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Metal/semiconductor superlattices represent a fascinating frontier in materials science and nanotechnology, where alternating layers of metals and semiconductors are precisely engineered at the atomic and nano-scales. Traditionally, epitaxial metal/semiconductor superlattice growth requires constituent materials from the same family, exhibiting identical structural symmetry and low lattice mismatch. Here, beyond this conventional constraint, a novel class of epitaxial lattice-matched metal/semiconductor superlattices is introduced that utilizes refractory hexagonal elemental transition metals and wide-bandgap III-nitride semiconductors. Exemplified by the Hf/AlN superlattices exhibiting coherent layer-by-layer epitaxial growth, cross-plane thermionic emission is observed through current-voltage measurements accomplished for the first time in any metal/semiconductor superlattices. Further, thermoreflectance measurements reveal significant enhancement in cross-plane Seebeck coefficients attributed to carrier energy filtering by Schottky barriers. Demonstration of artificially structured elemental-metal/wide-bandgap compound-semiconductor superlattices promises to usher in new fundamental physics studies and cutting-edge applications such as tunable hyperbolic metamaterials, quantum computing, and thermionic-emission-based thermoelectric and thermophotonic energy conversion devices., (© 2024 Wiley‐VCH GmbH.)

Optoelectronic reconfigurable logic gates are promising candidates to meet the multifunctional and energy-efficient requirements of integrated circuits. However, complex device architectures need more power and hinder multifunctional device applications. Here, we design vertical field-effect transistors (VFET) based on the two-dimensional (2D) graphene/MoS 2 /WSe 2 /graphene van der Waals heterojunction forming ohmic and Schottky contact. The modulation of the Schottky barrier via gate bias enables the device to switch between positive and negative photocurrents, which can effectively achieve optoelectronic reconfigurable logic gates (XNOR, NOR, NAND, AND, OR, and Inhibit) in a single device. Particularly, the transistor number is reduced by 75% for ("XNOR", "NOR", "NAND") and 83% for ("AND", "OR") gates compared to traditional logic circuits. This work provides a promising route for using a single device to realize optoelectronic reconfigurable logic gates, which can advance the development of high-speed, high-throughput, and intricate data processing in future optical computing applications.

Heterogeneous interfacial engineering has garnered widespread attention for optimizing polarization loss and enhancing the performance of electromagnetic wave absorption. A novel Kirkendall effect-assisted electrostatic self-assembly method is employed to construct a metal-organic framework (MOF, MIL-88A) decorated with Ni-Fe layered double hydroxide (LDH), forming a multilayer nano-cage coated with Ti 3 C 2 T x . By modulating the surface adsorption of Ti 3 C 2 T x on LDH, the heterointerfaces in MOF-LDH-MXene ternary composites exhibit excellent interfacial polarization loss. Additionally, the Ni-Fe LDH@Ti 3 C 2 T x nano-cage exhibits a large specific surface area, abundant defects, and a large number of heterojunction structures, resulting in excellent electromagnetic wave absorption performance. The MIL-88A@Ni-Fe LDH@Ti 3 C 2 T x -1.0 nano-cage achieves a reflection loss value of -46.7 dB at a thickness of 1.4 mm and an effective absorption bandwidth of 5.12 GHz at a thickness of 1.8 mm. The heterojunction interface composed of Ni-Fe LDH and Ti 3 C 2 T x helps to enhance polarization loss. Additionally, Ti 3 C 2 T x forms a conductive network on the surface, while the cavity between the MIL-88A core and the Ni-Fe LDH shell facilitates multiple attenuations by increasing the transmission path of internal incident waves. This work may reveal a new structural design of multi-component composites by heterointerfaces engineering for electromagnetic wave absorption., (© 2024 Wiley‐VCH GmbH.)

Molybdenum disulfide (MoS 2 ) is a representative two-dimensional layered transition-metal dichalcogenide semiconductor. Layer-number-dependent electronic properties are attractive in the development of nanomaterial-based electronics for a wide range of applications including sensors, switches, and amplifiers. MoS 2 field-effect transistors (FETs) have been studied as promising future nanoelectronic devices with desirable features of atomic-level thickness and high electrical properties. When a naturally n -doped MoS 2 is contacted with metals, a strong Fermi-level pinning effect adjusts a Schottky barrier and influences its electronic characteristics significantly. In this study, we investigate multilayer MoS 2 Schottky barrier FETs (SBFETs), emphasizing the metal-contact impact on device performance via computational device modeling. We find that p -type MoS 2 SBFETs may be built with appropriate metals and gate voltage control. Furthermore, we propose ambipolar multilayer MoS 2 SBFETs with asymmetric metal electrodes, which exhibit gate-voltage dependent ambipolar transport behavior through optimizing metal contacts in MoS 2 device. Introducing a dual-split gate geometry, the MoS 2 SBFETs can further operate in four distinct configurations: p  -  p , n  -  n , p  -  n , and n  -  p . Electrical characteristics are calculated, and improved performance of a high rectification ratio can be feasible as an attractive feature for efficient electrical and photonic devices., (Creative Commons Attribution license.)

Selectors are critical components for reducing the sneak path leakage currents in emerging resistive random-access memory (RRAM) arrays. Two-dimensional (2D) materials provide a rich choice of materials with van der Waals stacking to form the heterostructure selectors with controllable energy barriers. Here, we experimentally demonstrate 2D-material-based heterostructure selectors with exponential current-voltage ( I - V ) relationships and integrate them with hafnium oxide (HfO x )-based RRAMs, forming one-selector-one-resistor (1S1R) cells. The multilayer graphene (MG)/tungsten disulfide (WS 2 )/platinum (Pt) selector contains two asymmetric heterojunctions with different Schottky barriers, which lead to highly nonlinear and asymmetric I - V characteristics. The 2D selectors in 1S1R cells can successfully drive RRAMs, reduce sneak path leakage current by more than 100 times, and provide the set compliance current. The 1S1R cells are further modeled and integrated into both planar and 3D memory arrays, with circuit-level simulations demonstrating that the presence of 2D selectors in large memory arrays can reduce the power consumption by up to 86%, improve the read/write margin by up to 31%, and avoid write failure. Such a platform holds high potential for constructing 3D high-density memories and performing in-memory computing.

Optoelectronic synaptic devices, integrating light sensing and information processing capabilities, have emerged as advantageous tools for the implementation of visual neuromorphic computing. However, the transient light-triggered response characteristic typically results in unstable memory retention times and restricted current response ranges, posing significant challenges to the development and practical application of neural network systems. In response to these limitations, this study developed a nonvolatile optoelectronic memory based on the indium tin oxide (ITO)/Au nanoparticles (NPs)/amorphous Ga 2 O 3 (a-Ga 2 O 3 )/Pt structure. Unlike conventional optoelectronic memories, this device features a modification with Au NPs that markedly enhances the Schottky barrier height at the interface. Au NPs function as a charge-trapping layer for sensitive and large-scale modulation of the barrier by the light field, thereby enabling the nonvolatile reversal of the device's barrier polarity. This innovative approach enables controllable multilevel data storage with an ultra large on/off ratio (∼10 4 ) and excellent retention capability exceeding 12,000 s. Additionally, the device emulates essential synaptic functions and demonstrates potential application values in visual weak signal perception and image memory. This study introduces a mechanism for Schottky barrier polarity control and presents a promising strategy for the development of future high-performance integrated devices and optoelectronic synaptic elements.

Mimicking fundamental synaptic working principles with memristors contributes an essential step toward constructing brain-inspired, high-efficiency neuromorphic systems that surpass von Neumann system computers. Here, an electroforming-free planar-type memristor based on a CsPbBr 3 single crystal is proposed and exhibits excellent resistive switching (RS) behaviors including stable endurance, ultralow power consumption, and fast switching speed. Furthermore, an optically tunable RS performance is demonstrated by manipulating irradiation intensity and wavelength. Optical analysis techniques such as steady-state photoluminescence and time-resolved photoluminescence are employed to investigate the distribution of Br ions and vacancies before and after quantitative polarization, describing migration dynamic processes to elucidate the RS mechanism. Importantly, a CsPbBr 3 single crystal, as the optoelectronic synapse, shows unique potential to emulate photoenhanced synaptic functions such as excitatory postsynaptic current, paired-pulse facilitation, long-term potentiation/depression, spike-timing-dependent plasticity, spike-voltage-dependent plasticity, and learning-forgetting-relearning process with ultralow per synapse event energy consumption. A classical Pavlov's dog experiment is simulated with a combination of optical and electrical stimulation. Finally, pattern recognition with simulated artificial neural networks based on our synapse reached an accuracy of 93.11%. The special strategy and superior RS characteristics of optoelectronic synapses provide a pathway toward high-performance, energy-efficient neuromorphic electronics.

The latest synthesized monolayer (ML) MoSi 2 N 4 material exhibits stability in ambient conditions, suitable bandgap, and high mobilities. Its potential as a next-generation transistor channel material has been demonstrated through quantum transport simulations. However, in practical two-dimensional (2D) material transistors, the electrical contacts formed by the channel and the electrode must be optimized, as they are crucial for determining the efficiency of carrier injection. We employed the density functional theory (DFT) combined with the nonequilibrium Green's function (NEGF) method to systematically explore the vertical and horizontal interfaces between the typical metal electrodes and the ML MoSi 2 N 4 . The DFT+NEGF method incorporates the coupling between the electrode and the channel, which is crucial for quantum transport. Among these metals, Sc and Ti form n -type Ohmic contacts with zero tunneling barriers at both vertical and horizontal interfaces with ML MoSi 2 N 4 , making them optimal for contact metals. In-ML MoSi 2 N 4 contacts display zero Schottky barriers but a 3.11 eV tunneling barrier. Cu and Au establish n -type Schottky contacts, while Pt forms a p -type contact. The Fermi pinning factors of the metal-ML MoSi 2 N 4 contacts for both electrons and holes are above 0.51, much higher than the typical 2D semiconductors. Moreover, there is a strong positive correlation between the Fermi pinning factor and the band gap, with a Spearman rank correlation coefficient of 0.897 and a p -value below 0.001. Our work provides insight into the contact optimization for the ML MoSi 2 N 4 transistors and highlights the promising potential of ML MoSi 2 N 4 as the channel material for the next-generation FETs.

First-principle calculations based on density functional theory are employed to investigate the impact of graphene insertion on the electronic properties and Schottky barrier of MoS 2 /metals (Mg, Al, In, Cu, Ag, Au, Pd, Ti, and Sc) without deteriorating the intrinsic properties of the MoS 2 layer. The results reveal that the charge transfer mainly occurs at the interface between the graphene and metal layers, with smaller transfer at the interface between bi-layer garphene or between graphene and MoS 2 . And the tunneling barrier exists at the interface between graphene and MoS 2 , which hinders electron injection from graphene to MoS 2 . Importantly, the Schottky barrier height ( Φ SB,N ) decreases upon graphene insertion into MoS 2 /metal contacts. Specifically, for single-layer graphene, the Φ SB,N of MoS 2 contacted with Mg, In, Sc, and Ti are - 0.116 eV, - 0.116 eV, - 0.014 eV, and - 0.116 eV, respectively. Furthermore, with bilayer graphene, when by inserting bi-layer graphene, the negative n-type Schottky barrier of - 0.086 eV, - 0.114 eV, - 0.059 eV, - 0.008 eV, and - 0.0636 eV are observed for MoS 2 contacted with the respective metals, respectively. These findings provide a practical guidance for developing and designing high-performance transition metal dichalcogenide nanoelectronic devices., (© 2024. The Author(s).)

In this paper, we introduce a novel Forkshape nanosheet Inductive Tunnel Field-Effect Transistor (FS-iTFET) featuring a Gate-All-Around structure and a full-line tunneling heterojunction channel. The overlapping gate and source contact regions create a strong and uniform electric field in the channel. Furthermore, the metal-semiconductor Schottky junction in the intrinsic source region induces the required carriers without the need for doping. This innovative design achieves both a steeper subthreshold swing (SS) and a higher ON-state current (I ON ). Using calibration-based simulations with Sentaurus TCAD, we compare the performance of three newly designed device structures: the conventional Nanosheet Tunnel Field-Effect Transistor (NS-TFET), the Nanosheet Line-tunneling TFET (NS-LTFET), and the proposed FS-iTFET. Simulation results show that, compared to the traditional NS-TFET, the NS-LTFET with its full line-tunneling structure improves the average subthreshold swing (SS AVG ) by 19.2%. More significantly, the FS-iTFET, utilizing the Schottky-inductive source, further improves the SS AVG by 49% and achieves a superior I ON /I OFF ratio. Additionally, we explore the impact of Trap-Assisted Tunneling on the performance of the three different integrations. The FS-iTFET consistently demonstrates superior performance across various metrics, highlighting its potential in advancing tunnel field-effect transistor technology., (© 2024. The Author(s).)

Iridium, the most widely used anode catalyst in proton exchange membrane water electrolysis (PEMWE), must be used minimally due to its high price and limited supply. However, reducing iridium loading poses challenges due to abnormally large anode polarization. Herein, we present an anode catalyst layer (CL) based on a one-dimensional iridium nanofiber that enables a high current density operation of 3 A cm -2 at 1.86 V, even at an ultralow loading (0.07 mg Ir cm -2 ). The performance is maintained even with a Pt coating-free porous transport layer (PTL) because our nanofiber CL circumvents the interfacial electron transport problem caused by the native oxide on the Ti PTL. We attribute this to the low work function and the low-ionomer-exposed surface of the nanofiber CL, which prevent the formation of Schottky contact at the native oxide interface. These results highlight the significance of optimizing the electronic properties of the CL/PTL interface for low-iridium-loading PEMWE.

Owing to the outstanding properties provided by nontrivial band topology, topological phases of matter are considered as a promising platform towards low-dissipation electronics, efficient spin-charge conversion, and topological quantum computation. Achieving ferroelectricity in topological materials enables the non-volatile control of the quantum states, which could greatly facilitate topological electronic research. However, ferroelectricity is generally incompatible with systems featuring metallicity due to the screening effect of free carriers. In this study, we report the observation of memristive switching based on the ferroelectric surface state of a topological semimetal (TaSe 4 ) 2 I. We find that the surface state of (TaSe 4 ) 2 I presents out-of-plane ferroelectric polarization due to surface reconstruction. With the combination of ferroelectric surface and charge-density-wave-gapped bulk states, an electric-switchable barrier height can be achieved in (TaSe 4 ) 2 I-metal contact. By employing a multi-terminal-grounding design, we manage to construct a prototype ferroelectric memristor based on (TaSe 4 ) 2 I with on/off ratio up to 10 3 , endurance over 10 3 cycles, and good retention characteristics. The origin of the ferroelectric surface state is further investigated by first-principles calculations, which reveal an interplay between ferroelectricity and band topology. The emergence of ferroelectricity in (TaSe 4 ) 2 I not only demonstrates it as a rare but essential case of ferroelectric topological materials, but also opens new routes towards the implementation of topological materials in functional electronic devices., (Copyright © 2024 Science China Press. Published by Elsevier B.V. All rights reserved.)

The contact resistance formed between MoS 2 and metal electrodes plays a key role in MoS 2 -based electronic devices. The Schottky barrier height (SBH) is a crucial parameter for determining the contact resistance. However, the SBH is difficult to modulate because of the strong Fermi-level pinning (FLP) at MoS 2 -metal interfaces. Here, we investigate the FLP effect and the contact types of monolayer and multilayer MoS 2 -metal van der Waals (vdW) interfaces using density functional theory (DFT) calculations based on Perdew-Burke-Ernzerhof (PBE) level. It has been demonstrated that, compared with monolayer MoS 2 -metal close interfaces, the FLP effect can be significantly reduced in monolayer MoS 2 -metal vdW interfaces. Furthermore, as the layer number of MoS 2 increases from 1L to 4L, the FLP effect is first weakened and then increased, which can be attributed to the charge redistribution at the MoS 2 -metal and MoS 2 -MoS 2 interfaces. In addition, the p-type Schottky contact can be achieved in 1L-4L MoS 2 -Pt, 3L MoS 2 -Au, and 2L-3L MoS 2 -Pd vdW interfaces, which is useful for realizing complementary metal oxide semiconductor (CMOS) logic circuits. These findings indicated that the FLP and contact types can be effectively modulated at MoS 2 -metal vdW interfaces by selecting the layer number of MoS 2 .

Designing two-dimensional (2D) heterojunctions with rapid response and minimal energy consumption holds immense significance for the advancement of the next generation of electronic devices. Here, we construct a series of Schottky heterojunctions based on TiB 4 monolayer and group-IV monochalcogenide monolayers MX (M = Ge, Sn; X = S, Se, Te). Using first-principles calculations, we investigate the structural stability, Schottky contact barrier, tunneling probability, and optical properties of MX/TiB 4 heterojunctions. The calculated binding energies reveal that X-type MX/TiB 4 heterojunctions exhibit more stable structures than M- and C-type stacking modes. Schottky barrier heights (SBHs) indicate that X-type GeSe/TiB 4 and GeTe/TiB 4 form n-type Schottky contacts with SBHs of 0.497 and 0.132 eV, respectively, while SnS/TiB 4 and SnSe/TiB 4 form p-type Schottky contacts with SBHs of 0.557 and 0.418 eV, respectively. Moreover, X-type MX/TiB 4 heterojunctions exhibit high susceptibility to interlayer electron tunneling due to their large tunneling probability and strong interlayer interaction. Meanwhile, enhanced optical absorption capacity in MX/TiB 4 heterojunctions is also observed compared with individual TiB 4 and MX monolayers. By applying in-plane biaxial strain, the transformation of MX/TiB 4 heterojunctions from a Schottky contact to an Ohmic contact can also be realized. Our findings could offer valuable candidate materials and guidance for the design of the next generation of nanodevices with high electronic and optical performances.

The extreme sensitivity of 2D-layered materials to environmental adsorbates, which is typically seen as a challenge, is harnessed in this study to fine-tune the material properties. This work investigates the impact of environmental adsorbates on electrical properties by studying metal-semiconductor-metal (MSM) devices fabricated on CVD-synthesized SnSe flakes. The freshly prepared devices exhibit positive photoconductivity (PPC), whereas they gradually develop negative photoconductivity (NPC) after being exposed to an ambient environment for ∼1 day. While the photodetectors based on positive photoconductivity exhibit a responsivity and detectivity of 6.1 A/W and 5.06 × 10 8 Jones, the same for the negative photoconductivity-based photodetector reaches up to 36.3 A/W and 1.49 × 10 9 Jones, respectively. In addition, the noise-equivalent power of the NPC photodetector decreases by 300 times as compared to the PPC device, which implies a prominent detection capability of the NPC device against weak photo signals. To substantiate the hypothesis that negative photoconductivity stems from the photodesorption of water and oxygen molecules on the dangling bonds of SnSe flakes, the flakes are etched along the most active planes (010) with a focused laser beam in an inert environment, which enhances responsivity by 43%, supporting negative photoconductivity linked to photodesorption. Furthermore, the humidity-dependent dark current variation of the NPC photodetectors is used to design a humidity sensor for human respiration monitoring with faster response and recovery times of 0.72 and 0.68 s, respectively. These findings open up the possibility of tuning the photoelectrical response of layered materials in a facile manner to develop future sensors and optoelectronic multifunctional devices.

In our pursuit of high-power terahertz (THz) wave generation, we propose innovative edge-terminated single-drift region (SDR) multi-quantum well (MQW) impact avalanche transit time (IMPATT) structures based on the Al x Ga 1- x N/GaN/Al x Ga 1- x N material system, with a fixed aluminum mole fraction of x = 0.3. Two distinct MQW diode configurations, namely p + -n junction-based and Schottky barrier diode structures, were investigated for their THz potential. To enhance reverse breakdown characteristics, we propose employing mesa etching and nitrogen ion implantation for edge termination, mitigating issues related to premature and soft breakdown. The THz performance is comprehensively evaluated through steady-state and high-frequency characterizations using a self-consistent quantum drift-diffusion (SCQDD) model. Our proposed Al 0.3 Ga 0.7 N/GaN/Al 0.3 Ga 0.7 N MQW diodes, as well as GaN-based single-drift region (SDR) and 3C-SiC/Si/3C-SiC MQW-based double-drift region (DDR) IMPATT diodes, are simulated. The Schottky barrier in the proposed diodes significantly reduces device series resistance, enhancing peak continuous wave power output to approximately 300 mW and DC to THz conversion efficiency to nearly 13% at 1.0 THz. Noise performance analysis reveals that MQW structures within the avalanche zone mitigate noise and improve overall performance. Benchmarking against state-of-the-art THz sources establishes the superiority of our proposed THz sources, highlighting their potential for advancing THz technology and its applications.

To address charge recombination in photocatalysis, the prevalent approach involves the use of noble metal cocatalysts. However, the precise factors influencing this performance variability based on cocatalyst selection have remained elusive. In this study, CdS hollow spheres loaded with distinct noble metal nanoparticles (Pt, Au, and Ru) are investigated by femtosecond transient absorption (fs-TA) spectroscopy. A more pronounced internal electric field leads to the creation of a larger Schottky barrier, with the order Pt-CdS > Au-CdS > Ru-CdS. Owing to these varying Schottky barrier heights, the interface electron transfer rate (K e ) and efficiency (η e ) of metal-CdS in acetonitrile (ACN) exhibit the following trend: Ru-CdS > Au-CdS > Pt-CdS. However, the trends of K e and η e for metal-CdS in water are different (Ru-CdS > Pt-CdS > Au-CdS) due to the influence of water, leading to the consumption of photogenerated electrons and affecting the metal/CdS interface state. Although Ru-CdS displays the highest K e and η e , its overall photocatalytic performance, particularly in H 2 production, lags behind that of Pt-CdS due to the electron backflow from Ru to CdS. This work offers a fresh perspective on the origin of performance differences and provides valuable insights for cocatalyst design and construction., (© 2023 Wiley‐VCH GmbH.)

Two-dimensional (2D) transition-metal dichalcogenides (TMDs) offer advantages over traditional silicon in future electronics but are hampered by the prominent high contact resistance of metal-TMD interfaces, especially for p-type TMDs. Here, we present high-performance p-type MoTe 2 field-effect transistors via a nondestructive van der Waals (vdW) transfer process, establishing low contact resistance between the 2D MoTe 2 semiconductor and the PtTe 2 semimetal. The integration of PtTe 2 as contacts in MoTe 2 field-effect transistors leads to significantly improved electrical characteristics compared to conventional metal contacts, evidenced by a mobility increase to 80 cm 2 V -1 s -1 , an on-state current rise to 5.0 μA/μm, and a reduction in Schottky barrier height (SBH) to 48 meV. Such a low SBH in quasi-van der Waals contacts can be assigned to the low electrical resistivity of PtTe 2 and the high efficiency of carrier injection at the 2D semimetal/2D semiconductor interfaces. Imaging via transmission electron microscopy reveals that the 2D semimetal/two-dimensional semiconductor interfaces are atomically flat and exceptionally clean. This interface engineering strategy could enable low-resistance contacts based on vdW architectures in a facile manner, providing opportunities for 2D materials for next-generation optoelectronics and electronics.

Memristors integrated into a crossbar-array architecture (CAA) are promising candidates for analog in-memory computing accelerators. However, the relatively low reliability of the memristor device and sneak current issues in CAA remain the main obstacles. Alkali ion-based interface-type memristors are promising solutions for implementing highly reliable memristor devices and neuromorphic hardware. This interface-type device benefits from self-rectifying and forming-free resistive switching (RS), and exhibits relatively low variation from device to device and cycle to cycle. In a previous report, we introduced an in situ grown Na/TiO 2 memristor using atomic layer deposition (ALD) and proposed a RS mechanism from experimentally measured Schottky barrier modulation. Self-rectifying RS characteristics were observed by the asymmetric distribution of Na dopants and oxygen vacancies as the Ti metal used as the adhesion layer for the bottom electrode diffuses over the Pt electrode at 250 °C during the ALD process and is doped into the TiO 2 layer. Here, we theoretically verify the modulation of the Schottky barrier at the TiO 2 /Pt electrode interface by Na ions. This study fabricated a Pt/Na/TiO 2 /Pt memristor device and confirmed its self-rectifying RS characteristics and stable retention characteristics for 24 h at 85 °C. Additionally, this device exhibited relative standard deviations of 27 and 7% in the high and low resistance states, respectively, in terms of cycle-to-cycle variation. To verify the RS mechanism, we conducted density functional theory simulations to analyze the impact of Na cations at interstitial sites on the Schottky barrier. Our findings can contribute to both fundamental understanding and the design of high-performance memristor devices for neuromorphic computing.

Photodynamic therapy's antitumor efficacy is hindered by the inefficient generation of reactive oxygen species (ROS) due to the photogenerated electron-hole pairs recombination of photosensitizers (PS). Therefore, there is an urgent need to develop efficient PSs with enhanced carrier dynamics. Herein, we designed Schottky junctions composed of cobalt tetroxide and palladium nanocubes (Co 3 O 4 @Pd) with a built-in electric field as effective PS. The built-in electric field enhanced photogenerated charge separation and migration, resulting in the generation of abundant electron-hole pairs and allowing effective production of ROS. Thanks to the built-in electric field, the photocurrent intensity and carrier lifetime of Co 3 O 4 @Pd were approximately 2 and 3 times those of Co 3 O 4 , respectively. Besides, the signal intensity of hydroxyl radical and singlet oxygen increased to 253.4% and 135.9%, respectively. Moreover, the localized surface plasmon resonance effect of Pd also enhanced the photothermal conversion efficiency of Co 3 O 4 @Pd to 40.50%. In vitro cellular level and in vivo xenograft model evaluations demonstrated that Co 3 O 4 @Pd could generate large amounts of ROS, trigger apoptosis, and inhibit tumor growth under near-infrared laser irradiation. Generally, this study reveals the contribution of the built-in electric field to improving photodynamic performance and provides new ideas for designing efficient inorganic PSs.

Plasmonic Schottky devices have attracted considerable attention for use in practical applications based on photoelectric conversion, because they enable light to be harvested below the bandgap of semiconductors. In particular, silicon-based (Si) plasmonic Schottky devices have great potential for useful photodetection in the near-infrared region. However, the internal quantum efficiency (IQE) values of previously reported devices are low because the Schottky barrier is excessively high. Here, we are the first to develop AuAg nanoalloy-n-type Si plasmonic Schottky devices by cathodic arc plasma deposition. Interestingly, it is found that a novel nanostructure, which leads to the improvement of responsivities, is formed. Moreover, these plasmonic nanostructures can be fabricated in only ∼1 min. The fabricated AuAg nanoparticle-film structure enables proper control of the Schottky barrier height and increases the area of the Schottky interface for electron transfer. As a result, the considerably enhanced IQE of our device at a telecommunication wavelength of 1310 nm (1550 nm) without external bias is 4.6 (6.5) times higher than those in previous reports, and these responsivities are a record high. This approach can be applied to realize efficient photodetection in the NIR region and extend the use of light below the bandgap of semiconductors. This paves the way for future application advancements in a variety of fields, including photodetection, imaging, photovoltaics, and photochemistry.

Ferroelectric memristors hold immense promise for advanced memory and neuromorphic computing. However, they face limitations due to low readout current density in conventional designs with low-conductive ferroelectric channels, especially at the nanoscale. Here, we report a ferroelectric-mediated memristor utilizing a 2D MoS 2 nanoribbon channel with an ultrascaled cross-sectional area of <1000 nm 2 , defined by a ferroelectric BaTiO 3 nanoribbon stacked on top. Strikingly, the Schottky barrier at the MoS 2 contact can be effectively tuned by the charge transfers coupled with quasi-zero-dimensional polarization charges formed at the two ends of the nanoribbon, which results in distinctive resistance switching accompanied by multiple negative differential resistance showing the high-current density of >10 4 A/cm 2 . The associated space charges in BaTiO 3 are minimized to ∼3.7% of the polarization charges, preserving nonvolatile polarization. This achievement establishes ferroelectric-mediated nanoscale semiconductor memristors with high readout current density as promising candidates for memory and highly energy-efficient in-memory computing applications.

By using a simple device architecture along with a simple process design and a low thermal-budget of a maximum of 100 °C for passivating metal/semiconductor interfaces, a Schottky barrier MOSFET device with a low subthreshold slope of 70 mV dec -1 could be developed. This device is enabled after passivation of the metal/silicon interface (found at the source/drain regions) with ultra-thin SiO x films, followed by the e-beam evaporation of high- quality aluminum and by using atomic-layer deposition for HfO 2 as a gate oxide. All of these fabrication steps were designed in a sequential process so that a gate-last recipe could minimize the defect density at the aluminum/silicon and HfO 2 /silicon interfaces, thus preserving the Schottky barrier height and ultimately, the outstanding performance of the transistor. This device is fully integrated into silicon after standard CMOS-compatible processing, so that it could be easily adopted into front-end-of-line or even in back-end-of-line stages of an integrated circuit, where low thermal budget is required and where its functionality could be increased by developing additional and fast logic., (© 2023 IOP Publishing Ltd.)

Development of bifunctional hydrazine oxidation and oxygen reduction electrocatalysts with high activity and stability is of great significance for the implementation of direct hydrazine fuel cells. Combining zero-dimensional metal nanoparticles with three-dimensional nitrogen-doped carbon nanosheets is an attractive strategy for balancing performance and cost. However, the precise construction of these composites remains a significant challenge, and thorough study of their interaction mechanisms is lacking. Herein, the Cu NPs /Cu SA -NPCF catalyst was constructed by anchoring copper nanoparticles on a three-dimensional nitrogen-doped porous carbon nanosheet framework through coordination of polyvinyl pyrrolidone and copper ions. The Schottky barrier of metal-semiconductor matched the Fermi level of the rectifying contact, thus enabling directional electron transfer. The resulting electron-deficient Cu nanoparticles surface exhibited Lewis acidity, which was beneficial to adsorption of hydrazine molecule. While the electron-enriched Cu-N 4 /carbon surface improved the adsorption of oxygen molecule, and accelerated electron supply from Cu-N 4 active sites to various oxygen intermediates. The Cu NPs /Cu SA -NPCF Mott-Schottky catalyst exhibited excellent catalytic activity for hydrazine oxidation reaction and oxygen reduction reaction in an alkaline media. The directional manipulation of electron transfer in heterogeneous materials was an attractive universal synthesis method, providing new approach for the preparation of efficient and stable hydrazine fuel cell catalysts., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Two-dimensional (2D) materials hold great promise for future complementary metal-oxide semiconductor (CMOS) technology. However, the lack of effective methods to tune the Schottky barrier poses a challenge in constructing high-performance complementary circuits from the same material. Here, we reveal that the polarity of pristine MoTe 2 field-effect transistors (FETs) with minimized air exposure is n-type, irrespective of the metal contact type. The fabricated n-FETs with palladium contact can reach electron currents up to 275 μA/μm at V DS = 2 V. For p-FETs, we introduce a novel nitric oxide doping strategy, allowing a controlled transition of MoTe 2 FETs from n-type to unipolar p-type. By doping only in the contact region, we demonstrate hole currents up to 170 μA/μm at V DS = -2 V with preserved I on / I off ratios of 10 5 . Finally, we present a complementary inverter circuit comprising the high-performance n- and p-type FETs based on MoTe 2 , promoting the application of 2D materials in future electronic systems.

Owing to the tunable bandgap and high thermodynamic stability, anisotropic monolayer (ML) GeAs have arisen as an attractive candidate for electronic and optoelectronic applications. The contact properties of ML GeAs with 2D metal (graphene, Ti 2 CF 2 , V 2 CF 2 , and Ti 3 C 2 O 2 ) and Cu electrodes are explored along two principal axes in field-effect transistors (FET) by employing ab initio electronic structure calculations and quantum transport simulations. Weak van der Waals interactions are found between ML GeAs and the 2D metal electrodes with the band structure of ML GeAs kept the same, while there is a strong interaction between ML GeAs and the Cu metal electrode, resulting in the obvious hybridization of the band structure. Isotropic contact properties are seen along the two principal directions. P -type lateral Schottky contacts are established in ML GeAs FETs with Ti 3 C 2 O 2 , graphene, and Ti 2 CF 2 metals, with a hole Schottky barrier height (SBH) of 0.12 (0.20), 0.15 (0.11), and 0.29 (0.21) eV along the armchair (zigzag) direction, respectively, and an n -type lateral Schottky contact is established with the Cu electrode with an electron SBH of 0.64 (0.57) eV. Surprisingly, ML GeAs forms ideal p -type Ohmic contacts with the V 2 CF 2 electrode. The results provide a theoretical foundation for comprehending the interactions between ML GeAs and metals, as well as for designing high-performance ML GeAs FETs.

BiFeO 3 /La 0.7 Sr 0.3 MnO 3 (BFO/LSMO) epitaxial heterostructures were successfully synthesized by pulsed laser deposition on (001)-oriented SrTiO 3 single-crystal substrates with Au top electrodes. Stable bipolar resistive switching characteristics regulated by ferroelectric polarization reversal was observed in the Au/BFO/LSMO heterostructures. The conduction mechanism was revealed to follow the Schottky emission model, and the Schottky barriers in high-resistance and low-resistance states were estimated based on temperature-dependent current-voltage curves. Further, the observed memristive behavior was interpreted via the modulation effect on the depletion region width and the Schottky barrier height caused by ferroelectric polarization reversal, combining with the oxygen vacancies migration near the BFO/LSMO interface.

Cu 2 ZnSnS 4 (CZTS) active material-based resistive random-access memory (RRAM) devices are investigated to understand the impact of three different Cu, Ag, and Al top electrodes. The dual resistance switching (RS) behaviour of spin coated CZTS on ITO/Glass is investigated up to 10 2 cycles. The stability of all the devices (Cu/CZTS/ITO, Ag/CZTS/ITO, and Al/CZTS/ITO) is investigated up to 10 3  sec in low- (LRS) and high- (HRS) resistance states at 0.2 V read voltage. The endurance up to 10 2 cycles with 30 msec switching width shows stable write and erase current. Weibull cumulative distribution plots suggest that Ag top electrode is relatively more stable for set and reset state with 33.61 and 25.02 shape factors, respectively. The charge carrier transportation is explained by double logarithmic plots, Schottky emission plots, and band diagrams, substantiating that at lower applied electric field intrinsic copper ions dominate in Cu/CZTS/ITO, whereas, at higher electric filed, top electrodes (Cu and Ag) dominate over intrinsic copper ions. Intrinsic Cu + in CZTS plays a decisive role in resistive switching with Al electrode. Further, the impedance spectroscopy measurements suggest that Cu + and Ag + diffusion is the main source for the resistive switching with Cu and Ag electrodes., (© 2023 Wiley-VCH GmbH.)

The electrical behavior and the photoresponse of rhenium disulfide field-effect transistors (FETs) have been widely studied; however, only a few works have investigated the photocurrent as a function of temperature. In this paper, we perform the electrical characterization of few-layer ReS 2 -based FETs with Cr-Au contacts over a wide temperature range. We exploit the temperature-dependent transfer and output characteristics to estimate the effective Schottky barrier at the Cr-Au/ReS 2 interface and to investigate the temperature behavior of parameters, such as the threshold voltage, carrier concentration, mobility, and subthreshold swing. Through time-resolved photocurrent measurements, we show that the photocurrent increases with temperature and exhibits a linear dependence on the incident light power at both low and room temperatures and a longer rise/decay time at higher temperatures. We surmise that the photocurrent is affected by the photobolometric effect and light-induced desorption of adsorbates which are facilitated by the high temperature and the low pressure.

Controlling the domain evolution is critical both for optimizing ferroelectric properties and for designing functional electronic devices. Here we report an approach of using the Schottky barrier formed at the metal/ferroelectric interface to tailor the self-polarization states of a model ferroelectric thin film heterostructure system SrRuO 3 /(Bi,Sm)FeO 3 . Upon complementary investigations of the piezoresponse force microscopy, electric transport measurements, X-ray photoelectron/absorption spectra, and theoretical studies, we demonstrate that Sm doping changes the concentration and spatial distribution of oxygen vacancies with the tunable host Fermi level which modulates the SrRuO 3 /(Bi,Sm)FeO 3 Schottky barrier and the depolarization field, leading to the evolution of the system from a single domain of downward polarization to polydomain states. Accompanied by such modulation on self-polarization, we further tailor the symmetry of the resistive switching behaviors and achieve a colossal on/off ratio of ∼1.1 × 10 6 in the corresponding SrRuO 3 /BiFeO 3 /Pt ferroelectric diodes (FDs). In addition, the present FD also exhibits a fast operation speed of ∼30 ns with a potential for sub-nanosecond and an ultralow writing current density of ∼132 A/cm 2 . Our studies provide a way for engineering self-polarization and reveal its strong link to the device performance, facilitating FDs as a competitive memristor candidate used for neuromorphic computing.

As a ferromagnetic semiconductor, two-dimensional (2D) Cr 2 Ge 2 Te 6 holds significant implications for electronic and spintronic devices. To achieve 2D electronics, it is essential to integrate Cr 2 Ge 2 Te 6 with 2D electrodes to form Schottky-barrier-free Ohmic contacts with enhanced carrier injection efficiency. Herein, by using first-principles calculations based on density-functional theory, we systematically investigate the structural, energetic, electronic and magnetic properties of 2D heterojunctions by combining Cr 2 Ge 2 Te 6 with a series of 2D metals, including graphene, ZrCl, NbS 2 , TaS 2 , TaSe 2 , Zn 3 C 2 , Hg 3 C 2 , and Zr 2 N. Results show that NbS 2 , TaS 2 , TaSe 2 , Zn 3 C 2 , Hg 3 C 2 , and Zr 2 N form Ohmic contacts with Cr 2 Ge 2 Te 6 , in contrast to graphene and ZrCl that exhibit a finite Schottky barrier. By examining the tunneling barriers and Fermi level shift, we reveal that the heterojunctions with Zn 3 C 2 and Hg 3 C 2 as electrodes exhibit advantages of both high electron injection efficiency and spin injection efficiency, for which an apparent decrease of the magnetic moment of Cr atoms in Cr 2 Ge 2 Te 6 can be observed. These findings not only provide physical insights into the role of interfacial interaction in regulating the physical properties of 2D heterojunctions, but also pave way for the development of high-performance spintronic nanodevices for practical implementation., (© 2023 IOP Publishing Ltd.)

For the complementary operation of two-dimensional (2D) material-based field-effect transistors (FETs), high-performance p-type FETs are essential. In this study, we applied surface charge-transfer doping from WO x , which has a large work function of ∼6.5 eV, selectively to the access region of WS 2 and WSe 2 by covering the channel region with h -BN. By reducing the Schottky barrier width at the contact and injecting holes into the valence band, the p-type conversion of intrinsically n-type trilayer WSe 2 FET was successfully achieved. However, trilayer WS 2 did not show clear p-type conversion because its valence band maximum is 0.66 eV lower than that of trilayer WSe 2 . Although inorganic WO x boasts high air stability and fabrication process compatibility due to its high thermal budget, the trap sites in WO x cause large hysteresis during back gate operation of WSe 2 FETs. However, by using top gate (TG) operation with an h -BN protection layer as a TG insulator, a high-performance p-type WSe 2 FET with negligible hysteresis was achieved.

Ambipolar field-effect transistors (FETs) possessing both electron and hole carriers enable implementation of novel reconfigurable transistors, artificial synaptic transistors, and output polarity controllable (OPC) amplifiers. Here, we fabricated a two-dimensional (2D) material-based complementary ambipolar FET and investigated its electrical characteristics. Properties of ohmic-like contacts at source/drain sides were verified from output characteristics and temperature-dependent measurements. The symmetry of electron and hole currents can be easily achieved by optimization of the MoS 2 or WSe 2 channels, different from the conventional ambipolar FET with fundamental issues related to Schottky barriers. In addition, we demonstrated successful operation of a complementary inverter and OPC amplifier, using the fabricated complementary ambipolar FET based on 2D materials., (© 2023 IOP Publishing Ltd.)

The increasing interest in two-dimensional materials with unique crystal structures and novel band characteristics has provided numerous new strategies and paradigms in the field of photodetection. However, as the demand for wide-spectrum detection increases, the size of integrated systems and the limitations of mission modules pose significant challenges to existing devices. In this paper, we present a van der Waals heterostructure photodetector based on Ta 2 NiSe 5 /WSe 2 , leveraging the inherent characteristics of heterostructures. Our results demonstrate that this detector exhibits excellent broad-spectrum detection ability from the visible to the infrared bands at room temperature, achieving an extremely high on/off ratio, without the need for an external bias voltage. Furthermore, compared to a pure material detector, it exhibits a fast response and low dark currents (~3.6 pA), with rise and fall times of 278 μs and 283 μs for the response rate, respectively. Our findings provide a promising method for wide-spectrum detection and enrich the diversity of room-temperature photoelectric detection.

The ultrathin nature of two-dimensional (2D) materials opens up opportunities for creating devices that are substantially thinner than using traditional bulk materials. In this article, monolayer 2D materials grown by the chemical vapor deposition method are used to fabricate ultrathin all-2D lateral diodes. We show that placing graphene electrodes below and above the WS 2 monolayer, instead of the same side, results in a lateral device with two different Schottky barrier heights. Due to the natural dielectric environment, the bottom graphene layer is wedged between the WS 2 and the SiO 2 substrate, which has a different doping level than the top graphene layer that is in contact with WS 2 and air. The lateral separation of these two graphene electrodes results in a lateral metal-semiconductor-metal junction with two asymmetric barriers but yet retains its ultrathin form of two-layer thickness. The rectification and diode behavior can be exploited in transistors, photodiodes, and light-emitting devices. We show that the device exhibits a rectification ratio up to 90 under a laser power of 1.37 μW at a bias voltage of ±3 V. We demonstrate that both the back-gate voltage and laser illumination can tune the rectification behavior of the device. Furthermore, the device can generate strong red electroluminescence in the WS 2 area across the two graphene electrodes under an average flowing current of 2.16 × 10 -5 A. This work contributes to the current understanding of the 2D metal-semiconductor heterojunction and offers an idea to obtain all-2D Schottky diodes by retaining the ultrathin device concept.

This article addresses the synthesis of Fe 3+ doped TiO 2 nanoparticles with variations of molar concentrations of Fe 3+ and their adequate use as potential photocatalysts for Photocatalysis applications. Synthesized photocatalysts were characterized thoroughly by different analytical techniques in terms of morphological, chemical, structural, crystalline, optical, electronic structure, surface area etc properties. The occurrence of red shift phenomenon of the energy band gap attributes to the transfer of charges and transition between the d electrons of dopant and conduction band (CB) or valence band (VB) of TiO 2 . The doping of Fe 3+ ions generates more trap sites for charge carriers with the surface trap sites. Thorough experimental conclusions revealed that the Fe 3+ ions necessarily regulate the catalytic property of TiO 2 nanomaterial. The obtained total degradation efficiency rate of Methylene Blue (MB) was 93.3% in the presence of 0.1 M Fe 3+ in the host material and for Malachite Green Oxalate the efficiency was 100% in the presence of 0.05 M and 0.1 M Fe 3+ in the host material. In both the cases the total visible light irradiation time was 90 min. The adsorption properties of the photocatalysts have been also performed in a dark for 90 min in the presence of MB dye. However, till now there are hardly reported photocatalysts which shows complete degradation of these toxic organic dyes by visible light driven photocatalysis. of potential values of valence and conduction band shows the production of active oxidizing species for hydrogen yield and the possible mechanism of the Schottky barrier has been proposed. A schematic diagram of visible light driven Photocatalysis has been pictured showing degradation activity of Fe 3+ -TiO 2 catalysts sample., (© 2023 IOP Publishing Ltd.)

A novel Schottky barrier MOSFET with quad gate and with source engineering has been proposed in this work. A high-κ dielectric is used at the source side of the channel, while SiO 2 is used at the drain side of the channel. To improve the carrier mobility, a SiGe pocket region is created at the source side of the channel. Physical and electrical characteristics of the proposed device are compared with conventional double gate Schottky barrier MOSFET. It has been observed that the proposed device exhibits better performance, with a higher I ON /I OFF ratio and lower subthreshold slope. The high-κ dielectric, along with the SiGe pocket region, improves tunneling probability, while aluminum, along with SiO 2 at the drain side, broadens the drain/channel Schottky barrier and reduces the hole tunneling probability, resulting in a reduced OFF-state current. Further, the proposed device is used as a biosensor to detect both the charged and neutral biomolecules. Biosensors are made by creating a nanocavity in the dielectric region near the source end of the channel to capture biomolecules. Biomolecules such as streptavidin, biotin, APTES, cellulose and DNA have unique dielectric constants, which modulates the electrical parameters of the device. Different electrical parameters, viz., the electric field, surface potential and drain current, are analyzed for each biomolecule. It has been observed that drain current increases with the dielectric constant of the biomolecules. Furthermore, the sensitivity and selectivity of the proposed biosensors is better than that of conventional biosensors made using double gate Schottky barrier MOSFETs. Sensitivity is almost twice that of a conventional sensor, while selectivity is six to twelve times higher than a conventional one.

The ferroelectric photovoltaic effect has been extensively studied for possible applications in energy conversion and photo-electrics. The reversible spontaneous polarization gives rise to a switchable photovoltaic behavior. However, despite its long history, the origin of the ferroelectric photovoltaic effect still lacks a full understanding since multiple mechanisms such as bulk and Schottky-barrier-related interface effects are involved. Herein, we report a comprehensive study on the photovoltaic response of BiFeO 3 -based vertical heterostructures, using multiple strategies to clarify its origin. We found that, under white light illumination, polarization-modulated Schottky barrier at the interface is the dominating mechanism. By varying the top metal contacts, only the photovoltaic effect of the polarization downward state is strongly modulated, suggesting selective interface contribution in different polarization states. A Schottky-barrier-free device shows negligible photovoltaic effect, suggesting the lack of bulk photovoltaic effect in vertical heterostructures under white light illumination.

Since memristors as an emerging nonlinear electronic component have been considered the most promising candidate for integrating nonvolatile memory and advanced computing technology, the in-depth reveal of the memristive mechanism and the realization of hardware fabrication have facilitated their wide applications in next-generation artificial intelligence. Flexible memristors have shown great promising prospects in wearable electronics and artificial electronic skin (e-skin), but in-depth research on the physical mechanism is still lacking. Here, a flexible memristive device with a Ag/HfO x /Ti/PET crossbar structure was fabricated, and a remarkable analog switching characteristic similar to synaptic behavior was observed. Through detailed data fitting and in-depth physical mechanism analysis, it is confirmed that the analog switching characteristics of the device are mainly caused by carrier tunneling. Furthermore, the memristive properties of the Ag/HfO x /Ag/PET device can be attributed to the conductive filaments formed by the redox reaction of the active metal Ag. Finally, the interfacial barrier is extracted by the Arrhenius diagram and the energy band diagram, which is drawn to clearly demonstrate the conduction mechanism of charge trapping in the device. Therefore, the HfO x -based flexible memristor with analog switching behavior and stable memory performance lays the foundation for cutting-edge applications in wearable electronics and smart e-skin.

Artificial neurons as the basic units of spiking neural network (SNN) have attracted increasing interest in energy-efficient neuromorphic computing. 2D transition metal dichalcogenide (TMD)-based devices have great potential for high-performance and low-power artificial neural devices, owing to their unique ion motion, interface engineering, and resistive switching behaviors. Although there are widespread applications of TMD-based artificial synapses in neural networks, TMD-based neurons are seldom reported due to the lack of bio-plausible multi-mechanisms to mimic leaking, integrating, and firing biological behaviors without external assistance. In this work, for the first time, a methodology is developed by introducing the hybrid effect of charge trapping (CT) and Schottky barrier (SB) in MoS 2 FETs for barristor memory and one-transistor (1T) compact artificial neuron realization. By correlating the CT and SB processes, quasi-volatile and resistive switching behaviors are realized on the fabricated MoS 2 FET and utilized to mimic the accumulating, leaking, and firing biological behaviors of neurons. Therefore, based on a single quasi-volatile CT-SB MoS 2 barristor memory, a 1T compact neuron of the basic leaky-integral-and-fire (LIF) function is demonstrated without a peripheral circuit. Furthermore, a spiking neural network (SNN) based on the CT-SB MoS 2 barristor neurons is simulated and implemented in pattern classification with high accuracy approaching 95.82%. This work provides a highly integrated and inherently low-energy implementation for neural networks.

Charge carrier transfer efficiency as a crucial factor determines the performance of heterogeneous photocatalysis. Here, we demonstrate a simple nanohybrid structure of BaTiO 3 -Au (BTO-Au) for the efficient selective oxidization of benzyl alcohol to benzaldehyde upon piezotronic effect boosted plasmonic photocharge carrier transfer. With the aid of ultrasonic mechanical vibration, the reaction rate of the photocatalytic organic conversion would be considerably accelerated, which is about 4.2 and 6.2 times higher than those driven by sole visible light irradiation and sole ultrasonication, respectively. Photoelectrochemical tests under ultrasonic stimuli reveal the BTO-Au catalytic system is independent of the light intensity, showing a consistent photocurrent density, over a wide range of incident light brightness. The largely enhanced photocatalytic activity can be ascribed to the synergetic effect of surface plasmonic resonance (SPR)-piezotronic coupling by which a built-in electric field induced by the piezotronic effect significantly favors the oriented mobilization of energetic charge carriers generated by the SPR effect at the heterojunction. Notably, a decrease of the Schottky barrier height of ∼0.3 eV at the BTO-Au interface is verified experimentally, due to the band bending of BTO induced by the piezotronic effect, which can greatly augment the hot electron transfer efficiency. This work highlights the coupling of the piezotronic effect with SPR within the BTO-Au nanostructure as a versatile and promising route for efficient charge transfer in photocatalytic organic conversion.

Single layers of two-dimensional (2D) materials hold the promise for further miniaturization of semiconductor electronic devices. However, the metal-semiconductor contact resistance limits device performance. To mitigate this problem, we propose modulation doping, specifically a doping layer placed on the opposite side of a metal-semiconductor interface. Using first-principles calculations to obtain the band alignment, we show that the Schottky barrier height and, consequently, the contact resistance at the metal-semiconductor interface can be reduced by modulation doping. We demonstrate the feasibility of this approach for a single-layer tungsten diselenide (WSe 2 ) channel and 2D MXene modulation doping layers, interfaced with several different metal contacts. Our results indicate that the Fermi level of the metal can be shifted across the entire band gap. This approach can be straight-forwardly generalized for other 2D semiconductors and a wide variety of doping layers.

Quantum dot (QD) gas sensors are one of the most useful nanotechnologies applied to protect people from unnecessary harm. This work theoretically explores the mechanism in QD gas sensors in order to advance the prudent design of relevant products. The theoretical model employed in this research is similar to the process in plants' photosynthesis, referred to as charge separation of light harvesting. In this work, we investigate the details of energy transport in QD gas sensors carried by electrons from the circuit. We demonstrate theoretically how the effects of temperature and gas detection affect electron transport. To analyze thoroughly, the potential energy referred to as the Schotthy barrier perturbed by gasses is considered. Moreover, the energy transfer efficiency (ETE) of QD gas sensors for oxidizing or reducing gas is shown in the simulation. The results imply that the electron transport between QDs (raising the current and lessening the current) depends on a parameter corresponding with the Schotthy barrier. In regard to thermal energy portrayed by phonon baths, a higher temperature shortens the time duration of energy transport in QDs, hence raising energy transfer efficiency and energy current. Our model can be applied to further QD gas sensors' design and manufacture., (Copyright © 2022 Suntijitrungruang, Lakronwat, Uthailiang, Pongkitiwanichakul and Boonchui.)

Ultralow-power electronics is critical to wearable, portable, and implantable applications where the systems could only have access to very limited electrical power supply or even be self-powered. Here, we report on a type of Schottky barrier (SB) contacted single-walled carbon nanotube (SWCNT) network film field-effect-transistors (FETs) that are operated in the subthreshold region to achieve ultralow-power applications. The thin high-k gate dielectric and the overlap between the gate and the source electrodes offer highly efficient gate electrostatic control over the SWCNT channel and the SB at the source contact, resulting in steep subthreshold switching characteristics with a small subthreshold swing (∼67 mV dec -1 ), a large current on/off ratio (∼10 6 ), and a low off-state current (∼0.5 pA). A p -channel metal-oxide-semiconductor inverter built with the subthreshold SB-SWCNT-FETs exhibits a well-defined logic functionality and small-signal amplification capability under a low supply voltage (∼0.5 V) and an ultralow power (∼0.05 pW μ m -1 ). The low-voltage and deep subthreshold operations reported here could lay an essential foundation for high-performance and ultralow-power SWCNTs-based electronics., (© 2022 IOP Publishing Ltd.)

Two-dimensional semiconductors have great potential for beyond-silicon electronics. However, because of the lack of controllable doping methods, Fermi level pinning, and van der Waals (vdW) gaps at the metal-semiconductor interfaces, these devices exhibit high electrical contact resistances, restricting their practical applications. Here, we report a general contact-resistance-lowering strategy by constructing vertical metal-semiconductor-metal memristor structures at the contact regions and setting them into a nonvolatile low-resistance state through a memristive forming process. Through this, we reduce the contact resistances of MoS 2 field-effect transistors (FETs) by at least one order of magnitude and improve the on-state current densities of MoTe 2 FETs by about two orders of magnitude. We also demonstrate that this strategy is applicable to other two-dimensional semiconductors, including MoSe 2 , WS 2 , and WSe 2 , and a variety of contact metals, including Au, Cu, Ni, and Pd. The good stability and universality indicate the great potential for technological applications.

Two-dimensional materials have the potential to be applied in flexible and transparent electronics. In this study, single-layer MoS 2 field-effect transistors (FETs) with Au/Ti-graphene heteroelectrodes were fabricated to examine the effect of the electrodes on the electrical properties of the MoS 2 FETs. The contact barrier potential was tuned using an electric field. Asymmetrical gate behavior was observed owing to the difference between the MoS 2 FETs, specifically between the MoS 2 FETs with Au/Ti electrodes and those with graphene electrodes. The contact barrier of the MoS 2 FETs with Au/Ti electrodes did not change with the electric field. However, the contact barrier at the MoS 2 -graphene interface could be modulated. The MoS 2 FETs with Au/Ti-graphene electrodes exhibited enhanced on/off ratios (~10 2 times) and electron mobility (~2.5 times) compared to the MoS 2 FETs with Au/Ti electrodes. These results could improve the understanding of desirable contact formation for high-performance MoS 2 FETs and provide a facile route for viable electronic applications.

Ultrathin 2D semiconductor devices are considered to have beyond-silicon potential but are severely troubled by the high Schottky barriers of the metal-semiconductor contacts, especially for p-type semiconductors. Due to the severe Fermi-level pinning effect and the lack of conventional semimetals with high work functions, their Schottky hole barriers are hardly removed. Here, an all-van-der-Waals barrier-free hole contact between p-type tellurene semiconductor and layered 1T'-WS 2 semimetal is reported, which achieves a zero Schottky barrier height of 3 ± 9 meV and a high field-effect mobility of ≈1304 cm 2 V -1 s -1 . The formation of such contacts can be attributed to the higher work function of ≈4.95 eV of the 1T'-WS 2 semimetal, which is in sharp contrast with low work function (4.1-4.7 eV) of conventional semimetals. The study defines an available strategy for eliminating the Schottky barrier of metal-semiconductor contacts, facilitating 2D-semiconductor-based electronics and optoelectronics to extend Moore's law., (© 2022 Wiley-VCH GmbH.)

Two-dimensional (2D) Janus materials have attracted significant attention due to their asymmetrical structures and unique electronic properties. In this work, by using the first-principles calculation based on density functional theory, we systematically investigate the electronic properties of 6 types of Janus- X Ga 2 Y/ Graphene van der Waals heterostructures (vdWHs). The results show that the Janus- X Ga 2 Y/ Graphene vdWHs are connected by weak interlayer vdW forces and can form n-type Schottky contact, p-type Schottky contact or Ohmic contact when the spin-orbit coupling (SOC) is not considered. However, when considering SOC, only the SeGa2S/G and G/SeGa2S vdWHs show n-type Schottky contact, and other vdWHs show Ohmic contacts. In addition, the Schottky barriers and contact types of SeGa 2 S/Graphene and Graphene/SeGa 2 S vdWHs can be effectively modulated by interlayer distance and biaxial strain. They can be transformed from intrinsic n-type Schottky contact to p-type Schottky contact when the interlayer distances are smaller than 2.65 Å and 2.90 Å, respectively. They can also be transformed to Ohmic contact by applying external biaxial strain. Our work can provide useful guidelines for designing Schottky nanodiodes, field effect transistors or other low-resistance nanodevices based on the 2D vdWHs., (© 2022 IOP Publishing Ltd.)

A novel heterojunction composite BiPt/KTa 0.5 Nb 0.5 O 3 (KTN) was designed and synthesized through a combination of hydrothermal and precipitation procedures. Bi and Pt contents were optimized. The best 1 %Bi-0.25 %Pt/KTN sample presented better photocatalytic performance in ammonia synthesis than KTN, 1 %Bi/KTN, and 0.25 %Pt/KTN. Under simulated sunlight, the NH 3 generation rate of the best BiPt/KTN reached 6.3 times that of pure KTN. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) analysis revealed that BiPt alloy nanoparticles were formed and decorated on the surface of KTN nanocubes. The PtBi alloy provided an appropriate Schottky barrier with a height between those of Pt/KTN and Bi/KTN. The barrier can efficiently capture photogenerated charge carriers while also preventing their backflow and recombination. Thus, the PtBi/KTN presented the best capability in charge separation, thereby displaying the highest photocatalytic activity in the N 2 -to-NH 3 reaction. Additionally, the loaded BiPt alloy also broadened the photoresponse of KTN to the visible light region via its surface plasmon resonance effect, which was another reason for the increased photoactivity. This study not only provided a potential photocatalyst for photocatalytic nitrogen fixation but also showed new ideas for the design of highly efficient catalysts via bimetal alloy modification., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

All-inorganic lead-free perovskite CsSnBr 3 , has been proved good stability and optoelectronic properties in theory and experiment. However, the interfacial electronic properties of metal/CsSnBr 3 are still unclear in electronic devices. Herein, we systematically investigate the interfacial properties of metal electrodes (Al, Ag and Au) and CsSnBr 3 with different atomic terminals (SnBr 2 -T and CsBr-T) through the first-principles calculation. SnBr 2 -T and CsBr-T have various contact types and Schottky barriers due to their different interaction strengths with metals. In particular, the moderate interlayer coupling strength with Al leads to the ultra-low Schottky barrier and tunneling barrier, which makes Al possess the best contact performance among the studied metals. Furthermore, the external electric field can be effective in regulating the Schottky barrier and realizing the Ohmic contact. These findings provide useful guidance for the design of perovskite-based nanoelectronic devices with high performance., (© 2022 IOP Publishing Ltd.)