TaS2 Research Articles

Beyond the Platinum Era─Scalable Preparation and Electrochemical Activation of TaS2 Flakes.

Among 2D materials, transition-metal dichalcogenides (TMDCs) of group 5 metals recently have attracted substantial interest due to their superior electrocatalytic activity toward hydrogen evolution reaction (HER). However, a straightforward and efficient synthesis of the TMDCs which can be easily scaled up is missing. Herein, we report an innovative, simple, and scalable method for tantalum disulfide (TaS2) synthesis, involving CS2 as a sulfurizing agent and Ta2O5 as a metal precursor. The structure of the created TaS2 flakes was analyzed by Raman, XRD, XPS, SEM, and HRTEM techniques. It was demonstrated that a tuning between 1T (metallic) and 3R (semiconductor) TaS2 phases can be accomplished by varying the reaction conditions. The created materials were tested for HER, and the electrocatalytic activity of both phases was significantly enhanced by electrochemical self-activation, up to that comparable with the Pt one. The final values of the Tafel slopes of activated TaS2 were found to be 35 and 43 mV/dec for 3R-TaS2 and 1T-TaS2, respectively, with the corresponding overpotentials of 63 and 109 mV required to reach a current density of 10 mA/cm2. We also investigated the mechanism of flake activation, which can be attributed to the changes in the flake morphology and surface chemistry. Our work provides a scalable and simple synthesis method to produce transition-metal sulfides which could replace the platinum catalyst in water splitting technology.

Highly Sensitive Humidity Sensor Based on Tapered No-Core Fiber Coated with Tantalum Disulfide

Highly Sensitive Humidity Sensor Based on Tapered No-Core Fiber Coated with Tantalum Disulfide

Realization of ultra-low friction coefficient in thin-film solid lubricant coatings containing nano-sized layers of molybdenum and tantalum disulfides

Solid lubricating coatings consisting of alternating layers of molybdenum and tungsten disulfide were obtained by the method of reactive pulsed laser deposition. The layers were deposited at temperatures of 400 and 500 °C, which caused the formation of a layered packing of atoms characteristic of the hexagonal 2H-phase. The layer thickness was about 10 nm, and the basal planes of the layered atomic packing were oriented predominantly parallel to the substrate surface over the entire thickness of the layers. The study of tribological properties was carried out by the method of sliding a ball over a disk in a nitrogen atmosphere with varying the load on the counter body from 5 to 9 N. The value of the friction coefficient depended on the load on the counter body. The lowest value of the coefficient of friction was 0.01, and it was found under the highest load for coatings obtained at 500 °C. A decrease in the coating deposition temperature had a negative effect on the antifriction properties of the coating.

Engineering Vacancies at the 2D Nanocrystals for Robust Bifunctional Electrocatalysts.

Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) through water decomposition are feasible methods to produce green and clean energy. Herein, we report a facile two-step strategy for the preparation of non-noble metal defect-rich nanosheets by an electrochemical process at room temperature. First-principle calculations are used to study the bifunctional catalytic reaction mechanism of defect engineering in transition-metal dichalcogenides (TMDs); from the first-principle calculations, we predicted that the rich S vacancies on the nanosheet promoted electron transfer and reduced the energy barrier of electrocatalysis. As a substantiation, we conducted HER/OER electrochemical characterizations and found that the defect-rich atomic-thick tantalum sulfide is a kind of dual-function electrocatalyst with enhanced comprehensive properties of Tafel slope (39 mV/dec for HER, 38 mV/dec for OER) and low overpotential (0.099 V for HER, 0.153 V for OER) in acidic and alkaline environments, respectively. Likewise, the defect-rich catalysts exhibit high stability in acidic and alkaline solutions, which have potential applications as electrocatalysts for the large-scale production of hydrogen and oxygen.

Constructing 1 T-2 H TaS2 nanosheets with architecture and defect engineering for enhance hydrogen evolution reaction

Tailoring tantalum disulfide (TaS2) electrocatalysts with tunable stacking architecture and phase structure is of great importance for advancement of hydrogen evolution reaction (HER). In this work, stacking architecture- and phase- modulated tantalum disulfide nanosheets are reported through a facile liquid phase synthesis strategy. Accordion-like nanosheets, vertical nanosheets and ultrathin nanosheets are named according to their obvious stacking architecture, and 1 T-2 H mixed phase structures containing different degrees of 2 H phases are realized. High-resolution transmission electron microscopy shows that there are obvious lattice defects in the nanosheets. Tantalum disulfide nanosheets synergistically integrate multiple advantages of nanostructure engineering, phase engineering and defect engineering. In the HER process, the ultrathin tantalum disulfide nanosheet structure is conducive to the in-plane electron transfer, and its close contact with the electrode surface makes the charge transfer faster and has the best HER activity. The overpotential of the ultrathin nanosheet electrocatalyst at 10 mA cm−2 is 280 mV. After 10,000 CV cycles and over 40 h of i-t test, the catalyst still has high stability in acidic media. Theoretical calculations show that the addition of 2 H phase structure and rich defects improves the intrinsic activity and active sites, and jointly promotes the improvement of HER performance. Our work integrates a variety of optimal regulation methods into TaS2 nanosheets, providing a new idea for the construction of advanced electrocatalysts for water electrolysis.

Investigations on the electrochemistry and reactivity of tantalum species in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide using X-ray photoelectron spectroscopy (in situ and ex-situ XPS)

Tantalum is a metal whose properties enable it to be used in a wide range of technological applications. In the present work, the underlying electrochemical processes of tantalum species in ionic liquids (ILs) are investigated using in situ X-ray photoelectron spectroscopy (XPS) in ultra-high vacuum. For this purpose electrochemical deposition of tantalum on a gold wire from 0.1 mol/L TaF5 in a 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py1,4]TFSI) electrolyte was studied by in situ electrochemical XPS. The cyclic voltammogram shows two reduction peaks and one oxidation peak, indicating a complex electrochemical behaviour. The electrochemical in situ XPS gives evidence of a reduction reaction, although no metallic tantalum could be detected on the gold wire. In order to investigate the reactivity of tantalum in more detail, thin IL films were prepared on tantalum by physical vapor deposition and these were examined by XPS. Decomposition reactions were observed with the formation of subhalides, oxyfluorides, or tantalum sulfides, showing the decomposition of the ionic liquid. The decomposition products indicate the splitting of the C-F bond of the TFSI anion.

Broadband 1T-polytype tantalum disulfide saturable absorber for solid-state bulk lasers

1T-polytype tantalum disulfide ( 1 T-TaS 2 ), an emerging strongly correlated material, features a narrow bandgap of 0.2 eV, bridging the gap between zero-bandgap graphene and large-bandgap 2D nonlinear optical (NLO) materials. Combined with its intense light absorption, high carrier concentration, and high mobility, 1 T-TaS 2 shows considerable potential for applications in broadband optoelectronic devices. However, its NLO characteristics and related applications have rarely been explored. Here, 1 T-TaS 2 nanosheets are prepared by chemical vapor deposition. The ultrafast carrier dynamics in the 400–1100 nm range and broadband NLO performance in the 515–2500 nm range are systematically studied using femtosecond lasers. An obvious saturable absorption phenomenon is observed in the visible to IR range. The nonlinear absorption coefficient is measured to be − 22.60 ± 0.52 cm MW − 1 under 1030 nm, which is larger than that of other typical 2D saturable absorber (SA) materials (graphene, black phosphorus, and MoS 2 ) under similar experimental conditions. Based on these findings, using 1 T-TaS 2 as a new SA, passively Q-switched laser operations are successfully performed at 1.06, 1.34, and 1.94 μm. The results highlight the promise of 1 T-TaS 2 for broadband optical modulators and provide a potential candidate material system for mid-IR nonlinear optical applications.

Magnetic memory and spontaneous vortices in a van der Waals superconductor.

Doped Mott insulators exhibit some of the most intriguing quantum phases of matter, including quantum spin liquids, unconventional superconductors and non-Fermi liquid metals1-3. Such phases often arise when itinerant electrons are close to a Mott insulating state, and thus experience strong spatial correlations. Proximity between different layers of van der Waals heterostructures naturally realizes a platform for experimentally studying the relationship between localized, correlated electrons and itinerant electrons. Here we explore this relationship by studying the magnetic landscape of tantalum disulfide 4Hb-TaS2, which realizes an alternating stacking of a candidate spin liquid and a superconductor4. We report on a spontaneous vortex phase whose vortex density can be trained in the normal state. We show that time-reversal symmetry is broken in the normal state, indicating the presence of a magnetic phase independent of the superconductor. Notably, this phase does not generate ferromagnetic signals that are detectable using conventional techniques. We use scanning superconducting quantum interference device microscopy to show that it is incompatible with ferromagnetic ordering. The discovery of this unusual magnetic phase illustrates how combining superconductivity with a strongly correlated system can lead to unexpected physics.

2H Tantalum Disulfide Nanosheets as Substrates for Ultrasensitive SERS-Based Sensing

2H Tantalum Disulfide Nanosheets as Substrates for Ultrasensitive SERS-Based Sensing

Oxidation of tantalum disulfide (TaS2) films for gate dielectric and process design of two-dimensional field-effect device

Ta-based high-κ dielectrics can be synthesized via the oxidation of TaS2 films. In this study, we investigated the wet and dry oxidation of TaS2 films via thermal annealing and plasma irradiation, respectively. The specific vibration observed via Raman spectroscopy, the bonding states observed via x-ray photoelectron spectroscopy, and capacitance measurements confirmed the oxidation of TaS2 films with a dielectric constant of ∼14.9. Moreover, the electrical transport of the TaS2 films along the in-plane direction indicated a change in conductivity before and after the oxidation. The thickness of the oxidized film was estimated. Accordingly, the layer-by-layer oxidation was limited to approximately 50 nm via plasma irradiation, whereas the TaS2 films within 150 nm were fully oxidized via thermal annealing in ambient air. Therefore, a Ta-oxide/TaS2 structure was fabricated as a stack material of insulator and metal when the thickness of the pristine film was greater than 50 nm. In addition, Ta-oxide films were integrated into bottom-gated two-dimensional (2D) field-effect transistors (FETs) using the dry transfer method. 2D FETs with multilayer MoTe2 and MoS2 films as p-type and n-type channels, respectively, were successfully fabricated. In particular, the Ta-oxide film synthesized via dry oxidation was used as a gate dielectric, and the device process could be simplified because the Ta-oxide/TaS2 heterostructure can function as a stack material for gate insulators and gate electrodes. An anti-ambipolar transistor consisting of an MoTe2/MoS2 heterojunction was also fabricated. For the transfer characteristics, a relatively sharp on-state bias range below 10 V and sufficiently high peak-to-valley ratio of 106 at V DS = 3 V were obtained using the high-κ gate dielectric of Ta-oxide despite the presence of the multilayer channels (∼20 nm).

Structure and Magnetism of Iron- and Chromium-Intercalated Niobium and Tantalum Disulfides.

Transition metal dichalcogenides (TMDs) intercalated with spin-bearing transition metal centers are a diverse class of magnetic materials where the spin density and ordering behavior can be varied by the choice of host lattice, intercalant identity, level of intercalation, and intercalant disorder. Each of these degrees of freedom alters the interplay between several key magnetic interactions to produce disparate collective electronic and magnetic phases. The array of magnetic and electronic behavior typified by these systems renders them distinctive platforms for realizing tunable magnetism in solid-state materials and promising candidates for spin-based electronic devices. This Perspective provides an overview of the rich magnetism displayed by transition metal-intercalated TMDs by considering Fe- and Cr-intercalated NbS2 and TaS2. These four exemplars of this large family of materials exhibit a wide range of magnetic properties, including sharp switching of magnetic states, current-driven magnetic switching, and chiral spin textures. An understanding of the fundamental origins of the resultant magnetic/electronic phases in these materials is discussed in the context of composition, bonding, electronic structure, and magnetic anisotropy in each case study.

Photo-induced exfoliation—A facile synthesis route for atomristor prototype

Brain inspired memory prototypes, such as atomristors, are touted as next generation two terminal memories for neuromorphic computation. To make rapid progress toward developing such atomic scale memory, a facile technique to fabricate atomristor prototypes has to be developed. In this work, one such simple and lithography free technique to fabricate an atomristor prototype using photoexfoliated monolayer molybdenum di-sulfide (MoS2) is illustrated. Resistive switching characteristics of the atomristor were demonstrated by applying a write voltage pulse of 10 (SET) and −5 V (RESET) for 100 s between the active tantalum di-sulfide (TaS2) and inert indium tin oxide electrodes. During the SET process (ON state), the Ta2+ ions from the active electrode diffuse through monolayer MoS2 to create a number of parallel conducting channels. The persistence of the conducting channel even after removing the SET bias drives the atomristor to the low resistance state. On applying the “RESET” bias, the device resistance increased by a factor of five possibly due to the rupturing of the conducting channel. On cyclically applying the “SET” and “RESET” biases, the device was switched between low and high resistance states with excellent repeatability. Interestingly, it was also observed that the switching ratio increased on increasing the SET bias making this device a promising candidate for realizing tunable write once read many (WORM) memory devices.

Wound Healing Properties and Structural Analysis of Four Geographical Areas’ Natural Clays

Clays are fine particle materials that harden after drying. The difference in their structure is the key to their efficacy and their subsequent application. The current study aims to evaluate the wound healing property of four countries (C1:Iraq, C2:Turkey, C3:Azerbaijan and C4:Russia) clay samples by excision model using Sprague dawley rats also the chemical analysis of the samples was performed using X-ray diffraction (XRD) and X-ray Fluorescence (XRF) methods. Results revealed that the best wound healing activities were given by C1, C3, C4 and C2 respectively with healing percentages (76%, 71%, 62%, and 60%), respectively. XRD results revealed the presence of Calcium carbonate and CalciumMagnesium carbonate in C1, Dolomite and Calcium-Magnesium carbonate in C2, Cobalt Tantalum Sulfide in C3, Finally Quartz and Silicon Oxide in C4. On the other hand, XRF analysis showed the appearance of different major and trace elements with different quantities in each clay type. We conclude that different countries clays enclose wound healing property with diverse ranges and this diversity is due to their chemical and mineral structures.

Ab initio theory of magnetism in two-dimensional 1T−TaS2

We investigate, using a first-principles density-functional methodology, the nature of magnetism in monolayer $1T$-phase of tantalum disulfide ($1T$-TaS$_2$ ). Magnetism in the insulating phase of TaS$_2$ is a longstanding puzzle and has led to a variety of theoretical proposals including notably the realization of a two-dimensional quantum-spin-liquid phase. By means of non-collinear spin calculations, we derive $\textit{ab initio}$ spin Hamiltonians including two-spin bilinear Heisenberg exchange, as well as biquadratic and four-spin ring-exchange couplings. We find that both quadratic and quartic interactions are consistently ferromagnetic, for all the functionals considered. Relativistic calculations predict substantial magnetocrystalline anisotropy. Altogether, our results suggest that this material may realize an easy-plane XXZ quantum ferromagnet with large anisotropy.

Tantalum disulfide nanosheets for the generation of polarization domain wall solitons and polarization locked vector solitons

Tantalum disulfide (TaS2) has been employed for catalysis and optical switch due to its tunable band gap, strong photoluminescence, and controllable size. However, its nonlinear optical response and applications in ultrafast optics have not been exploited. In this work, TaS2 based saturable absorber (TaS2-SA) is prepared, which exhibits strong saturable absorption characteristics with modulation depth of 8.5%. Based on the TaS2-SA, polarization domain wall solitons and polarization locked vector solitons are successfully realized. To the best of our knowledge, this is the first study of the polarization characteristics of TaS2 based fiber lasers. Our findings suggest that TaS2 is a promising nonlinear optical material and provide a valuable method for the development of TaS2 based ultrafast photonic devices.

Four-phonon and electron-phonon scattering effects on thermal properties in two-dimensional 2H-TaS2.

Thermal transport characteristics of monolayer trigonal prismatic tantalum disulfide (2H-TaS2) are investigated using first-principles calculations combined with the Boltzmann transport equation. Due to a large acoustic-optical phonon gap of 1.85 THz, the four-phonon (4ph) scattering significantly reduces the room-temperature phononic thermal conductivity (κph). With the further inclusion of phonon-electron scattering, κph reduces to 1.78 W mK-1. Nevertheless, the total thermal conductivity (κtotal) of 7.82 W mK-1 is dominated by the electronic thermal conductivity (κe) of 6.04 W mK-1. Due to the electron-phonon coupling, κe differs from the typical estimation based on the Wiedemann-Franz law with a constant Sommerfeld value. This work provides new insights into the physical mechanisms for thermal transport in metallic 2D systems with strong anharmonic and electron-phonon coupling effects. The phonon scattering beyond three-phonon (3ph) scattering and even κe are typically overlooked in computations, and the constant Sommerfeld value is widely used for separating κe and κph from the experimental thermal conductivity. These conclusions have implications for both the computational and experimental measurements of the thermal properties of transition metal dichalcogenides.

Vacancy assisted growth of copper tantalum sulfide nanocrystals

Cu3TaS4, a ternary chalcogenide, is a promising photovoltaic material. The growth of Cu3TaS4 occurs via the formation of Cu2−xS with Cu vacancies. Ta incorporation occurs in the Cu2−xS at Cu vacancy sites, followed by diffusion of Ta to form Cu3TaS4.

Toward nonthermal control of excited quantum materials: framework and investigations by ultrafast electron scattering and imaging

Quantum material systems upon applying ultrashort laser pulses provide a rich platform to access excited material phases and their transformations that are not entirely like their equilibrium counterparts. The addressability and potential controls of metastable or long-trapped out-of-equilibrium phases have motivated interests both for the purposes of understanding the nonequilibrium physics and advancing the quantum technologies. Thus far, the dynamical spectroscopic probes eminently focus on microscopic electronic and phonon responses. For characterizing the long-range dynamics, such as order parameter fields and fluctuation effects, the ultrafast scattering probes offer direct sensitivity. Bridging the connections between the microscopic dynamics and macroscopic responses is central toward establishing the nonequilibrium physics behind the light-induced phases. Here, we present a path toward such understanding by cross-examining the structure factors associated with different dynamical states obtained from ultrafast electrons scattering, imaging, and modeling. We give the basic theoretical framework on describing the non-equilibrium scattering problems and briefly describe how such framework relates to the out-of-equilibrium phenomena. We give effective models outlining the emergences of nonthermal critical points, hidden phases, and non-equilibrium relaxational responses from vacuum-suspended rare?earth tritellurides, tantalum disulfides thin films, and vanadium dioxide nanocrystalline materials upon light excitations.

Engineering Domain Wall Electronic States in Strongly Correlated van der Waals Material of 1T-TaS2.

Although a few physical methods were demonstrated for domain wall engineering in various electronic or ferroic materials with broken discrete symmetries, the direct control over the electronic properties of individual domain walls has been extremely limited. Here, we introduce a chemical method to tune the electronic property of domain walls in 1T tantalum disulfide. By using scanning tunneling microscopy and spectroscopy techniques, we find that indium adatoms on 1T-TaS2 have distinct behaviors on the domains with different bulk terminations. Moreover, the adatoms form their own chains along the edges of neighboring domains. The density functional theory calculations reveal a 1D Mott insulating state on a modified domain wall, resulting from the degenerated spin-polarized bands with electron doping from adsorbates and charge transfer from neighboring domains. This work suggests that chemical decoration by adsorbates can be widely used to tune local electronic states of domain walls and various 2D materials.

Synthesis of vertically aligned wafer-scale tantalum disulfide using high-Ar/H2S ratio plasma

Nanostructural modification of two-dimensional (2D) materials has attracted significant attention for enhancing hydrogen evolution reaction (HER) activity. In this study, the nanostructure of TaS2 films was controlled by controlling the Ar/H2S gas ratio used in plasma-enhanced chemical vapor deposition (PECVD). At a high Ar/H2S gas ratio, vertically aligned TaS2 (V-TaS2) films were formed over a large-area (4 in) at a temperature of 250 °C, which, to the best of our knowledge, is the lowest temperature reported for PECVD. Furthermore, the plasma species formed in the injected gas at various Ar/H2S gas ratios were analyzed using optical emission spectroscopy to determine the synthesis mechanism. In addition, the 4 in wafer-scale V-TaS2 was analyzed by x-ray photoelectron spectroscopy, transmission electron microscopy, and atomic force microscopy, and the HER performance of the as-synthesized TaS2 fabricated with various Ar/H2S ratios was measured. The results revealed that, depending on the film structure of TaS2, the HER performance can be enhanced owing to its structural advantage. Furthermore, the excellent stability and robustness of V-TaS2 was confirmed by conducting 1000 HER cycles and post-HER material characterization. This study provides important insights into the plasma-assisted nanostructural modification of 2D materials for application as enhanced electrocatalysts.