Solution-processed inks of two-dimensional (2D) semiconductors, such as molybdenum disulfide (MoS2), hold great promise for enabling low-cost, printed electronic devices. To optimize critical performance metrics like network conductivity, large-aspect-ratio (kNS≫100) nanosheets are essential to yield low-resistance flake-to-flake junctions. While electrochemical exfoliation with ammonium salts has emerged as a viable method for producing high-aspect ratio semiconducting nanosheets, the process parameters remain underexplored. In this work, we systematically investigate the role of alkylammonium ion size in the electrochemical exfoliation of MoS2, demonstrating control over nanosheet lengths (L ∼ 1-3 μm) and nanosheet thicknesses (tNS∼1-4 nm), leading to kNS values between 400 and 2500. The nanosheet aspect ratio is closely linked to ion size via the energetics of exfoliation. We fabricate networks from these nanosheets and characterize their electrical properties, revealing that higher-aspect-ratio nanosheets yield significantly more conductive networks, achieving conductivities up to 6000 Sm-1. Our electrical measurements show that the network conductivity is consistent with a simple model and is limited by internanosheet junctions whose resistance scales inversely with nanosheet area. These findings suggest that ion size determines nanosheet dimensions, which in turn determine network conductivity.

The transition metal carbide (TMC) family has been previously studied for various catalytic, mechanical, and electronic applications, and recently TMCs have been isolated into the ultrathin limit. A bottom-up approach has been developed to synthesize non-layered, ultrathin TMCs (UThTMCs). In this work, liquid metal assisted chemical vapor deposition is used to control the growth of different phases of tungsten carbide. In particular, WC and W2C single crystal nanoplates are synthesized when using copper and gallium, respectively, as the tungsten diffusion barrier. First principles calculations confirm the stability found experimentally in the two synthesized carbide phases. We also report the first low temperature measurements of electronic transport in WC below 300 mK and ultrathin W2C down to 1.8 K. We find that WC does not enter a superconducting state, while UThTMCs of W2C enter a quasi-2D superconducting state below 2.8 K. Our results provide new ground on the synthesis of other UThTMCs with controlled crystal phase. Given the richness of phases among metal carbides and the related transition metal nitride family, further research will be motivated by this work to isolate novel carbide and nitride phases in this ultrathin limit. Finally, it is important to note that the electronic transport of UThTMCs follows a quasi-2D regime and further systems should be evaluated and compared, especially the superconducting phases. These UThTMCs and their heterointerfaces could find important applications in electrocatalysis, carbide plasmonics, transparent conducting films, and materials for effective radiation shielding due to their high density and ability to absorb neutrons and gamma rays.

Doping in transition-metal dichalcogenide (TMD) monolayers provides a powerful method to precisely tailor their electronic, optical, and catalytic properties for advanced technological applications, including optoelectronics, catalysis, and quantum technologies. However, the doping efficiency and outcomes in these materials are strongly influenced by the complex interactions between introduced dopants and intrinsic defects, particularly sulfur vacancies. This coupling between dopants and defects can lead to distinctly different behaviors depending on the doping concentration, presenting significant challenges in the predictable and controlled design of TMD properties. For example, in this work we systematically varied the p-type vanadium(V) doping density in tungsten disulfide (WS2) monolayers and observed a transition in doping behavior. At low concentrations, V-dopants enhance the native optical properties of WS2, as evidenced by increased photoluminescence, without introducing new electronic states. However, at higher concentrations, V-dopants promote the formation of vanadium-sulfur vacancy complexes that generate midgap states, with energies that can be precisely tuned by controlling the vanadium concentration. Using a combination of excitation- and temperature-dependent photoluminescence microscopy, atomic-resolution scanning transmission electron microscopy, and first-principles calculations, we identify attractive interactions between p-type V-dopants and n-type monosulfur vacancies. Our results provide a mechanistic understanding of how enthalpic dopant-defect interactions versus entropic effects govern the balance between property enhancement and perturbation of TMDs and suggest a pathway toward the rational design of doping strategies for next-generation optoelectronic, catalytic, and quantum devices.

We study the Raman signature of stripe domains in monolayer WxMo1-xS2 alloys, characterized using experimental techniques and density functional theory (DFT) calculations. These stripe domains were found in star-shaped monolayer WS2 exhibiting a high concentration of molybdenum (Mo) atoms in its central region, and unique Raman peaks that were not previously reported. We attribute these peaks to the splitting of the original doubly degenerate E2g modes, arising from the lower symmetry of the W-Mo stripe domains. We confirm the stripe presence and location using high-resolution scanning transmission electron microscopy (STEM) imaging and use DFT to elucidate the structural, electronic, and vibrational properties of the stripes when the stoichiometry corresponds to W0.5Mo0.5S2. The findings provide insight into the evolution of the Raman spectra as stripe domains arise in TMD alloys, thus contributing to a broader understanding of the influence of atomic-level structural modifications on material properties.

We study the Raman signature of stripe domains in monolayer W x Mo1-x S2 alloys, characterized using experimental techniques and density functional theory (DFT) calculations. These stripe domains were found in star-shaped monolayer WS2 exhibiting a high concentration of molybdenum (Mo) atoms in its central region, and unique Raman peaks that were not previously reported. We attribute these peaks to the splitting of the original doubly degenerate E2g modes, arising from the lower symmetry of the W-Mo stripe domains. We confirm the stripe presence and location using high-resolution scanning transmission electron microscopy (STEM) imaging and use DFT to elucidate the structural, electronic, and vibrational properties of the stripes when the stoichiometry corresponds to W0.5Mo0.5S2. The findings provide insight into the evolution of the Raman spectra as stripe domains arise in TMD alloys, thus contributing to a broader understanding of the influence of atomic-level structural modifications on material properties.

Non-layered transition metal carbides (TMCs) and layered transition metal dichalcogenides (TMDs) are two well-studied material families that have individually received considerable attention over the past century. In recent years, with the shift towards two-dimensional materials and heterostructures, a field has emerged that is focused on the structure and properties of TMC/TMD heterostructures, which through chemical conversion exhibit diverse types of heterostructure configuration that host coupled 2D-3D interfaces, giving rise to exotic properties. In this Review, we highlight experimental and computational efforts to understand the routes to fabricate TMC/TMD heterostructures. Furthermore, we showcase how controlling these heterostructures can lead to emergent electronic transport, optical properties and improved catalytic properties.

Within the realm of two-dimensional materials, monolayer transition metal dichalcogenide semiconductors boasting intrinsic band gaps of 1-2 eV are regarded as promising candidates for channel materials in nextgeneration transistors. The judicious choice of electrodes is paramount to achieving low-resistance contacts, thereby enhancing the performance of nanoelectronic devices. Therefore, the exploration of novel metalsemiconductor combinations and a comprehensive grasp of the atomistic nature of interfaces are indispensable. In this work, we present a systematic examination of vertical Moir & eacute; pattern contacts between WC and WS 2 or WSe 2 , with the termination atoms (tungsten or carbon termination) being investigated through density-functional theory calculations. The Moir & eacute; pattern heterostructure is found to exhibit greater energetic favorability when compared to coherent epitaxial strain heterostructures. Our analyses encompass an in-depth exploration of the interface structure, effective potential, electron localization function, Bader charge, energy bands, and density of states within these heterostructures. These investigations reveal the formation of Schottky barriers within these systems, with the dominant carrier type and height of the Schottky barriers being under the control of the termination atoms. Metal-induced gap states formed in the interfaces give rise to a strong Fermi-level pinning. We conclude that the WC/WSe 2 heterostructure with carbon terminations in WC have the smallest p -type Schottky-barrier height of 0.08 eV among all other heterostructures considered. Transport properties are assessed using the Simmons tunneling injection model. These findings yield valuable insights that can be leveraged in the design of high-performance nanoelectronic d built upon two-dimensional materials.

In silicon field-effect transistors (FETs), degenerate doping of the channel beneath the source and drain regions is used to create high-performance n- and p-type devices by reducing the contact resistance. Two-dimensional semiconductors have, in contrast, relied on metal-work-function engineering. This approach has led to the development of effective n-type 2D FETs due to the Fermi-level pinning occurring near the conduction band, but it is challenging with p-type FETs. Here we show that the degenerate p-type doping of molybdenum diselenide and tungsten diselenide—achieved through substitutional doping with vanadium, niobium and tantalum—can reduce the contact resistance to as low as 95 Ω µm in multilayers. This, though, comes at the cost of poor electrostatic control, and we find that the doping effectiveness—and its impact on electrostatic control—is reduced in thinner layers due to strong quantum confinement effects. We, therefore, develop a high-performance p-type 2D molybdenum diselenide FET using a layer-by-layer thinning method to create a device with thin layers at the channel and thick doped layers at the contact regions. Substitutionally doped two-dimensional diselenides can be used to make p-type field-effect transistors with reduced contact resistance and good electrostatic control by varying the thickness of the channel and contact regions.

In recent years, the rapid advancement of materials science and the desire for new functions has led to an enormous demand for novel materials, which could be used in various applications. As a result, hybrid materials have gained the interest of the scientific community due to the infinite combinations of individual components, which could lead to materials with unique properties. In this study, a carbon dots (CDs)-CuFe2O4 nanohybrid material was successfully prepared through a solvothermal process and utilized as an adsorbent for the removal of Congo Red (CR) dye from aqueous environment. The nanohybrid material combines interactive surface functional groups due to CDs and high magnetic saturation due to CuFe2O4 nanoparticles, resulting in enhanced selectivity towards CR dye and easy separation after utilization with an external magnet. The as-prepared material was characterized by various techniques, including XRD, micro-Raman, FT-IR, HR-TEM/EDS, N-2 porosimetry, and SQUID. Finally, its capability in the removal efficiency of CR dye was investigated at different initial CR concentrations, contact times and pH values via UV-Vis spectroscopy.

Monolayers of molybdenum disulfide (MoS2) are the most studied two-dimensional (2D) transition-metal dichalcogenides (TMDs), due to its exceptional optical, electronic, and opto-electronic properties. Recent studies have shown the possibility of incorporating a small amount of magnetic transition metals (e.g., Fe, Co, Mn, V) into MoS2 to form a 2D dilute magnetic semiconductor (2D-DMS). However, the origin of the observed ferromagnetism has remained elusive, due to the presence of randomly generated sulfur vacancies during synthesis that can pair with magnetic dopants to form complex dopant-vacancy configurations altering the magnetic order induced by the dopants. By combining high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging with first-principles density functional theory (DFT) calculations and magnetometry data, we demonstrate the critical effects of sulfur vacancies and their pairings with vanadium atoms on the magnetic ordering in V-doped MoS2 (V-MoS2) monolayers. Additionally, we fabricated a series of field effect transistors on these V-MoS2 monolayers and observed the emergence of p-type behavior as the vanadium concentration increased. Our study sheds light on the origin of ferromagnetism in V-MoS2 monolayers and provides a foundation for future research on defect engineering to tune the electronic and magnetic properties of atomically thin TMD-based DMSs.

Multi-walled carbon nanotubes co-doped with sulfur and nitrogen (S–N-MWCNTs) were produced onto silicon/silicon oxide by means of chemical vapor deposition (CVD) upon decomposition of dimethyl sulfoxide (DMSO) and acetonitrile (ACN) in the presence of ferrocene (FeCp2). The synthesized S–N-MWCNTs were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) combined with energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and electrochemical impedance spectroscopy (EIS). The electrochemical response of S–N-MWCNTs towards oxidation of ascorbic acid (AA), dopamine (DA), uric acid (UA), and glucose (GL) was investigated in phosphate buffer solution (PBS) (pH 7.4) by means of cyclic voltammetry (CV). Strong dependence of electrochemical quality of S–N-MWCNTs on the concentration of decomposed DMSO precursor was observed. Namely, upon increasing the percentage of decayed DMSO from 1.0 up to 2.0

Engineering the electronic bandgap is of utmost importance in diverse domains ranging from information processing and communication technology to sensing and renewable energy applications. Transition metal dichalcogenides (TMDCs) provide an ideal platform for achieving this goal through techniques including alloying, doping, and creating in-plane or out-of-plane heterostructures. Here, we report on the synthesis and characterization of atomically controlled two-dimensional graded alloy of MoxW1-xS2, wherein the center region is Mo rich and gradually transitions towards a higher concentration of W atoms at the edges. This unique alloy structure leads to a continuously tunable bandgap, ranging from 1.85 eV in the center to 1.95 eV at the edges consistent with the larger band gap of WS2 relative to MoS2. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy showed the presence of sulfur monovacancy, VS, whose concentration varied across the graded MoxW1-xS2 layer as a function of Mo content with the highest value in the Mo rich center region. Optical spectroscopy measurements supported by ab initio calculations reveal a doublet electronic state of VS, which was split due to the spin-orbit interaction, with energy levels close to the conduction band or deep in the band gap depending on whether the vacancy is surrounded by W atoms or Mo atoms. This unique electronic configuration of VS in the alloy gave rise to four spin-allowed optical transitions between the VS levels and the valence bands. Our work highlights the potential of simultaneous defect and optical engineering of novel devices based on these 2D monolayers.

In this study, carbon quantum dots (C-QDs), prepared via hydrothermal-microwave procedures, were successfully combined with nanostructured titania (TiO 2 ). The photocatalytic oxidation/reduction activity of the C-QDs/TiO 2 composite films was evaluated in the decomposition of organic-inorganic contaminants from aqueous solutions under UV illumination. Physicochemical characterizations were applied to investigate the crystal structure of the carbon quantum dots and the composites. It was found that the prepared C-QDs/TiO 2 composites had great contribution to the photocatalytic reduction of hexavalent chromium (Cr +6 ) species and 4-Nitrophenol (PNP) as well as to the photocatalytic oxidation of methylene blue (MB) and Rhodamine B (RhB) dyes. The mechanism of the photocatalytic reaction was studied with trapping experiments, revealing that the electron (e − ) radical species were powerfully supported for the photocatalytic reduction of Cr +6 and PNP and the holes ( h + ) are the main active species for the photocatalytic oxidation reactions.

This work demonstrates the band-type engineering and the detailed charge transport mechanism upon visible light illumination for various configurations of vertically stacked monolayers of MoS2-ReS2 grown by a two-step chemical vapour deposition method. In order to understand the stacking order of both materials has a direct impact on the band alignment arrangements, we investigate the optical properties of both ReS2-MoS2 stacking configurations using micro-photoluminescence and interestingly observed the change in the band alignment upon changing the stacking order (ReS2-MoS2 and MoS2-ReS2). The formation of the vertically stacked heterostructure is further validated by observing its morphology by HR-TEM. The MoS2 on top of ReS2 yielded Type II and ReS2 on top of MoS2 yielded type I band alignment. The fabricated photodetector exhibits responsivities of 152 A W-1 for pristine ReS2, 72 A W-1 for MoS2 on top, and 400 A W-1 for ReS2 on top respectively for visible light illumination of 554 nm suggesting that the stacking configuration of the monolayer TMDs play a vital role in the performance of the optoelectronic properties. The detailed study of such configurations of vertically stacked 2D heterostructure is essential to better understand the optimal configuration for the development of highly responsive photodetectors.

Single-crystal Er3+:YAG has long been used as a laser material, and recent work has shown polycrystalline ceramic Er3+:YAG to be a suitable laser material, with benefits of lower cost and easier production. However, relatively little work has been done with the synthesis and spectroscopic characterization of Er3+:YAG nanocrystals. In this work, we present the synthesis of nanocrystalline Er3+:YAG and the results of comparative spectroscopic characterization with single-crystal and polycrystalline ceramic counterparts. The results show good agreement between the optical properties of the three hosts, with the nanocrystals demonstrating relatively higher intensity in the 1.53 μm emission. These results demonstrate the viability of Er3+:YAG nanocrystals as a potential laser material.

The ability to control the density and spatial distribution of substitutional dopants in semiconductors is crucial for achieving desired physicochemical properties. Substitutional doping with adjustable doping levels has been previously demonstrated in 2D transition metal dichalcogenides (TMDs); however, the spatial control of dopant distribution remains an open field. In this work, edge termination is demonstrated as an important characteristic of 2D TMD monocrystals that affects the distribution of substitutional dopants. Particularly, in chemical vapor deposition (CVD)-grown monolayer WS2 , it is found that a higher density of transition metal dopants is always incorporated in sulfur-terminated domains when compared to tungsten-terminated domains. Two representative examples demonstrate this spatial distribution control, including hexagonal iron- and vanadium-doped WS2 monolayers. Density functional theory (DFT) calculations are further performed, indicating that the edge-dependent dopant distribution is due to a strong binding of tungsten atoms at tungsten-zigzag edges, resulting in the formation of open sites at sulfur-zigzag edges that enable preferential dopant incorporation. Based on these results, it is envisioned that edge termination in crystalline TMD monolayers can be utilized as a novel and effective knob for engineering the spatial distribution of substitutional dopants, leading to in-plane hetero-/multi-junctions that display fascinating electronic, optoelectronic, and magnetic properties.

The Effect of Edge Termination In article number 2205800, Humberto Terrones, Ana Laura Elías, Mauricio Terrones, and co-workers demonstrate the importance of atomic edge termination in determining the spatial distribution of substitutional dopants in 2D transition metal dichalcogenide (TMD) hexagonal monolayers. Preferential iron and vanadium doping occurs on the sulfur-terminated edges of the hexagonal monolayers, causing a decrease in photoluminescence intensity and forming binary optical/electrical domains.

MXenes, a large family of titanium carbides and nitrides, have emerged as potential electromagnetic interference (EMI) shielding materials due to their outstanding electrical properties and lightness. However, the fragility of structures constructed exclusively from these two-dimensional materials suggests the complementary use of other nanomaterials as primary building blocks, with MXenes serving as active-conductive fillers. Compared to MXenes alone, these hybrid structures demonstrate significant mechanical improvements without a significant loss of electrical properties due to the synergy between porosity and the lamellar structure. This study explores the use of biodegradable cellulose nanofibrils (CNFs) as non-active building blocks for the fabrication of nanohybrid structures. We use Ti3C2Tx MXenes as active-conductive nanofillers in a simple process where both components are dispersed and freeze-dried to produce EMI shielding aerogels. This process minimizes MXene waste while maintaining total shielding effectiveness (SET) values around 20 dB. The way in which MXenes are incorporated into the final material is crucial, and a method to optimize their properties and achieve the obtained SET values has been identified.

Piezoelectricity in low-dimensional materials and metal-semiconductor junctions has attracted recent attention. Herein, a 2D in-plane metal-semiconductor junction made of multilayer 2H and 1T' phases of molybdenum(IV) telluride (MoTe2 ) is investigated. Strong piezoelectric response is observed using piezoresponse force microscopy at the 2H-1T' junction, despite that the multilayers of each individual phase are weakly piezoelectric. The experimental results and density functional theory calculations suggest that the amplified piezoelectric response observed at the junction is due to the charge transfer across the semiconducting and metallic junctions resulting in the formation of dipoles and excess charge density, allowing the engineering of piezoelectric response in atomically thin materials.

Atomically thin two-dimensional (2D) materials have gained significant attention from the research community in the fabrication of high-performance optoelectronic devices. Even though there are various techniques to improve the responsivity of the photodetector, the key factor limiting the performance of the photodetectors is constrained photodetection spectral range in the electromagnetic spectrum. In this work, a mixed-dimensional 0D/2D SnS2-QDs/monolayer MoS2 hybrid is fabricated for high-performance and broadband (UV-visible-near-infrared (NIR)) photodetector. Monolayer MoS2 is deposited on SiO2/Si using chemical vapor deposition (CVD), and SnS2-QDs are prepared using a low-cost solution-processing method. The high performance of the fabricated 0D/2D photodetector is ascribed to the band bending and built-in potential created at the junction of SnS2-QDs and MoS2, which enhances the injection and separation efficiency of the photoexcited charge carriers. The mixed-dimensional structure also suppresses the dark current of the photodetector. The decorated SnS2-QDs on monolayer MoS2 not only improve the performance of the device but also extends the spectral range to the UV region. Photoresponsivity of the device for UV, visible, and NIR region is found to be ∼278, ∼ 435, and ∼189 A/W, respectively. Fabricated devices showed maximum responsivity under the visible region attributed to the high absorbance of monolayer MoS2. The response time of the fabricated device is measured as ∼100 ms. These results reveal that the development of a mixed-dimensional (0D/2D) SnS2-QDs/MoS2-based high-performance and broadband photodetector is technologically promising for next-generation optoelectronic applications.