Ferromagnetic and nonmagnetic 1T′ charge density wave states in transition metal dichalcogenides: Physical mechanisms and charge doping induced reversible transition (original) (raw)
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2020
Single-layer transition metal dichalcogenides (TMDCs) can adopt two distinct structures corresponding to different coordination of the metal atoms. TMDCs adopting the T-type structure exhibit a rich and diverse set of phenomena, including charge density waves (CDW) in a √(13)×√(13) supercell pattern in TaS_2 and TaSe_2, and a possible excitonic insulating phase in TiSe_2. These properties make the T-TMDCs desirable components of layered heterostructure devices. In order to predict the emergent properties of combinations of different layered materials, one needs simple and accurate models for the constituent layers which can take into account potential effects of lattice mismatch, relaxation, strain, and structural distortion. Previous studies have developed ab initio tight-binding Hamiltonians for H-type TMDCs [arXiv:1709.07510]. Here we extend this work to include T-type TMDCs. We demonstrate the capabilities of our model using three example systems: a 1-dimensional sinusoidal ripp...
The Recent Progress of Two-Dimensional Transition Metal Dichalcogenides and Their Phase Transition
Crystals
Graphene is attracting much attention in condensed matter physics and material science in the two-dimensional(2D) system due to its special structure, and mechanical and electronic properties. However, the lack of electronic bandgap and uncontrollable phase structure greatly limit its application in semiconductors, such as power conversion devices, optoelectronic devices, transistors, etc. During the past few decades, 2D transition metal dichalcogenides (TMDs) with much more phase structures have attracted intensive research interest in fundamental studies and practical applications for energy storage, as catalysts, and in piezoelectricity, energy harvesting, electronics, optoelectronic, and spintronics. The controllable phase transition also provides another degree of freedom to pave the way for more novel devices. In this review, we introduce the abundant phase structures of 2D-TMDs, including 2H, 1T, 1T’ and charge density waves, and highlight the corresponding attractive propert...
2020
Daniel T. Larson ,1 Wei Chen ,1,2 Steven B. Torrisi,1 Jennifer Coulter,3 Shiang Fang ,1,4,* and Efthimios Kaxiras1,3,† 1Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA 2Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, USA 3John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA 4Department of Physics and Astronomy, Center for Materials Theory, Rutgers University, Piscataway, New Jersey 08854, USA
Two-Dimensional Transition Metal Dichalcogenide Alloys: Stability and Electronic Properties
The Journal of Physical Chemistry Letters, 2012
Using density-functional theory calculations, we study the stability and electronic properties of single layers of mixed transition metal dichalcogenides (TMDs), such as MoS 2x Se 2(1−x) , which can be referred to as two-dimensional (2D) random alloys. We demonstrate that mixed MoS 2 /MoSe 2 / MoTe 2 compounds are thermodynamically stable at room temperature, so that such materials can be manufactured using chemical-vapor deposition technique or exfoliated from the bulk mixed materials. By applying the effective band structure approach, we further study the electronic structure of the mixed 2D compounds and show that general features of the band structures are similar to those of their binary constituents. The direct gap in these materials can continuously be tuned, pointing toward possible applications of 2D TMD alloys in photonics. SECTION: Plasmonics, Optical Materials, and Hard Matter I n many bulk ternary semiconductor compounds, such as GaInAs 1 or CdZnTe, 2 the band gap depends continuously on constituent composition, making it possible to tune the electronic and optical properties of these materials for uses in specific applications, such as solar cells, radiation detectors, or gas sensors. 3,4 These compounds are random substitutional alloys without translational long-range order. Recently, several two-dimensional (2D) materials, such as graphene, 5 hexagonal boron-nitride (h-BN), 6 and silica bilayer 7,8 were manufactured. These nanostructures possess many fascinating properties that can be used in various applications. 9 Notably, graphene is a semimetal, while h-BN is a wide gap semiconductor. Taking into account the similarities in the atomic structure of these two materials, the possibilities for creating a mixed BCN system with a gap tunable by component concentration have been envisioned. However, theory 10,11 and experiments 12 have indicated that 2D BCN materials are thermodynamically unstable and that h-BN and graphene tend to segregate. This approach, however, may prove to be successful in 2D transition metal dichalcogenides (TMDs). Most of the bulk TMDs are layered compounds with a common structural formula MeCh 2 , where Me stands for transition metals (Mo, W, Ti, etc.) and Ch for chalcogens (S, Se, Te), similar crystal structure and lattice constants. Like graphene and h-BN, 2D TMDs can be manufactured not only by mechanical 9,13 and chemical 14,15 exfoliation of their layered bulk counterparts, but also directly by chemical vapor deposition (CVD) 16−18 or twostep thermolysis. 19 These 2D materials are expected to have electronic properties varying from metals to wide-gap semiconductors, as their bulk counterparts, 20,21 and excellent mechanical characteristics. 22,23 Several nanoelectronic 13,24 and
npj 2D Materials and Applications
Using first-principles calculations, we investigate the magnetic order in two-dimensional (2D) transition-metal-dichalcogenide (TMD) monolayers: MoS2, MoSe2, MoTe2, WSe2, and WS2 substitutionally doped with period four transition-metals (Ti, V, Cr, Mn, Fe, Co, Ni). We uncover five distinct magnetically ordered states among the 35 distinct TMD-dopant pairs: the non-magnetic (NM), the ferromagnetic with out-of-plane spin polarization (Z FM), the out-of-plane polarized clustered FMs (clustered Z FM), the in-plane polarized FMs (X–Y FM), and the anti-ferromagnetic (AFM) state. Ni and Ti dopants result in an NM state for all considered TMDs, while Cr dopants result in an anti-ferromagnetically ordered state for all the TMDs. Most remarkably, we find that Fe, Mn, Co, and V result in an FM ordered state for all the TMDs, except for MoTe2. Finally, we show that V-doped MoSe2 and WSe2, and Mn-doped MoS2, are the most suitable candidates for realizing a room-temperature FM at a 16–18% atomic ...
Structural and Electronic Properties of Intercalated Transition Metal Dichalcogenides Compounds
Bibechana, 2022
The structural and electronic properties of Transition Metal Dichalcogenides Compound (TMDC) TiS2 and its intercalated compound like FeTiS2 are reported in the present work using Density Functional Theory (DFT). The Generalized Gradient Approximation (GGA) with ultra-soft pseudopotential are used under Quantum ESPRESSO code. From the theoretical data, it is concluded that, the energy band structure of the TiS2 material has been a small indirect band gap and possess a semiconductor characteristic, while the doped intercalated compound like FeTiS2, the energy bands are overlapped in the Fermi region, which possess metallic characteristics. Also, FeTiS2 is a ferromagnetic material with spin up and spin down nature observed from the band structure data.
Energy Scaling of Compositional Disorder in Ternary Transition‐Metal Dichalcogenide Monolayers
Advanced Electronic Materials, 2021
to play a crucial role as essential building blocks in future high-tech devices. [1-8] Already in the late 1960s, early studies on the structural and electronic properties of bulk TMDs had started and are detailed in a report by Wilson and Yoffe. [9] TMDs are layered materials which combine a transition metal (M: Mo, W, Ti, Zr, etc.) and a chalcogen (X: S, Se, or Te) in the general formula MX 2 with one layer of M atoms sandwiched between two layers of X atoms. [10] Group VIB TMDs with a 2H structural phase (e.g., MoSe 2) are the most explored representatives of such systems. They are characterized by an intrinsic bandgap within the visible and near-infrared regions. [11] Furthermore, the material system exhibits a transition from an indirect to a direct bandgap located at the K or K′ points of the hexagonal Brillouin zone, linked to a decrease in the number of layers from the bulk crystal to a monolayer. [12,13] Moreover, such materials also possess a strong spin-orbit interaction due to the presence of a relatively heavy transition metal along with huge exciton binding energies [14-16] resulting from a strong Coulomb interaction and a lack of dielectric screening. These properties lead to a valence-band splitting that strongly affects Alloying semiconductors are often used to tune the material properties desired for device applications. The price for this tunability is the extra disorder caused by alloying. In order to reveal the features of the disorder potential in alloys of atomically thin transition-metal dichalcogenides (TMDs) such as Mo x W 1−x Se 2 , the exciton photoluminescence is measured in a broad temperature range between 10 and 200 K. In contrast to the binary materials MoSe 2 and WSe 2 , the ternary system demonstrates non-monotonous temperature dependences of the luminescence Stokes shift and of the luminescence linewidth. Such behavior is a strong indication of a disorder potential that creates localized states for excitons and affects the exciton dynamics responsible for the observed non-monotonous temperature dependences. A comparison between the experimental data and the results obtained by Monte Carlo computer simulations provides information on the energy scale of the disorder potential and also on the shape of the density of localized states created by disorder. Statistical spatial fluctuations in the distribution of the chemically different material constituents are revealed to cause the disorder potential responsible for the observed effects. A deeper understanding of the disorderinduced effects is vital for prospective TMD alloy-based devices.
Physical Review B, 2012
Using the first-principles calculations, we explore the electronic structures of 2H-MX 2 (M = Mo, W; X = S, Se, Te). When the number of layers reduces to a single layer, the indirect gap of bulk becomes a direct gap with larger gap and the band curvatures are found to lead to the drastic changes of effective masses. On the other hand, when the strain is applied on the single layer, the direct gap becomes an indirect gap and the effective masses vary. Especially, the tensile strain reduces the gap energy and effective masses while the compressive strain enhances them. Furthermore, the much larger tensile stress leads to become metallic.
Nanoscale, 2014
Binary alloys present a promising venue for band gap engineering and tuning of other mechanical and electronic properties of materials. Here we use the density-functional theory and cluster expansion to investigate the thermodynamic stability and electronic properties of 2D transition metal dichalcogenide (TMD) binary alloys. We find that mixing electron-accepting or electron-donating transition metals with 2D TMD semiconductors leads to degenerate p-or n-doping, respectively, effectively rendering them metallic. We then proceed to investigate the electronic properties of semiconductor-semiconductor alloys. The exploration of the configurational space of the 2D molybdenum-tungsten disulfide (Mo 1Àx W x S 2 ) alloy beyond the mean field approximation yields insights into anisotropy of the electron and hole effective masses in this material. The effective hole mass in the 2D Mo 1Àx W x S 2 is nearly isotropic and is predicted to change almost linearly with the tungsten concentration x. In contrast, the effective electron mass shows significant spatial anisotropy. The values of the band gap in 2D Mo 1Àx W x S 2 and MoSe 2(1Àx) S 2x are found to be configuration-dependent, exposing the limitations of the mean field approach to band gap analysis in alloys.