Ultrathin MoS2 Research Articles

Perfect Absorption and Strong Coupling in Supported MoS2 Multilayers.

Perfect absorption and strong coupling are two highly sought-after regimes of light-matter interactions. Both regimes have been studied as separate phenomena in excitonic 2D materials, particularly in MoS2. However, the structures used to reach these regimes often require intricate nanofabrication. Here, we demonstrate the occurrence of perfect absorption and strong coupling in thin MoS2 multilayers supported by a glass substrate. We measure reflection spectra of mechanically exfoliated MoS2 flakes at various angles beyond the light-line via Fourier plane imaging and spectroscopy and find that absorption in MoS2 monolayers increases up to 74% at the C-exciton by illuminating at the critical angle. Perfect absorption is achieved for ultrathin MoS2 flakes (4-8 layers) with a notable angle and frequency sensitivity to the exact number of layers. By calculating zeros and poles of the scattering matrix in the complex frequency plane, we identify perfect absorption (zeros) and strong coupling (poles) conditions for thin (<10 layers) and thick (>10 layers) limits. Our findings reveal rich physics of light-matter interactions in bare MoS2 flakes, which could be useful for nanophotonic and light harvesting applications.

Ultrathin MoS2 nanosheets decorated on NiSe nanowire arrays as advanced trifunctional electrocatalyst for overall water splitting and urea electrolysis

Developing highly-efficient and low-cost electrocatalysts act as pressing impacts on the flourishing of hydrogen energy, including electrochemical water splitting is a kind of prevailing energy conversion technology. However, it is hampered by the high activation barrier of oxygen evolution reaction (OER). Herein, a hybrid electrocatalyst with trifunctional and 3D core–shell structure is designed by hydrothermal process in order to achieve outstanding OER, hydrogen evolution reaction (HER) and urea oxidation reaction (UOR) properties. NiSe@MoS2/NF catalyst is composed of the heterogeneous interface formed by NiSe nanowire arrays which supported by nickel foam and MoS2 nanosheets. The synergistic effect and strong electronic interaction between the interface display the dominant impact of OER, HER and UOR. Especially in basic electrolyte, the potential is as low as 310 mV at 100 mA cm−2, even Tafel slope is 70.8 mV dec-1, representing the predominant OER property. The HER and UOR also demonstrate enormous prospect with 210, 233 mV at 100 mA cm−2. When NiSe@MoS2/NF||NiSe@MoS2/NF catalyst as anode and cathode, only requires potential of 1.48 V at 10 mA cm−2 for overall water splitting test. The work offers a plain, high-efficiency and inexpensive method to evolve the progressive trifunctional electrocatalysts for other energy-related applications.

Quantitative Characterization of the Anisotropic Thermal Properties of Encapsulated Two-Dimensional MoS2 Nanofilms.

Two-dimensional (2D) semiconductors exhibit unique physical properties at the limit of a few atomic layers that are desirable for optoelectronic, spintronic, and electronic applications. Some of these materials require ambient encapsulation to preserve their properties from environmental degradation. While encapsulating 2D semiconductors is essential to device functionality, they also impact heat management due to the reduced thermal conductivity of the 2D material. There are limited experimental reports on in-plane thermal conductivity measurements in encapsulated 2D semiconductors. These measurements are particularly challenging in ultrathin films with a lower thermal conductivity than graphene since it may be difficult to separate the thermal effects of the sample from the encapsulating layers. To address this challenge, we integrated the frequency domain thermoreflectance (FDTR) and optothermal Raman spectroscopy (OTRS) techniques in the same experimental platform. First, we use the FDTR technique to characterize the cross-plane thermal conductivity and thermal boundary conductance. Next, we measure the in-plane thermal conductivity by model-based analysis of the OTRS measurements, using the cross-plane properties obtained from the FDTR measurements as input parameters. We provide experimental data for the first time on the thickness-dependent in-plane thermal conductivity of ultrathin MoS2 nanofilms encapsulated by alumina (Al2O3) and silica (SiO2) thin films. The measured thermal conductivity increased from 26.0 ± 10.0 W m-1 K-1 for monolayer MoS2 to 39.8 ± 10.8 W m-1 K-1 for the six-layer films. We also show that the thickness-dependent cross-plane thermal boundary conductance of the Al2O3/MoS2/SiO2 interface is limited by the low thermal conductance (18.5 MW m-2 K-1) of the MoS2/SiO2 interface, which has important implications on heat management in SiO2-supported and encased MoS2 devices. The measurement methods can be generalized to other 2D materials to study their anisotropic thermal properties.

Co3+-rich CoFe-PBA encapsulated in ultrathin MoS2 sheath as integrated core-shell architectures for highly efficient OER

Highly active and stable oxygen evolution reaction (OER) electrocatalyst is the key component of sustainable water splitting reaction. Controllable core-shell engineering is one of the most effective strategies for modulating the local electronic structure of active sites to enhance catalytic activity. Herein, we design a nano-cube of Co3+-rich CoFe Prussian blue analogues coated with controllable MoS2 shell heterostructures as OER electrocatalyst by simple solvothermal method, named as CoIIIFe-PBA/MoS2. Importantly, CoIIIFe-PBA/MoS2 possesses an extremely low overpotential of 306 mV at the current density of 100 mA cm−2, a small Tafel slope of 36.2 mV dec−1 and excellent stability for OER. The results of spectroscopic characterizations reveal that the Co3+ species with more 3d electron orbits origin from the charge transfer between CoFe-PBA and MoS2 core-shell interface, which promotes the electron accepting and results in the higher electrochemical activity. This research offers unique insight to design other advanced electrocatalysts with high-valent transition metal ions and core-shell structure.

Perspective on ultrathin layered Ni-doped MoS2 hybrid nanostructures for the enhancement of electrochemical properties in supercapacitors

Over the last two decades, extensive study has been done on two-dimensional Molybdenum Sulphide (MoS2) due to its outstanding features in energy storage applications. Although MoS2 has a lot of active sulphur edges, the presence of inactive surfaces leads to limit conductivity and efficiency. Hence, in this article, we aimed to promote the additional active sites by doping various weight percentages (2%, 4%, 6%, 8% and 10%) of Nickel (Ni) into the MoS2 matrix by simple hydrothermal technique, and their doping effects were investigated with the help of Physio-chemical analyses. X-ray diffraction (XRD) pattern, Raman, and chemical composition (XPS) analyses were used to confirm the Ni incorporationin MoS2 nanosheets. Microscopic investigations demonstrated that Ni-doped MoS2 nanosheets were vertically aligned with enhanced interlayer spacing. Cyclic voltammetry, Galvanostatic charge–discharge, and electrochemical impedance spectroscopy investigations were used to characterize the electrochemical characteristics. The 6% Ni-doped MoS2 electrode material showed better CSP of 528.7 F/g @ 1 A/g and excellent electrochemical stability (85% of capacitance retention after 10,000 cycles at 5 A/g) compared to other electrode materials. Furthermore, the solid-state asymmetric supercapacitor was assembled using Ni-doped MoS2 and graphite as anode and cathode materials and analysed the electrochemical properties in the two-electrode system. To determine the impact of the Ni-atom on the MoS2 surface, first-principles computations were performed. Further, it was examined for electronic band structure, the projected density of states (PDOS) and Bader charge transfer analyses.

Enhanced Visible-Light Response of Ultrathin Er-Doped MoS2 Nanosheets through a Wet-Chemical Method

Doping is one of the important technologies for modifying the properties of two-dimensional (2D) transition metal dichalcogenides (TMDs). Herein, ultrathin Er-doped MoS2 nanosheets with an enhanced visible-light response have been synthesized by a wet-chemical method. The few-layer characteristic of the MoS2:Er nanosheets is beneficial from the H2S generated during the preparation process. Near-infrared emission at ∼1530 nm from MoS2:Er nanosheets has been observed under 980 nm laser excitation, which corresponds to the energy transition from 4I13/2 to 4I15/2 of Er3+. Meanwhile, the enhanced visible-light response of MoS2:Er has been demonstrated by the photocatalytic performance (removing rhodamine B) and photocurrent response compared with undoped MoS2. Based on the experiments and density functional theory calculation, the enhanced visible-light response is attributed to the improved separation capability of photogenerated electron–hole pairs of the ultrathin MoS2:Er nanosheets. Er-doping induces an increase of S vacancies and the energy transfer between Er3+ ions and the host. The work demonstrates a developed universal and recyclable synthesis strategy for various metal-doped MoS2 nanosheets and their applications in the fields of photocatalysis and photodetection.

Controlled Differentiation of Human Neural Progenitor Cells on Molybdenum Disulfide/Graphene Oxide Heterojunction Scaffolds by Photostimulation.

Ultrathin MoS2-MoO3-x heterojunction nanosheets with unique features were introduced as biocompatible, non-cytotoxic, and visible light-sensitive stimulator layers for the controlled differentiation of human neural progenitor cells (hNPCs) into nervous lineages. hNPC differentiation was also investigated on reduced graphene oxide (rGO)-containing scaffolds, that is, rGO and rGO/MoS2-MoO3-x nanosheets. In darkness, hNPC differentiation into neurons increased on MoS2-MoO3-x by a factor of 2.7 due to the excellent biophysical cues and further increased on rGO/MoS2-MoO3-x by a factor of 4.4 due to a synergistic effect induced by the rGO. The MoO3-x domains with antioxidant activity and LSPR absorption induced p-type doping in MoS2-MoO3-x. Under photostimulation, the hNPCs on the MoS2-MoO3-x exhibited higher differentiation into glial cells by a factor of 1.4, and the decrease in photo-electron current to hNPCs due to the induction of more p-type doping in the MoS2-MoO3-x. While the increase in neuronal differentiation of hNPCs on rGO/MoS2-MoO3-x by a factor of 1.8 was ascribed to the presence of rGO as an ultrafast electron transferor which quickly transferred photogenerated electrons to hNPCs before their transfer to free radicals, these results demonstrated the promising potential of MoS2-based scaffolds for applying in the controllable repair and/or regeneration of diseases/disorders related to the nervous system.

Untangling the intertwined: metallic to semiconducting phase transition of colloidal MoS2 nanoplatelets and nanosheets.

2D semiconducting transition metal dichalcogenides (TMDCs) are highly promising materials for future spin- and valleytronic applications and exhibit an ultrafast response to external (optical) stimuli which is essential for optoelectronics. Colloidal nanochemistry on the other hand is an emerging alternative for the synthesis of 2D TMDC nanosheet (NS) ensembles, allowing for the control of the reaction via tunable precursor and ligand chemistry. Up to now, wet-chemical colloidal syntheses yielded intertwined/agglomerated NSs with a large lateral size. Here, we show a synthesis method for 2D mono- and bilayer MoS2 nanoplatelets with a particularly small lateral size (NPLs, 7.4 nm ± 2.2 nm) and MoS2 NSs (22 nm ± 9 nm) as a reference by adjusting the molybdenum precursor concentration in the reaction. We find that in colloidal 2D MoS2 syntheses initially a mixture of the stable semiconducting and the metastable metallic crystal phase is formed. 2D MoS2 NPLs and NSs then both undergo a full transformation to the semiconducting crystal phase by the end of the reaction, which we quantify by X-ray photoelectron spectroscopy. Phase pure semiconducting MoS2 NPLs with a lateral size approaching the MoS2 exciton Bohr radius exhibit strong additional lateral confinement, leading to a drastically shortened decay of the A and B exciton which is characterized by ultrafast transient absorption spectroscopy. Our findings represent an important step for utilizing colloidal TMDCs, for example small MoS2 NPLs represent an excellent starting point for the growth of heterostructures for future colloidal photonics.

Flat-optics hybrid MoS2/polymer films for photochemical conversion.

Novel light harvesting platforms and strategies are crucial to develop renewable photon to energy conversion technologies that overcome the current global energy and environmental challenges. Two-dimensional (2D) transition metal dichalcogenide (TMD) semiconductor layers are particularly attractive for photoconversion applications but new ultra-compact photon harvesting schemes are urgently required to mitigate their poor photon absorption properties. Here, we propose a flat-optics scheme based on nanogrooved ultra-thin MoS2 layers conformally grown onto large area (cm2 scale) nanopatterned templates. The subwavelength re-shaping of the 2D-TMD layers promotes the excitation of photonic Rayleigh anomaly (RA) modes, uniquely boosting a strong in-plane electromagnetic confinement. By tailoring the illumination conditions, we demonstrate effective tuning of the photonic anomalies over a broadband visible spectrum across the absorption band of relevant polluting dye molecules. Thanks to the strong photonic in-plane confinement, we achieve a resonant enhancement of the photodissociation rate of methylene blue (MB) molecules, well above a factor of 2. These results highlight the potential of flat-optics photon harvesting schemes for boosting photoconversion efficiency in large-scale hybrid 2D-TMD/polymer layers, with a strong impact in various applications ranging from new-generation photonics to waste water remediation and renewable energy storage.

Sulfur-deficient MoS2-carbon hollow nanospheres for synergistic trapping and electrocatalytic conversion of polysulfides.

Lithium-sulfur battery is one of the most promising candidates for next-generation energy storage systems, but the serious shuttle effect and sluggish reaction kinetics of polysulfides impair its practical applications. Herein, sulfur-deficient MoS2/carbon hollow nanospheres (MoS2-CHNs) are firstly synthesized by a NaCl-template pyrolysis and employed as sulfur host for lithium-sulfur batteries. TEM analysis reveals that carbon hollow nanospheres existing in the composite are the backbones that help to immobilize the ultrathin MoS2 nanosheets and ensure their large specific surface area. The MoS2 nanosheets consist of 5-10 layers of MoS2 with rich sulfur vacancies. The first principle calculation demonstrates that sulfur vacancy led to an intensively enhanced binding energy (-4.70eV) towards Li2S6 compared to the pristine MoS2 (-1.57eV). It suppressed the shuttle effect efficiently. The catalytic experiments reveal that MoS2-CHNs have a superior ability for the nucleation of Li2S and bidirectional electrocatalytic capability for the conversion of polysulfide. The large storage space inside MoS2-CHNs can work as a reservoir for intermediate polysulfides to substantially reduce the concentration overpotential. Due to this advantageous structural design of MoS2-CHNs electrode, its reversible capacity remains 1139 mAh g-1 after 100 cycles at 0.2C, and 600 mAh g-1 after 500 cycles at 5C with a sulfur loading of 5mgcm-2. Even though the sulfur loading increases to 10mgcm-2, the Li-S battery delivers a stable capacity of 978 mAh g-1 after 50 cycles at 0.2C. So the MoS2-CHNs demonstrate a promising application for high-energy Li-S batteries.

Поверхностная функционализация квазидвумерного MoS2 в азотной и кислородной плазме

The paper deals with the experimental and theoretical study of the interaction of quasi-two-dimensional MoS2 films with nitrogen and oxygen plasmas in order to reveal the main mechanisms of their surface functionalization and to analyze its effects on the structure and properties of the films. Diagnostics of samples before and after treatment with radicals and ions was performed ex situ by Raman spectroscopy, spectroscopic ellipsometry, atomic force microscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The results of the experimental study showed that nitrogen and oxygen plasma treatment of ultrathin MoS2 films leads to the modification of the near-surface layers of the samples due to the removal of sulfur and the incorporation of incident atoms into forming vacancies. Nitrogen and oxygen ions with even low (less than 30 eV) energy causes partial removal of upper layers of the films leading to their partial destruction, while remote plasma (mainly by thermal radicals) guarantees more ‘soft’ treatment of films. The obtained spectroscopic data also indicated different effects of radicals (thermal O and N atoms) on the MoS2 surface. To analyze these effects, the computer modelling with density functional theory method was carried out. Its results enables to reveal the main mechanisms of the surface functionalization of MoS2 monolayers and to explain the experimental data.

Promising MoS2 – ZnO hybrid nanocomposite photocatalyst for antibiotics, and dyes remediation in wastewater applications

In this work, a heterojunction system of ZnO nanorods (NRs) coupling with ultrathin MoS2 nanosheets (NSs) is designed through a facile and green microwave-assisted hydrothermal method. The purpose of this research is to investigate the use of a MoS2-ZnO hybrid nanocomposite as a photocatalyst for the degradation of sulfamethoxazole (SMX), trimethoprim (TMP), and meloxicam (MX) antibiotics, as well as Methylene blue (MB), malachite green (MG), and crystal violet (CV) dyes under simulating sunlight. The structural, morphological, optical, and textural properties of pristine ZnO NRs, MoS2 NSs, and their hybrid nanocomposite (MoS2-ZnO) are compared using XRD, TEM, SEM-EDX, UV-DRS, PL, and BET techniques. The MoS2-ZnO hybrid nanocomposite exhibited ZnO characteristic peaks with a very small MoS2 characteristic diffraction peak, indicating the heterojunction formation, as confirmed by TEM results. Furthermore, the MoS2-ZnO hybrid nanocomposite showed enhanced visible light absorption and surface area. The hybrid nanocomposite photocatalytic efficiency is higher than that of pristine ZnO NRs in all photocatalytic experiments. the Formation of heterojunction is the reason for improved performance due to increased charge carrier generation, separation, and transport, as confirmed by the PL technique. Moreover, The MoS2-ZnO revealed 100 % photocatalytic degradation efficiency after 30 min against SMX, MX, and MB pollutants respectively. Furthermore, complete photocatalytic degradation (100 %) is achieved after 90 min in the case of TMP, MG, and CV pollutants. Moreover, the possible photocatalytic mechanism has been clearly described, emphasizing the significance of OH. radicals and singlet oxygen (1O 2) in the degradation process. MoS2-ZnO hybrid nanocomposites can be considered promising photoactive materials for wastewater decontamination.

Friend or Foe? Revising the Role of Oxygen in the Tribological Performance of Solid Lubricant MoS2.

Molybdenum disulfide (MoS2) is a solid lubricant used in various forms, such as a dry lubricant by itself or as a component of a more complex coating. In both these forms, the effect of oxygen contamination on the sliding properties of the MoS2 coatings is traditionally considered detrimental, resulting in expensive technological processes to produce pure MoS2. Here, it is shown that the high oxygen content does not necessarily hinder the solid lubricant properties and may even result in a lower friction and wear when compared to pure MoS2. Mo-S-O coatings were fabricated by unbalanced magnetron sputtering and tribologically tested under vacuum conditions. Oxygen caused amorphization of the as-deposited coatings but did not prevent the triboactivated formation of an ultra-thin crystalline MoS2 tribolayer with the incorporated oxygen. Such an imperfect tribolayer was found to reduce the coefficient of friction to 0.02, a value lower than that of pure MoS2. Moreover, owing to the higher density and hardness of oxygen-containing films, the wear rate was also found to be lower. Molecular dynamics simulations performed using a newly developed Mo-S-O force field confirmed that such an imperfect tribolayer can mitigate friction in a manner comparable to that of MoS2.

High broadband light absorption in ultrathin MoS2 homojunction solar cells.

Transition metal dichalcogenides (TMDCs) have been proposed as light absorber materials for ultrathin solar cells. These materials are characterized by their strong light-matter interaction and the possibility to be assembled into devices at room temperature. Here, we model the optical absorptance of an ultrathin MoS2 absorber embedded in different designs of a 1D optical cavity. We find that up to 87% of the photons contained in the 300-700 nm range of the AM1.5G spectrum can be absorbed employing MoS2 absorbers as thin as 10 nm sandwiched between a h-BN top layer and an optically thick Ag reflector. An h-BN/MoS2/h-BN/Ag cavity produces 0.89 average absorptance for a 57-nm-thick MoS2 slab and it also maximizes the absorption of extremely thin absorbers, between 1 and 9 nm. We also model a possible large-scale device on a glass substrate combined with indium-tin oxide (ITO) whose absorptance is comparable to the other presented structures. The high broadband absorption in these light-trapping structures is caused by the amplification of the zeroth Fabry-Perot interference mode. This study demonstrates that light absorption in ultrathin solar cells based on nanometric TMDC absorbers can compete with conventional photovoltaic technology and provides different simple optical designs to choose from depending on the electronic characteristics of the TMDC junction.

Suppression of extra carriers for enhanced intrinsic piezoelectric properties of ultrathin MoS2 through various metal dopants

We study the piezoelectric behavior of metal-doped monolayer MoS2. Its three-dimensional charge density, work function (WF), and piezoresponse with various metal dopants are theoretically predicted based on density functional theory, and the real-time piezoelectric power of these samples is experimentally verified. Selected p-type metal dopants (Au, Ag, Pd, Pt, and Al) increase the WF of monolayer MoS2, affecting electron emission from the MoS2 surface. The reason is that p-type metal dopants suppress excess electrons and prevent screening effects. A nanogenerator constructed from Au-doped monolayer MoS2 has been used to explore the possibility of a practical device.

Deciphering the Space Charge Effect of the p-n Junction between Copper Sulfides and Molybdenum Selenides for Efficient Water Electrolysis in a Wide pH Range.

Space charge transfer is crucial for an efficient electrocatalytic process, especially for narrow-band-gap metal sulfides/selenides. Herein, we designed and synthesized a core-shell structure which is an ultrathin MoSe2 nanosheet coated CuS hollow nanoboxes (CuS@MoSe2) to form an open p-n junction structure. The space charge effect in the p-n junction region will greatly improve electron mass transfer and conduction, and also have abundant active interfaces. It was used as a bifunctional electrocatalyst for water oxidation at a wide pH range. It exhibits a low overpotential of 49 mV for the HER and 236 mV for the OER at a current density of 10 mA·cm-2 in acidic pH, 72 mV for the HER and 219 mV at 10 mA·cm-2 for the OER in alkaline pH, and 62 mV for the HER and 230 mV at 10 mA·cm-2 for the OER under neutral conditions. The experimental results and density functional theory calculations testify that the p-n junction in CuS@MoSe2 designed and synthesized has a strong space charge region with a synergistic effect. The built-in field can boost the electron transport during the electrocatalytic process and can stabilize the charged active center of the p-n junction. This will be beneficial to improve the electrocatalytic performance. This work provides the understanding of semiconductor heterojunction applications and regulating the electronic structure of active sites.

Fabrication of MoS2/CdIn2S4 Z-scheme heterojunctions with fast interface electronic transfer for highly efficient photocatalytic degradations of multiple organic pollutants

In this work, a novel Z-scheme MoS2/CdIn2S4 (MS-CIS) face-to-face heterostructure with excellent photocatalytic activities for multiple organic pollutant degradation was designed and constructed by a green mild in-situ hydrothermal method, where CdIn2S4 nano-octahedra coated on the surfaces of ultra-thin MoS2 nanosheets to form a face-to-face interface contact. The photocatalytic performance was systematically evaluated by the degradation of Oxytetracycline (OTC) under simulated visible light condition. Compared to MoS2 and CdIn2S4, the as-obtained MS-CIS-3 sample showed significantly improved photocatalytic activities toward OTC degradation, and the rate constant of MS-CIS-3 was 1.29959 h−1, which was 2.31 and 34.16 times those of CdIn2S4 (0.56303 h−1) and MoS2 (0.03804 h−1). The reason for the improvement in photocatalytic performance was that the MS-CIS heterostructure possessed a larger face-to-face contact area which could provide more charge transfer nanochannels, effectively shorten the photogenerated electron transport path and increase the electron-hole separation efficiency. In addition, the possible reaction routes of OTC and the photocatalytic reaction mechanism of MS-CIS sample were also discussed in detail. Furthermore, the MS-CIS-3 heterostructure with excellent photostability and repeatability also possessed outstanding degradation activities for both tetracycline hydrochloride (TCH) and 2-Mercaptobenzothiazole (MBT). This work may provide a promising strategy to synthesize other Z-scheme face-to-face heterostructure photocatalysts with highly efficient photocatalytic activity to solve environmental pollution.

Selective-Epitaxial Hybrid of Tripartite Semiconducting Sulfides for Enhanced Solar-to-Hydrogen Conversion.

The design and synthesis of advanced semiconductors is crucial for the full utilization of solar energy. Herein, colloidal selective-epitaxial hybrid of tripartite semiconducting sulfides CuInS2 Cd(In)SMoS2 heteronanostructures (HNs) via lateral- and vertical-epitaxial growths, followed by cation exchange reactions, are reported. The lateral-epitaxial CuInS2 and Cd(In)S enable effective visible to near-infrared (NIR) solar spectrum absorption, and the vertical-epitaxial ultrathin MoS2 offer sufficient edge sulfur sites for the hydrogen evolution reaction (HER). Furthermore, the integrated structures exhibit unique epitaxial-staggered type II band alignments for continuous charge separation. They achieve the H2 evolution rate up to 8 mmol h-1 g-1 , which is ≈35 times higher than bare CdS and show no deactivation after long-term cycling, representing one of the most efficient and robust noble-metal-free photocatalysts. This design principle and transformation protocol open a new way for creating all-in-one multifunctional catalysts in a predictable manner.

PtO2-decorated MoS2 ultrathin nanostructures for enhanced NH3 gas sensing properties

Recently, transition metal dichalcogenides (TMDs) have attracted much attention due to their high surface-to-volume ratio, various active edge sites, and adjustable bandgaps. However, in general, TMDs still exhibit low gas response and incomplete recovery. Surface modification is an effective way to facilitate the adsorption and desorption processes, thus enhancing the TMD gas sensor's sensing performance. In this study, a PtO2-decorated MoS2 nanostructure gas sensor was fabricated using a chemical reduction process. The result showed that the as-obtained nanostructures consist of accumulated ultrathin MoS2 nanosheets decorated with spherical PtO2 nanoparticles. The gas response of the as-obtained PtO2-decorated MoS2 gas sensor toward NH3 is remarkably high, with 450% upon 500 ppm NH3, which is almost 20 times higher than that of the pristine MoS2 nanostructure gas sensor in their optimal working conditions. The enhancement in gas sensing properties was attributed to the catalytic spillover effect of PtO2 nanoparticles as well as the formation of p-p heterojunction on the MoS2 surface.

All-Printed Ultrahigh-Responsivity MoS2 Nanosheet Photodetectors Enabled by Megasonic Exfoliation.

Printed 2Dmaterials, derived from solution-processed inks, offer scalable and cost-effective routes to mechanically flexible optoelectronics. With micrometer-scale control and broad processing latitude, aerosol-jet printing (AJP) is of particular interest for all-printed circuits and systems. Here, AJP is utilized to achieve ultrahigh-responsivity photodetectors consisting of well-aligned, percolating networks of semiconducting MoS2 nanosheets and graphene electrodes on flexible polyimide substrates. Ultrathin (≈1.2nm thick) and high-aspect-ratio (≈1μm lateral size) MoS2 nanosheets are obtained by electrochemical intercalation followed by megasonic atomization during AJP, which not only aerosolizes the inks but also further exfoliates the nanosheets. The incorporation of the high-boiling-point solvent terpineol into the MoS2 ink is critical for achieving a highly aligned and flat thin-film morphology following AJP as confirmed by grazing-incidence wide-angle X-ray scattering and atomic force microscopy. Following AJP, curing is achieved with photonic annealing, which yields quasi-ohmic contacts and photoactive channels with responsivities exceeding 103 AW-1 that outperform previously reported all-printed visible-light photodetectors by over three orders of magnitude. Megasonic exfoliation coupled with properly designed AJP ink formulations enables the superlative optoelectronic properties of ultrathin MoS2 nanosheets to be preserved and exploited for the scalable additive manufacturing of mechanically flexible optoelectronics.