Transition Metal Trichalcogenides Research Articles

Strong anisotropic transport properties of quasi-one-dimensional ZrTe3 nanoribbons

Transition metal trichalcogenides (TMTCs) with quasi-one-dimensional (quasi-1D) structures have attracted extensive interest in diverse fields because of their unique electronic properties. Herein, we report strong in-plane anisotropic transport properties of ZrTe3 nanoribbons, which originate from their quasi-1D structures. ZrTe3 nanoribbons were mechanically exfoliated from bulk single crystals, and transport properties, including electrical conductivity (σ) and Seebeck coefficient (S), were measured in the longitudinal and transverse directions of the rectangular nanoribbons. σ was higher in the transverse direction than that in the longitudinal direction. S measurement revealed further clear anisotropic characteristics, and positive and negative S values were obtained in the longitudinal and transverse directions, respectively. Furthermore, a significant change in the transport properties was observed with a post treatment, and the potential of ZrTe3 for transport property modulation was confirmed. We believe that our findings will contribute to the understanding of anisotropic transport in quasi-1D ZrTe3 and expansion of the application fields of quasi-1D ZrTe3.

From Insulator to Superconductor: A Series of Pressure-Driven Transitions in Quasi-One-Dimensional TiS3 Nanoribbons.

Transition metal trichalcogenides (TMTCs) offer remarkable opportunities for tuning electronic states through modifications in chemical composition, temperature, and pressure. Despite considerable interest in TMTCs, there remain significant knowledge gaps concerning the evolution of their electronic properties under compression. In this study, we employ experimental and theoretical approaches to comprehensively explore the high-pressure behavior of the electronic properties of TiS3, a quasi-one-dimensional (Q1D) semiconductor, across various temperature ranges. Through high-pressure electrical resistance and magnetic measurements at elevated pressures, we uncover a distinctive sequence of phase transitions within TiS3, encompassing a transformation from an insulating state at ambient pressure to the emergence of an incipient superconducting state above 70 GPa. Our findings provide compelling evidence that superconductivity at low temperatures of ∼2.9 K is a fundamental characteristic of TiS3, shedding new light on the intriguing high-pressure electronic properties of TiS3 and underscoring the broader implications of our discoveries for TMTCs in general.

Salt-Assisted Vapor-Liquid-Solid Growth of 1D van der Waals Materials.

The method of salt-assisted vapor-liquid-solid (VLS) growth is introduced to synthesize 1D nanostructures of trichalcogenide van der Waals (vdW) materials, exemplified by niobium trisulfide (NbS3). The method uses a unique catalyst consisting of an alloy of Au and an alkali metal halide (NaCl) to enable rapid and directional growth. High yields of two types of NbS3 1D nanostructures, nanowires and nanoribbons, each with sub-ten nanometer diameter, tens of micrometers length, and distinct 1D morphology and growth orientation are demonstrated. Strategies to control the location, size, and morphology of growth, and extend the growth method to synthesize other transition metal trichalcogenides, NbSe3 and TiS3, as nanowires are demonstrated. Finally, the role of the Au-NaCl alloy catalyst in guiding VLS synthesis is described and the growth mechanism based on the relationships measured between structure (growth orientation, morphology, and dimensions) and growth conditions (catalyst volume and growth time) is discussed. These results introduce opportunities to expand the library of emerging 1D vdW materials to make use of their unique properties through controlled growth at nanoscale dimensions.

Fast Charge‐Transfer Rates in Li‐CO2 Batteries with a Coupled Cation‐Electron Transfer Process

AbstractLi‐CO2 batteries with a high theoretical energy density (1876 Wh kg−1) have unique benefits for reversible carbon fixation for energy storage systems. However, due to lack of stable and highly active catalysts, the long‐term operation of Li‐CO2 batteries is limited to low current densities (mainly <0.2 mA cm−2) that are far from practical conditions. In this work, it is discovered that, with an ionic liquid‐based electrolyte, highly active and stable transition metal trichalcogenide alloy catalysts of Sb0.67Bi1.33X3 (X = S, Te) enable operation of the Li‐CO2 battery at a very high current rate of 1 mA cm−2 for up to 220 cycles. It is revealed that: i) the type of chalcogenide (Te vs S) significantly affects the electronic and catalytic properties of the catalysts, ii) a coupled cation‐electron charge transfer process facilitates the carbon dioxide reduction reaction (CO2RR) occurring during discharge, and iii) the concentration of ionic liquid in the electrolyte controls the number of participating CO2 molecules in reactions. A combination of these key factors is found to be crucial for a successful operation of the Li‐CO2 chemistry at high current rates. This work introduces a new class of catalysts with potential to fundamentally solve challenges of this type of batteries.

Advancing intrinsic carrier mobility estimation in transition metal trichalcogenide monolayers using DFT-BTE

The Boltzmann transport equation (BTE) based intrinsic carrier mobility estimation significantly improves accuracy, which is crucial for assessing the performances of the materials within the devices. Herein, we explore the highly anisotropic, semiconducting 2D transition metal trichalcogenide monolayers (TMTC) MX3 (M = Ti, Zr, Hf and X = S, Se) for their transport properties. Remarkably, the electron carrier mobility obtained by combining BTE with density functional theory (DFT) in TiS3 monolayer has reached ∼1400 cm2/V.s. This finding stands in stark contrast to the electron mobility of ∼104 cm2/V·s obtained using a formalism built on the effective mass approximation. The marked disparity in mobility estimation underscores the crucial role played by the BTE in elevating precision. Alongside, a pronounced anisotropy in carrier mobility has been observed in these monolayers, particularly concerning lattice directions and electron-to-hole carrier mobility. Overall, this study seeks to fill out the voids and focuses on accurate estimation of high carrier mobility in TMTC monolayers using DFT-BTE.

First-principles prediction of a two-dimensional semiconductor ferromagnetism in Cr2X2Se6 (X = Al, Ga, In) materials

Based on first-principles calculations, I have predicted the existence of a new class of two-dimensional (2D) transition-metal tri-chalcogenides (TMTCs) materials with the chemical formula Cr2X2Se6 (X = Al, Ga, In). The molecular dynamics and phonon dispersion calculations showed that these materials are thermally and dynamically stable, suggesting that they can be synthesized in the laboratory. Cr2X2Se6 structures are all semiconductors with an indirect bandgap, and the bandgap sizes decrease as the X atom changes from Al to Ga to In. For instance, the bandgaps of Cr2Al2Se6, Cr2Ga2Se6, and Cr2In2Se6 are 1.29, 0.91, and 0.86 eV, respectively. The Cr2X2Se6 monolayer structures exhibit ferromagnetic order and possess an out-of-plane magnetic anisotropy energy (MAE), which increases in magnitude from Al to In along the periodic table. The Curie temperature (Tc) of Cr2X2Se6 monolayers was determined using Monte Carlo simulations based on Heisenberg's model. The Tc exhibited the expected dependence on X atoms. The Cr2X2Se6 monolayers exhibit strong absorption and reflection coefficients in the visible region, with an absorption coefficient of about 105 cm−1. Overall, the discovery and development of new 2D materials with interesting electronic, magnetic, and optical properties offer many opportunities for developing new spintronic and magneto-optical devices that can be used in many different applications.

Flexibility and anisotropy of MX3 (M = Zr, Hf; X = S, Se): New semiconductors with high photovoltaic performance

Optoelectronic functional materials with flexible and in-plane anisotropic properties has been a significant development direction of nanotechnology due to wearable and polarized optoelectronic applications. Herein, the elasticity, global band dispersion, optical dielectric properties of environmentally friendly IVB-VIA layered transition metal trichalcogenides (MX3, M = Zr, Hf; X = S, Se) are investigated systematically by density functional theory with different kinds of van der Waals correction and hybrid functional. The low elastic modulus suggests that they are appropriate for the design of flexible optoelectronic devices. Originating from the effect of d states of chalcogens and s states of transition metals, the dispersion of the valence band edge of monolayer MX3 shows that the effective mass of carriers along the wave vector kx is much heavier than that of carriers along the wave vector ky. This means that the mobility of carriers exhibits obvious in-plane anisotropy. Meanwhile, the optical dielectric properties of monolayer MX3 as well as absorbed photon flux (Jabs) of the related heterostructures display noteworthy in-plane anisotropy in the visible-IR region. The ratio of Jabs from different direction reaches up to 1.7. This work could not only promote understanding of rich photophyiscal properties of transition metal trichalcogenides, but also provide a theoretical reference for the invention of high-performance optoelectronic devices with high flexibility and anisotropy.

Establishing stability of the novel layered ternary tri-chalogenide materials: Emergence of a new generation of earth abundant HER catalysts

Energetic and structural stability of thirteen novel ternary transition metal tri-chalcogenide layers, claimed to be promising catalysts for hydrogen evolution reaction (HER), are studied. Detailed analyses of electronic structure, and mechanical and phonon properties establish that ten out of the thirteen materials are stable. Further analyses establish that these are chemically in the same class as the known layered ternary transition metal tri-chalcogenide materials. These lead us to claim that it should be possible to synthesize these materials experimentally, thus enlarging the list of candidate materials that can replace platinum as HER catalysts.

Laser irradiation induced structural transformation in layered transition metal trichalcogenide nanoflakes

Laser irradiation is a powerful tool in inducing changes in lattice structures and properties of two-dimensional (2D) materials through processes such as heating, bleaching, catalysis, etc. However, the underlying mechanisms of such transformations vary dramatically in different 2D materials. Here, we report the structural transformation of layered titanium trisulfide (TiS3) to titanium disulfide (TiS2) after irradiation. We systematically characterized the dependence of the transformation on laser power, flake thickness, irradiation time, and vacuum conditions using microscopic and spectroscopic methods. The underlying mechanism is confirmed as the heat-induced materials decomposition, a process that also occurs in many other transition metal trichalcogenide materials. Furthermore, we demonstrate that this spatial-resolved method also enables the creation of in-plane TiS3-TiS2 heterostructures. Our study identifies a new family of 2D materials that undergo a structural transformation after laser irradiation and enriches the methods available for developing new prototypes of low-dimensional devices in the future.

Augmenting bi-functional catalytic efficiency in vanadium based pseudo-monolayer: Chemical paradigm of functionalization, vacancy and external stimuli

Since the exfoliation of graphene, two-dimensional (2D) ultrathin materials have attracted a lot of attention in several applications for energy harvesting for the ongoing quest for green and sustainable environment. One of such ultrathin materials could be envisaged in the form transition metal tri-chalcogenide based 2D pseudo-monolayers. In this theoretical work, we have rigorously investigated the bi-functional catalytic reaction mechanism corresponding to water-splitting on vanadium-based tri-chalcogenide monolayers VS3. The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are the two main reactions which consist water splitting process, which are being explored in VS3 system from the perspective of first principles electronic structure calculations within the framework of density functional theory (DFT) formalism. We have explored the effect of functionalization, vacancy induced defect and external strain (both bi-axial and uni-axial) on the catalytic activity, which can be reflected from the over-potential corresponding to the reaction coordinate mapping constructed from the adsorption free energy values. We have also determined the projected density of states, work function, charge density distribution and correlated all such electronic structure analysis with the catalytic activity enhancement in the VS3 pseudo monolayer. Overall, we have investigated the competing effect of strain, functionalization, and vacancy induced defect on the bi-functional catalytic activity enhancement, which can be further experimentally validated for efficient hydrogen generation. Our systematic electronic structure calculations reveals the defected and nitrogen doped VS3 as the promising candidate for HER and OER activity respectively, which have been further enhanced under the influence of external strain.

Magnetic Second‐Order Topological Insulator: An Experimentally Feasible 2D CrSiTe3

Abstract2D second‐order topological insulators (SOTIs) have sparked significant interest, but currently, the proposed realistic 2D materials for SOTIs are limited to nonmagnetic systems. In this study, for the first time, a single layer of chalcogenide CrSiTe3—an experimentally realized transition metal trichalcogenide is proposed with a layer structure—as a 2D ferromagnetic (FM) SOTI. Based on first‐principles calculations, this study confirms that the CrSiTe3 monolayer exhibits a nontrivial gapped bulk state in the spin‐up channel and a trivial gapped bulk state in the spin‐down channel. Based on the higher‐order bulk–boundary correspondence, it demonstrates that the CrSiTe3 monolayer exhibits topologically protected corner states with a quantized fractional charge () in the spin‐up channel. Notably, unlike previous nonmagnetic examples, the topological corner states of the CrSiTe3 monolayer are spin‐polarized and pinned at the corners of the sample in real space. Furthermore, the CrSiTe3 monolayer retains SOTI features when the spin–orbit coupling (SOC) is considered, as evidenced by the corner charge and corner states distribution. Finally, by applying biaxial strain and hole doping, this study transforms the magnetic insulating bulk states into spin‐gapless semiconducting and half‐metallic bulk states, respectively. Importantly, the topological corner states persist in the spin‐up channel under these conditions.

Lithium superoxide-based high rate Li-Air batteries enabled by Di-iridium sulfur bridge active sites

Li-oxygen (Li-O2) batteries can potentially provide much higher energy density than Li-ion batteries; however, the practical application of these batteries is hindered due to several drawbacks such as low current rates and high overpotential for the charging process. In this paper, we report a novel Li-Air battery system that operates under high current rates (up to 1mAcm−2) with LiO2 as the primary discharge product instead of the commonly reported Li2O2. This LiO2 based battery at high rates is through a combination of an as-synthesized new one-dimensional (1D) transition metal trichalcogenide mid-entropy alloy of SnIrS3.6 as a cathode catalyst and an electrolyte blend with a SnI2 bi-functional additive. It is revealed that SnIrS3.6 has a microporous structure composed of six- and five-coordinated metal atoms, forming octahedral and triangular bipyramids which has not been observed in other layered chalcogeide materials. DFT calculations reveal that the SnIrS3.6 structure can result in LiO2 formation through di-iridium sulfur bridge active sites that results in strong binding of O2 and LiO2 preventing disproportionation to Li2O2 and enabling high rates. This finding will open a new perspective in designing advanced LiO2-based Li-O2 batteries for real practices.

Synergistic Effect of TiS3 and Ti3C2Tx MXene for Temperature-Tunable p-/n-Type Gas Sensing

We propose a strategy for highly tunable gas sensors, in which a MXene is combined with a sacrificial material that could be controllably oxidized upon mild annealing to form oxide nanoparticles that alter the sensing response. A controlled annealing of such composite generally retains the integrity of MXene sheets while gradually converting the sacrificial material to a metal oxide that could form semiconductor heterojunctions with MXene, fine-tuning its sensor properties. This strategy is demonstrated using gas sensors based on Ti3C2Tx MXene mixed with TiS3, a semiconducting transition metal trichalcogenide. Compared to pristine MXene, the Ti3C2Tx-TiS3 composite exhibited a significantly improved sensor response to ethanol, which served as a model analyte, both at room temperature and upon annealing. Furthermore, as a less thermally stable material than the MXene, TiS3 oxidizes faster than Ti3C2Tx at elevated temperatures, producing TiO2 nanoparticles that strongly affect the sensing response. A pristine Ti3C2Tx exhibits a p-type sensor response to ethanol at room temperature. Upon annealing, Ti3C2Tx gradually degrades to TiO2, changing the sensor response to n-type above ∼300 °C. The addition of TiS3 allows for the general preservation of MXene as the sensor material, as the temperature of the p–n transition decreases to about 200 °C, at which Ti3C2Tx is generally stable. This approach can likely be applied to a great variety of combinations of various MXenes and sacrificial compounds with sensor properties that could be tuned via annealing for specific analytes or applications.

Intertwined electronic and magnetic structure of the van-der-Waals antiferromagnet Fe2P2S6

Many unusual and promising properties have been reported recently for the transition metal trichalcogenides of the type MPS3 (M = V, Mn, Fe, Ni ...), such as maintaining magnetic order to the atomically thin limit, ultra-sharp many-body excitons, metal-insulator transitions and, especially for Fe2P2S6, giant linear dichroism among others. Here we conduct a detailed investigation of the electronic structure of Fe2P2S6 using angle-resolved photoemission spectroscopy, q-dependent electron energy loss spectroscopy, optical spectroscopies and density functional theory. Fe2P2S6 is a Mott insulator with a gap of Egap ≈ 1.4 eV and zigzag antiferromagnetism below TN = 119 K. The low energy excitations are dominated by Fe 3d states. Large and sign-changing linear dichroism is observed. We provide a microscopic mechanism explaining key properties of the linear dichroism based on the correlated character of the electronic structure, thereby elucidating the nature of the spin-charge coupling in Fe2P2S6 and related materials.

Polarization‐Driven Ultrafast Optical Switching in TiS3 Nanoribbons via Anisotropic Hot Carrier Dynamics

AbstractLayered quasi‐1D nanomaterials exhibit strong linear dichroism and effective light‐matter interactions, promising for novel information devices driven by light‐polarization. In particular, their optical anisotropy and ultrafast photoresponse allow for polarization‐controlled nanophotonic switches and modulators. However, the technology still requires substantial further studies due to an insufficient understanding of modulation mechanisms and limited investigations of a few materials. Here, transient absorption (TA) microscopy is employed to investigate the ultrafast polarization‐based optical switching in TiS3 nanoribbons, a rising quasi‐1D material of the transition metal trichalcogenide family. Highly anisotropic sub‐picosecond near‐infrared modulation is observed, which is most pronounced when the polarization of the probe pulse is aligned with the nanoribbon axis but disappears as the polarization is rotated to the perpendicular orientation. The authors attribute this significant dependence on the probe polarization to the hot carrier‐induced broadening of an anisotropic interband resonance, as supported by analyses of transient TA line shapes and first principles calculated optical transitions. Furthermore, a strong pump polarization‐dependent modulation is obtained by tuning the pumping energy, enabling highly anisotropic all‐optical switching controlled solely by polarization. These results offer comprehensive information on both probe‐ and pump‐polarization‐based modulations and a deeper physical understanding of polarization‐dependent photoresponse through ultrafast hot carrier dynamics.

First principle calculations: The electronic, optical, mechanical, and vibrational properties of TiS3

The computational predictions of transition-metal tri-chalcogenide (TMTCs) were performed using ab initio density functional theory (DFT) to investigate the electronic band structure, the partial density of states (PDOS), optical absorptions, dielectric functions, complex conductivity, reflectivity, refractive index, electron loss, the Poisson’s ratio, Young’s modulus, bulk-to-shear ratio, and phonon dispersion. The bandgap is measured from the valence band maximum (VBM) to the conduction band minimum (CBM) with the G–Z transitions. This suggests that the material is an indirect bandgap semiconductor. The electronic bandgap ([Formula: see text] is significantly improved with nonlocal hybrid functionals, especially in HSE0s, with [Formula: see text] of 1.0[Formula: see text]eV, which is in excellent agreement with the experimental data. However, our data shows that the HF-LDA exchange correlations significantly overestimate the [Formula: see text] with 7.33[Formula: see text]eV. Also, our optical absorption data indicates a high absorption coefficient of about [Formula: see text][Formula: see text]cm[Formula: see text]. The absorption peak of 7.4[Formula: see text]eV indicates TiS3 can be applied in vacuum ultra-violet (VUV) applications. The reflectivity is also shown to be high, with over 90% of light being reflected. The mechanical stability of the monoclinic system can be testified by our elastic coefficients and the phonon dispersions.

Intercalation on Transition Metal Trichalcogenides via a Quasi‐Amorphous Phase with 1D Order (Adv. Funct. Mater. 10/2023)

Transition Metal Trichalcogenides In article number 2208702, Masaya Fujioka and co-workers successfully intercalate ions into 1D structural transition metal trichalcogenides with a trigonal prismatic structure, leading to a 1D structural intercalation compound with an octahedral structure through a quasi-amorphous phase. This unique amorphous phase with 1D order has the potential to exhibit various functions depending on the ion concentration. Here they show that the two crystal phases with trigonal prismatic and octahedral structures are connected via a quasi-amorphous phase.

Study of ZrS3-based field-effect transistors toward the understanding of the mechanisms of light-enhanced gas sensing by transition metal trichalcogenides

Study of ZrS3-based field-effect transistors toward the understanding of the mechanisms of light-enhanced gas sensing by transition metal trichalcogenides

Universal scaling between on-site Coulomb repulsion and numbers of core and valence electrons in transition metal trichalcogenides

Electron correlations that determine a broad spectrum of the physical properties of transition metal compounds are largely manifested by the on-site Coulomb repulsion U, which so far has been mainly evaluated on a case-by-case basis. Here we employ a linear response method based on constrained local density approximation to systematically investigate U in representative classes of transition metal trichalcogenides, with the transition metals covering all the unfilled 3d, 4d, and 5d orbitals. We uncover a characteristic scaling dependence of U on two elemental physical parameters, namely, the numbers of the core and valence electrons. Such a universal scaling law reflects the intuition that more unfilled d electrons residing on a smaller spherical core will feel stronger Coulomb repulsion. Next, by using the artificial intelligence-based SISSO (Sure Independence Screening and Sparsifying Operator) approach, we identify a more sophisticated descriptor that not only further refines the scaling law, but also captures the crystal-field splitting effect as pictorially reflected by invoking an elliptical core instead of a spherical core. The approach developed in this study should find transferability in other classes of transition metal compounds.

Intercalation on Transition Metal Trichalcogenides via a Quasi‐Amorphous Phase with 1D Order

AbstractIntercalation into 1D transition metal trichalcogenides (TMTs) in which fibers are bonded by a weak van der Waals force can be expected to create various intercalation compounds and develop unique physical properties according to the combination of the host materials and guest ions. However, structural changes via intercalation into 1D TMTs are not as simple as those in 2D transition metal dichalcogenides (TMDs) and are still not understood comprehensively. ZrTe3: a typical compound with a 1D trigonal prismatic structure, belongs to TMTs. Herein, through the Ag introduction to ZrTe3 via solid‐state intercalation, a novel crystal phase with a 1D octahedral structure and a quasi‐amorphous (QA) phase during the structural transition are discovered; the QA phase is a novel state of matter in which long‐range order is lost while retaining 1D order. Based on the Ag concentration, the transport properties are flexibly modulated from superconductivity to semiconductivity. Density functional theory calculations indicate the attraction between Ag ions and the pair diffusion due to their attraction. Furthermore, judging the attraction or repulsion between guest ions predicts whether to induce a QA phase or simple lattice expansion like the intercalation into 2D TMDs.