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The practical application of two-dimensional (2D) semiconductors for high-performance electronics requires the integration with large-scale and high-quality dielectrics-which however have been challenging to deposit to date, owing to their dangling-bonds-free surface. Here, we report a dry dielectric integration strategy that enables the transfer of wafer-scale and high-κ dielectrics on top of 2D semiconductors. By utilizing an ultra-thin buffer layer, sub-3 nm thin Al2O3 or HfO2 dielectrics could be pre-deposited and then mechanically dry-transferred on top of MoS2 monolayers. The transferred ultra-thin dielectric film could retain wafer-scale flatness and uniformity without any cracks, demonstrating a capacitance up to 2.8 μF/cm2, equivalent oxide thickness down to 1.2 nm, and leakage currents of ~10-7 A/cm2. The fabricated top-gate MoS2 transistors showed intrinsic properties without doping effects, exhibiting on-off ratios of ~107, subthreshold swing down to 68 mV/dec, and lowest interface states of 7.6×109 cm-2 eV-1. We also show that the scalable top-gate arrays can be used to construct functional logic gates. Our study provides a feasible route towards the vdW integration of high-κ dielectric films using an industry-compatible ALD process with well-controlled thickness, uniformity and scalability.

Two-dimensional (2D) semiconductors have attracted considerable attention for the development of ultra-thin body transistors. However, the polarity control of 2D transistors and the achievement of complementary logic functions remain critical challenges. Here, we report a doping-free strategy to modulate the polarity of WSe2 transistors using same contact metal but different integration methods. By applying low-energy van der Waals integration of Au electrodes, we observed robust and optimized p-type transistor behavior, which is in great contrast to the transistors fabricated on the same WSe2 flake using conventional deposited Au contacts with pronounced n-type characteristics. With the ability to switch majority carrier type and to achieve optimized contact for both electrons and holes, a doping-free logic inverter is demonstrated with higher voltage gain of 340, at the bias voltage of 5.5 V. Furthermore, the simple polarity control strategy is extended for realizing more complex logic functions such as NAND and NOR.

In atomically-thin two-dimensional (2D) semiconductors, the nonuniformity in current flow due to its edge states may alter and even dictate the charge transport properties of the entire device. However, the influence of the edge states on electrical transport in 2D materials has not been sufficiently explored to date. Here, we systematically quantify the edge state contribution to electrical transport in monolayer MoS2/WSe2 field-effect transistors, revealing that the charge transport at low temperature is dominated by the edge conduction with the nonlinear behavior. The metallic edge states are revealed by scanning probe microscopy, scanning Kelvin probe force microscopy and first-principle calculations. Further analyses demonstrate that the edge-state dominated nonlinear transport shows a universal power-law scaling relationship with both temperature and bias voltage, which can be well explained by the 1D Luttinger liquid theory. These findings demonstrate the Luttinger liquid behavior in 2D materials and offer important insights into designing 2D electronics.

Two-dimensional van der Waals heterostructures (vdWHs) have attracted considerable interest.sup.1-4. However, most vdWHs reported so far are created by an arduous micromechanical exfoliation and manual restacking process.sup.5, which--although versatile for proof-of-concept demonstrations.sup.6-16 and fundamental studies.sup.17-30--is clearly not scalable for practical technologies. Here we report a general synthetic strategy for two-dimensional vdWH arrays between metallic transition-metal dichalcogenides (m-TMDs) and semiconducting TMDs (s-TMDs). By selectively patterning nucleation sites on monolayer or bilayer s-TMDs, we precisely control the nucleation and growth of diverse m-TMDs with designable periodic arrangements and tunable lateral dimensions at the predesignated spatial locations, producing a series of vdWH arrays, including VSe.sub.2/WSe.sub.2, NiTe.sub.2/WSe.sub.2, CoTe.sub.2/WSe.sub.2, NbTe.sub.2/WSe.sub.2, VS.sub.2/WSe.sub.2, VSe.sub.2/MoS.sub.2 and VSe.sub.2/WS.sub.2. Systematic scanning transmission electron microscopy studies reveal nearly ideal vdW interfaces with widely tunable moiré superlattices. With the atomically clean vdW interface, we further show that the m-TMDs function as highly reliable synthetic vdW contacts for the underlying WSe.sub.2 with excellent device performance and yield, delivering a high ON-current density of up to 900 microamperes per micrometre in bilayer WSe.sub.2 transistors. This general synthesis of diverse two-dimensional vdWH arrays provides a versatile material platform for exploring exotic physics and promises a scalable pathway to high-performance devices. A general strategy for the synthesis of two-dimensional van der Waals heterostructure arrays is used to produce high-performance electronic devices, showing the potential of this scalable approach for practical technologies., Author(s): Jia Li [sup.1] , Xiangdong Yang [sup.1] , Yang Liu [sup.2] , Bolong Huang [sup.3] , Ruixia Wu [sup.1] , Zhengwei Zhang [sup.1] , Bei Zhao [sup.1] , Huifang [...]

Exploring the dynamic structural evolution of electrocatalysts during reactions represents a fundamental objective in the realm of electrocatalytic mechanism research. In pursuit of this objective, we synthesized PhenPtCl2 nanosheets, revealing a N2-Pt-Cl2 coordination structure through various characterization techniques. Remarkably, the electrocatalytic performance of these PhenPtCl2 nanosheets for hydrogen evolution reaction (HER) surpasses that of the commercial Pt/C catalyst across the entire pH range. Furthermore, our discovery of the dynamic coordination changes occurring in the N2-Pt-Cl2 active sites during the electrocatalytic process, as clarified through in situ Raman and X-ray photoelectron spectroscopy, is particularly noteworthy. These changes transition from Phen-Pt-Cl2 to Phen-Pt-Cl and ultimately to Phen-Pt. The Phen-Pt intermediate plays a pivotal role in the electrocatalytic HER, dynamically coordinating with Cl- ions in the electrolyte. Additionally, the unsaturated, two-coordinated Pt within Phen-Pt provides additional space and electrons to enhance both H+ adsorption and H2 evolution. This research illuminates the intricate dynamic coordination evolution and structural adaptability of PhenPtCl2 nanosheets, firmly establishing them as a promising candidate for efficient and tunable electrocatalysts. Exploring the dynamic structural evolution of electrocatalysts during electrochemical reactions is imperative. Here, the authors constructed 2D PhenPtCl2 nanosheets with Phen-Pt-Cl2 coordination structure which exhibit dynamic coordination evolution during hydrogen evolution reaction and good performance across the full pH range [ABSTRACT FROM AUTHOR]

With the gradual depletion of traditional zinc resources, the full use of various non‐traditional zinc‐containing resources has received intensive attention. However, the efficient recovery of zinc ions with low concentrations remains challenging. Here efficient and continuous recovery of zinc ions in ammoniacal chloride media by a flat supported liquid membrane system is achieved, using Cyanex923 and TBP mixed extractant as the membrane phase. This article discusses the synergistic effect between Aliquat336, Cyanex923 and TBP, the effects of feed pH, total ammonia concentration, Cl− concentration and temperature on Zn(II) transport. [ABSTRACT FROM AUTHOR]

Single crystal metal halide perovskites thin films are considered to be a promising optical, optoelectronic materials with extraordinary performance due to their low defect densities. However, it is still difficult to achieve large‐scale perovskite single‐crystal thin films (SCTFs) with tunable bandgap by vapor‐phase deposition method. Herein, the synthesis of CsPbCl3(1–x)Br3x SCTFs with centimeter size (1 cm × 1 cm) via vapor‐phase deposition is reported. The Br composition of CsPbCl3(1–x)Br3x SCTFs can be gradually tuned from x = 0 to x = 1, leading the corresponding bandgap to change from 2.29 to 2.91 eV. Additionally, an low‐threshold (≈23.9 µJ cm−2) amplified spontaneous emission is achieved based on CsPbCl3(1–x)Br3x SCTFs at room temperature, and the wavelength is tuned from 432 to 547 nm by varying the Cl/Br ratio. Importantly, the high‐quality CsPbCl3(1–x)Br3x SCTFs are ideal optical gain medium with high gain up to 1369.8 ± 101.2 cm−1. This study not only provides a versatile method to fabricate high quality CsPbCl3(1–x)Br3x SCTFs with different Cl/Br ratio, but also paves the way for further research of color‐tunable perovskite lasing. [ABSTRACT FROM AUTHOR]

The increase of gate leakage current when the gate dielectric layer is thinned is a key issue for device scalability. For scaling down the integrated circuits, a thin gate dielectric layer with a low leakage current is essential. Currently, changing the dielectric layer material or enhancing the surface contact between the gate dielectric and the channel material is the most common way to reduce gate leakage current in devices. Herein, we report a technique of enhancing the surface contact between the gate dielectric and the metal electrode, that is constructing an Au/Al2O3/Si metalâ€"oxideâ€"semiconductor device by replacing the typical evaporated electrode/dielectric layer contact with a transferred electrode/high- Îş dielectric layer contact. The contact with a mild, non-invasive interface can ensure the intrinsic insulation of the dielectric layer. By applying 2â€"40 nm Al2O3 as the dielectric layer, the current densityâ€"electrical field (J â€" E) measurement reveals that the dielectric leakage generated by the transferred electrode is less than that obtained by the typical evaporated electrode with a ratio of 0.3 × 101 ∼ 5 × 106 at V bias = 1 V. Furthermore, at J  = 1 mA cmâˆ'2, the withstand voltage can be raised by 100â€"102 times over that of an evaporated electrode. The capacitanceâ€"voltage (C â€" V) test shows that the transferred metal electrode can efficiently scale the equivalent oxide layer thickness (EOT) to 1.58 nm, which is a relatively smaller value than the overall reported Si-based device’s EOT. This finding successfully illustrates that the transferred electrode/dielectric layer’s mild contact can balance the scaling of the gate dielectric layer with a minimal leakage current and constantly reduce the EOT. Our enhanced electrode/dielectric contact approach provides a straightforward and effective pathway for further scaling of devices in integrated circuits and significantly decreases the overall integrated circuit’s static power consumption (ICs). [ABSTRACT FROM AUTHOR]

Two-dimensional materials and their heterojunctions have received extensive attention in fundamental and applied research of photonics, electronics, and spintronics. Herein, we stacked SnS2, FePS3, and graphene (Gr) nanosheets into SnS2/FePS3/Gr van der Waals heterojunction, which exhibits broadband photoresponse from an ultraviolet region (405 nm) to an infrared region (850 nm) in atmosphere at room temperature. It was found that the dominated carrier of SnS2/FePS3 and SnS2/FePS3/Gr hererojunction was different in the electrical transport. The photoresponsivity of SnS2/FePS3/Gr heterojunction was about two orders of magnitude higher than that of SnS2 and FePS3 and SnS2/FePS3 heterojunction. The response time of SnS2/FePS3/Gr heterojunction was slightly shorter than that of SnS2/FePS3 heterojunction and two orders of magnitude shorter than that of SnS2 and FePS3 under the 450 nm laser. The high responsivity and short response time of SnS2/FePS3/Gr heterojunction should be attributed to the type II band alignment and short channel distance in the vertical direction where electrons and holes can be separated and transit fast. Our result offered an opportunity for realization of the high-performance and broadband photodetector. [ABSTRACT FROM AUTHOR]

A prerequisite for widespread applications of atomically thin transition metal dichalcogenides in future electronics is to achieve reliable electrical contacts, which is of considerable challenge due to the difficulties in selectively doping and inevitable physical damages of these atomically thin materials during typical metal integration process. Here, we report the in situ growth of ultrathin metallic NiSe single crystals on WSe2 in which the metallic NiSe nanosheets function as the contact electrodes to WSe2, creating an interface that is essentially free from chemical disorder. The NiSe/WSe2 heterostructures also exhibit well-aligned lattice orientation between the two layers, forming a periodic Moiré pattern. Electrical transport studies demonstrate that the NiSe nanosheets exhibit an excellent metallic feature, as evidenced by the extra-high electrical conductivity of up to 1.6×106 S·m−1. The WSe2 transistors with the NiSe contact show field-effect mobilities (μFE) more than double that with Cr/Au electrodes. This study demonstrates an effective pathway to achieve reliable electrical contacts to the atomically thin 2D materials, and maybe readily extended for fabricating 2D/2D low-resistance contacts for a variety of transition metal dichalcogenides. [ABSTRACT FROM AUTHOR]

The mixed-dimensional integration of two-dimensional (2D) materials with non-2D materials can give rise to prominent advances in performance or function. To date, the mixed-dimensional one-dimensional (1D)/2D heterostructures have been fabricated using various physical assembly approaches. However, direct epitaxial growth method which has notable advantages in preparing large-scale products and obtaining perfect interfaces is rarely investigated. Herein, we demonstrate for the first time the direct synthesis of the 1D/2D mixed-dimensional heterostructures by sequential vapor-phase growth of Sb2Se3 nanowires on WS2 monolayers. X-ray diffraction (XRD) pattern and Raman spectrum confirm the composition of the Sb2Se3/WS2 heterostructures. Transmission electron microscope (TEM) measurement demonstrates high quality of the heterostructures. Electrical transport characterization reveals that Sb2Se3 nanowire exhibits p-type characteristic and that WS2 monolayer exhibits n-type behavior, and that the p-n diode from 1D/2D mixed-dimensional Sb2Se3/WS2 heterostructure possesses obvious current rectification behavior. Optoelectronic measurements of the heterostructures show apparent photovoltaic response with an open-circuit voltage of 0.19 V, photoresponsivity of 1.51 A/W (Vds = 5 V) and fast response time of less than 8 ms. The van der Waals epitaxial growth mode of Sb2Se3 nanowires on WS2 monolayers is verified by stripping the Sb2Se3 nanowire from the heterostructures using tape. Together, the direct van der Waals epitaxy opens a facile pathway to 1D/2D mixed-dimensional heterostructures for functional electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) van der Waals (vdWs) metal-semiconductor heterostructures with atomically sharp interface and matched work functions have recently attracted great attention due to their unique electronic and optoelectronic properties. Here we report the vapor phase epitaxial growth of large-scale vertical Sb/WSe2 metal-semiconductor vdWs heterostructures with uniform stacking orientation. Compared with the growth on SiO2/Si substrate, the thickness of Sb nanosheet on WSe2 can be reduced effectively to monolayer. We construct Sb-WSe2-Au asymmetric electrodes photodiode based on the Sb/WSe2 heterostructures. Electrical transport measurements indicate that the photodiode show obvious rectifying effect. Optoelectronic characterizations show prominent photoresponse with a high photoresposivity of 364 mA/W, a fast response time of less than 8 ms, a large open-circuit voltage of 0.27 V and a maximum electrical power output of 0.11 nW. The direct growth of high-quality metal-semiconductor vdWs heterostructures may open up new realms in 2D functional electronics and optoelectronics. [ABSTRACT FROM AUTHOR]