deposition sulfurization at various temperatures (550 °C, 650 °C, and 750 °C) of either precursor molybdenum metal (Mo) or molybdenum trioxide (MoO3) deposited on silicon/silicon dioxide (Si/SiO2) via e-beam evaporation. Monolayer, bilayer, and few layers sulfurized samples have been grown and verified by Raman, photoluminescence spectroscopy, XRD, XPS, and AFM. MoO3 sulfurization provided monolayer growth in comparison to Mo sulfurization under the same conditions and precursor thicknesses. Optical microscopy showed the homogeneous nature of grown samples. A main finding of this work is that MoO3 sulfurization produced higher quality MoS2 as compared to those grown by an Mo precursor. Device characteristics based on monolayer MoO3 sulfurized MoS2-x include nonvolatile resistive switching with Ion/Ioff ≈ 104 at a relatively low operating bias of ±1 V. In addition, field-effect transistor characteristics revealed p-type material growth with a carrier mobility ∼ 41 cm2 V-1 s-1, which is in contrast to typically observed n-type characteristics.

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Recently, nonvolatile resistive switching memory effects have been actively studied in two-dimensional (2D) transition metal dichalcogenides and boron nitrides to advance future memory and neuromorphic computing applications. Here, we report on radiofrequency (RF) switches utilizing hexagonal boron nitride (h-BN) memristors that afford operation in the millimeter-wave (mmWave) range. Notably, silver (Ag) electrodes to h-BN offer outstanding nonvolatile bipolar resistive switching characteristics with a high ON/OFF switching ratio of 1011 and low switching voltage below 0.34 V. In addition, the switch exhibits a low insertion loss of 0.50 dB and high isolation of 23 dB across the D-band spectrum (110 to 170 GHz). Furthermore, the S21 insertion loss can be tuned through five orders of current compliance magnitude, which increases the application prospects for atomic switches. These results can enable the switch to become a key component for future reconfigurable wireless and 6G communication systems.

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Molybdenum trioxide (MoO3), an important transition metal oxide (TMO), has been extensively investigated over the past few decades due to its potential in existing and emerging technologies, including catalysis, energy and data storage, electrochromic devices, and sensors. Recently, the growing interest in two-dimensional (2D) materials, often rich in interesting properties and functionalities compared to their bulk counterparts, has led to the investigation of 2D MoO3. However, the realization of large-area true 2D (single to few atom layers thick) MoO3 is yet to be achieved. Here, we demonstrate a facile route to obtain wafer-scale monolayer amorphous MoO3 using 2D MoS2 as a starting material, followed by UV-ozone oxidation at a substrate temperature as low as 120 °C. This simple yet effective process yields smooth, continuous, uniform, and stable monolayer oxide with wafer-scale homogeneity, as confirmed by several characterization techniques, including atomic force microscopy, numerous spectroscopy methods, and scanning transmission electron microscopy. Furthermore, using the subnanometer MoO3 as the active layer sandwiched between two metal electrodes, we demonstrate the thinnest oxide-based nonvolatile resistive switching memory with a low voltage operation and a high ON/OFF ratio. These results (potentially extendable to other TMOs) will enable further exploration of subnanometer stoichiometric MoO3, extending the frontiers of ultrathin flexible oxide materials and devices.

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Hydrogen-peroxide-based low-temperature sterilization is a new sterilization technology for temperature-dependent medical devices. The effect of the process parameters of hydrogen-peroxide-based sterilizer on the sterilization performance of process challenge devices (PCDs) needs to be investigated. Sterilant amount, operating temperature, vacuum pressure, diffusion time, and chamber loading of the sterilizer on the sterilization performance of PCDs were adjusted. Seven PCDs with various morphologies and material containing biological indicators (BI) (EZTest, Geobacillus stearothermophilus) were used to evaluate the sterilization performance. The sterilization success rates of PCDs were 86, 71, and 57% with controlled temperature and pressure, diffusion time, and sterilant volume injection, respectively. The PCD material and structure also obviously affected sterilization performance. The sterilization of PCD A is the least successful for all parameters. Meanwhile, the sterilization of PCD B was influenced by the diffusion time and the sterilant injection volume. PCD B and PCD C were successfully sterilized by controlling the temperature and pressure. The weights and volume of the sterilization loading chamber resulted in a different sterilization performance. Sterilization performances of PCD 1, PCD 2, and PCD 3 were <70, <90, and 100%, respectively. Sterilant volume, sterilant diffusion time, pressure, temperature, PCD types, and chamber loading were proven to be important process parameters of sterilizer that affect the sterilization performance of vaporized-hydrogen-peroxide-based sterilizers.

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Ultra-thin two-dimensional semiconducting crystals in their monolayer and few-layer forms show promising aspects in nanoelectronic applications. However, the ultra-thin nature of two-dimensional crystals inevitably results in high contact resistance from limited channel/contact volume as well as device-to-device variability, which seriously limit reliable applications using two-dimensional semiconductors. Here, we incorporate rather thick two-dimensional layered semiconducting crystals for reliable vertical diodes showing excellent Ohmic and Schottky contacts. Using the vertical transport of WSe2, we demonstrate devices which are functional at various frequency ranges from megahertz AM demodulation of audio signals, to gigahertz rectification for fifth-generation wireless electronics, to ultraviolet-visible photodetection. The WSe2 exhibits an excellent Ohmic contact to bottom platinum electrode with record-low contact resistance (~50 Ω) and an exemplary Schottky junction to top transparent conducting oxide electrode. Our semitransparent vertical WSe2 Schottky diodes could be a key component of future high frequency electronics in the era of fifth-generation wireless communication.

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Highly efficient anode materials with novel compositions for Li-ion batteries are actively being researched. Multicomponent metal selenite is a promising candidate, capable of improving their electrochemical performance through the formation of metal oxide and selenide heterostructure nanocrystals during the first cycle. Here, the binary nickel-cobalt selenite derived from Ni-Co Prussian blue analogs (PBA) is chosen as the first target material: the Ni-Co PBA are selenized and partially oxidized in sequence, yielding (NiCo)SeO3 phase with a small amount of metal selenate. The conversion mechanism of (NiCo)SeO3 for Li-ion storage is studied by cyclic voltammetry, in situ X-ray diffraction, ex situ X-ray photoelectron spectroscopy, in situ electrochemical impedance spectroscopy, and ex situ transmission electron microscopy. The reversible reaction mechanism of (NiCo)SeO3 with the Li ions is described by the reaction: NiO + CoO + xSeO2 + (1 - x)Se + (4x + 6)Li+ + (4x + 6)e- ↔ Ni + Co + (2x + 2)Li2 O + Li2 Se. To enhance electrochemical properties, polydopamine-derived carbon is uniformly coated on (NiCo)SeO3 , resulting in excellent cycling and rate performances for Li-ion storage. The discharge capacity of C-coated (NiCo)SeO3 is 680 mAh g-1 for the 1500th cycle when cycled at a current density of 5 A g-1 .

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This study investigated the oxidative stress and hemocyte responses of Pacific abalone exposed to various water temperatures (4, 6, 8, and 10 °C) and salinities (26, 30, and 34 psu) for 7 days, to identify their tolerance ranges of temperature and salinity. The survival rate of Pacific abalone ranged from 98.7 to 100% at 8 °C and 10 °C, but dropped to 25-55% at 4 °C at all levels of salinity. The levels of superoxide dismutase and glutathione in the hemolymph were significantly higher at 4 °C and 6 °C than in the controls in all salinity groups, indicating that these temperatures induced greater stress in the Pacific abalone. Total hemocyte count was lowest at 6 °C in the 26 psu group. The percentages of apoptotic and necrotic cells were higher in the 26 psu group than in the other salinity groups, and higher in the 4 °C and 6 °C groups than in the other temperature groups. These results indicate that the lowest tolerance to water temperature and salinity in the Pacific abalone was 8 °C and 30 psu, respectively.

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The two-dimensional transition-metal dichalcogenide semiconductor MoS2 has received extensive attention for decades because of its outstanding electrical and mechanical properties for next-generation devices. One weakness of MoS2, however, is that it shows only n-type conduction, revealing its limitations for homogeneous PN diodes and complementary inverters. Here, we introduce a charge-transfer method to modify the conduction property of MoS2 from n- to p-type. We initially deposited an n-type InGaZnO (IGZO) film on top of the MoS2 flake so that electron charges might be transferred from MoS2 to IGZO during air ambient annealing. As a result, electron charges were depleted in MoS2. Such charge depletion lowered the MoS2 Fermi level, which makes hole conduction favorable in MoS2 when optimum source/drain electrodes with a high work function are selected. Our IGZO-supported MoS2 flake field effect transistors (FETs) clearly display channel-type conversion from n- to p-channel in this way. Under short- and long-annealing conditions, n- and p-channel MoS2 FETs are achieved, respectively, and a low-voltage complementary inverter is demonstrated using both channels in a single MoS2 flake.

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CONSORF is a fully automatic high-accuracy identification system that provides consensus prokaryotic CDS information. It first predicts the CDSs supported by consensus alignments. The alignments are derived from multiple genome-to-proteome comparisons with other prokaryotes using the FASTX program. Then, it fills the empty genomic regions with the CDSs supported by consensus ab initio predictions. From those consensus results, CONSORF provides prediction reliability scores, predicted frame-shifts, alternative start sites and best pair-wise match information against other prokaryotes. These results are easily accessed from a website.

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