[en] A technique for directly growing two-dimensional (2D) materials onto conventional semiconductor substrates, enabling high-throughput and large-area capability, is required to realise competitive 2D transition metal dichalcogenide devices. A reactive sputtering method based on H₂S gas molecules and sequential in situ post-annealing treatment in the same chamber was proposed to compensate for the relatively deficient sulfur atoms in the sputtering of MoS₂ and then applied to a 2D MoS₂/p-Si heterojunction photodevice. X-ray photoelectron, Raman, and UV–visible spectroscopy analysis of the as-deposited Ar/H₂S MoS₂ film were performed, indicating that the stoichiometry and quality of the as-deposited MoS₂ can be further improved compared with the Ar-only MoS₂ sputtering method. For example, Ar/H₂S MoS₂ photodiode has lower defect densities than that of Ar MoS₂. We also determined that the factors affecting photodetector performance can be optimised in the 8–12 nm deposited thickness range. (paper)

[en] Artificial synapses based on 2D MoS${}_2$ memtransistors have recently attracted considerable attention as a promising device architecture for complex neuromorphic systems. However, previous memtransistor devices occasionally cause uncontrollable analog switching and unreliable synaptic plasticity due to random variations in the field-induced defect migration. Herein, a highly reliable 2D MoS${}_2$/Nb${}_2$O${}_5$ heterostructure memtransistor device is demonstrated, in which the Nb${}_2$O${}_5$ interlayer thickness is a critical material parameter to induce and tune analog switching characteristics of the 2D MoS${}_2$. Ultraviolet photoelectron spectroscopy and photoluminescence analyses reveal that the Schottky barrier height at the 2D channel-electrode junction of the MoS${}_2$/Nb${}_2$O${}_5$ heterostructure films is increased, leading to more effective contact barrier modulation and allowing more reliable resistive switching. The 2D/oxide memtransistors attain dual-terminal (drain and gate) stimulated heterosynaptic plasticity and highly precise multi-states. In addition, the memtransistor devices show an extremely low power consumption of ≈6 pJ and reliable potentiation/depression endurance characteristics over 2000 pulses. A high pattern recognition accuracy of ≈94.2% is finally achieved from the synaptic plasticity modulated by the drain pulse configuration using an image pattern recognition simulation. Thus, the novel 2D/oxide memtransistor makes a potential neuromorphic circuitry more flexible and energy-efficient, promoting the development of more advanced neuromorphic systems. (© 2021 Wiley‐VCH GmbH)

[en] Ion-based electrochemical random-access memory (ECRAM) is proposed for synaptic applications owing to its promising characteristics that have the potential to accelerate data processing through neuromorphic systems. However, attaining ideal synaptic functionalities and constructing high-density vertical synapse arrays are challenging due to issues related to uncontrolled ion migration and constraints in 3D multi-stacking. Here, a breakthrough using 3D stackable Li ion-based vertical-sensing ECRAM (VS-ECRAM) is presented with an ion-permeable ultrathin WS${}_2$ electrode synthesized through low-temperature (200 °C) atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD). The direct AP-PECVD of the WO${}_x$ channel layer induces WS${}_2$ formation in the surface region, which exhibits sufficient electrical conductivity to function as an electrode. By utilizing the WS${}_2$ electrode as an ion-barrier layer in the VS-ECRAM synapse, excellent weight update linearity and cycling variability are achieved due to the finely controlled ion migration. Furthermore, a two-layer stacked 3D VS-ECRAM is successfully fabricated through the vertical WS${}_2$ formation, and independent weight updates without any disturbance are confirmed. Finally, a high pattern recognition accuracy of 95.22% is obtained using a multi-layer perceptron-based neural network. Therefore, the proposed 3D stackable WS${}_2$-based VS-ECRAM exhibits a strong potential for application in high-density neuromorphic devices with excellent synaptic performances. (© 2024 Wiley‐VCH GmbH)

[en] Highlights: • Developments of sensitive methods to detect aflatoxin B1 in food. • Explanations of the prominent roles and application principles of various nanomaterials used in AFB1 detection. • The strategies of nanomaterials implemented in AFB1 detection: sample pretreatment, immunoassays and biosensors. • Challenges faced by nanomaterials used in AFB1 detection and the shortcomings of previous research works. -- Abstract: Aflatoxin B1(AFB1) is one of the most toxic mycotoxins produced by fungi and results in inevitable contamination of food and feed at very low concentrations. Therefore, there is an urgent need to implement selective, sensitive and highly convenient methods for the determination of aflatoxin B1. Among these methods, the progress of nanomaterials, owing to their high performances and versatile properties, offers great prospects for realizing highly sensitive, selective and simple detection of AFB1, overcoming the restrictions of traditional methods such as process-complicated, time-consuming, labor-intensive and instruments-expensive. Many nanomaterials have been used for the immobilization of biomolecules as signal generators or fluorescent quenchers or for signal amplification in AFB1 detection. This review highlights recent progress that has been made in the development of nanoparticle-based assays and focuses on the analytical potential of nanomaterials, such as Au/Ag nanoparticles (Au/Ag NPs), carbon-based nanoparticles (CBNs), magnetic nanoparticles (MNPs), Quantum dots (QDs) and novel nanomaterials, including up-conversion nanoparticles (UCNPs), metal-organic frameworks (MOFs) and nanomaterial-functional DNA intelligent hydrogels, as well as hybrid nanostructures. The determination of AFB1 is divided into three aspects: sample pretreatment prior to AFB1 detection, immunoassays and biosensors. The details of the detection methods and their application principles are described, and the challenges and opportunities in the field of food analysis are described.

[en] Highlights: • Fabrication of heterojunctions by stacking n-type MoS₂ film on a p-type Ge epilayer. • Temperature-dependent current-voltage characteristics of the MoS₂/p-type Ge device. • The charge transport mechanism in three regimes. • The thermionic emission is dominant in the high-temperature regime. • The trap-assisted tunneling mechanism is dominant in the low-temperature regime. Significant effort has been devoted to constructing two-dimensional transition metal dichalcogenides-based hybrid heterojunctions with enhanced performance or unique functionalities for versatile device applications in emerging electronics and optoelectronics. In this study, we report the temperature-dependent electronic charge transport characteristics in MoS₂/p-type Ge heterojunction diodes. From the current-voltage (I-V) characteristics of the heterojunction device, it is observed that different transport phenomena can occur depending upon the temperature and bias voltage. The charge transport is dominated by thermionic emission in the high-temperature regime above 300 K, whereas in low-temperature regime below 300 K, the charge transport mechanism transitions from the thermionic emission to the tunneling mechanism associated with trap sites. In particular, the I-V characteristics in the low-temperature regime show a transition from the direct tunneling at a low bias to the Fowler-Nordheim tunneling mechanism at a high bias. This could be well described by the electrical analyses on temperature-dependent I-V behavior and corresponding energy band diagrams.