Te Monolayers Research Articles

Graphenylene/Janus transition metal dichalcogenides XMoY (X≠Y = S, Te, Se) as novel van der Waals heterostructures for optoelectronic applications

Recently synthesized graphenylene (Gr) is the first example of a non-delocalized sp2-carbon monolayer. It is promising for nanoelectronic and energy storage applications. This paper presents investigation of novel van der Waals heterostructures obtained by stacking graphenylene and Janus XMoY (X≠Y = S, Se, Te) monolayers by DFT-based calculations. The negative energy of interlayer interaction, small deformations after heterostructure optimization indicate stability of novel structures under normal conditions. Gr/SeMoS and Gr/TeMoSe are narrow-gap semiconductors, and Gr/TeMoS possesses semimetallic properties. External transverse electric field can change both the gap and bands alignment of Gr/SeMoS and Gr/TeMoS heterojunctions. The band gap of Gr/TeMoSe can also be adjusted by electric field, but the band alignment remains unchanged. It is found that novel van der Waals heterostructures exhibit strong absorption (up to 13⋅105 cm−1) in the visible range. The dependence of the electronic structure on rotation angle of graphenylene monolayer in the Gr/SeMoS heterostructure is discussed.

Janus B2XY (X, Y = S, Se, Te) monolayers as piezoelectric Materials: A First-Principle study

Herein the piezoelectric properties of two-dimensional (2D) Janus B2XY (X, Y = S, Se, Te) monolayers are studied using first principles calculations. Theoretical results reveal that their in-plane piezoelectric response is comparable with that of the well-known 2D piezoelectric materials. Meanwhile, single-layer B2STe can play a role in top/bottom technologies because of considerable out-of-plane piezoelectricity. On the other hand, exerting tensile biaxial strain prominently enhance the piezoelectric effect of all B2XY monolayers. Their structures are still dynamically and mechanically stable under biaxial strain. In brief, this work defines the B2XY monolayers as ultrathin piezoelectric materials, and thus will stimulate related experimental discoveries.

Two-dimensional spin-gapless semiconductors: A mini-review.

In the past decade, two-dimensional (2D) materials and spintronic materials have been rapidly developing in recent years. 2D spin-gapless semiconductors (SGSs) are a novel class of ferromagnetic 2D spintronic materials with possible high Curie temperature, 100% spin-polarization, possible one-dimensional or zero-dimensional topological signatures, and other exciting spin transport properties. In this mini-review, we summarize a series of ideal 2D SGSs in the last 3 years, including 2D oxalate-based metal-organic frameworks, 2D single-layer Fe2I2, 2D Cr2X3 (X = S, Se, and Te) monolayer with the honeycomb kagome (HK) lattice, 2D CrGa2Se4 monolayer, 2D HK Mn–cyanogen lattice, 2D MnNF monolayer, and 2D Fe4N2 pentagon crystal. The mini-review also discusses the unique magnetic, electronic, topological, and spin-transport properties and the possible application of these 2D SGSs. The mini-review can be regarded as an improved understanding of the current state of 2D SGSs in recent 3 years.

Doped 2D VX2 (X = S, Se, Te) monolayers as electrocatalysts for ammonia production: A DFT based study

Electrocatalytic nitrogen fixation under ambient conditions on vanadium dichalcogenides (VX2) with non-metal dopants has been explored herein. Understanding the interface chemistry, inherent electronic and acute synergistic nature of non-metal dopants on two unique phases of VX2 has been meticulously explored through a scrutiny of several non-metal atoms as catalytic centers. The efficacity of N2 chemisorption and NN bond activation has been implemented as crucial parameters to realize boron and carbon doped VX2 monolayers to be electrocatalytically active for nitrogen reduction reaction (NRR). Detailed investigation on the NRR mechanism brings out the pivotal role of thermodynamic favourability for product formation obtained from Gibbs free energy differences. The charge transfer on N and π-π* orbital hybridization and electron “donor–acceptor” mechanism between the non-metal and N2 has been found to modulate the electrocatalytic barrier for NRR on VX2 monolayers. This study proposes boron doped VS2 as an efficient chemically feasible, earth abundant sustainable electrocatalyst for NRR with an overpotential as low as 0.06 eV.

A Theoretical Investigation on the Physical Properties of Zirconium Trichalcogenides, ZrS3, ZrSe3 and ZrTe3 Monolayers

In a recent advance, zirconium triselenide (ZrSe3) nanosheets with anisotropic and strain-tunable excitonic response were experimentally fabricated. Motivated by the aforementioned progress, we conduct first-principle calculations to explore the structural, dynamic, Raman response, electronic, single-layer exfoliation energies, and mechanical features of the ZrX3 (X = S, Se, Te) monolayers. Acquired phonon dispersion relations reveal the dynamical stability of the ZrX3 (X = S, Se, Te) monolayers. In order to isolate single-layer crystals from bulk counterparts, exfoliation energies of 0.32, 0.37, and 0.4 J/m2 are predicted for the isolation of ZrS3, ZrSe3, and ZrTe3 monolayers, which are comparable to those of graphene. ZrS3 and ZrSe3 monolayers are found to be indirect gap semiconductors, with HSE06 band gaps of 1.93 and 1.01 eV, whereas the ZrTe3 monolayer yields a metallic character. It is shown that the ZrX3 nanosheets are relatively strong, but with highly anisotropic mechanical responses. This work provides a useful vision concerning the critical physical properties of ZrX3 (X = S, Se, Te) nanosheets.

High thermoelectric performance induced by strong anharmonic effects in monolayer (PbX)2 (X = S, Se, Te)

Enhanced thermoelectric performance is restricted greatly by the interaction of various transport parameters, and this bottleneck urgently requires a solution. In this paper, first-principles calculations and Boltzmann transport theory are used to study the thermoelectric performance of two-dimensional (PbX)2 (X=S,Se,Te) monolayers, and it is found that the thermoelectric performance can be enhanced significantly by applying a biaxial tensile strain. The room-temperature ZT values of the p-type (PbS)2, (PbSe)2, and (PbTe)2 in zigzag (armchair) directions are boosted as high as 1.97 (1.35), 2.26 (1.31), and 2.45 (1.59), respectively. The results show that it is mainly attributed to the significantly reduced phonon thermal conductivity. Moreover, the sharply reduced phonon thermal conductivity is mainly due to the enhancement of the phonon scattering rate caused by strong phonon anharmonicity. In addition, the excellent ZT value of the p-type (PbX)2 (X=S, Se, Te) monolayer exhibits their potential application in the thermoelectric field, and the external strain has a good prospect in enhancing the thermoelectric performance.

MX (M = Au, Ag; X = S, Se, Te) monolayers: Promising photocatalysts for oxygen evolution reaction with excellent light capture capability

Oxygen evolution reaction (OER) is an important step in photocatalytic overall water splitting, and the search for photocatalytic OER catalysts with good light-harvesting ability has always been a hot topic. Herein, a new series of group-11 chalcogenides MX (M = Au, Ag; X = S, Se, Te) single layers are predicted by DFT calculations. The formation energy, phonon dispersion spectra and AIMD are calculated to certificate that MX monolayers are highly stable. MX monolayers are indirect bandgap semiconductors with bandgaps of 0.89–2.21 eV and their carrier mobilities [250.11–989.71 cm2/(V⋅s)]are also confirmed to be superior or comparable to that of MoS2 [∼200 cm2/(V⋅s)]. More particularly, their absorption of sunlight can reach the infrared light region, which far exceeds other commonly reported OER catalysts. Finally, it is confirmed that AuS, AuSe and AgS are potential photocatalytic OER agents, in which AuSe shows the best performance because it can spontaneously undergo OER under pH = 7 and light conditions. Moreover, we also hope that MX (M = Au, Ag; X = S, Se, Te) monolayers can be widely used in optoelectronic devices due to their excellent light capture performances.

Exploring the potential of Ti2BT2 (T = F, Cl, Br, I, O, S, Se and Te) monolayers as anode materials for lithium and sodium ion batteries

Introducing functional groups to two-dimensional transition metal borides (MBenes) is an effective way to ameliorate the properties of MBenes as electrode materials for rechargeable lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). Herein, we investigated the electrochemical performances of Ti2BT2 (T = F, Cl, Br, I, O, S, Se and Te) as anode materials for LIBs and SIBs using first-principles calculations. Firstly, the metallic nature of Ti2BT2 endows them with excellent conductivities. Besides, the phonon dispersions and ab initio molecular dynamics simulations (AIMD) were conducted to estimate the dynamic and thermal stability of Ti2BT2. Additionally, Ti2BSe2 has slight high specific capacity of 405 mA h g−1 for LIBs and Ti2BS2 possesses ultra-high specific capacity of 942 mA h g−1 for SIBs. Furthermore, the low diffusion energy barriers endow ultra-high charge/discharge rate and suitable open circuit voltages ensure the safety of battery performance. The encouraging results indicate that Ti2BSe2 and Ti2BS2 are outstanding candidates as electrode materials for LIBs and SIBs, respectively. Our work not only screened out excellent electrode materials for metal-ion batteries, but also provided constructive suggestions for the development of next-generation high-performance electrode materials.

Rashba states localized to InSe layer in InSe/GaTe(InTe) heterostructure

The zero potential gradient in 2D III-VI chalcogenides NX (N = Ga, In; X = S, Se, Te) monolayers hinders the Rashba spin splitting (RSS), which limits their application in spintronics. Here, we construct InSe/GaTe and InSe/InTe van der Waals (vdW) heterostructures and investigate their Rashba SOC effect on the basis of first-principles calculations. The occurrence of internal electric field in the heterostructures induces spin splitting conduction band minimum (CBM). Rashba characteristic of the spin splitting can be confirmed through the band structures and spin textures. The projected energy bands suggest that the RSS state in both heterostructures mainly roots in InSe layers. Furthermore, in-plane strain, vertical strain, and the external electric field are all proved to be effective methods to regulate the RSS. When an in-plane strain of 6% is exerted, the Rashba coefficient can become as high as 1.33 eV Å and 1.26 eV Å for InSe/GaTe and InSe/InTe, respectively. The occurrence of controllable RSS at CBM makes the both heterostructures become potential candidate materials for spintronic devices.

Electrocatalytic Reduction of N2 to NH3 Over Defective 1T'-WX2 (X=S, Se, Te) Monolayers.

Defects in transition metal dichalcogenides (TMDs) can serve as active sites in catalytic reactions. In this work, by means of first-principles calculations, the catalytic activities of WX2 (X=S, Se, Te) monolayers in the 1T' phase with both vacancy defects (missing chalcogen atoms, X Vd ) and antisite defects (replacing chalcogen atoms with W atoms, X Ad ) were evaluated for the nitrogen reduction reaction (NRR). Results showed that all these defective catalysts had great potential toward electrocatalytic ammonia synthesis by exhibiting low limiting potentials (UL ). Over 1T'-WTe2 @Te Vd , 1T'-WS2 @S Ad , 1T'-WSe2 @Se Ad , and 1T'-WTe2 @Te Ad , the corresponding UL values were -0.49, -0.21, -0.19, and -0.15 V, much smaller than that of the benchmark catalyst, the Ru (0001) surface (UL =-0.98 V). Furthermore, the hydrogen evolution reaction (HER) was inhibited. 1T'-WX2 monolayers with the antisite defects showed better NRR activity than those with the vacancy defects because of the smaller steric hindrance at the former. Results suggest that the steric effect at the active surface sites should be utilized to develop better catalysts.

Characterization of two dimensional ferromagnetic binary and Janus manganese dichalcogenides

We present a first-principles and anisotropic Heisenberg based study of electronic, finite temperature magnetic and thermal properties of two-dimensional binary MnX2 (X = S, Se, Te) and Janus MnXX′ (X, X′ = S, Se, Te) monolayers. All Mn dichalcogenides monolayers are dynamically stable with out-of-plane easy-axis ferromagnetic ground state. The ferromagnetic spin state is robust against external electric field. The strength of magnetic anisotropy is determined by the type of chalcogen atoms. The magnetic anisotropy can be tuned by an applied electric field in Janus Mn dichalcogenides monolayers contain heavy Te atom. The spin polarized electronic structure is strongly dependent on chalcogen atoms and varies from semiconductor (e.g. MnS2) to metallic (e.g. MnTe2) state. The dispersion relation of magnetic excited states is obtained by applying the linear order Holstein–Primakoff transformation to the anisotropic Heisenberg Hamiltonian. We find out high Curie temperature for Mn dichalcogenides by a self consistent calculation of magnetization as a function of temperature. Finally, at low temperature the phonon and magnon contribution to the heat capacity of Mn dichalcogenides are estimated as quadratic and linear temperature dependence, respectively.

NiX2 (X = S, Se, and Te) Monolayers: Promising Anodes in Li/Na-Ion Batteries and Superconductors

Based on the density functional theory calculations, we report the stability, electron structure, and potential applications in single-layer (SL) NiX2 (X = S, Se, and Te) that show high thermal, dynamical, and mechanical stability and possess ultralow isotropic Young’s modulus. Moreover, these NiS2, NiSe2, and NiTe2 monolayers have high energy storage capacities of 874, 496, and 342 mA h g–1 and low diffusion energy barriers of 0.23/0.24/0.27 and 0.12/0.13/0.12 eV when used as anodes in lithium-ion batteries and sodium-ion batteries, respectively. SL NiS2 and NiSe2 show semiconducting traits in their freestanding crystals. Specifically, the 2D NiTe2 monolayer is determined to be an intrinsic superconductor with a transition temperature (Tc) of ∼2.24 K. The Tc can be improved to 5.48 K when subjected to an in-plane compressive strain of 6%. These results enrich the family of transition metal-based 2D materials with multifunctionality and facilitate further experimental efforts toward next-generation nanodevices.

Multiferroicity and giant in-plane negative Poisson\u2019s ratio in wurtzite monolayers

Monolayers of layered materials, such as graphite and molybdenum dichalcogenides, have been the focus of materials science in the last decades. Here, we reveal benign stability and intriguing physical properties in the thinnest monolayer wurtzite (wz) semiconductors, which can be exfoliated from their bulk and stacked to reform the wz crystals. The candidate ZnX and CdX (X = S, Se, Te) monolayers possess low cleavage energy and direct bandgaps, which harbor strongly coupled ferroelectricity and ferroelasticity with low transition barriers, giant in-plane negative Poisson’s ratio, as well as giant Rashba spin splitting, enabling the co-tunability of spin splitting and auxetic magnitudes via multiferroic switching. These wz monolayers can be used as building blocks of devices structures, due to their inherent “self-healable” capacity, which offer more flexibility for semiconductor fabrication and provide a natural platform to probe the interplay of multiple physical effects, bringing light into the rich physics in tetrahedral semiconductors.

First-principles screening upon Janus PtXY (X, Y = S, Se and Te) monolayer under applied biaxial strains and electric fields

In this paper, we using the first-principles theory systemically investigate the geometric and electronic properties of the PtXY (X, Y = S, Se and Te) monolayers under the applied biaxial strains and electric fields. The optimized morphologies, deformation charge density, band structure and orbital DOS are plotted and analyzed. Our findings indicate that the applied biaxial strains can largely impact the morphologies of the PtXY systems while the electric fields do not. Given the remarkable charge-transfer crossing the X and Y planes caused by applied biaxial strains and electric field, the electronic property as well as the bandgap of the PtXY systems are modulated largely. It is conclude that PtSSe monolayer is a proper tensile sensing material while the PtSTe and PtSeTe monolayers are potential compressive sensing candidate. Meanwhile, PtSSe and PtSTe systems have desirable linear sensitivity to the applied electric field in terms of electrical conductivity, while the PtSeTe monolayer is only linearly sensitive for the negative electric field. The I-V analysis reveals the resistance property of the PtXY monolayers under various voltages and is consistent with the BS analysis. Our work uncover the physicochemical properties of the PtXY monolayer for typical applications and give the guidance to unfold a new orientation to explore novel semiconductor devices.

Trigonal multivalent polonium monolayers with intrinsic quantum spin Hall effects

Two-dimensional (2D) topological insulators, a type of the extraordinary quantum electronic states, have attracted considerable interest due to their unique electronic properties and promising potential applications. Recently, the successful fabrication of 2D Te monolayers (i.e. tellurene) in experiments (Zhu et al., Phys Rev Lett 119:106101, 2017) has promoted researches on the group-VI monolayer materials. With first-principles calculations and tight-binding (TB) method, we investigate the structures and electronic states of 2D polonium (poloniumene), in which Po is a congener of Te. The poloniumene is found to have the tendency of forming a three-atomic-layer 1 T-MoS2-like structure (called trigonal poloniumene), namely, the central-layer Po atoms behave metal-like, while the two-outer-layer Po atoms are semiconductor-like. This unique multivalent behavior of the Po atoms is conducive to the structural stability of the monolayer, which is found to be an intrinsic quantum spin Hall insulator with a large band gap. The nontrivial topology originates from the p_{x,y} - p_{z} band inversion, which can be understood based on a built TB model. The poloniumene with different congener elements doped is also explored. Our results provide a thorough understanding of structures and electronic states of 2D polonium-related materials.

Asymmetric XMoSiN[formula omitted] (X=S, Se, Te) monolayers as novel promising 2D materials for nanoelectronics and photovoltaics

In this paper, we study asymmetric 2D materials XMoSiN2 constructed and optimized from MoSi2N4 by deleting SiN from one side and replacing remaining N atoms from the same side with chalcogen X atoms (sulfur, selenium, or tellurium). The new structure is a hybrid of a transition metal dichalcogenide and a 2D material from the MoSi2N4 family. We justify the dynamical stability of novel 2D materials. High binding energy (>7.5 eV/atom) is typical for the monolayers under study. Estimated built-in electric field (∼1.3−2 eV/Å) can serve to separate effectively photogenerated charge carriers in the single monolayer. Demonstrated high mechanical strength (2D Young modulus E∼300 N/m, in-plane stress limit >17 N/m), noticeable sensitivity of the electronic and optical properties to deformations of monolayers, and weak sensitivity to an external transverse electric field indicate that the proposed 2D materials are of great promise for applications in flexible opto- and nanoelectronics.

Structural, electronic, and transport properties of quintuple atomic Janus monolayers Ga2SX2 ( X= O, S, Se, Te): First-principles predictions

Two-dimensional Janus structures with vertical intrinsic electric fields exhibit many interesting physical properties that are not possible with symmetric materials. We systematically investigate the structural, electronic, and transport properties of quintuple-layer atomic Janus ${\mathrm{Ga}}_{2}\mathrm{S}{X}_{2}$ ($X=$ O, S, Se, Te) monolayers using the first-principles calculations. The stability of the Janus structures is evaluated via the analysis of their phonon dispersion curves, cohesive and formation energies, and elastic constants. The existence of a vertical internal electric field due to the lack of mirror symmetry has resulted in a vacuum level difference between the two sides of the investigated Janus structures. At the ground state, while the Janus ${\mathrm{Ga}}_{2}\mathrm{S}{\mathrm{O}}_{2}$ is metallic, the other three configurations (${\mathrm{Ga}}_{2}{\mathrm{S}}_{3}, {\mathrm{Ga}}_{2}\mathrm{S}{\mathrm{Se}}_{2}$, and ${\mathrm{Ga}}_{2}\mathrm{S}{\mathrm{Te}}_{2}$) are semiconductors with indirect band gaps. The electronic properties of ${\mathrm{Ga}}_{2}\mathrm{S}{X}_{2}$ monolayers can be altered by strain engineering. In particular, the indirect--direct band gap and semiconductor-metal phase transitions were observed when the biaxial strain was introduced. The carrier mobilities of the semiconducting Janus monolayers are directional anisotropic due to their anisotropy of the deformation potential constant. It is found that all three semiconducting Janus monolayers have high electron mobility, up to 930.34 ${\mathrm{cm}}^{2}$/V s, which is suitable for applications in next-generation electronic devices.

Coexistence of magnetism in SnX (X = S, Se, Te) monolayers by the adsorption of 3d transition-metal atoms

Magnetism can be induced in two-dimensional (2D) group IV monochalcogenide monolayers (MLs) by the decoration of transition-metal (TM) atoms. The induced magnetism in the group IV monochalcogenides enhances their potentiality in 2D spintronic devices, which has attracted extensive attention nowadays. In this context, the structural, electronic, and magnetic properties of transition metal atoms (Mn, Fe, Co) adsorbed SnX (X = S, Se, Te) MLs are investigated by using first-principles calculations. The TM atoms adsorbed SnX MLs are found to be energetically stable with the pnma space-group, and show the semiconducting nature with electronic band gaps in the range of 0.52–1.05 eV revealing the negligible spin–orbit coupling effect in most of the studied systems. The asymmetry between spin majority and spin minority channels is revealed in the electronic density of states of the adsorbed systems, which is mainly contributed by the hybridization of the 3d orbitals of TM atoms with the 4p and 4s orbitals of Sn and X atoms. Magnetic states are realized for SnX atoms in the adsorbed systems with the induced magnetic moments between −0.03 to −0.33 μB, which indicates the antiferromagnetic alignment between TM atoms and neighboring SnX atoms. Co adsorbed SnSe and Fe adsorbed SnTe MLs are found to have significant magneto-crystalline anisotropy energy values of 0.37 and 0.84 meV/TM atom, respectively, with the preferred perpendicular direction. In addition, the p-type doping is induced in the SnX MLs as indicated by the calculation of charge transfer between the adsorbed TM and SnX atoms. The results demonstrate potential applications of TM atoms adsorbed SnX MLs for spintronic and magnetic storage devices.

Low-cost pentagonal NiX2 (X = S, Se, and Te) monolayers with strong anisotropy as potential thermoelectric materials.

Pentagonal compounds, as a new family of 2D materials, have recently been extensively studied in the fields of electrocatalysis, photovoltaics, and thermoelectrics. Encouraged by the successful synthesis of pentagonal PdSe2, the thermoelectric properties of low-cost pentagonal NiX2 (X = S, Se, and Te) monolayers are theoretically predicted with the help of first-principles calculations and the semiclassical Boltzmann transport theory. The high dynamic and thermal stabilities of pentagonal NiX2 (X = S, Se, and Te) monolayers are confirmed according to the phonon dispersion spectrums and ab initio molecular dynamics (AIMD) simulations. Indirect semiconductor features with wide bandgaps of 2.44, 2.31, and 1.88 eV at the Heyd-Scuseria-Ernzerhof (HSE06) level are discovered for pentagonal NiS2, NiSe2, and NiTe2 monolayers. Combining the Boltzmann transport equation and deformation potential theory, the Seebeck coefficient, power factor, and thermoelectric figure of merit (ZT) of NiX2 (X = S, Se, and Te) monolayers are evaluated from 300 to 600 K. The strongly anisotropic ZT values are discovered, which are attributed to the significant differences in electrical and thermal transport along the x and y directions. In addition, low lattice thermal conductivities are observed at 600 K for the pentagonal NiTe2 monolayer, accompanying higher ZT values of 1.81 and 1.58 along the x and y directions. The predicted thermoelectric properties indicate that the low-cost pentagonal NiSe2 and NiTe2 monolayers are potential anisotropic thermoelectric materials with high performance.

Cr3X4 (X = Se, Te) monolayers as a new platform to realize robust spin filters, spin diodes and spin valves.

Two-dimensional ferromagnetic (FM) half-metals are promising candidates for advanced spintronic devices with small size and high capacity. Motivated by a recent report on controlling the synthesis of FM Cr3Te4 nanosheets, herein, to explore their potential application in spintronics, we designed spintronic devices based on Cr3X4 (X = Se, Te) monolayers and investigated their spin transport properties. We found that the Cr3Te4 monolayer based device shows spin filtering and a dual-spin diode effect when applying a bias voltage, while the Cr3Se4 monolayer is an excellent platform to realize a spin valve. These different transport properties are primarily ascribed to the semiconducting spin channel, which is close to and away from the Fermi level in Cr3Te4 and Cr3Se4 monolayers, respectively. Interestingly, the current in the Cr3Se4 monolayer based device also displays a negative differential resistance effect (NDRE) and a high magnetoresistance ratio (up to 2 × 103). Moreover, we found a thermally induced spin filtering effect and a NDRE at the Cr3Se4 junction under a temperature gradient instead of a bias voltage. These theoretical findings highlight the potential of Cr3X4 (X = Se, Te) monolayers in spintronic applications and put forward realistic materials to realize nanoscale spintronic devices.