S2 Alloy Research Articles

(Invited) Synthesis and Application of 1D vdW Heterostructures Based on Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs) with diverse optical and electronic properties (metallic or semiconducting) depending on chiral indices (n, m) have been the key nanomaterials in advanced applications [1,2]. Even though a mixture of metallic and semiconducting SWCNT can be used for bulk and film-form applications such as batteries and solar cells [3], the controlled growth of (n, m) or the sorting of (n, m) is essential for electronics applications such as field effect transistors (FET) [4]. On the other hand, the controlled modulation of properties can also be possible either by employing the inner space of the SWCNTs to encapsulate various materials or by externally wrapping the SWCNT template with additional atomic layers [5]. Here, I mainly discuss the latter case as a one-dimensional (1D) van der Waals (vdW) heterostructure based on SWCNT [6]. We have demonstrated the atomically precise one-dimensional (1D) van der Waals (vdW) heterostructure -- SWCNTs, boron nitride nanotubes (BNNTs), and molybdenum disulfide (MoS2) sequentially wrapped in radial direction -- by chemical vapor deposition in 2020 [6]. One of the obvious extensions of this work is the use of BNNT-SWCNT [7], which have superior semiconductor properties such as field effect transistors [8,9]. We have developed various characterization techniques for BNNT-SWCNT for the growth optimization and quality control of BNNT in various kinds of SWCNT [10-12]. Yet another extension is the various kinds of transition metal dichalcogenides (TMD) nanotubes. We have optimized CVD conditions for various metal dichalcogenides such as tungsten disulfide (WS2), niobium disulfide (NbS2), and molybdenum diselenide (MoSe2) so far in addition to the original MoS2. Here, we further broaden the concept of 1D vdW heterostructure by combining 2 transition metal species. By setting WS2 growth right after the MoS2 growth, we can observe the axial junction of the outermost tube, MoS2 - WS2. The junction is atomically smooth within a few nanometers. On the other hand, by setting the 2 transition metal species at the same CVD time, we can observe {WxMo(1-x)}S2 alloy nanotube. Both axial junction and alloy nanotubes are preferentially monolayers.Part of this work was supported by JSPS KAKENHI Grant Numbers JP23H00174, JP23H05443 and by JST, CREST Grant Number JPMJCR20B5, Japan.

Microsecond-Scale Transient Thermal Sensing Enabled by Flexible Mo1-xWxS2 Alloys.

Real-time thermal sensing through flexible temperature sensors in extreme environments is critically essential for precisely monitoring chemical reactions, propellant combustions, and metallurgy processes. However, despite their low response speed, most existing thermal sensors and related sensing materials will degrade or even lose their sensing performances at either high or low temperatures. Achieving a microsecond response time over an ultrawide temperature range remains challenging. Here, we design a flexible temperature sensor that employs ultrathin and consecutive Mo1-x W x S2 alloy films constructed via inkjet printing and a thermal annealing strategy. The sensing elements exhibit a broad work range (20 to 823 K on polyimide and 1,073 K on flexible mica) and a record-low response time (about 30 μs). These properties enable the sensors to detect instantaneous temperature variations induced by contact with liquid nitrogen, water droplets, and flames. Furthermore, a thermal sensing array offers the spatial mapping of arbitrary shapes, heat conduction, and cold traces even under bending deformation. This approach paves the way for designing unique sensitive materials and flexible sensors for transient sensing under harsh conditions.

Electrochemical performance of Cu6Sn5 alloy anode materials for lithium-ion batteries fabricated by controlled electrodeposition.

Combining electrodeposition and heat treatment is an effective method to successfully fabricate Cu6Sn5 alloy materials, in which the S2 alloy electrode is electrodeposited at 1.2 A dm-2 current density with uniform and compact morphology. The characterization results show that monoclinic η'-Cu6Sn5 and hexagonal η-Cu6Sn5 phases fabricated at the appropriate current density exhibit excellent electrochemical performance. The optimal Cu6Sn5 alloy anode material boasts not just a significantly high discharge specific capacity of 890.2 mA h g-1 with an initial coulombic efficiency (ICE) of 73.96%, but also achieves an adequate discharge specific capacity of 287.1 after 50 cycles at 100 mA h g-1. Moreover, the electrodeposited Cu6Sn5 alloy materials also possessed a lower transfer resistance of 42.45 Ω and an improved lithium-ion diffusion coefficient of 2.665 × 10-15 cm2 s-1 at the current density of 1.2 A dm-2. Therefore, preparing the Cu6Sn5 alloy thin-film electrode could be a cost-effective and straightforward method by electrodeposition from cyanide-free plating baths to develop anode components suitable for lithium-ion battery applications.

Enhancing the mechanical properties of Mg-Zn-Al-Cu-Mn alloy via MgCO3 inoculation treatment: Experimental studies and first-principles calculations

In this work, the low-cost Mg-10Zn-1Al-0.5Cu-0.3Mn without or with the addition of MgCO3 (labeled as S1 and S2 alloys) was successfully fabricated by a rapid-setting water-cooling method. The average grain size of the as-cast alloy decreased from 38.5 to 22.5 µm with the addition of MgCO3. S2 alloy possessed excellent ultimate tensile strength and elongation of 275.6 MPa and 17.5 % in the solid solution state, which were approximately 21.6 and 82.3 % higher than those of the S1 alloy. The transmission electron microscopy results showed that the MnAl2O4 phase with a high melting point was formed in the melt of S1 alloy by adding 1 wt% MgCO3, which had a phase relationship of (101)Mg||(311)MnAl2O4. Additionally, the results of edge-to-edge matching model showed that the MnAl2O4 phase tended to grow on the Mg matrix phase. The results of the first-principles calculations exhibited that the (101)Mg||(311)MnAl2O4 interface with MnO terminations was a strong interface. The MnAl2O4 phase could be regarded as heterogeneous nucleation points to improve the nucleation rate and thus to refine the grain and enhance the strength. This study can vigorously provide a certain guide for the grain refinement of Mg-Zn based alloys containing Mn.

Excitons dynamic modulation by tailoring size of high-entropy Mo0.64W0.36S2 alloy

Two-dimensional transition metal disulfides with tailored optical response are vital to demonstrate versatile optoelectronic devices and nanophotonic elements. In this work, using transient absorption spectroscopy in conjunction with density functional theory calculations, we demonstrate ultrafast excitons absorption modulation via tailoring the size of a transition-metal dichalcogenide alloy Mo0.64W0.36S2 nanosheet. As the size of the nanosheet increases from 9 ± 5 to 190 ± 121 nm, peak positions of the A and B excitons vary from 666 to 675 nm and 626 to 638 nm, respectively. Furthermore, the decay lifetimes of A excitons slow down from 1.16 to 1.84 ps when the size changes from 9 ± 5 to 190 ± 121 nm. It is shown that the exciton diffusion and decay properties can be modulated by the components and structure modulation, which is beneficial for the optimal design and optimization of optoelectronic devices.

Chemiresistive gas sensor based on Mo0.5W0.5S2 alloy nanoparticles with good selectivity and ppb-level limit of detection to ammonia.

Transition metal dichalcogenides (TMDs) are promising materials for chemiresistive gas sensor, while TMD alloys (two chalcogenide or/and metal elements) with tunable electronic structures have drawn little attention in gas sensing. Herein, Mo0.5W0.5S2 alloy nanoparticles (NPs) were prepared by a facile sonication exfoliation method and then tested for ammonia sensing. The crystal structure, geometric morphology, and elemental composition of Mo0.5W0.5S2 NPs were investigated. The gas sensing measurements demonstrated Mo0.5W0.5S2 NPs with good response to ammonia at 80 °C with alimit of detection down to 500 part per billion (ppb). The sensor also displayed good stability as well as superb selectivity to ammonia in the presence of interferences, such as methanol, acetone, benzene, and cyclohexane. The theoretical calculations revealed Mo and W atoms at edges (such as Mo0.5W0.5S2 (010)) of sheet-like NPs as the active sites for ammonia adsorption. Electrons donated by the adsorbed ammonia were combined with holes in p-type Mo0.5W0.5S2 NPs, and the concentration of the main charge carrier was reduced, resulting in resistance enhancement.

High-temperature corrosion behaviours of nickel–iron-based alloys with different molybdenum and tungsten contents in a coal ash/flue gas environment

Abstract High-temperature coal ash/flue gas corrosion behaviours of three nickel–iron based superalloys for boiler tubes with different Mo and W contents (1.8% Mo + 1.2% W for S1 alloy, 0.8% Mo + 0.2% W for S2 alloy, and 0.5% Mo + 2.2% W for S3 alloy) at 650 and 700°C were studied. The microstructure, phase compositions, and morphologies together with element distribution for corrosion products were investigated with a metallographic microscope, a scanning electron microscope equipped with an energy-dispersive spectroscope, and X-ray diffractometer. The results show that the corrosion resistance of the Ni–Fe-based alloy decreases with the increasing total content of Mo and W in the alloy at both 650 and 700°C; the outer layer of the corrosion products was mainly composed of FeCr2O4 while the inner layer was mainly composed of Cr2O3. Peeling of the oxide films formed on the surfaces of S1 and S3 alloys was observed but no obvious spalling was observed for the S2 alloy. The reactions among Mo, W, and S in the coal ash/flue gas increased the internal stress in the oxide scale, which would cause the failure of the oxide scale.

2D Transition Metal Dichalcogenide with Increased Entropy for Piezoelectric Electronics.

Piezoelectricity in 2D transition metal dichalcogenides (TMDs) has attracted considerable interest because of their excellent flexibility and high piezoelectric coefficient compared to conventional piezoelectric bulk materials. However, the ability to regulate the piezoelectric properties is limited because the entropy is constant for certain binary TMDs other than multielement ones. Herein, in order to increase the entropy, a ternary TMDs alloy, Mo1- x Wx S2 , with different W concentrations, is synthesized. The W concentration in the Mo1- x Wx S2 alloy can be controlled precisely in the low-supersaturation synthesis and the entropy can be tuned accordingly. The Mo0.46 W0.54 S2 alloy (x= 0.54) has the highest configurational entropy and best piezoelectric properties, such as a piezoelectric coefficient of 4.22 pm V-1 and a piezoelectric output current of 150 pA at 0.24% strain. More importantly, it can be combined into a larger package to increase the output current to 600 pA to cater to self-powered applications. Combining with excellent mechanical durability, a mechanical sensor based on the Mo0.46 W0.54 S2 alloy is demonstrated for real-time health monitoring.

First principles study of the structural, electronic, magnetic and optical properties of the Fe doped CoS2 thin films

The structural stability, electronic, magnetic and optical properties of the Fe doped CoS2 bulk alloy and the thin films with different terminations are studied by the first-principle calculations. The bulk Co0.75Fe0.25S2 alloy is 100% spin polarized, and there are new impurity valence bands near Fermi level in both the spin-up and spin-down channels of the band structures. The fracture of Co-S or Fe-S chemical bonds and the change of S-S dimer bonds are the key factors affecting the properties of the films. The surface energy of SS-SS-CoCo termination film under the S-rich and Co-rich boundary conditions is the lowest, and spin polarization maintains -100%. Although the spin polarization of CoFe terminated film is high (-90.2%), but its surface energy is high which lead to the unstable feature. The magnetic moment of the thin film is mainly contributed by the spin magnetic moment of the Co and Fe atoms. The magnetic moments of the atoms at outer layer differ significantly from those at the central layer due to the change of crystal field and the influence of surface effect. Fe doping and termination selection can modulate the optical properties of CoS2 effectively.

An investigation on the microstructure and mechanical properties of Al0.3CoCrFeNi high entropy alloy with a heterogeneous microstructure

In this study, the Al0.3CoCrFeNi high entropy alloy (HEA) with various heterogeneous microstructures was designed and fabricated through different process histories, such as severely cold-rolled plus annealing at low temperature for a long time (S1), cryo-rolled plus annealing at intermediate temperature (S2), cold-rolled plus annealing at intermediate temperature (S3). The microstructures were analyzed by SEM, EBSD, and TEM. The results showed that the heterogeneous grain structure of S1 alloy was composed of stretched original grains and fine recrystallized grains. Besides, the L12-(Ni, Co)3Al type phase was also observed within the face-centered cubic (FCC) matrix of the S1 alloy. However, the S2 and S3 alloys consisted of stretched original grains, survived original grains, fully recrystallized equiaxed grains, and B2 precipitates. Moreover, a mount of nano-deformation twins was also incorporated in the matrix of S2 alloy. Furthermore, the S2 alloy exhibited a superior balance of high ultimate tensile strength of ∼1019 MPa and high elongation of ∼28% as compared to S1 and S3 alloys due to its complex heterogeneous microstructure. This research would provide guidance for designing the heterogeneous structure in the FCC HEA and facilitate establishing the relationships between the heterogeneous structure and mechanical properties.

Nature of optical excitations and bandgap of Re x Mo1−x S2 alloy at nanoscale probed from high resolution low loss electron energy loss spectroscopy

The two-dimensional (2D) transitional metal dichalcogenides (TMDS) have become an intensive research topic recently. The alloys of these TMDs have offered continuous tunability of the bandstructure and carrier concentration, providing a new opportunity for various device applications. Here the rich variations in optical excitations in Re x Mo1−x S2 alloy at the nanoscale region are shown. The alloy bandgap and charge response are probed by low-loss high-resolution transmission electron energy loss spectroscopy (HR-EELS). Concurrent density functional theory calculations revealed many electronic structures from n-type semiconductors to metallic and p-type semiconducting nature with band bowing effect. The alloying-induced Peierls distortion leads to a change in crystal symmetry and decreased interlayer coupling. These alloys undergo indirect to direct bandgap transition with the function of Re concentration. These unique correlated structural and electronic properties of these 2D alloys can be potentially applicable for various electronic and optoelectronic devices.

Microscopic hardness and dynamic mechanical analysis of rapidly solidified Fe-based amorphous alloys

A systematic work was conducted to investigate the nanoindentation, dynamic relaxation, high-temperature rheological behavior, and structural relaxation after high-temperature deformation of Fe52-xCo20NixB19Si5Nb4 (x = 7,12,17, labeled as S1, S2 and S3) metallic glass. The results of nanoindentation indicate that the hardness of amorphous alloy reduces first and then enhances with the increase of Ni content. S1 alloy exhibits the highest hardness of 13–16 GPa, while relatively excellent compression plasticity is reached in S2 alloy. Besides, the glass transition temperature (Tg), initial crystallization temperature (Tx), α relaxation temperature (Tα) and internal friction change at different temperatures were determined and compared. The critical temperature, strain rate during non-Newton to Newtonian rheology and Newtonian viscosity at Tg temperature were discussed. Moreover, it was found that the activation volume improved and then decreased due to structural relaxation. At last, combined with the width of the supercooled liquid region, relaxation behavior and rheological viscosity at high temperature, the microstructure evolution of the three kinds of metallic glass under Tg temperature deformation was explained.

Transition from Crystal to Metallic Glass and Micromechanical Property Change of Fe-B-Si Alloy During Rapid Solidification

The effects of high undercooling and a large cooling rate can be achieved by the use of a containerless drop tube technique, which is conducive to rapid solidification and formation of a metastable phase. Here, the rapid solidification of Fe78Si13B9 (S1) and Fe78Si9B13 (S2) alloys was completed under microgravity condition. Based on theoretical calculations, a maximum undercooling of 433 K (0.29 TL) and 412 K (0.28 TL) was obtained, respectively. The microstructure evolution and the formation of an amorphous-nanocrystalline structure for the two alloys were compared and analyzed. The results show that S2 alloy has better amorphous forming ability and higher hardness. During the solidification of S1 alloy, the primary phase α-Fe grows by the manner of dendrites, and the secondary dendrite arm spacing decreases exponentially with increased undercooling. An amorphous-nanocrystalline structure is developed when the undercooling is increased up to 388 K; S2 alloy forms an amorphous-nanocrystalline structure at an undercooling of 275 K and is completely amorphized after exceeding an undercooling of 402 K. In addition, the hardness and elastic modulus are acquired by nanoindentation technology under different degrees of undercooling. The phase constitution, morphology, distribution, and grain refinement of the alloys have important effects on the micromechanical properties of these alloys.

Enhancing photo-detection properties of Sb0.15Sn0.85S2 alloy

Alloy engineering is a potential technique in producing a high performance optoelectronic device. Single crystals of Sb0.15Sn0.85S2 ternary alloys are grown by technique of direct vapour transport. As-grown crystals are used to fabricate metal-semiconductor-metal device for photodetection. The photodetector exhibits consistent performance and good reproducibility towards light. Moreover, it shows proficient sensitivity towards the bias voltages ranging from 5 V to 50 V under white light of 80 mW cm−2 intensity. The detector is exploited for its photoresponse at a fixed intensity of 0.3 mW cm−2 for different illumination wavelengths (480 nm, 570 nm and 670 nm) and thicknesses (20 μm, 15 μm and 11 μm). The results showed highest photo-response for 480 nm illumination. The present findings showed the detector demonstrated excellent performance under various illuminations at different bias voltages an essential need for high performance device. The study can provide innovative direction to future optoelectronics devices.

Synthesis of Large-Scale Single-Layer Mo1-X W x S2 Alloys with Highly Uniform and Tunable Photoluminescence

Single-layer transition metal dichalcogenides (TMDs) exhibit high carrier mobility and photoluminescence; thus, the materials are well suitable for next-generation optoelectronic and nano-electronic devices application. It is essential to fabricate large-scale single-layer TMDs film with uniform and desirable spectral wavelengths. Here, we report the synthesis of optically uniform single-layer Mo1-x W x S2 alloys by a two-step CVD method followed by a laser thinning process and investigations on their excitonic behavior with compositional changes. The amount of W content (x) in the Mo1-x W x S2 alloy is systemically controlled by the co-sputtering technique, and the post-laser process allows layer-by-layer thinning of the as-synthesized few-layer Mo1-x W x S2 alloys down to a single-layer. Photoluminescence (PL) and Raman mapping analyses suggest that the laser-thinning of the Mo1-x W x S2 alloys is a self-limiting process caused via heat dissipation to the substrate, resulting in a spatially uniform single-layer Mo1-x W x S2 alloy films. As W content (x) increases, the single-layer alloys reveal controlled optical band gaps ranging from 1.871 to 1.971 eV. Furthermore, we found that the number of excessive charge carriers decreases as x increases, resulting in the change in the predominant component of the PL emission from trions for single-layer MoS2 to neutral excitons for single-layer WS2.

Alloy engineering to promote photodetection in InxSn1−xS2 and SbxSn1−xS2 ternary alloys

To produce high performance optoelectronic devices, ternary alloys prepared by indium (In), antimony (Sb), tin (Sn) and sulphur (S), the InxSn1−xS2 and SbxSn1−xS2 (x = 0, 0.05, 0.15), are exploited for their application in moderately fast photodetection. The single crystals of InxSn1−xS2 and SbxSn1−xS2 (x = 0, 0.05, 0.15) alloys are grown by direct vapour transport technique. The photodetectors based on single crystals are examined for 670 nm illumination having power intensity of 3 mW/cm2. For quantitative analysis, the typical detector parameters such as photo-responsivity, specific detectivity and external quantum efficiency are calculated. The improvement in photodetection with significantly enhanced detector parameters and fast a response is realized due to doping in SnS2. The highest responsivity of 15.48 mA/W with response time of 240 ms is achieved in Sb0.15Sn0.85S2 alloy. The present findings of enhanced photodetection due to alloy engineering can be of great advantage in intended applications of these compounds in the field of optoelectronics.

Two-Dimensional MoxW1\u2212xS2 Graded Alloys: Growth and Optical Properties

Two-dimensional (2D) transition metal dichalcogenides can be alloyed by substitution at the metal atom site with negligible effect on lattice strain, but with significant influence on optical and electrical properties. In this work, we establish the relationship between composition and optical properties of the MoxW1−xS2 alloy by investigating the effect of continuously-varying composition on photoluminescence intensity. We developed a new process for growth of two-dimensional MoxW1−xS2 alloys that span nearly the full composition range along a single crystal, thus avoiding any sample-related heterogeneities. The graded alloy crystals were grown using a diffusion-based chemical vapor deposition (CVD) method that starts by synthesizing a WS2 crystal with a graded point defect distribution, followed by Mo alloying in the second stage. We show that point defects promote the diffusion and alloying, as confirmed by Raman and photoluminescence measurements, density functional theory calculations of the reaction path, and observation that no alloying occurs in CVD-treated exfoliated crystals with low defect density. We observe a significant dependence of the optical quantum yield as a function of the alloy composition reaching the maximum intensity for the equicompositional Mo0.5W0.5S2 alloy. Furthermore, we map the growth-induced strain distribution within the alloyed crystals to decouple composition and strain effects on optical properties: at the same composition, we observe significant decrease in quantum yield with induced strain. Our approach is generally applicable to other 2D materials as well as the optimization of other composition-dependent properties within a single crystal.

(Invited) Epitaxial Growth of 2D Transition Metal Dichalcogenide Monolayers, Alloys and Heterostructures

Two-dimensional (2D) transition metal dichalcogenides (TMDs) comprise a compelling class of new materials with intriguing properties that arise from their ultra-thin form, thickness-dependent bandstructure, large exciton binding energies and unusual spin and valley polarization physics. The majority of the research that has been carried out thus far employs ultra-thin TMD flakes exfoliated from bulk crystals but future device development requires the ability to synthesize large area single crystal films and heterostructures. Our research is aimed at the development of an epitaxial growth technology for TMDs and related layered chalcogenides based on gas source/metalorganic chemical vapor deposition (CVD/MOCVD) to enable monolayer growth over large substrate areas and layer-by-layer growth of heterostructures. Our recent studies have focused on the epitaxial growth of WSe2 and (Mo,W)S2 monolayer films, alloys and heterostructures using metal hexacarbonyl and hydride chalcogen precursors on substrates including sapphire and hexagonal boron nitride (hBN). A multi-step precursor modulation growth method was developed to independently control nucleation density and the lateral growth rate of TMD domains on the substrate. This approach also enables an estimation of metal-species surface diffusivity and domain growth rate as a function of growth conditions providing insight into the fundamental mechanisms of monolayer growth. Using the multi-step growth process, coalesced monolayer and few-layer TMD films were obtained on sapphire substrates up to 2” in diameter at growth rates on the order of ~ 1 monolayer/hour. In-plane X-ray diffraction demonstrates that the films are epitaxially oriented with respect to the sapphire resulting from a merging of 0o and 60o oriented domains. Room temperature photoluminescence (PL) measurements demonstrate strong emission peaks in the range of ~1.6 eV for WSe2 and ~2.0 eV for WS2 monolayers with lateral variations that may arise from residual strain in the films. (Mo,W)S2 alloy growth using simultaneous flows of Mo and W hexacarbonyl precursors reveals evidence of atomic scale ordering of Mo and W atoms within the monolayer. Growth and characterization of MoS2/WS2 and WSe2/WS2 vertical heterostructures will also be discussed.

Low-temperature Synthesis of Heterostructures of Transition Metal Dichalcogenide Alloys (WxMo1-xS2) and Graphene with Superior Catalytic Performance for Hydrogen Evolution.

Large-area (∼cm2) films of vertical heterostructures formed by alternating graphene and transition-metal dichalcogenide (TMD) alloys are obtained by wet chemical routes followed by a thermal treatment at low temperature. In particular, we synthesized stacked graphene and WxMo1-xS2 alloy phases that were used as hydrogen evolution catalysts. We observed a Tafel slope of 38.7 mV dec-1 and 96 mV onset potential (at current density of 10 mA cm-2) when the heterostructure alloy was annealed at 300 °C. These results indicate that heterostructures formed by graphene and W0.4Mo0.6S2 alloys are far more efficient than WS2 and MoS2 by at least a factor of 2, and they are superior compared to other reported TMD systems. This strategy offers a cheap and low temperature synthesis alternative able to replace Pt in the hydrogen evolution reaction (HER). Furthermore, the catalytic activity of the alloy is stable over time, i.e., the catalytic activity does not experience a significant change even after 1000 cycles. Using density functional theory calculations, we found that this enhanced hydrogen evolution in the WxMo1-xS2 alloys is mainly due to the lower energy barrier created by a favorable overlap of the d-orbitals from the transition metals and the s-orbitals of H2; with the lowest energy barrier occurring for the W0.4Mo0.6S2 alloy. Thus, it is now possible to further improve the performance of the "inert" TMD basal plane via metal alloying, in addition to the previously reported strategies such as creation of point defects, vacancies and edges. The synthesis of graphene/W0.4Mo0.6S2 produced at relatively low temperatures is scalable and could be used as an effective low cost Pt-free catalyst.

Promoting the Performance of Layered-Material Photodetectors by Alloy Engineering.

The successful peeling of graphene heralded the era of van der Waals material (vdWM) electronics. However, photodetectors based on semiconducting transition metal dichalcogenides (TMDs), formulated as MX2 (M = Mo, W; X = S, Se), often suffer either poor responsivity or long response time because of their high density of deep-level defect states (DLDSs). Alloy engineering, which can shift the DLDSs to shallow-level defect states, is proposed to be an efficient strategy to solve this problem. However, proof-of-concept is still lacking, which is probably because of the absence of a facile technology to grow high-quality alloyed TMDs. Here, we report the growth of large-scale and high-quality Mo0.5W0.5S2 alloy films via pulsed laser deposition (PLD). We demonstrate that the resulting Mo0.5W0.5S2 photodetector possesses a stable photoresponse from 370 to 1064 nm. The photocurrent exhibits positive dependence on both the source-drain voltage and incident power density, providing good tunability for multifunctional photoelectrical applications. We also establish that, because of the suppression of DLDSs with alloy engineering, the Mo0.5W0.5S2 photodetector achieves a good responsivity of 5.8 A/W and a response time shorter than 150 ms. The working mechanism for the suppression of DLDSs in Mo0.5W0.5S2 is unveiled by qualitatively analyzing the alloying-dressed band structure. In conclusion, the excellent performance of the PLD-grown Mo0.5W0.5S2 photodetector may pave the way for next-generation photodetection. The approach shown here represents a fundamental and universal scenario for the development of alloyed TMDs.