MoS2 Films Research Articles

Spatially Precise Light-Activated Dedoping in Wafer-Scale MoS2 Films.

2D materials, particularly transition metal dichalcogenides (TMDCs), have shown great potential for microelectronics and optoelectronics. However, a major challenge in commercializing these materials is the inability to control their dopingat a wafer scale with high spatial fidelity. Interface chemistry is used with the underlying substrate oxide and concomitant exposure to visible light in ambient conditions for photo-dedoping wafer scale MoS2. It is hypothesized that the oxide layer traps photoexcited holes, leaving behind long-lived electrons that become available for surface reactions with ambient air at sulfur vacancies (defect sites) resulting in dedoping. Additionally, high fidelity spatial control is showcased over the dedoping process, by laser writing, and fine control achieved over the degree of doping by modulating the illumination time and power density. This localized change in MoS2 doping density is very stable (at least 7 days) and robust to processing conditions like high temperature and vacuum. The scalability and ease of implementation of this approach can address one of the major issues preventing the "Lab to Fab" transition of 2D materials and facilitate its seamless integration for commercial applications in multi-logic devices, inverters, and other optoelectronic devices.

Highly responsive gas sensors based on grain boundary–rich polycrystalline few-layer MoS2 films for NO2 detection

Abstract This study addresses the issues of insufficient sensitivity and poor reversibility for NO2 detection by successfully fabricating a sensor based on uniform and high-quality few-layer MoS2 polycrystalline material using chemical vapor deposition. This approach aims to improve the response of the sensor by exploiting the abundance of grain boundary (GB) defects in polycrystalline MoS2 membranes. Comprehensive surface morphology analysis of the few-layer MoS2 polycrystalline films was conducted using microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy to characterize their chemical composition and properties. Subsequently, evaluation of 1–100-ppm NO2 was conducted at room temperature (25°C). The results show excellent performance of the sensor, with a response range of 11–82.24. Notably, under ultraviolet excitation at room temperature, this sensor exhibits a response time of only 41 s to 50 ppm of NO2 with complete recovery and improved sensitivity, maintaining reliable stability over eight weeks. Furthermore, the findings reveal that the sensor demonstrates high selectivity toward NO2 gas with limit of detection and limit of qualification values of 10 and 34 ppb, respectively. Owing to the abundant adsorption sites provided by GB defects in polycrystalline thin films, the response performance of the sensor is effectively enhanced. This study provides valuable insights into the future design and development of high-performance NO2 gas sensors.

Mechanisms of Controllable Growth and Ohmic Contact of Two-Dimensional Molybdenum Disulfide: Insight from Atomistic Simulations.

ConspectusTwo-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs), in particular molybdenum disulfide (MoS2), have recently attracted huge interest due to their proper bandgap, high mobility at 2D limit, and easy-to-integrate planar structure, which are very promising for extending Moore's law in postsilicon electronics technology. Great effort has been devoted toward such a goal since the demonstration of protype MoS2 devices with high room-temperature on/off current ratios, ultralow standby power consumption, and atomic level scaling capacity down to sub-1-nm technology node. However, there are still several key challenges that need to be addressed prior to the real application of MoS2-based electronics technology. The controllable growth of wafer-scale single-crystal MoS2 on industry-compatible insulating substrates is the prerequisite of application while the currently synthesized MoS2 films mostly are polycrystalline with limited sizes of single-crystal domains and may involve metal substrates. The precise layer-control is also very important for MoS2 growth since its electronic properties are layer-dependent, whereas the layer-by-layer growth of multilayer MoS2 dominated by the van der Waals (vdW) epitaxy leads to poor thickness uniformity and noncontinuously distributed domains. High density up to 1013 cm-2 of sulfur vacancies (SVs) in grown MoS2 can cause unfavorable carrier scatting and electronic properties variations and will inevitably disturb the device performance. The dangling-bond-free surface of MoS2 gives rise to an inherent vdW gap at metal-semiconductor (M-S) contact, which leads to high electrical resistance and poor current-delivery capability at the contact interface and thereby substantially limits the performances of MoS2 devices.In this Account, we briefly review recent experimental and theoretical attempts for addressing the aforementioned challenges and present our own insights from atomistic simulations. We theoretically revealed the vital role of substrate steps for guiding unidirectional nucleation of monolayer MoS2 and uniform nucleation and edge-aligned growth of bilayer MoS2 by advanced simulations. The established thermodynamic mechanisms have successfully directed the experimental works on the controllable growth of 2 in. single-crystal monolayer and centimeter-scale uniform bilayer MoS2. The postgrowth repair mechanism of SV defect in MoS2 via thiol chemistry treatment has been theoretically explored with the consideration of side reaction of surface functionalization to help experimentally reduce SV defect density by 75%. Beyond the atomic level understanding, theoretical simulations proposed the electronic states hybridization mechanism across the semimetal-MoS2 vdW interface, thereby guiding experimental effort for realizing Ohmic contact at the MoS2-Sb(0112) vdW interface with record-low contact resistance.These advances provide a sound basis with an atomic-level understanding for addressing the related issues. However, there are still notable gaps in terms of system size and time scale of dynamics between atomistic simulations and experimental observations for the studies of MoS2 growth and interfaces. The combination of multiscale simulations and artificial intelligence technology is expected to narrow these gaps and provide a more insightful understanding of the controllable growth and interfacial properties modulation of MoS2. We conclude the Account with the standing challenges and outlook on future research directions from the theoretical perspective.

Improved Process Stability and Light Detection in Phototransistors via Inverted MoS2/a‐IGZO Heterojunction Integration

The integration of molybdenum disulfide (MoS2) with other semiconductors to form heterojunction phototransistors demonstrates potential for optoelectronic applications due to their strong interaction with light and tunable bandgaps. Conventionally, bottom‐gate phototransistors based on MoS2 and amorphous indium–gallium–zinc oxide (a‐IGZO) are fabricated by deposition of the a‐IGZO film on the gate dielectric, followed by deposition of the MoS2 film, resulting in a MoS2/a‐IGZO heterojunction. In this study, an inverted MoS2/a‐IGZO (or denoted as a‐IGZO/MoS2) heterojunction integration for bottom‐gate phototransistors, where the MoS2 film is deposited on the gate dielectric first, followed by the deposition of the a‐IGZO film, is presented. This configuration is designed to enhance the processability and electrical properties of the phototransistor. Under visible light exposure with a low optical power density of 5.3 μW cm−2, the a‐IGZO/MoS2 heterojunction phototransistor demonstrates significantly improved photoresponsivity (1.6, 2.8, and 17 A W−1 at 635, 520, and 405 nm wavelengths, respectively) compared to the MoS2 single‐channel phototransistor. Time‐dependent photoresponse measurements reveal that the a‐IGZO/MoS2 heterojunction phototransistor responds more quickly to light changes and generates a tenfold‐greater photocurrent than that of the MoS2 single‐channel phototransistor.

Pulsed laser deposition of MoS2 thin films at different mean kinetic plasma energies

In recent years, molybdenum disulfide has become a material of great interest for research for electronic and optoelectronic applications due to its 2-dimensional graphene-like structure and its bandgap within the visible spectrum. In this work, thin films of MoS2 were grown using pulsed laser deposition on glass substrates at room temperature and at deposition pressure of 2 × 10−5 Torr. We ablated a MoS2 target obtained by compressing high-purity powders, with a Nd-YAG pulsed laser with a wavelength of 1064 nm, 6 ns pulse width, and 10 Hz repetition rate. Laser produced plasmas were diagnosed by means of the time-of-flight technique using a Langmuir planar probe, from which mean kinetic energy and density of ions were estimated. Experimental control is more reliable using plasma parameters rather than fluence. The crystalline properties of the deposits were characterized using Raman spectroscopy and X-Ray diffraction; their chemical analysis was carried out by X-ray photoelectron spectroscopy; their thickness and morphology were characterized using atomic force microscopy and scanning electron microscopy, respectively. Results are discussed as a function of mean kinetic energy variations. It was observed that as the mean kinetic energy of the plasma decreased, the crystallinity improved and the crystal size increased.

In-plane and out-of-plane domain orientation dispersions in 1 to 3 monolayers epitaxial WS2 and MoS2 films on GaN(0001) film/sapphire(0001)

Transition-metal dichalcogenides and their heterostructures have attractive potential applications in electronics and optoelectronics. Wafer scale 1 to 3 monolayers WS2 and MoS2 ultrathin films on GaN/sapphire substrates were grown by metal organic chemical vapor deposition. Azimuthal reflection high-energy electron diffraction (ARHEED) was used to characterize the long-range order of these TMDC ultrathin films. The RHEED patterns of WS2 and MoS2 show stripes and arcs but the MoS2 on GaN shows sharp spots in addition to stripes and arcs. The 2D map constructed from ARHEED patterns shows that WS2 is epitaxial and has an in-plane domain orientation dispersion. For the MoS2 on GaN/sapphire substrate, the 2D map shows concentric continuous rings for each diffraction order of MoS2 and GaN indicating that the in-plane MoS2 domain orientation and GaN nanocrystals are random. The out-of-plane orientation dispersion of MoS2 on the GaN substrate is larger than that of WS2 on the GaN substrate. The observations of stripes, arcs, and spots from RHEED patterns and the 2D maps reveal the deviation of ultrathin epitaxial films from its perfect epitaxy, especially the TMDC domain orientation dispersion over a large area. These rich findings from 2D maps broaden the application of ARHEED in more than one monolayer thick 2D materials.

Spectroscopic Study of Strain, Oxidation, and Formation of Few-Layer Graphene at Steel Surfaces Tribologically Tested against MoS2 Films.

MoS2 not only has unique optoelectronic properties realizing photonic and semiconductor applications but also serves as a promising solid lubricant in tribological three-body contacts due to its advantageous friction and wear behavior. Its functionality is defined by elementary processes including strain, oxidation processes, and material mixing. However, these mechanisms were not elucidated for MoS2 having transferred from the MoS2 film synthesized at the main body to a steel counter body during tribological ball-on-disk tests. Using spatially and spectrally high-resolved Raman spectroscopy, we study the compressive and tensile strain within the MoS2 transfer material and analyze the oxidation of molybdenum, sulfur, and iron. In addition, we elaborate on the impact of transition metals modifying the MoS2 films on the strain distribution and oxidation processes. Decreasing intensities of the MoS2 Raman lines are accompanied with enhanced intensities of sulphur and molybdenum oxide Raman signatures which are particularly agglomerated at the edges of the tribological track. The formation of tribochemical oxides, including Mo4O11 in the Magnéli-phase, depends weakly on the type of modifying element, and an oxidation of a modification element itself is not detected. We also identified a tribologically induced formation of disordered few-layer graphene at counter-body surface areas which experienced weak thermo-mechanical tribological load. Our results characterize structural and chemical features of the MoS2 transfer material, thus predicting material failure at the microscopic level.

Frictional properties and environmental adaptability of Ti-MoS2/WC multilayer films

Magnetron-sputtered molybdenum disulfide films are extensively utilized as solid lubricating coatings in space applications as a result of their low friction coefficient and minimal contamination. However, MoS2-based films are sensitive to hygrothermal and oxidation environment, and are easily oxidized to form MoO3, which results in high friction and wear of the films, significantly reducing their operational lifespan. Especially when the spacecraft adopts the launching mode of coastal launch or ocean platform, the performance deterioration caused by oxidation of MoS2 films during transportation, storage and launch is more serious. Therefore, to enhance the frictional performance and oxidation resistance of the films in humid and salt spray environments, the Ti-MoS2/WC multilayer films with preferred (002) crystal plane orientation were prepared, achieving a friction coefficient of 0.009 in a vacuum environment and a wear rate of 1.1×10-7 mm3/N∗m. In particular, the film can maintain this extremely low coefficient of friction even after exposure to moisture or salt spray. These findings demonstrate that the dual doping of Ti and WC and the design of multilayer structures enable MoS2 films to achieve outstanding frictional performance and oxidation resistance. This is crucial for designing MoS2 films with excellent environmental adaptability.

Cascade amplification-based triple probe biosensor for high-precision DNA hybridization detection of lung cancer gene

As an essential biomarker for diagnosing and treating various diseases, low-cost, quantitative detection methods for complementary DNA (cDNA) have received much attention. The surface plasmon resonance (SPR) sensing technique is an effective measurement scheme, but the ambient temperature and pH variations have a non-negligible impact. In this work, we developed a triple-probe SPR sensing system for detecting cDNA concentration, temperature, and pH. In order to satisfy the triple parameter measurements, we used a microstructured optical fiber as the sensing platform, silver and gold films as the excitation layer, and a MoS2 film as the modulation layer. First, we explore the modulation mechanism of SPR and the conditions for excitation of triple SPR and demonstrate that the carrier concentration is a crucial factor affecting the resonance wavelength. Then, the feasibility of the sensing system for triple-probing is theoretically analyzed. Finally, in the experiment, the optimal parameters of the sensor were determined, and the triple parameter detection was successfully realized. The experimental results show that the three probes can work independently, and the hybridized DNA probe can realize the selective detection of cDNA with a sensitivity of 0.249 nm/(nmol/l). The maximum sensitivity of the pH probe and the temperature probe are 51.5 nm/pH and 6.14 nm/°C. In addition, the experimental results show that the sensing probes have excellent reproducibility. This paper’s innovation is using the fiber optic SPR effect to achieve quantitative detection for cDNA, temperature detection, and pH detection. Therefore, the sensor has a promising future in early diagnosis and biosensing.

Mechanical properties and tribological behavior of hard phase doped Pb/MoS2 composite films

MoS2 is commonly used as a lubricant in spacecraft applications, and it is necessary to improve the vacuum tribological properties of MoS2 films. Thus, in the current study, hard phase (Ta, Ti, and TiN) and soft metal (Pb) double-doped MoS2 composite films were designed and prepared using an unbalanced magnetron sputtering system. The microstructures and mechanical and tribological properties of the hard-soft phase doped Pb/MoS2 composite films were systematically investigated. The results showed that the synergistic effect of the hard and soft metals gave a denser MoS2 structure denser. In addition, an amorphous structure was generated along with fine crystals, leading to a structure typical of nanocrystals embedded in an amorphous phase. Furthermore, compared with the Ti-doped Pb/MoS2 film, the doped alternative hard phase (i.e. Ta and TiN) improves the mechanical properties, among which the adhesion strength of Ta-Pb/MoS2 film is the highest, and the hardness of TiN-Pb/MoS2 film is the highest. Importantly, the soft metal Pb and its sulfide are excellent lubricants, while the hard phase ensures the long-term reliability of the films. Overall, these soft-hard bimetallic-doped MoS2 films exhibit superior tribological properties to their un-doped equivalents.

Nuclear irradiation resistance of MoS2-based nanocomposite films: Insights from in situ macroscopic tribometry

In situ performance enhancement of solid lubricating materials are pivotal for the advancement of nuclear facilities. Here, we conducted in situ tribotests against 5.4 MeV Xe20+ ion irradiation for Ti-doped (MoST) and C/Ti co-doped (MoSCT) MoS2 films. The pristine MoST film outperformed MoSCT film but suffered severe degradation owing to irradiation-induced hardening of the amorphized MoS2 phase. Carbon co-doping effectively mitigated the hardening issue through irradiation-induced graphitization of the carbon phase, thereby enhancing the irradiation resistance of MoS2-based films. Both in situ and ex situ irradiation did not adversely affect the shearing-induced re-ordering of MoS2 basal planes, but they inhibit the graphitization and selective release of non-lubricative carbon phase, resulting in an increase in the film wear rate to 7.34 × 10−7 mm3/N·m.

Vertical Current Transport in Monolayer MoS<sub>2</sub> Heterojunctions with 4H-SiC Fabricated by Sulfurization of Ultra-Thin MoO<sub>x</sub> Films

In this paper, we report on the growth of highly uniform MoS2 films, mostly consisting of monolayers, on SiC surfaces with different doping levels (n- SiC epitaxy, ~1016 cm-3, and n+ SiC substrate, ~1019 cm-3) by sulfurization of a pre-deposited ultra-thin MoOx films. MoS2 layers are lowly strained (~0.12% tensile strain) and highly p-type doped (<Nh>≈4×1019 cm−3), due to MoO3 residues still present after the sulfurization process. Nanoscale resolution I-V analyses by conductive atomic force microscopy (C-AFM) show a strongly rectifying behavior for MoS2 junction with n- SiC, whereas the p+ MoS2/n+ SiC junction exhibits an enhanced reverse current and a negative differential behavior under forward bias. This latter observation, indicating the occurrence of band-to-band-tunneling from the occupied states of n+ SiC conduction band to the empty states of p+ MoS2 valence band, is a confirmation of the very sharp hetero-interface between the two materials. These results pave the way to the fabrication of ultra-fast switching Esaki diodes on 4H-SiC.

Layer and orientation dependent optical anisotropic response of CVD grown MoS2 films under resonance/non-resonance excitation

The MoS2hasgained worldwide research interest owing to their strong light-matter interaction and their rich physics that offers unprecedented potential for next-generation nanotechnology applications. Theirelectrical and thermal properties are mainly governed by interaction mechanism of electrons with phonons and thus, studying the polarization-dependent anisotropic phonon response ofMoS2are of great interest. Here, we discuss the evolution of phonon modes with increasing layer number and their respective phonon DOS. Further, the optical anisotropic responseis experimentally investigated using ARPRSstudy for CVD-grown triangular MoS2with different layer numbers and different excitations, and has been discussedbased ontheory that includes deformation potential and Fröhlich interaction.Further, the ARPRS study of horizontally and vertically oriented MoS2films are studied. Thedifferent anisotropic response of vertically oriented film is observed due to symmetry breaking of the vertical nanosheets, thus providing wide-field applications in MoS2-based photonic and optoelectronic devices.

Influence of High-κ Dielectrics Integration on ALD-Based MoS2 Field-Effect Transistor Performance.

The integration of high-κ dielectrics on MoS2 field-effect transistors (FETs) is essential for the realization of MoS2 in ultrascaled nanoelectronic devices and circuits. Most studies covering this topic are based on exfoliated MoS2 flakes or chemical vapor deposition (CVD) grown MoS2 films, whereas other techniques, such as atomic layer deposition (ALD), are also gaining attention for the growth of MoS2 in recent years. In this work, we grow large-area MoS2 by means of plasma-enhanced (PE-)ALD and evaluate the influence of high-κ dielectrics on the properties of ALD-based MoS2 FETs through electrical characterization combined with surface-chemical and high-resolution scanning transmission electron microscopy (HR-STEM) analyses. We grow HfO x , AlO x , or both by means of PE-ALD or thermal ALD on our fabricated devices and show that, in addition to the dielectric constant, three other major parameters related to the processing of the dielectrics can simultaneously affect the MoS2 FET electrical characteristics and govern its doping. These parameters are the stoichiometry of the dielectric, its carbon impurity content, and the degree to which the MoS2 surface oxidizes upon the dielectric growth. When grown at 100 °C, our HfO x films are oxygen-vacant whereas our AlO x films are oxygen-rich. In addition, carbon impurities are incorporated into the dielectrics at low deposition temperatures, being one of the likely causes of the MoS2 FET overall n-type performance in all of the studied cases. Our investigations also reveal that PE-ALD of HfO x or AlO x oxidizes the MoS2 surface, whereas thermal ALD AlO x leaves MoS2 almost intact. In this respect, if thermal ALD AlO x of proper thickness is grown between MoS2 and HfO x , it can reduce the degree to which the MoS2 surface oxidizes by HfO x and meanwhile improve the total dielectric constant, altogether leading to the most optimal electrical performance in ALD-based MoS2 FETs.

(Invited) Low Temperature Atomic Layer Deposition Processes for Large-Area Synthesis of 2D Transition Metal Dichalcogenides

2D materials have been the focus of intense research in the last decade due to their unique physical properties. This presentation will highlight our recent progress on the large-area synthesis of two-dimensional transition metal chalcogenides for nanoelectronics using advanced atomic layer deposition cycle schemes. First, how we can use advanced cycle schemes to deposit wafer-scale polycrystalline MoS2 thin films at very low temperatures down to 100 °C. We have identified the critical role of hydrogen during the plasma step in controlling the composition and properties of molybdenum sulfide films. By increasing the H2/H2S ratio or adding an extra hydrogen plasma step to our ALD process, we are able to deposit pure polycrystalline MoS2 films at temperatures as low as 100 °C. To the best of our knowledge, this represents the lowest temperature for crystalline MoS2 films prepared by any chemical gas-phase method.[1]The most dominant methods for preparing MoS2 via ALD is to alternately expose a substrate to a metalorganic precursor and a hydrogen sulfide (H2S) or a plasma containing H2S. H2S is a corrosive, toxic, and flammable gas that is heavier than air, which makes it hazardous and expensive to store, install, and transport. Alternative sulfur precursors in the solid or liquid phase would be beneficial in terms of cost and safety and would require the installation of no additional hardware for most ALD reactors. In the second half of this contribution, the widely researched ALD process using bis(tert-butylimido)bis(dimethylamino)molybdenum(IV) ((tBuN)2(NMe2)2Mo) and H2S plasma is compared to a novel ALD process using (tBuN)2(NMe2)2Mo, hydrogen plasma, and di-tert-butyl disulfide (TBDS), which is an inexpensive, liquid-phase sulfur precursor.[1] M. Mattinen et al., Chem. Mater. (2022), 34, 5104

Sputtered Deposited Cu Functionalized MoS2 Nanoworm Thin Films for Nitrogen Dioxide (NO2) Gas Sensor

Semiconducting nanostructures thin films are used in state-of-arts applications due to their heightened physical properties. Semiconducting metal sulfides nanostructures are a growing asset in current semiconductor technology due to their extraordinary physical, chemical, and electronic properties and their outstanding applications in different sensing and optoelectronic devices. The gas sensing capability of semiconducting nanostructures is a recent research interest of many researchers. The MoS2 thin films were grown using reactive sputteringand the sensing performance of pure MoS2 and Cu-MoS2 thin films was studied towards nitrogen dioxide (NO2) gas concentrations (2-200 ppm) at the optimum working temperature of 100℃. The Cu-MoS2 sensor provides a high sensing response as compared to the pure MoS2 thin-film sensor towards 20 ppm of NO2 gas with a fast response and recovery time of 54 s and 82 s, respectively. It was observed that the proposed sensor chip displays an almost stable signal up to the 5th cycle. It is observed that the proposed sensor device exhibits the highest response (30%) to NO2 concerning weak response (10%) towards additional potentially interfering gases (NH3, CO, and H2) at 100°C. It reveals that the Cu-MoS2 thin-film sensor chip is highly selective to NO2 gas at 100 °C.

(Invited) 2D Semiconductors from Spin-on Molecular Chemistries for Direct Large-Scale Integration

In this talk, I will discuss our recent developments centered on a process to produce fully soluble solutions from a unique molecular chemistry. This enables the creation of wafer-scale monolayers of MoS2, a prominent 2D semiconductor for logic and memory devices. This molecule can be dissolved in common solvents and spin-coated onto various substrates, including crystalline substrates, printed electrodes, and polymers. It can also be integrated into gate-all-around (GAA) 3D transistor structures for logic devices. Our method of rapidly synthesizing large-area MoS2 films, particularly in monolayer form via spin-coating, represents a novelty, as it hasn't been demonstrated previously with a single-source chemistry. This advancement is a significant step toward scalable synthesis of wafer-scale 2D semiconductor thin films, eliminating the need for post-growth wafer transfer techniques, a requirement with films grown by chemical vapor deposition (CVD) methods. Our fabrication process highlights the potential of using a single-source chemical precursor to develop monolayer 2D semiconductors that exhibit commendable transport characteristics and optical properties, which enhance with rising crystallization temperatures. Consequently, it holds promise as a semiconductor for microelectronic transistor channels in both back-end-of-line (BEOL) and front-end-of-line (FEOL) architectures.

(Invited) Revolving the Mechanical Stress in Batteries by Using Microcantilever

Although the generation of mechanical stress in the anode material is suggested as a possible reason for electrode degradation and fading of storage capacity in batteries, only limited knowledge of the electrode stress and its evolution is available at present. Here, we show real-time monitoring of the interfacial stress of a few-layer MoS2 system under the sodiation/desodiation process using microcantilever electrodes. During the first sodiation with a voltage plateau of 1.0 to 0.85 V, the MoS2 exhibits a compressive stress (2.1 Nm−1), which is substantially smaller than that measured (9.8 Nm−1) during subsequent plateaus at 0.85 to 0.4 V due to the differential volume expansion of the MoS2 film. The conversion reaction to Mo below 0.1 V generates an anomalous compressive stress of 43 Nm−1 with detrimental effects. These results also suggest the existence of a separate discharge stage between 0.6 and 0.1 V, where the generated stress is only approximately one-third of that observed below 0.1 V. This approach can be adapted to help resolve the localized stress in a wide range of electrode materials, to gain additional insights into mechanical effects of charge storage, and for long-lifetime battery design.

N-doped MoS2@indium tin oxide (ITO) core–shell nanowires for high-performance ammonium ion micro-supercapacitor

Ammonium (NH4+) ion aqueous supercapacitors have gained significant attention due to their notable cost-effectiveness, safety profile, and environmental benefits. Despite this, the optimization of the capacitive performance of electrode materials for NH4+ ion storage remains inadequate. To tackle these challenges, we present a composite electrode depend upon molybdenum disulfide (MoS2) and indium tin oxide nanowires (MoS2@ITO NWs) as the primary host for (NH4+) ions. Additionally, we introduce a straightforward radio frequency nitrogen (N) plasma technique to incorporate nitrogen doping into the MoS2 film, thereby enhancing its performance. The introduction of N plasma doping into two-dimensional MoS2 results in an expansion of the interlayer distance and an improvement in electronic conductivity. This, in turn, facilitates the facile and highly reversible insertion and extraction of NH4+ ions during cycling. Consequently, the N plasma doping significantly enhances the device areal capacitance of MoS2@ITO NWs, increasing it from 78.6 to 161.8 mF cm−2 at 1 mA cm−2, with an exceptional capacity retention (>89.2% after 10 000 cycles) and superior rate capability up to 10 mA cm−2. The integration N of atoms within the straightforward hierarchical core–shell design strategy exhibits promising prospects for bolstering the performance of metal sulfide electrodes and other high-capacity electrode materials aimed at energy storage applications.

Improvement of Contact Resistance and 3D Integration of 2D Material Field‐Effect Transistors Using Semi‐Metallic PtSe2 Contacts

AbstractIn this work, the potential of 2D semi‐metallic PtSe2 as source/drain (S/D) contacts for 2D material field‐effect‐transistors (FETs) through theoretical and experimental investigations, is explored. From the density functional theory (DFT) calculations, semi‐metallic PtSe2 can inject electrons and holes into MoS2 and WSe2, respectively, indicating the feasibility of PtSe2 contacts for both n‐ and p‐metal‐oxide‐semiconductor FETs (n‐/p‐MOSFETs). Indeed, experimentally fabricated flake‐level MoS2 n‐MOSFETs and WSe2 p‐MOSFETs exhibit a significant reduction in contact resistance with semi‐metallic PtSe2 contacts compared to conventional Ti/Au contacts. To demonstrate the applicability for large‐area electronics, MoS2 n‐MOSFETs are fabricated with semi‐metallic PtSe2 contacts using chemical vapor deposition‐grown MoS2 and PtSe2 films. These devices exhibit outstanding performance metrics, including high on‐state current (≈10−7 A/µm) and large on/off ratio (>107). Furthermore, by employing these high‐performance MoS2 n‐MOSFETs, vertically stacked n‐MOS inverters are successfully demonstrated, suggesting that 3D integration of 2D material FETs is possible using semi‐metallic PtSe2 contacts.