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Transition metal selenides (TMSes) are considered promising candidates for the anodes of sodium‐ion batteries (SIBs) due to their substantial theoretical capacity. However, TMSes still face with inferior cycling lifespan caused by sluggish Na+ diffusion kinetics and vigorous volume variations during dis/charge processes. Engineering heterostructure is an attractive solution for rapid Na+ transfer, and introducing carbonaceous materials also facilitates enhanced conductivity and structural stability. Herein, CoSe/MoSe2 heterostructure combined with homogeneous carbon composites are rational designed. The kinetic analysis and theoretical calculations verified that heterointerface engineering induced build‐in electric field effect can amplifies the Na+ diffusion kinetics, while carbon contributes to enhanced electrical conductivity and structural stability. Expectedly, the CoSe/MoSe2‐C exhibits high capacity and extremely ultra‐long lifespan (320.9 mAh g−1 at 2.0 A g−1 over 10,000 cycles with an average decay of only 0.01781 mAh g−1 per cycle). Furthermore, in situ X‐ray diffraction (XRD), ex situ X‐ray photoelectorn (XPS), and high‐resolution electron microscopy (HRTEM) are exploited to explore the Na+ storage mechanism. In addition, the Na3V2(PO4)3@rGO//CoSe/MoSe2‐C (NVP@rGO//CoSe/MoSe2‐C) pouch‐type full‐cells are successfully assembled and delivered satisfactory performance. This research presents a viable strategy for the targeted engineering of TMSes aimed at enhancing the efficiency of SIBs. [ABSTRACT FROM AUTHOR] more...

Single-layer transition metal dichalcogenides (TMDCs) are showing promising thermoelectric applications due to their superior stability and electronic transport properties. Unfortunately, the intrinsic high lattice thermal conductivity prevents their further improvement of thermoelectric performance. Motivated by recent experimental synthesis of two-dimensional TMDC heterostructures and superlattices, we propose to minimize the lattice thermal conductivity of single-layer MoS2 and MoSe2 using the lateral superlattice (LS) as building blocks. First-principles calculations with the phonon Boltzmann transport equation reveal a remarkably low lattice thermal conductivity of MoS2-MoSe2 LS due to the enhanced anharmonic phonon scattering as compared to the individual single-layer. We also show that the strong phonon anisotropy of MoS2-MoSe2 LS is primarily ascribed to the out-of-plane quadratic acoustic branch and orientation-dependent anharmonic scattering. Our calculations clearly demonstrate the advantages of LS structure in minimizing the lattice thermal conductivity of single-layer TMDCs and also accelerate their related applications in the field of renewable energy. [ABSTRACT FROM AUTHOR] more...

Being at the origin of an ohmic contact, the MoSe2 interfacial layer at the Mo/Cu(In,Ga)Se2 interface in CIGS (Cu(In,Ga)Se2 and related compounds) based solar cells has allowed for very high lightto- electricity conversion efficiencies up to 22.3%. This article gives new insights into the formation and the structural properties of this interfacial layer. Different selenization-steps of a Mo covered glass substrate prior to the CIGS deposition by co-evaporation led to MoSe2 interfacial layers with varying thickness and orientation, as observed by x-ray diffraction and atomic resolution transmission electron microscopy. A novel model based on the anisotropy of the Se diffusion coefficient in MoSe2 is proposed to explain the results. While the series resistance of finished CIGS solar cells is found to correlate with the MoSe2 orientation, the adhesion forces between the CIGS absorber layer and the Mo substrate stay constant. Their counter-intuitive non-correlation with the configuration of the MoSe2 interfacial layer is discussed and related to work from the literature. [ABSTRACT FROM AUTHOR] more...

Layered molybdenum diselenide (MoSe2) nanosheets were formed by the weak Van der Waals forces of attraction between Se and Mo atoms. MoSe2 has a larger space between the adjacent layers and smaller band gaps in the range of 0.85 to ~ 1.6 eV. In this study, MoSe2 nanosheets decorated nickel oxide (NiO) nanorods have been synthesized by hydrothermal method using sodium molybdate and selenium metal powder. NiO/MoSe2 composite formation was confirmed by powder X-ray diffraction analysis. In addition, the presence of MoSe2 nanosheets on NiO nanorods were confirmed by field emission scanning electron microscopy, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The Nyquist plots of NiO/MoSe2 coated glassy carbon electrode (GCE) was indicated that it had lower charge transfer resistance compared to NiO/GCE and MoSe2/GCE. Furthermore, as-prepared NiO/MoSe2/GCE was used to detect glucose in alkaline solution by cyclic voltammetry and amperometry techniques. The NiO/MoSe2/GCE was exhibited a linear response for the oxidation of glucose from 50 µM to 15.5 mM (R2 = 0.9842) at 0.5 V by amperometry. The sensor response time and the limit of detection were found to be 2 s and 0.6 µM for glucose. Moreover, selectivity of the NiO/MoSe2 sensor was tested in the presence of common interferent molecules such as hydrogen peroxide, fructose, lactose, ascorbic acid, uric acid, and dopamine. It was found that NiO/MoSe2/GCE did not respond to these interfering biomolecules. In addition, NiO/MoSe2/GCE had shown high stability, reproducibility and repeatability. Finally, the practical application of the sensor was demonstrated by detecting glucose in human blood serum with the acceptable recovery. [ABSTRACT FROM AUTHOR] more...

We report on the synthesis, characterization and in-situ Raman spectroscopy analysis of hydrogenation in ultrathin crystalline MoSe2 deposits. We use a controllable vapor phase synthesis method using MoSe2 powder as the only precursor, to fabricate nano- to micro-size few layer thick MoSe2 deposits with tunable number densities on SiO2/Si substrates. We employ this controllable synthesis method to correlate characteristic Raman spectroscopy response of MoSe2 at ca. 242 cm−1 (A1g) and ca. 280 cm−1 (E2g1) with the thickness of the deposits acquired from atomic force microscopy (AFM). We also use this array of well-defined atomically thin MoSe2 deposits to study possible hydrogenation effects on select architectures using in-situ Raman spectroscopy. Interestingly, our analysis indicates that ultrathin MoSe2 deposits with exposed edges show a blue shift of 1–2 cm−1 when exposed to H2 flow at 150–250 sccm for 2–4 hours in a sealed reaction cell. Exposure to Ar flow under same condition reverses the observed shift in the A1g mode of the select MoSe2 deposits. Our measurements provide in-situ evidence for hydrogen adsorption on MoSe2 deposits at room temperature and insight into the possible active sites for hydrogen reactions on layered dichalcogenides at lower dimensions. [ABSTRACT FROM AUTHOR] more...

Abstract Two-dimensional (2D) atomic layered transition metal dichalcogenides are promising candidates for use in next generation optoelectronics. However, the low responsivity observed in monolayer MoSe 2 photodetectors (PDs) requires strategies to enhance photoelectric performance. Here, we introduce a method to produce few-layer MoSe 2 with large continuous area for high-performance optoelectronic devices, using atomic layer deposition (ALD) and a chemical vapor deposition (CVD) chamber. The as-synthesized ultrathin MoSe 2 films were characterized by atomic force microscopy (AFM) and transmission electron microscopy (TEM), revealing six polycrystalline layers of hexagonal structure and with an interlayer spacing of 0.66 nm. Few-layer MoSe 2 metal-semiconductor-metal (MSM) PDs were prepared with different optically active areas. The PD with a finger spacing of 5 μm exhibited remarkable performance with responsivity, response time, and detectivity of 859 mA/W, 38 ms, and 1.55 × 1011 jones, respectively, making these PDs significantly superior to most previously described MoSe 2 PDs and many other 2D semiconductors devices. The use of large-area films and the facile fabrication process described here present a viable route to mass production, opening avenues to develop atomically thin MoSe 2 PDs for industrial applications. Graphical abstract Image 1 Highlights • 2D few-layer MoSe 2 with large-area continuous were successfully synthesized. • The 6-layers MoSe 2 film with an interlayer spacing of 0.66 nm was identified. • MoSe 2 Photodetectors were prepared with different active areas for comparison. • A responsivity of 859 mA/W and a high detectivity of 1.55 × 1011 jones were obtained. [ABSTRACT FROM AUTHOR] more...

Graphical abstract Highlights • Hollow MoSe 2 /CdSe nanospheres were prepared by one-pot solvothermal strategy. • It is first time to synthesize hollow MoSe 2 nanostructure without templates. • Both experimental and DFT calculations reveal the Z-scheme mechanism. • Full spectrum harvest, hollow structure and charge separation induce remarkable activity. • The Langmuir adsorption, low pH and thermal effect benefits to photocatalysis. Abstract For better use of solar energy, the development of full-spectrum photocatalysts has attracted most attentions. In this research, uniform hollow MoSe 2 /CdSe nanospheres (250 nm) were prepared by one-pot solvothermal strategy. It is the first time to synthesize hollow MoSe 2 based nanostructure without any template/surfactant assistance. By varying reaction time, the formation mechanism was investigated, illuminating that the novel hollow structure is derived from the Kirkendall Effect. Both experimental and density functional theory (DFT) calculations reveal the Z-scheme mechanism of the charge transfer in the heterostructure. The hollow MoSe 2 /CdSe nanospheres (MC2) possess the remarkable photocatalytic activity in degradation of Cr(VI) (125 mg g−1, simulated sunlight), owing to the high harvest of full spectrum, porous hollow structure and effective charge separation/transfer. Furthermore, the photocatalytic process was further studied in detail, showing that the Langmuir single-layer adsorption behavior, low pH value condition, and thermal effect also benefit to the high photoreduction performance. Benefiting from the Z-scheme mechanism, the high redox activity make sure the water splitting capacity of MC2 (7120.0 and 348.0 μmol h−1 g−1 of H 2 and O 2 evolution) under simulated sunlight irradiation and its AQY for H 2 evolution at 670 nm reaches up to 27.2% (50 mg MC2). [ABSTRACT FROM AUTHOR] more...

Highlights • Metallic octahedral prismatic 1T- and trigonal prismatic bulk crystal 2H-phase MoS 2. • The work functions are ∼3.5 eV and ∼3.3 eV for 1T- and 2H-phase MoS 2 respectively. • Photoluminescence intensity gradually decrease with synthesized temperature. Abstract Molybdenum di-sulfide thin films of thickness <1500 Å, were prepared by the dip-coating technique at different baking temperatures within the range 400 °C–450 °C using methanolic solution of ammonium molybdate and ammonium thiocyanate and hence studied their different properties using X-ray diffraction (XRD), UV-vis spectroscopy, Photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS) and Current-Voltage (I-V) relationship measurements. XRD result shows that the MoS 2 films are mixed metallic octahedral prismatic 1T- and trigonal prismatic bulk crystal 2H-phases. The I-V relationships show higher electrical conductivity for the films prepared at 400 °C and 450 °C than the films prepared at 425 °C. XPS measurement also shows the formation of mixed phases of MoS 2 thin films as revealed by XRD. We have estimated the valence band maximum (VBM) and work functions from higher and lower energy range of UPS (He-I) spectra of MoS 2 thin films prepared at 425 °C and 450 °C. The VBM are ∼4.4 eV & ∼4.2 eV and their work functions are ∼3.5 eV & ∼3.3 eV respectively that are correlated with conductivity and formation of mixed phases of MoS 2 thin films. [ABSTRACT FROM AUTHOR] more...

Abstract Electrochemical supercapacitors are vital for the advancement of energy storage devices. Herein, we report the synthesis of molybdenum selenide (MoSe 2), tungsten-doped molybdenum selenide (W MoSe 2) and their graphene (G) composites (W MoSe 2 /G) via a facile hydrothermal method. Physiochemical properties of the as-synthesized samples are examined using X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller measurements, scanning electron microscopy, high resolution transmission electron microscopy and energy dispersive X-ray spectroscopy measurements. Used as working electrodes for supercapacitors, MoSe 2 nanostructures could deliver the specific capacitance of 106 F g−1 at 2 mV s−1 scan rate. Further, doping with tungsten (W) demonstrates the variation of specific capacitances with 2 M % of tungsten as the optimum doping amount, delivering the maximum specific capacitance of 147 F g−1. Furthermore, graphene composites of these nanostructures deliver the enhanced specific capacitances of 248 F g−1 and complimented with excellent capacitance retention capability of 102% for 20000 cycles. Graphical abstract Image 1 Highlights • Molybdenum selenides (MoSe 2) were prepared employing hydrothermal method. • Tungsten (W) doping enhanced the specific capacitances of electrodes. • Specific capacitance depends on W-doping concentration. • Graphene composites display enhanced specific capacitance and cyclic retention. [ABSTRACT FROM AUTHOR] more...

Graphical abstract The interlayer-expanded 1 T-MoSe 2 cocatalyst modified 2D-C 3 N 4 exhibits an ultra-high hydrogen evolution rate of 1672.6 μmol g−1 h−1 with AQE of 5.2% at 420 nm. The giant improved HER performance can be ascribed to the enhanced charge separation efficiency and favorable hydrogen evolution capacity of cocatalyst. Highlights • The interlayer-expanded 1T-MoSe 2 is for the first time utilized as cocatalyst in photocatalytic hydrogen evolution. • The MoSe 2 cocatalyst can effectively boost the HER performance of 2D-C 3 N 4 with AQE = 5.2% at 420 nm. • The interlayer-expanded 1T-phase structure leads to favorable hydrogen evolution capacity of MoSe 2 benifiting for HER. Abstract Visible-light-driven photocatalytic hydrogen evolution reaction (HER) is of far-reaching significance to address the energy and environmental issues. Owing to the seriously limited charge separation and surface catalytic conversion efficiency, cocatalyts especially noble-metals (e.g. Pt) are fundamentally required for this reaction. Transitional metal dichalcogenides (TMDs) represent a type of promising nonprecious cocatalysts, but they still lack effective strategies to optimize the performance. In this work, we report a rational design of MoSe 2 to form interlayer-expanded 1T-phase structure, to maximize the cocatalytic activity for photocatalytic HER by optimizing the surface activation ability for reaction molecule at both edge and basal sites. In a practical photocatalytic reaction, when intergrated with a semiconductor (two-dimensional carbon nitride, 2D-C 3 N 4), the hybrid exhibits a satisfactory hydrogen evolution rate (1672.6 μmol g−1 h−1, with external quantum efficiency of 5.2% at 420 nm) that greatly higher than the normal spacing 2H-MoSe 2 (186.7 μmol g−1 h−1) and most noble-metals (e.g. Au, Ag, Pd). The giant improved HER performance strongly demonstrates the superiority of the presented phase and interlayer engineering strategy. The formation mechanism of the specialized structure and the key factor affecting the performance are also discussed. This work may provide new avenues for the design of TMDs-based catalysts toward HER application. [ABSTRACT FROM AUTHOR] more...

Abstract Mimicking the natural photosynthesis system, artificial photocatalysis facilitates effective utilization of solar energy for environmental sustainability and hydrogen energy production. In this work, the robust and efficient carbon fiber has been successfully incorporated into the interface between WO 3 nanodots and MoSe 2 needles using the facile hydrothermal and solvothermal method. The suitable interfacial contact of heterogeneous photocatalysts plays a significant role in the separation/transfer of interfacial photogenerated electron-hole pairs and hetero-junction. It seems an efficient approach for enhanced photocatalytic performance since the greater area of contact could improve the interfacial rate of charge transfer. The phase structure of prepared WO 3 nanodots changed from the monoclinic to hexagonal phase by the addition of co-catalyst. The experimental results exhibited that carbon fiber played a tri-functional role to boost up the photocatalytic activity over MoSe 2 nanostructures. It's not only act as operative co-catalyst but could also serve as the conductive electron bridges, rather than general cocatalyst, to accumulate electrons and encourage the hydrogen generation kinetics over the WO 3 photocatalysts. More interestingly, the WO 3 −1% MoSe 2 −1.5% carbon fiber and WO 3 −1%MoSe 2 nanocomposites demonstrated the excellent rates of hydrogen evolution 438.7 and 356.2 mmol/g.h, which were 7.6 and 6.17 times higher when compared to that of pure MoSe 2 , respectively. Under the visible light excitation, the atomically junction encourages fast electron transfer from nanofibers to MoSe 2 to suppress the rapid recombination kinetics within WO 3 nanodots and extend the lifetime of WO 3 charge carrier's, thereby releasing more photogenerated electrons with higher reducing power for hydrogen evolution. The current work can contribute with new perspectives and mechanistic insight for the design and development of heterogeneous photocatalysts WO 3 based nanostructures using the combination of MoSe 2 and trifunctional carbon nanofibers for environment and energy harvesting applications. [ABSTRACT FROM AUTHOR] more...

Highlights • MoSe 2 /MoS 2 heterojunction is fabricated according to heterojunction engineering. • There are electronic modulations in the MoSe 2 /MoS 2 heterostructure. • MoSe 2 /MoS 2 serves as bifunctional material for HER and supercapacitance performance. • It exhibits HER with small Tafel slope, lower overpotential, and excellent stability. • MoSe 2 /MoS 2 heterostructure delivers high specific capacitance with good retention. Abstract Two-dimensional (2D) heterojunction held together by van der Waals or covalent interactions give high flexibility in modifying their electrocatalytic activity and ion storage performance, since the surface work function and electronic states are dependent on the topmost layer, also the overall heterostructure. The MoSe 2 /MoS 2 heterostructure based on 2D MoSe 2 thin-flake and MoS 2 nanosheet was designed through heterojunction engineering and prepared by epitaxial growth process. The abundant interfaces in the MoSe 2 /MoS 2 heterostructure not only enable more exposed active sites for electrochemical reaction, but also facilitate the charge transport due to the open porous space within the interlaced nanosheet arrays, arising from with the synergistic effect by the combination of MoS 2 and MoSe 2. As expected, the MoSe 2 /MoS 2 heterostructure exhibits excellent hydrogen evolution property with a small Tafel slope of 61 mV dec−1, lower overpotential of 162 mV at 10 mA cm−2, and long-term stability. It also delivers a much boosted supercapacitance performance with a high specific capacitance of 1229.6F g−1 at 1 A g−1 and 92.8% capacitance retention after 2000 cycles. The asymmetric supercapacitor made of the MoSe 2 /MoS 2 //nitrogen-doped carbon shows a stable potential window of 1.8 V. [ABSTRACT FROM AUTHOR] more...

Highlights • The first report of fluorescence quenching of MoS 2 QDs by Fe3+ ion, to our best knowledge. • The fluorescent MoS 2 QDs–Fe3+ sensor operates conveniently and effectively in extremely low concentrations. • The fluorescent MoS 2 QDs–Fe3+ sensor is label free and has good selectivity. Abstract MoS 2 quantum dots were successfully prepared by a one-step hydrothermal exfoliation procedure. The prepared MoS 2 quantum dots are monodispersed and have a circular shape, with an average diameter of 4.67 nm. Excited by UV-light, MoS 2 quantum dots emit blue-purple fluorescence, and the fluorescence intensity is suppressed with the addition of Fe3+ ions. On this basis a novel fluorescent MoS 2 quantum dots–Fe3+ label-free detection system is proposed. The decay curves of fluorescence show that the fluorescence quenching follows a static process. The binding stoichiometry ratio of Fe3+ ions toward MoS 2 quantum dots is recognized as 1:1, based on the Benesi-Hildebrand and Job's plot methods. For the concentration range of 0–50 μmol/L, the Fe3+ and fluorescence intensity are linearly related to 99.39%. The detection limit reaches 1 μmol/L. Several common ions were also examined that have little cross-influence on the fluorescence intensity of the MoS 2 quantum dots. The fluorescent MoS 2 quantum dots–Fe3+ probe has good performances and provides a novel, convenient and effective approach for the detection of Fe3+ of extremely low concentrations. [ABSTRACT FROM AUTHOR] more...

Graphical abstract Highlights • A heterostructure composed of MoSe 2 and BP by vdW interactions is constructed. • The MoSe 2 -BP heterostructure exhibits enhanced electrocatalytic performance and excellent stability. • The BP nanosheets serve as the 2D substrate and offer a short paths for electron transfer. • The MoSe 2 nanosheets contribute abundant active sites released from agglomeration. Abstract The hydrogen evolution reaction (HER) is promising in the production of clean and sustainable energy and molybdenum diselenide (MoSe 2) is attractive for this process due to the excellent catalytic ability. However, its low intrinsic conductivity and vulnerability to aggregation have restricted wider application. Herein, a facile strategy to construct a heterostructure composed of MoSe 2 nanosheets and black phosphorus (BP) nanosheets by van der Waals (vdW) interactions is designed and described. Compared with the bare MoSe 2 nanosheets, the MoSe 2 -BP heterostructure has improved conductivity and more abundant active sites attributable to BP consequently facilitating electron transfer and preventing MoSe 2 from aggregation. In the HER assessment, the MoSe 2 -BP heterostructure delivers excellent electrocatalytic performance such as a low onset potential (200 mV), small Tafel slope (97 mV·dec−1), and excellent stability. The 2D heterostructured semiconductor has great potential in electrocatalytic applications. [ABSTRACT FROM AUTHOR] more...

Abstract The effects of vacancy and antisite defects, such as V Mo , V Mo2 far, V Mo2 close, V Se , V Se2 close, V MoSe3 , V MoSe6 and Mo Se2 on the electronic structure and magnetic properties of monolayer MoSe 2 were systematically investigated using the density functional theory calculation. The theoretical results indicate that the single Mo vacancy (V Mo) induces a large magnetic moment of 3.939 μ B and shows magnetic half-metallicity due to the Se unsaturated dangling bond around the Mo vacancies. Effective n-type doping can be achieved by the creation of Se vacancy (V Se and V Se2). However, the Se vacancy doped systems are nonmagnetic due to the formation of Mo-Mo metallic bonds around the Se vacancies, which results in the disappearance of Mo unsaturated dangling bonds. The V MoSe3 and V MoSe6 complex defects as well as Mo Se2 antisite defect have high formation energy of defects. The V MoSe3 remains nonmagnetic. However, the V MoSe6 and Mo Se2 defects induce a magnetic moment of 5.74 μ B and 1.92 μ B , respectively, which originates from the unpaired 4d electrons between the nearest-neighbor Mo atoms. These results show that the vacancies can engineer the electronic structure and magnetic properties of monolayer MoSe 2 , which makes it become novel candidates for photo-catalysis, photoluminescence and spintronic devices. Highlights • The effect of vacancy and antisite defects on monolayer MoSe 2 was investigated. • The V Mo induces a large magnetic moment and shows magnetic half-metallicity. • The V Se is nonmagnetic due to the formation of Mo-Mo metallic bonds. • The vacancies can engineer the magnetic properties of monolayer MoSe 2. [ABSTRACT FROM AUTHOR] more...

Abstract The solid lubricant MoS 2 was used as the reinforcement filler for the Polyamide12 material for the additive manufacturing process – selective laser sintering. The tribological and mechanical properties of the laser sintered PA12/MoS 2 and PA12 were investigated by the linear reciprocating ball-on-flat wear and impact tests. Results show that by incorporating the MoS 2 filler into the PA12 matrix, the impact properties was improved. The coefficient of friction and wear rate of the laser sintered PA12/MoS 2 were reduced significantly. The worn surface formed in the wear test was shallow and smoother for the PA12/MoS 2 , where only mild wear occurred. The XPS testing suggested the involvement of the mechanical-chemical reaction, which resulted the decomposing of the MoS 2 and the enhancement of the wear properties of the PA12/MoS 2. [ABSTRACT FROM AUTHOR] more...

Using first-principles calculations, we have investigated the electronic and optical properties of MoSe2 with Se vacancies (SVSe, α-DVSe, and β-DVSe) and further repaired by halogen atoms (F, Cl, Br and I). For the MoSe2 with Se vacancies, Cl, Br and I atoms can occupy the Se vacancies and form three bonds with the neighboring Mo atoms, but F atom only can form two F-Mo bonds with the lowest adsorption energies due to its smaller atomic radius. Halogen atoms possess one more electron than Se atom, which results in a local magnetic moment of 1µB for single vacancy and 2µB for double vacancies. The MoSe2 with Se vacancies exhibits n-type doping semiconductor, which agrees well with the experimental observations. After halogen atoms doping in the defective site, the defective levels shift from electron donor levels to the electron acceptor levels, and finally reduces the n-type doping from the defective structure through a p-doping process. Compared to the defective MoSe2, absorption enhancement around low energy area of 0∼3 eV is observed in the halogen-repaired MoSe2 structures. Our results provide new insights in structural repairing of the transition metal dichalcogenides and promote their remarkable properties for applications in optoelectronics. [ABSTRACT FROM AUTHOR] more...

Graphical abstract Abstract Metal chalcogenides with large active sites have been received great attention as an excellent catalyst due to their hierarchical structural properties. Here, we have demonstrated the synthesis of ytterbium-doped molybdenum selenide (YbMoSe 2) in the form of two-dimensional nanosheets by using a simple ultrasonic method. The formation of the crystal phase of prepared YbMoSe 2 nanosheets was studied by using the selective characterization techniques. The reported HRTEM confirmed that the introduction of heterogeneous spin of Yb with MoSe 2 creates the lattice distortion. Thus, the active sites can be increased by creating the lattice distortion on the basal plane of the metal chalcogenides nanosheets. The band gap study was carried out by using UV–visible spectrometer and demonstrated the decreasing band gap of MoSe 2 from 1.30 eV to 1.15 eV due to the Yb substitution/doping. The increasing active sites with decreasing band gap facilitate an excellent electronic conductivity and electrochemical activity. Furthermore, the electrocatalytic activity of YbMoSe 2 modified glassy carbon electrode (YbMoSe 2 /GCE) toward the sensing of diphenylamine (DPA) anti-scald agent. As expected, YbMoSe 2 /GCE showed a high level of electrochemical activity with a low limit of detection (0.004 µM) and excellent sensitivity (11.4 µA µM−1 cm−2) towards the detection of DPA. In addition, the superior selectivity, stability, and reproducibility of YbMoSe 2 /GCE also were recorded. The beneficial electrochemical activity of YbMoSe 2 /GCE offered the more advantages to detection of DPA in the food sample also. [ABSTRACT FROM AUTHOR] more...

Molybdenum diselenide (MoSe2) has attracted attention as a potential semiconductor platform. However, the as-synthesized MoSe2 field-effect transistors (FETs) tend to exhibit the arbitrary properties of n-type, p-type, or ambipolar behavior due to the uncontrolled growth condition. Here, two-step functionalization is proposed to achieve n-doping effect and long-term stability in chemical vapor deposition (CVD)-grown MoSe2 FETs using oxygen plasma treatment followed by the deposition of an Al2O3 layer. After the two-step surface functionalization procedure, three types of multilayer MoSe2 FETs are all converted to n-type with the improvement of their electrical characteristics and stability; the n-doped multilayer MoSe2 FETs exhibit an enhancement in field-effect mobility from 12.23 to 31.57 cm2 V-1 s-1 and a 3 times higher Ion/Ioff, compared to pristine multilayer MoSe2 FETs. This enhancement of electric performance is attributed to the oxidation of topmost MoSe2 to interfacial MoOx with SeOx induced by the oxygen plasma treatment, as well as to the existence of fixed positive charges in deposited Al2O3. The functionalized devices exhibit excellent stability against stress, as confirmed with negative bias illumination stress tests for 7200 s. Moreover, an environmental stability test for 21 days reveals no degradation in electric performance of MoSe2 FETs. [ABSTRACT FROM AUTHOR] more...

Here we report a highly active catalyst for hydrogen evolution reaction (HER) that is constructed by in situ growth of MoS 2 on the surface of MoSe 2 nanosheets (MoSe 2 @MoS 2 ). Compared with either single MoS 2 or MoSe 2 , the MoSe 2 @MoS 2 electrocatalyst exhibits better electrocatalytic activity with a small Tafel slope (60 mV dec −1 ) and a low onset overpotential (−161 mV). The good HER activity is attributed to its core-shell nanostructure, which can not only efficaciously suppress the aggregation of MoS 2 nanosheets, but also generate more active sites and produce a synergistic effect of the two components in the HER. This approach provides an effective pathway to improve HER activity of MoS 2 or MoSe 2 catalysts and can be used for other two-dimensional semiconductor electrocatalyst. [ABSTRACT FROM AUTHOR] more...

Abstract Cobalt phosphide (CoP) has been regarded as one of the most promising electrocatalysts to generate hydrogen gas by splitting water. However, the electrocatalytic performance of CoP is hindered by its relatively sluggish kinetics. Herein, a novel and effective electrocatalyst based on MoSe 2 nanosheets combining with CoP has been synthesized via a facile method. By electrochemistry test, it is found that all the composites display much better catalytic activities than pristine CoP and pure MoSe 2 nanosheets. In addition, the optimized composite can realize a current density of 155.14 mA/cm2 at the potential of −300 mV vs RHE and exhibit outstanding stability. This remarkable HER activity may result from the excellent electrical conductivity of MoSe 2 nanosheets and the synergistic effect between MoSe 2 nanosheets and CoP. Highlights • We prepared a novel and effective electrocatalyst combining CoP nanoparticles and MoSe 2 nanosheets for the first time. • We found the optimized mass ratios by CoP to MoSe 2. • CoP/MoSe 2 composites were prepared via a facile ultrasound method. • All the synthetic composites possess better catalytic activity than pure CoP nanoparticles and pristine MoSe 2 nanosheets. • The optimized composite can realize a current density of 155.14 mA/cm2 at the potential of −300 mV vs RHE. [ABSTRACT FROM AUTHOR] more...

In this study, a novel nanostructure of amorphous MoSe x was produced by a facile low-temperature hydrothermal method. Better adsorption and photodegradation of rhodamine B (RhB) and methylene blue (MB) were achieved with amorphous MoSe x than with crystalline MoSe x under dark conditions and visible light irradiation. More importantly, the catalytic mechanisms of the amorphous and crystalline samples were compared by free radical-trapping experiments. The results showed that the main active substance that increased the photocatalytic activity in amorphous MoSe x was superoxide radicals ( O 2 − ), whereas the main active substances for crystalline MoSe x were holes (h + ) and hydroxyl radicals ( OH). In addition, amorphous MoSe x had more unsaturated atoms and a greater specific surface area because of its unique amorphous structure, thus enhancing its photocatalytic performance and adsorption capacity. The study of amorphous molybdenum selenide provides a new idea for improving the photocatalytic activity of two-dimensional materials, which is of great significance. [ABSTRACT FROM AUTHOR] more...

One-dimensional nanostructures comprising MoSe 2 nanosheets and carbon with uniformly distributed nanovoids are prepared through the application of a simple selenization treatment to electrospun nanofibers. Size-controlled polystyrene nanobeads in the form of an aqueous suspension are introduced for the first time as an electrospinning solution, which enables the precise control of void size and uniform distribution of nanovoids in the one-dimensional (1D) nanostructure. The discharge capacity and Coulombic efficiency of the porous MoSe 2 /C composite nanofibers after the 200th cycle at a current density of 0.2 A g −1 are 454 mA h g −1 and 98.4%, implying efficient Na + ion insertion and extraction in the composites. In addition, a high discharge capacity of 280 mA h g −1 at a current density of 7.0 A g −1 demonstrates an excellent rate capability and fast Na + ion and electron transfer. Few-layered MoSe 2 and highly conductive carbon facilitate ion and electron diffusion during cycling. Uniformly distributed nanovoids in the structure can accommodate the volume expansion induced by electrochemical reaction of Na + ions with the composites and allow efficient penetration of electrolyte into electrodes. [ABSTRACT FROM AUTHOR] more...

Monolayer two-dimensional transition metal dichalcogenides (TMDs) such as MoSe2 are promising materials for chemical vapor sensing applications due to their unique monolayer structure, ease of fabrication, low cost, selectivity, sensitivity, and speed of response. To date, most chemical vapor and gas sensors that use TMDs are based on chemiresistive device properties. However, recent studies indicate that the optical properties, in particular the photoluminescence (PL), could be used to sense vapors as well. In this study, we examine the PL of MoSe2 while it is exposed to triethylamine, a strong electron donor and chemically relevant to nerve gas and explosive sensing. We observe a fast and significant decrease in the PL by as much as 75% during exposure. The PL begins to recover as soon as the vapor is switched off, indicating fast adsorption/desorption of the analyte. We analyze the data in terms of possible applications to chemical vapor sensing. [ABSTRACT FROM AUTHOR] more...

The magnetic properties of nonmetal (NM) doped (H, B, C, Si, N, P, As, O, S, Te, F, Cl, Br or I) monolayer MoSe 2 were investigated by first principle calculations. We have found that NM dopants with odd number of valence electrons can induce magnetism; on the contrary, NM dopants with even number of valence electrons cannot induce magnetism. More importantly, half metallic property has been found for H-, B-, F-, Cl-, Br- and I-doped MoSe 2 , characterized with 100% spin-polarization around the Fermi level. This work has important guidance for the realization of spin devices on monolayer MoSe 2 . [ABSTRACT FROM AUTHOR] more...

Abstract: Clean hydrogen production is highly promising to meet future global energy demands. The design of earth‐abundant materials with both high activity for hydrogen evolution reaction (HER) and electrochemical stability in both acidic and alkaline environments is needed, in order to enable practical applications. Here, the authors report a non‐noble 3d metal Cl‐chemical doping of liquid phase exfoliated single‐/few‐layer flakes of MoSe2 for creating MoSe2/3d metal oxide–hydr(oxy)oxide hybrid HER‐catalysts. It is proposed that the electron‐transfer from MoSe2 nanoflakes to metal cations and the chlorine complexation‐induced neutralization, as well as the in situ formation of metal oxide–hydr(oxy)oxides on the MoSe2 nanoflakes' surface, tailor the proton affinity of the catalysts, increasing the number and HER‐kinetics of their active sites in both acidic and alkaline electrolytes. The electrochemical coupling between doped‐MoSe2/metal oxide–hydr(oxy)oxide hybrids and single‐walled carbon nanotubes heterostructures further accelerates the HER process. Lastly, monolithic stacking of multiple heterostructures is reported as a facile electrode assembly strategy to achieve overpotential for a cathodic current density of 10 mA cm−2 of 0.081 and 0.064 V in 0.5 m H2SO4 and 1 m KOH, respectively. This opens up new opportunities to address the current density versus overpotential requirements targeted in pH‐universal hydrogen production. [ABSTRACT FROM AUTHOR] more...

Based on the advantages of MoS 2 and MoSe 2 , a new type of metal chalcogenide MoS x Se 2-x (taking MoS 1.5 Se 0.5 as an example in the article) with similar structures and functional complementation to MoS 2 and MoSe 2 is proposed. In the paper, MoS 1.5 Se 0.5 nanosheets supported by 3D reduced graphene oxide (MoS 1.5 Se 0.5 -3D rGO) have been synthesized by simply applying a solid-state reaction process together with a hydrothermal process. MoS 1.5 Se 0.5 nanosheets are homogeneously distributed into 3D porous networks of rGO and 3D-rGO, which exhibits a three-dimensionally interconnected wrinkle structure for MoS 1.5 Se 0.5 loading, and offers convenient channels for electron transport and lithium ion diffusion. MoS 1.5 Se 0.5 -3D rGO composite delivers a reversible capacity of 1100 mAh g −1 at the current density of 100 mA g −1 and up to 1225 mAh g −1 after 200 cycles. Meanwhile, the MoS 1.5 Se 0.5 -3D rGO composite has an outstanding rate performance with a high capacity retention of 375 mAh g −1 at the C-rate of 10 C (1 C = 680 mAh g −1 ), indicating that the MoS 1.5 Se 0.5 -3D rGO is a promising anode material for the lithium-ion storage. [ABSTRACT FROM AUTHOR] more...

As part of the device fabrication process, selenization step is required to crystallise the CIGS absorber layer. However, during high temperature selenization process, excessive formation of MoSe2 can lead to delamination of the film and adverse effect on electrical properties of the solar cells. In this paper, a new method is proposed to form a Molybdenum Oxide (MoOx) barrier layer in between of the Mo back contact using plasma jet under atmospheric based conditions. The effect of MoOx compound (MoO2 and MoO3) towards the efficiency of the device is investigated. It has been proven that a thin layer of MoOx barrier layer is able to control the formation of MoSe2 effectively and provide a significant improvement in electrical properties of the devices. A power conversion efficiency of 5.24% with least efficiency variation across the champion device was achieved which demonstrates the importance of this methodology on small area devices. [ABSTRACT FROM AUTHOR] more...

To endow catalyst supports with excellent co-catalytic activity is an effective way to strengthen methanol-tolerance of Pt-based catalysts towards oxygen reduction reaction (ORR). In this study, nitrogen-doped molybdenum selenide/biomass-derived carbon (N-MoSe 2 /BC) composite as a Pt-support/co-catalyst is prepared via a synchronous synthesis method to enhance methanol tolerance. The porous structure of N-MoSe 2 /BC with N-doping can improve the exposure of coordinated Mo–Se x sites along MoSe 2 edges and provide the oxygen diffusion channels to promote ORR activity. Pt-N-MoSe 2 /BC (Pt, 5 wt.%) shows high activity (14.83 mA cm −2 ) and selectivity (4e − pathway) towards ORR, promising durability (11.9% decline) and excellent tolerance against methanol-crossover effects, which are superior to those of commercial Pt/C (10 wt.%). With the introduction of pyridinic N, graphitic N and Mo−N x in MoSe 2 /BC, more active sites on Pt (111) facets are activated to enhance charge transfer efficiency and ORR activity. Both N-species in BC and exposed edge sites in N-MoSe 2 contribute to high methanol-tolerance and co-catalytic activity towards ORR. Therefore, the remarkable ORR activity is originated from the synergistic effects among well-distributed Pt, N-species, and active edge sites of MoSe 2 . Design of porous (N)-MoSe 2 /BC provides a promising direction for preparation of co-catalyst/support with strong methanol tolerance and ORR activity. [ABSTRACT FROM AUTHOR] more...

Controllable atmospheric pressure CVD has been optimized to grow transition metal dichalcogenide MoSe2 with tunable morphology at 750 °C on a silicon substrate with a native oxide layer of 250 nm. Utilizing tetrapotassium perylene-3,4,9,10-tetracarboxylate (PTAS) as a seed promoter and varying the vertical distance between the substrate and the precursor MoO3, different morphologies of MoSe2 were achieved, including 2D triangles, hexagons, 3D pyramids and vertically aligned MoSe2 sheets. We find that the shape of MoSe2 is highly dependent upon the distance h between the substrate and the precursor. The change in the morphology is attributed to the confinement of vapor (MoO3 and Se) precursors and their concentrations due to the change in h. These results are helpful in improving our understanding about the factors which influence the morphology (shape evolution) and also the continuous growth of MoSe2 films. [ABSTRACT FROM AUTHOR] more...

In order to seek a cost-effective and facile approach to synthesize counter electrode (CE) material used in dye-sensitized solar cells (DSSCs), MoSe 2 nanoflowers (300 ∼ 400 nm) with nanosphere hierarchical architecture were prepared successfully via a facile and economical hydrothermal method. The systematical electrochemical measurements including EIS, CV and Tafel polarization experiments illustrated that MoSe 2 nanoflowers exhibited superior electrocatalytic property. The excellent electrocatalytic performance could be due to abundant active sites, stable chemical property, enhanced exchange current density ( J 0 ) and decreased charge-transfer resistance ( R ct ) of the fabricated MoSe 2 nanoflowers. In addition, the DSSCs assembled by MoSe 2 CE achieved more remarkable photovoltaic performance (PCE = 7.01%) for I 3 − reduction than standard Pt CE (PCE = 6.38%), suggesting that MoSe 2 nanoflowers could be a promising alternative for CE material in DSSCs. [ABSTRACT FROM AUTHOR] more...

A mesoporous MoSe 2 /C composite is synthesized through a nano-casting technique along with heat treatment. Nano-silica particles are used as templates to create mesopores. Homogeneously dispersed Molybdenum and selenium particles in the starch substrate are reacted with each other to formed MoSe 2 nanosheets when subjected to heat-treatment. Meanwhile, the starch is carbonized into carbon. The mesoporous MoSe 2 /C composite is investigated as an anode material for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). It presents good storage capacity for both lithium ions and sodium ions. Under the current density of 200 mA g −1 , the mesoporous MoSe 2 /C composite exhibits reversible capacity of 618 mA h g −1 for LIBs and 360 mA h g −1 for SIBs after 300 cycles. The superior electrochemical performance could be ascribed to the mesoporous structure of MoSe 2 /C composite which provides sufficient space for accommodating huge volumetric expansion and the charge product, selenium. [ABSTRACT FROM AUTHOR] more...

Benefiting from improved electrical conductivity, the N-doped MoSe 2 nanosheets show substantially enhanced HER activity with a lower onset overpotential of approximately −135 mV and a smaller Tafel slope of 62 mV dec −1 , which exhibiting enhanced catalytic performance compared with that of pure MoSe 2 . The success of improving the HER performance via the introduction of N dopant offers a new opportunity in the development of high performance MoSe 2 -based electrocatalyst. [ABSTRACT FROM AUTHOR] more...

The illumination of monolayer transition metal dichalcogenides can dynamically photoionize donor centers, increasing the concentration of free carriers. Here, we investigate the effect of such photodoping on the interlayer exciton formed across a MoS2/MoSe2/MoS2 heterostructure. We first identify the photodoping effect by monitoring the increase in the trion dissociation energy, accompanied by a characteristic tuning of the exciton/trion photoluminescence (PL) intensity ratio in MoSe2 upon exposure to laser light. At the same time, the PL intensity of the interlayer exciton significantly decreases, while the combined PL intensity of the exciton and the trion in MoSe2 is enhanced, showing that the interlayer charge transfer can be controlled by the doping level. This effect is persistent on a timescale of several hours, provided that the sample is maintained under vacuum, suggesting a mechanism involving laser induced desorption of molecules physisorbed on the surface of the heterostructure. This hypothesis is supported by the observation of a significantly faster photodoping effect when the sample is excited with a pulsed laser with the same average power. [ABSTRACT FROM AUTHOR] more...

Abstract: Transition‐metal dichalcogenides (TMDs) are promising electrocatalysts toward the hydrogen evolution reaction (HER) in acid media, but they show significantly inferior activity in alkaline media due to the extremely sluggish water dissociation kinetics. Herein, CoSe2/MoSe2 heterostructures with CoSe2 quantum dots anchored on MoSe2 nanosheets are synthesized towards enhanced alkaline HER catalytic activity. The incorporation of CoSe2 is intended to construct additional water adsorption sites on the basal planes of MoSe2 to promote water dissociation. The CoSe2/MoSe2 heterostructures show substantially enhanced activity over MoSe2 and CoSe2 in 1  m KOH. The optimal overpotential required to reach a current density of 10 mA cm−2 is merely 218 mV, which is more than 100 mV greater than that of MoSe2, which is by far the best performance demonstrated for precious‐metal‐free catalysts. Detailed analyses based on electrochemical testing demonstrate that the water adsorption and subsequent dissociation process is accelerated by CoSe2 species with rich edge sites; meanwhile, MoSe2 species provide sufficient active sites for the adsorption and combination of adsorbed hydrogen (H.). These results provide an effective strategy for developing earth‐abundant catalysts with high activity for the alkaline HER, and are of great significance to promote the practical application of alkaline water electrolysis. [ABSTRACT FROM AUTHOR] more...

Abstract: Prussian blue (PB) represents a simple, economical, and eco‐friendly system as cathode material for sodium‐ion batteries (SIBs). However, structural problems usually worsen its experimental performance thus motivating the search for alternative synthetic strategies and the formation of composites that compensate these deficiencies. Herein, a straightforward approach for the preparation of PB/MoS2‐based nanocomposites is presented. MoS2 provides a 2D active support for the homogeneous nucleation of porous PB nanocrystals, which feature superior surface areas than those obtained by other methodologies, giving rise to a compact PB shell covering the full flake. The nanocomposite exhibits an excellent performance as cathode for SIBs with discharge capacity values up to 177 mA h g−1 and a specific capacitance of 354 F g−1. These values are even larger for the intercalation of K+ ions (up to 215 mA h g−1, reaching a specific capacitance of 489 F g−1). Compared to similar composites, superior performance can be ascribed to a synergistic effect of the coordination compound with the 2D material. [ABSTRACT FROM AUTHOR] more...

Abstract: Self‐charging supercapacitor power cell (SCSPC) received much attention for harvesting and storing energy in an integrated device, which paves the way for developing maintenance free autonomous power systems for various electronic devices. In this work, a new type of SCSPC device is fabricated comprising 2D molybdenum di‐selenide (MoSe2) as an energy storing electrode with polyvinylidene fluoride‐co‐hexafluoropropylene/tetraethylammonium tetrafluoroborate (PVDF‐co‐HFP/TEABF4) ion gelled polyvinylidene fluoride/sodium niobate (PVDF/NaNbO3) as the piezopolymer electrolyte. The fabricated SCSPC delivers a specific capacitance of 18.93 mF cm−2 with a specific energy of 37.90 mJ cm−2 at a specific power density of 268.91 µW cm−2 obtained at a constant discharge current of 0.5 mA. The MoSe2 SCSPC device can be self‐charged with the aid of mechanical deformation induced using the applied compressive force, thus making it harvest and store energy. The MoSe2 SCSPC device can be charged up to a maximum of 708 mV under a compressive force of 30 N in 100 s, and the mechanism of charge‐storage is discussed in detail. The experimental findings of this work demonstrate the high efficiency of the fabricated MoSe2 SCSPC device, which can provide new insights for developing sustainable power sources for the next generation wearable electronic applications. [ABSTRACT FROM AUTHOR] more...

Here, a novel coated composite, Er 3+ :YAlO 3 /Ta 2 O 5 /rGO/MoSe 2 , was successfully prepared by sol-hydrothermal and calcination methods, in which the MoSe 2 and reduced graphene oxide (rGO) hybrids as co-catalyst were used to act as the electron collector and active reaction sites. Er 3+ :YAlO 3 , MoSe 2 /rGO, Er 3+ :YAlO 3 /Ta 2 O 5 and Er 3+ :YAlO 3 /Ta 2 O 5 /rGO/MoSe 2 were all characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), Raman spectrum, UV–vis diffuse reflectance spectra (DRS) and transmission electron microscopy (TEM). UV–vis absorption and photoluminescence (PL) spectra of Er 3+ :YAlO 3 were also measured. The photocatalytic hydrogen production activity of Er 3+ :YAlO 3 /Ta 2 O 5 /rGO/MoSe 2 was examined under visible-light irradiation. The main influence factors such as initial solution pH and mass ratio of Ta 2 O 5 and MoSe 2 /rGO on visible-light photocatalytic hydrogen production activity of Er 3+ :YAlO 3 /Ta 2 O 5 /rGO/MoSe 2 were discussed in detail. The results showed that the coated composite (Er 3+ :YAlO 3 /Ta 2 O 5 /rGO/MoSe 2 ) with 99.25:0.75 mass ratio of Ta 2 O 5 and MoSe 2 /rGO in methanol aqueous solution at pH = 6.00 could display the highest photocatalytic hydrogen production activity. Furthermore, a high level of photocatalytic activity can be still maintained within five cycles under the same conditions. It implies that the novel coated composite, Er 3+ :YAlO 3 /Ta 2 O 5 /rGO/MoSe 2 , may be a promising photocatalyst utilizing solar energy for hydrogen production. [ABSTRACT FROM AUTHOR] more...

Organic modification of MoSe 2 sheets is firstly achieved by Atherton–Todd reaction, aiming at the acquisition of multifunctional MoSe 2 hybrid. Simultaneous enhancements in fire safety and mechanical property of thermalplastic polyurethane (TPU) are obtained with the presence of this hybrid. Strong interfacial interactions between the functionalized MoSe 2 sheets and TPU can be obtained, making more efficient load transfer from the weak polymer chains to the robust sheets. Besides, more coherent barrier network may be formed in polymer matrix, restraining the diffusion of decomposed fragments and reducing the supply for combustion fuel. Consequently, the decreases in heat release are observed for polymer composites. Notably, the releases of toxic gases, such as HCN and CO, are also suppressed by this barrier network, resulting in the reductions in fire toxicity. This work may open a new door for the functionalization of MoSe 2 sheets and evoke significant developments in its promising applications. [ABSTRACT FROM AUTHOR] more...

Despite huge efforts have been devoted to investigating ultrathin layers of two-dimensional (2D) transition-metal dichalcogenides (TMDs), their realistic applications in electronics and optoelectronics are hindered by limited scalability and uniformity of 2D thin layers. In this work, a two-step synthesis method was adopted to produce wafer-scale molybdenum diselenide (MoSe2) nanosheets. Molybdenum oxide (MoO3) thin film was initially prepared via atomic layer deposition (ALD) and followed by a selenization process in chemical vapor deposition (CVD) tube furnace. MoSe2 nanosheets with desired thickness can be obtained by tuning ALD cycles in preparing MoO3 layers. The synthesized MoSe2 films exhibited excellent layer controllability, homogeneity and wafer-scale uniformity. Few-layer structure of our MoSe2 with a polycrystalline crystal structure was verified by means of Raman and transmission electron microscopy (TEM) measurements. Moreover, arrays of MoSe2-based photodetectors with different device dimension were fabricated and the photo-responses of the devices were studied. The device exhibited a fast photo-response time of 50 ms, a high on/off ratio of ~ 24 and a good photo-responsivity of 11.7 mA/W, and it is found that the effective illumination area was a critical factor for application. The work opens up an attractive approach to realize the application of wafer-scale 2D materials in integrated optoelectronic-systems. [ABSTRACT FROM AUTHOR] more...

In this paper, three series of heterostructures of 2D transition metal dichalcogenides (including MoS2, MoSe2, MoTe2, WS2, WSe2, and WTe2) sandwiched by graphene (Gr), h-BN, and g-C3N4, which will be referred to as Gr sandwich heterostructures (SHS), h-BN-SHS, and g-C3N4-SHS in the rest of this paper, have been systematically studied firstly by using first-principle calculations. Gr-SHS are found to hold stable structures with an expanded band gap when MoSe2 and WSe2 are used as interlayers, indicating potential applications to Hall switch sensors. With the same type of interlayers, the stable h-BN-SHS shows additionally good response to visible light. In addition to good response to the visible light, effective electron-hole separation is also observed in g-C3N4-SHS. Such properties suggest structures in this sandwich type may be applied in plentiful areas, such as photocatalyst and solar cells. Moreover, the number and density of catalytically active sites in SHS may be dramatically increased. Consequently, we hope our findings could provide guidance for both the design of advanced materials and the corresponding nano-devices. [ABSTRACT FROM AUTHOR] more...

Abstract: Multilayer transition metal dichalcogenides (TMDs) potentially provide opportunities for large‐area electronics, including flexible displays and wearable sensors. However, most TMDs suffer from a Schottky barrier (SB) and nonuniform defects, which severely limit their electrical performances. Here, a novel chemical doping scheme is presented using poly‐(diketopyrrolopyrrole‐terthiophene) (PDPP3T) to compensate the defects and SB of multilayer molybdenum diselenide (MoSe2), exhibiting greatly enhanced electrical characteristics, including on‐current (≈2000‐fold higher) and photoresponsivity (≈10‐fold larger) over the baseline MoSe2 device. Based on comprehensive analysis using X‐ray photoelectron spectroscopy, grazing incidence wide‐angle X‐ray diffraction, atomic force microscopy, and near‐edge X‐ray absorption of fine structure, it is shown that two mechanisms (dipole‐induced and charge‐transfer doping effects) account for such enhancements in the multilayer MoSe2 device. The methodical generality of the strong n‐doping behavior of multilayer MoSe2 is further demonstrated by applying thiophene instead of PDPP3T. [ABSTRACT FROM AUTHOR] more...

Abstract: Sodium‐ion batteries (SIBs) are considered as a promising alternative to lithium‐ion batteries, due to the abundant reserves and low price of Na sources. To date, the development of anode materials for SIBs is still confronted with many serious problems. In this work, encapsulation‐type structured MoSe2@hollow carbon nanosphere (HCNS) materials assembled with expanded (002) planes few‐layer MoSe2 nanosheets confined in HCNS are successfully synthesized through a facile strategy. Notably, the interlayer spacing of the (002) planes is expanded to 1.02 nm, which is larger than the intrinsic value of pristine MoSe2 (0.64 nm). Furthermore, the few‐layer nanosheets are space‐confined in the inner cavity of the HCNS, forming hybrid MoSe2@HCNS structures. When evaluated as anode materials for SIBs, it shows excellent rate capabilities, ultralong cycling life with exceptional Coulombic efficiency even at high current density, maintaining 501 and 471 mA h g−1 over 1000 cycles at 1 and 3 A g−1, respectively. Even when cycled at current densities as high as 10 A g−1, a capacity retention of 382 mA h g−1 can be achieved. The expanded (002) planes, 2D few‐layer nanosheets, and unique carbon shell structure are responsible for the ultralong cycling and high rate performance. [ABSTRACT FROM AUTHOR] more...

MoSe2 represents important layered transition metal dichalcogenides (TMDs) that have high electrocatalytic activity in the hydrogen evolution reaction (HER). A key issue to achieve excellent electrochemical properties of MoSe2 is to synthesize nanostructures that are composed of few-layered MoSe2 with abundant exposure of active edge sites. Nanoflowers of layered materials are promising building blocks for photocatalysis due to their large specific surface area and a wealth of exposed edge sites. In this work, free-standing colloidal MoSe2 nanoflowers, with a size of 250 nm, were synthesized by employing a quick and nontoxic phosphine-free solution-processing approach. Oleic acid (OA), 1-octadecene (ODE) and 1-octylamine (OLA) were primarily used as solvents to control the morphology of MoSe2 nanostructures. Experimental results revealed that the shape evolution of MoSe2 nanostructures started with a first fast precipitation of amorphous materials followed by crystallization of a few layers of nanosheets. The prepared MoSe2 nanoflowers demonstrated excellent HER activities with low overpotentials and small Tafel slopes, and the chronopotentiometry responses revealed good stability, making them promising materials for the electrocatalytic HER. [ABSTRACT FROM AUTHOR] more...

Sheet-like MoSe 2 /C nanocomposites were synthesized and employed as the cathode of a rechargeable Mg 2+ /Li + hybrid battery for the first time, which exhibited an excellent electrochemical performance. The structure transformation of the MoSe 2 /C nanocomposite materials during the charge-discharge processes was identified by in situ XRD, and the electrochemical reactions taking place in the battery were evidenced. [ABSTRACT FROM AUTHOR] more...

A two-dimensional systems have attracted significant interest due to their outstanding physical, chemical and optoelectronic properties. This paper focuses on the detailed investigations of the electronic, phononic and superconducting properties of transition-metal dichalcogenide bilayers M Se 2 ( M = Mo, W) intercalated by calcium atoms. The first-principles calculations show that (MoSe 2 ) 2 Ca and (WSe 2 ) 2 Ca systems exhibit metallic behavior and weak phonon-mediated superconductivity with low critical temperature of 0.51 and 0.30 K, respectively. These results confirm other theoretical predictions and suggest that the investigated materials cannot be a good candidates for a nanoscale superconductors. [ABSTRACT FROM AUTHOR] more...

We report the adsorption properties of methanol (ML) and ethanol (EL) vapor molecules on to the monolayer MoSe 2 surface. Before, studying the adsorption behavior, the structural stability of MoSe 2 monolayer is ensured with formation energy. The stable monolayer MoSe 2 nanosheet is used as a base material for the adsorption of ML and EL vapor molecules. The interaction of ML and EL vapors on MoSe 2 surface layer is explored using the adsorption energy, energy gap variation and Bader charge analysis. We noticed the band gap variation between 1.43 and 1.88 eV upon adsorption of methanol and ethanol vapors on to MoSe 2 nanosheets. Also the adsorption energy is found in the range of −0.375 to −0.732 eV upon the interaction of alcohol molecules on MoSe 2 flakes. Besides, the density of states (DOS) spectrum and electron density clearly envisions the adsorption properties of ML and EL vapors on to the MoSe 2 monolayers. Furthermore, a short recovery time is noticed for MoSe 2 nanosheet material upon desorption of methanol and ethanol molecules. Moreover, the variation in the resistance of MoSe 2 base material is noticed upon adsorption of ML and EL molecules. The findings show that monolayer MoSe 2 nanosheets can be used as a chemi-resistance to detect the presence of ML and EL vapors in the environment. [ABSTRACT FROM AUTHOR] more...