The alloying of two-dimensional (2D) transition metal dichalcogenides (TMDs) is an established route to produce robust semiconductors with continuously tunable optoelectronic properties. However, typically reported methods for fabricating alloyed 2D TMD nanosheets are not suitable for the inexpensive, scalable production of large-area (m2) devices. Herein we describe a general method to afford large quantities of compositionally-tunable 2D TMD nanosheets using commercially available powders and liquid-phase exfoliation. Beginning with Mo(1-x)WxS(2) nanosheets, we demonstrate tunable optoelectronic properties as a function of composition. We extend this method to produce Mo0.5W0.5Se2 MoSSe, WSSe, and quaternary Mo0.5W0.5SSe nanosheets. High-resolution scanning transmission electron microscopy (STEM) imaging confirms the atomic arrangement of the nanosheets, while an array of spectroscopic techniques is used to characterize the chemical and optoelectronic properties. This transversal method represents an important step towards upscaling tailored TMD nanosheets with a broad range of tunable optoelectronic properties for large-area devices.

Defects in solids are unavoidable and can create complex electronic states that can significantly influence the electrical and optical properties of semiconductors. With the rapid progress in the integration of 2D semiconductors in practical devices, it is imperative to understand and characterize the influence of defects in this class of materials. Here, we examine the electrical response of defect filling and emission using deep level transient spectroscopy (DLTS) and reveal defect states and their hybridization in a monolayer MOCVD-grown material deposited on CMOS-compatible substrates. Supported by aberration-corrected STEM imaging and theoretical calculations, we find that neighboring sulfur vacancy pairs introduce additional shallow trap states via hybridization of individual vacancy levels. Even though such vacancy pairs only represent ~10% of the total defect concentration, they can have a substantial influence on the off currents and switching slopes of field-effect transistors based on 2D semiconductors. Our technique, which can quantify the energy states of different defects and their interactions, allows rapid and nondestructive electrical characterization of defect states important for the defect engineering of 2D semiconductors.

Monolayer MoS 2 has attracted significant attention owing to its excellent performance as an n‐type semiconductor from the transition metal dichalcogenide (TMDC) family. It is however strongly desired to develop controllable synthesis methods for 2D p‐type MoS 2 , which is crucial for complementary logic applications but remains difficult. In this work, high‐quality NbS 2 –MoS 2 lateral heterostructures are synthesized by one‐step metal–organic chemical vapor deposition (MOCVD) together with monolayer MoS 2 substitutionally doped by Nb, resulting in a p‐type doped behavior. The heterojunction shows a p‐type transfer characteristic with a high on/off current ratio of ≈10 4 , exceeding previously reported values. The band structure through the NbS 2 –MoS 2 heterojunction is investigated by density functional theory (DFT) and quantum transport simulations. This work provides a scalable approach to synthesize substitutionally doped TMDC materials and provides an insight into the interface between 2D metals and semiconductors in lateral heterostructures, which is imperative for the development of next‐generation nanoelectronics and highly integrated devices.

Memory devices have returned to the spotlight due to increasing interest in using in-memory computing architectures to make data-driven algorithms more energy-efficient. One of the main advantages of this architecture is the efficient performance of vector-matrix multiplications while avoiding the “von Neumann bottleneck.” Despite these promises, no single material platform meets all the requirements for the fabrication of this new processor technology. Recently, flash memories based on monolayer MoS2 have been shown to achieve ultra-fast operation, overcoming one of the main drawbacks of this memory type. Together with its other characteristics, this makes them a promising candidate for the base elements of this technology. However, the question remains of how to achieve large-area ultra-fast operation of MoS2 monolayer flash memories. In this work, we will compare large-area flash memories based on MoS2 used in past realizations of in-memory systems and analyze the improvements needed to achieve ultra-fast performance for in-memory applications.

Nanopores in two-dimensional (2D) membranes hold immense potential in single-molecule sensing, osmotic power generation, and information storage. Recent advances in 2D nanopores, especially on single-layer MoS 2 , focus on the scalable growth and manufacturing of nanopore devices. However, there still remains a bottleneck in controlling the nanopore stability in atomically thin membranes. Here, we evaluate the major factors responsible for the instability of the monolayer MoS 2 nanopores. We identify chemical oxidation and delamination of monolayers from their underlying substrates as the major reasons for the instability of MoS 2 nanopores. Surface modification of the substrate and reducing the oxygen from the measurement solution improves nanopore stability and dramatically increases their shelf-life. Understanding nanopore growth and stability can provide insights into controlling the pore size, shape and can enable long-term measurements with a high signal-to-noise ratio and engineering durable nanopore devices.

Among numerous thin film synthesis methods, metalorganic chemical vapor deposition performed in a showerhead reactor is the most promising one for broad use in scalable and commercially adaptable two-dimensional material synthesis processes. Adapting the most efficient monolayer growth methodologies from tube-furnace systems to vertical-showerhead geometries allows us to overcome the intrinsic process limitations and improve the overall monolayer yield quality. Here, we demonstrate large-area, monolayer molybdenum disulphide growth by combining gas-phase precursor supply with unique tube-furnace approaches of utilizing sodium molybdate pre-seeding solution spincoated on a substrate along with water vapor added during the growth step. The engineered process yields a high-quality, 4-inch scale monolayer film on sapphire wafers. The monolayer growth coverage, average crystal size and defect density were evaluated using Raman and photoluminescence spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and scanning transmission electron microscopy imaging. Our findings provide a direct step forward toward developing a reproducible and large-scale MoS2 synthesis with commercial showerhead reactors.

Tailoring the surface properties of 2D materials, such as transition metal dichalcogenides (TMDCs), at the nanoscale is becoming essential in the fabrication of various 2D material-based nanoelectronic devices. Due to the chemical inertness of their basal plane, the surface modification of 2D TMDCs is limited to their defective sites, often requiring special treatments, such as the conversion of the TMDC from its semiconducting into its metallic phase. In this work, we show that the basal plane of a semiconducting 2D TMDC, molybdenum disulfide (MoS2) can be modified electrochemically by electrografting of aryl-diazonium salt. To demonstrate the advantages of this method at the nanoscale, we perform electrografting of 3,5-bis(trifluoromethyl)benzenediazonium tetrafluoroborate on predefined MoS2 nanoribbons by addressing them individually via a different electrode. The ability to selectively address individually contacted 2D layers opens the possibility for specific surface modification of neighboring 2D nanostructures by different functional groups. This method could be extended to other aryl-diazonium compounds, and other 2D semiconducting materials.

Transition metal dichalcogenides (TMDs) represent a class of semiconducting two-dimensional (2D) materials with exciting properties. In particular, defects in 2D-TMDs and their molecular interactions with the environment can crucially affect their physical and chemical properties. However, mapping the spatial distribution and chemical reactivity of defects in liquid remains a challenge. Here, we demonstrate large area mapping of reactive sulfur-deficient defects in 2D-TMDs in aqueous solutions by coupling single-molecule localization microscopy with fluorescence labeling using thiol chemistry. Our method, reminiscent of PAINT strategies, relies on the specific binding of fluorescent probes hosting a thiol group to sulfur vacancies, allowing localization of the defects with an uncertainty down to 15 nm. Tuning the distance between the fluorophore and the docking thiol site allows us to control Föster resonance energy transfer (FRET) process and reveal grain boundaries and line defects due to the local irregular lattice structure. We further characterize the binding kinetics over a large range of pH conditions, evidencing the reversible adsorption of the thiol probes to the defects with a subsequent transitioning to irreversible binding in basic conditions. Our methodology provides a simple and fast alternative for large-scale mapping of nonradiative defects in 2D materials and can be used for in situ and spatially resolved monitoring of the interaction between chemical agents and defects in 2D materials that has general implications for defect engineering in aqueous condition.

Metallic two-dimensional (2D) transition metal dichalcogenides (TMDCs) are attracting great attention because of their interesting low-temperature properties such as superconductivity, magnetism, and charge density waves (CDW). However, further studies and practical applications are being slowed down by difficulties in synthesizing high-quality materials with a large grain size and well-determined thickness. In this work, we demonstrate epitaxial chemical vapor deposition (CVD) growth of 2D NbS2 crystals on a sapphire substrate, with a thickness-dependent structural phase transition. NbS2 crystals are epitaxially aligned by the underlying c-plane sapphire resulting in high-quality growth. The thickness of NbS2 is well controlled by growth parameters to be between 1.5 and 10 nm with a large grain size of up to 500 μm. As the thickness increases, we observe in our NbS2 a transition from a metallic 3R-polytype to a superconducting 2H-polytype, confirmed by Raman spectroscopy, aberration-corrected scanning transmission electron microscopy (STEM) and electrical transport measurements. A Berezinskii-Kosterlitz-Thouless (BKT) superconducting transition occurs in the CVD-grown 2H-phase NbS2 below the transition temperature (Tc) of 3 K. Our work demonstrates thickness and phase-controllable synthesis of high-quality superconducting 2D NbS2, which is imperative for its practical applications in next-generation TMDC-based electrical devices.

The surface modification of 2D semiconducting materials, such as transition metal dichalcogenides (TMDCs), is becoming important for a diverse range of applications, such as biosensing, catalysis, energy generation and energy storage. Due to the chemical inertness of their basal plane, the surface modification of 2D TMDCs is mainly limited to their defective sites, or it requires a conversion of TMDC from its semiconducting into a metallic phase. In this work, we show that the basal plane of a 2D semiconductor molybdenum disulfide (MoS2) can be modified by electrochemical grafting of aryl-diazonium salt, such as 3,5-bis(trifluoromethyl)benzenediazonium tetrafluoroborate. To investigate the applicability of this method, we perform electrografting on MoS2 nanoribbons by addressing them individually via a different electrode. High spatial selectivity of this method on the nanoscale opens the possibility for specific surface modification of neighboring 2D layers and nanostructures that are contacted by electrodes. This method could be potentially applicable to other 2D semiconducting materials that are active in the same potential window in which the electrochemical reduction of aryl diazonium salts occurs.

The growing importance of applications based on machine learning is driving the need to develop dedicated, energy-efficient electronic hardware. Compared with von Neumann architectures, which have separate processing and storage units, brain-inspired in-memory computing uses the same basic device structure for logic operations and data storage1–3, thus promising to reduce the energy cost of data-centred computing substantially4. Although there is ample research focused on exploring new device architectures, the engineering of material platforms suitable for such device designs remains a challenge. Two-dimensional materials5,6 such as semiconducting molybdenum disulphide, MoS2, could be promising candidates for such platforms thanks to their exceptional electrical and mechanical properties7–9. Here we report our exploration of large-area MoS2 as an active channel material for developing logic-in-memory devices and circuits based on floating-gate field-effect transistors (FGFETs). The conductance of our FGFETs can be precisely and continuously tuned, allowing us to use them as building blocks for reconfigurable logic circuits in which logic operations can be directly performed using the memory elements. After demonstrating a programmable NOR gate, we show that this design can be simply extended to implement more complex programmable logic and a functionally complete set of operations. Our findings highlight the potential of atomically thin semiconductors for the development of next-generation low-power electronics. Logic operations and reconfigurable circuits are demonstrated that can be directly implemented using memory elements based on floating-gate field-effect transistors with monolayer MoS2 as the active channel material.

High-quality and large-scale growth of monolayer molybdenum disulfide (MoS2) has caught intensive attention because of its potential in many applications due to unique electronic properties. Here, we report the wafer-scale growth of high-quality monolayer MoS2 on singlecrystalline sapphire and also on SiO2 substrates by a facile metal-organic chemical vapor deposition (MOCVD) method. Prior to growth, an aqueous solution of sodium molybdate (Na2MoO4) is spun onto the substrates as the molybdenum precursor and diethyl sulfide ((C2H5)2S) is used as the sulfur precursor during the growth. The grown MoS2 films exhibit crystallinity, good electrical performance (electron mobility of 22 cm2·V-1·s-1) and structural continuity maintained over the entire wafer. The sapphire substrates are reusable for subsequent growth. The same method is applied for the synthesis of tungsten disulfide (WS2). Our work provides a facile, reproducible and cost-efficient method for the scalable fabrication of high-quality monolayer MoS2 for versatile applications, such as electronic and optoelectronic devices as well as the membranes for desalination and power generation.

Janus, patchy, stripe-like, or random arrangements of molecules within the ligand shell of nanoparticles affect many properties. Among all existing ligand shell morphology characterization methods, the one based on mass spectroscopy is arguably the simplest. Its greatest limitation is that the results are qualitative. Here, we use a tailor-made Monte Carlo type program that fits the whole MALDI spectrum and generates a 3D model of the ligand shell. Quantitative description of the ligand shell in terms of nearest neighbor distribution and characteristic length scale can be readily extracted by the model, and are compared with the results of other characterization methods. A parameter related to the intermolecular interaction is extracted when this method is combined with NMR. This approach could become the routine method to characterize the ligand shell morphology of many nanoparticles and we provide an open access program to facilitate its use.

Amorphous AlSnO (a-ATO) thin films have been synthesized by a combustion solution process at low temperatures, with the Al:Sn molar ratio of 1:x (x = 11 − 7) in the precursors. The influence of compositions on the structural, optical, and electrical properties of AlSnO (ATO) films were investigated in detail. The X-ray diffraction patterns revealed that all the ATO films are amorphous in nature. All elements were distributed uniformly over the films, regardless of holes formed in the matrix with increasing Al contents. The a-ATO films had an average transmittance over 80% in the visible region, with enlarged optical band gap energies from 3.42 to 3.67 eV at elevated Al contents. Hall-effect measurements identified that weak p-type conductivity could be obtained at the high Al doping levels with Al:Sn ratios higher than 1:9. The realization of p-type a-ATO films by the combustion solution method may open a door to design p-type amorphous-oxide-semiconductor thin-film transistors for transparent electronics.

Effects of Zr-substitution on the structure, microstructure and microwave dielectric properties of Ba(Ni1/3Nb2/3)O3 ceramics have been investigated. A small amount of Zr-substitution facilitates the densification of Ba(Ni1/3Nb2/3)O3 ceramics. Within x≤0.05, the densification temperature decreases with increasing x in Ba[(Ni1/3Nb2/3)1−xZrx]O3, while it turns to increase for x>0.05. With increasing x, the grains become more homogeneous and closely contacted, and significantly increase in size for x=0.15–0.20. The B-site cations 1:2 ordering is destroyed by Zr-substitution, and only stabilizes for x≤0.04. B-site cations 1:1 ordering starts to form in x=0.04, and the 1:1 ordering degree first increases and then decreases with increasing x. Qf value decreases slightly in x=0.01 and then increases monotonously with x increasing from 0.02 to 0.20. The destroyed 1:2 ordering structure is responsible for the decreased Qf value in x=0.01, while the improved grain configuration dominates the increase of Qf value for x=0.02–0.20. The dielectric constant εr increases monotonously with increasing x, due to the higher polarizability of Zr ion than the average value of Ni/Nb ions. The temperature coefficient of resonant frequency τf shifts from negative to positive through zero with increasing x, which is ascribed to the highly positive τf value of the end member BaZrO3. The significant improvement of microwave dielectric properties has been achieved for x=0.10, higher εr, higher Qf as well as near zero τf value have been obtained: εr=31.8, Qf=36,100GHz, τf=7.8ppm/°C.