Low-Power Transistors with Ideal p-type Ohmic Contacts Based on VS/WSe van der Waals Heterostructures.

Achieving low-resistance Ohmic contacts with a vanishing Schottky barrier is crucial for enhancing the performance of two-dimensional (2D) field-effect transistors (FETs). In this paper, we present a theoretical investigation of VS/WSe-vdWHs-FETs with a gate length () in the range of 1-5 nm, using quantum transport simulations. The results show that a very low hole Schottky barrier height (-0.

Tunable multiple nonvolatile resistance states in a MnSe-based van der Waals multiferroic tunnel junction.

Two-dimensional (2D) van der Waals (vdW) multiferroic tunnel junctions (MFTJs) composed of a ferromagnetic metal and a ferroelectric barrier have controllable thickness and clean interface and can realize the coexistence of tunneling magnetoresistance (TMR) and tunneling electroresistance (TER). Therefore, they have enormous potential application in nonvolatile multistate memories. Here, using first principles combined with non-equilibrium Green's function method, we have systematically investigated the spin-dependent transport properties of FeGeTe/MnSe/FeGeTe vdW MFTJs with various numbers of barrier layers.

Sub-9 nm high-performance and low-power transistors based on an in-plane NbSe/MoSe/NbSe heterojunction.

Due to the ability to reduce the gate length of field-effect transistors (FETs) down to sub-10 nm without obviously affecting the performance of the device, the utilization of two-dimensional (2D) semiconductor materials as channel materials for FETs is of great interest. However, in-plane 2D/2D heterojunction FETs have received less attention in previous studies than vertical van der Waals heterojunction devices. Based on the above reasons, this study has investigated the transport properties of an in-plane NbSe/MoSe/NbSe heterojunction FET with different gate lengths by using quantum transport simulation.

The pure spin current and fully spin-polarized current induced by the photogalvanic effect and spin-Seebeck effect in halogen-decorated phosphorene.

The control of spin transport is a fundamental but crucial task in spintronics and realization of high spin polarization transport and pure spin currents is particularly desired. By combining the non-equilibrium Green's function with first principles calculations, it is shown that halogen adsorption can transform a black phosphorene monolayer from a nonmagnetic semiconductor to a magnetic semiconductor with two almost symmetric spin-split states near the Fermi level, which provides two isolated transport channels. Further investigations demonstrate that a device based on halogen-decorated phosphorene can behave multifunctionally, where a pure spin photocurrent and a fully spin-polarized photocurrent can be effectively controlled by tuning the photon energy or polarization angle of the incident light.

Potential outstanding physical properties of novel black arsenic phosphorus AsP/AsP phases: a first-principles investigation.

Black arsenic phosphorus AsP has been studied as an excellent candidate for electronic and optoelectronic applications. At the same time, the physical properties of As P alloys with other compositions were not investigated. In this work, we design seven AsP(P-I and P-II)/AsP(As-(I, II, III, IV and V)) phases with molecular dynamics stability.

The electromagnetic performance of transition metal-substituted monolayer black arsenic-phosphorus.

Recently, a new two-dimensional nonmagnetic semiconductor material, black arsenic-phosphorus (bAsP), has gained great research attention for experimental and theoretical works owing to its excellent physical properties. The present work attempted to investigate the electromagnetic properties of three 1 : 1 bAsP structures (bAsP-1, bAsP-2, and bAsP-3) substituted with transition metals (TM) by using first principles. Among these substituted bAsP systems, V substitutes P of bAsP-1, Ni substitutes As of bAsP-1, Mn substitutes P of bAsP-2, Fe substitutes As of bAsP-2 and Mn substitutes P of bAsP-3 and these are found to be half-metals.

Photon-assisted spin transport in blue phosphorene nanotubes.

We have investigated photon-assisted spin injection into blue phosphorene nanotubes (PNTs) with ferromagnetic cobalt electrodes by nonequilibrium Green's function combined with light-matter interaction based on the first-order Born approximation. The results show the photo-induced spin current. The spin up and spin down photocurrents flow in opposite directions for zigzag blue nanotubes (ZPNTs) with anti-parallel magnetic configuration of the electrodes.

First-Principles Study on the Thermoelectric Properties of FeAsS.

The electronic structure and thermoelectric properties of FeAsS are studied by the first-principles and the Boltzmann transport theory. The results show that FeAsS is a semiconductor with an indirect band gap of 0.73 eV.

Electrical-field tuned thermoelectric performance of graphene nanoribbon with sawtooth edges.

By using first-principle calculations combined with the non-equilibrium Green's function approach, we report that a vertical electrical field can modulate the thermoelectric performance of a graphene nanoribbon with sawtooth edges. The results show that the sawtooth graphene nanoribbon exhibits the spin-dependent Seebeck effect under the temperature gradients, and is strengthened by increasing the width of the sawtooth graphene nanoribbon. When the vertical electrical field is applied to the device, the spin-dependent Seebeck effect can also be enhanced.

Theoretical investigation of multiferroic metal-organic framework magnet [CHNH][Co(HCOO)]: Green's function method.

For the first presented magnetic ordering-induced multiferroics with a metal-organic framework (MOF) of formula [CHNH][Co(HCOO)], we theoretically investigate its multiple ferroics. It is found that Dzyaloshinskii-Moriya interaction is a main cause that leads to non-zero magnetization, and electric polarization, and the induced electric polarization can be regulated by magnetic fields. As an assistant mechanism, magnon-magnon interaction and quantum fluctuation play an important role on ferroelectrics and magnetism.

Negative differential resistance, perfect spin-filtering effect and tunnel magnetoresistance in vanadium-doped zigzag blue phosphorus nanoribbons.

We investigate the electronic and transport properties of vanadium-doped zigzag blue phosphorus nanoribbons by first-principles quantum transport calculations. We study the spin-dependent transport properties and obtain current-voltage curves showing obvious spin polarization and negative differential behaviors. These interesting transport behaviors can be explained by the band structure of the vanadium-doped zigzag blue phosphorus nanoribbons.

Half-metallicity of the (001), (111) and (110) surfaces of CoRuMnSi and interface half-metallicity of CoRuMnSi/CdS.

Recent studies have indicated that the quaternary Heusler alloy CoRuMnSi shows a half-metallic ferromagnetism (Kundu , , 7, (2017), 1803). The (111), (110), and (001) surfaces and the interfaces with CdS (111) substrate of the quaternary Heusler alloy CoRuMnSi were explored by carrying out a first-principles investigation based on a density functional theory. Calculations showed that the half metallicity can be preserved for the Si-terminated (111) surface and subsurface while the half-metallicity approved in the bulk CoRuMnSi is destroyed at Co, Ru, and Mn-terminations (111) surfaces and subsurfaces.

Thermoelectric transport properties of Ti doped/adsorbed monolayer blue phosphorene.

Thermoelectric transport properties of Ti doped or adsorbed monolayer blue phosphorene are investigated by density functional theory combined with the nonequilibrium Green's function formalism. The thermal giant magnetoresistance and a nearly 100% spin polarization which solely relies on the temperature gradient of electrodes without bias or gate voltage are observed. Moreover, the spin Seebeck effect is also found.

Engineering of charge carriers via a two-dimensional heterostructure to enhance the thermoelectric figure of merit.

High band degeneracy and glassy phonon transport are two remarkable features of highly efficient thermoelectric (TE) materials. The former promotes the power factor, while the latter aims to break the lower limit of lattice thermal conductivity through phonon scattering. Herein, we use the unique possibility offered by a two-dimensional superlattice-monolayer structure (SLM) to engineer the band degeneracy, charge density and phonon spectrum to maximize the thermoelectric figure of merit (ZT).

Half-metallic and magnetic semiconducting behaviors of metal-doped blue phosphorus nanoribbons from first-principles calculations.

We investigate the electronic and magnetic properties of substitutional metal atom impurities in two-dimensional (2D) blue phosphorene nanoribbons using first-principles calculations. In impure zigzag blue phosphorene nanoribbons (zBPNRs), a metal atom substitutes for a P atom at position "A/B". The V-"B"structure shows half-metallic properties, while the Mn-"A/B", V-"A", Fe-"B", and Cr-"A/B" structures show magnetic semiconductor properties.

Transition-metal-doped group-IV monochalcogenides: a combination of two-dimensional triferroics and diluted magnetic semiconductors.

We report the first-principles evidence of a series of two-dimensional triferroics (ferromagnetic + ferroelectric + ferroelastic), which can be obtained by doping transition-metal ions in group-IV monochalcogenide (SnS, SnSe, GeS, GeSe) monolayers, noting that a ferromagnetic Fe-doped SnS monolayer has recently been realized (Li B et al 2017 Nat. Commun. 8 1958).

Strain-induced enhancement of thermoelectric performance of TiS monolayer based on first-principles phonon and electron band structures.

Using first-principle calculations combined with Boltzmann transport theory, we investigate the biaxial strain effect on the electronic and phonon thermal transport properties of a 1 T (CdI-type) structural TiS monolayer, a recent experimental two-dimensional (2D) material. It is found that the electronic band structure can be effectively modulated and that the band gap experiences an indirect-direct-indirect transition with increasing tensile strain. The band convergence induced by the tensile strain increases the Seebeck coefficient and the power factor, while the lattice thermal conductivity is decreased under the tensile strain due to the decreasing group velocity and the increasing scattering chances between the acoustic phonon modes and the optical phonon modes, which together greatly increase the thermoelectric performance.

Multiple thermal spin transport performances of graphene nanoribbon heterojuction co-doped with Nitrogen and Boron.

Graphene nanoribbon is a popular material in spintronics owing to its unique electronic properties. Here, we propose a novel spin caloritronics device based on zigzag graphene nanoribbon (ZGNR), which is a heterojunction consisting of a pure single-hydrogen-terminated ZGNR and one doped with nitrogen and boron. Using the density functional theory combined with the non-equilibrium Green's function, we investigate the thermal spin transport properties of the heterojunction under different magnetic configurations only by a temperature gradient without an external gate or bias voltage.

Control over the magnetism and transition between high- and low-spin states of an adatom on trilayer graphene.

Using density-functional theory, we investigate the electronic and magnetic properties of an adatom (Na, Cu and Fe) on ABA- and ABC-stacked (Bernal and rhombohedral) trilayer graphenes. In particular, we study the influence of an applied gate voltage on magnetism, as it modifies the electronic states of the trilayer graphene (TLG) as well as changes the adatom spin states. Our study performed for a choice of three different adatoms (Na, Cu, and Fe) shows that the nature of adatom-graphene bonding evolves from ionic to covalent in moving from an alkali metal (Na) to a transition metal (Cu or Fe).

Spin-dependent thermoelectric effects in Fe-C doped monolayer MoS.

By using the non-equilibrium Green's function with density functional theory, we have studied the thermal spin transport properties of Fe-C cluster doped monolayer MoS. The results show that the device has a perfect Seebeck effect under temperature difference without gate voltage or bias voltage. Moreover, we also find the thermal colossal magnetoresistance effect, which is as high as 10%.

Temperature-controlled colossal magnetoresistance and perfect spin Seebeck effect in hybrid graphene/boron nitride nanoribbons.

Thermal spin transport properties of graphene and hexagonal boron nitride nanoribbon heterojunctions have been investigated using density functional theory calculations combined with the Keldysh nonequilibrium Green's function approach. The results showed that the perfect spin Seebeck effect and analogy negative differential thermoelectric resistance occurred in the device under a temperature difference without a gate or bias voltage. An intriguing thermally induced colossal magnetoresistance without gate regulation was also observed, which can be switched between a positive and negative value with temperature control.

Ferroelectricity in Covalently functionalized Two-dimensional Materials: Integration of High-mobility Semiconductors and Nonvolatile Memory.

Realization of ferroelectric semiconductors by conjoining ferroelectricity with semiconductors remains a challenging task because most present-day ferroelectric materials are unsuitable for such a combination due to their wide bandgaps. Herein, we show first-principles evidence toward the realization of a new class of two-dimensional (2D) ferroelectric semiconductors through covalent functionalization of many prevailing 2D materials. Members in this new class of 2D ferroelectric semiconductors include covalently functionalized germanene, and stanene (Nat.

Half-metallic YN monolayer: dual spin filtering, dual spin diode and spin Seebeck effects.

Most of the pristine graphene-like two-dimensional materials have been found to be non-magnetic, and the emergence of magnetism usually needs an external electric field, substrate, strain, vacancy, or doping, which is not easily controlled in an experiment, limiting the potential applications in spintronics. Very recently, layered transition-metal dinitrides were explored experimentally and theoretically, and a pristine YN monolayer was predicted to be a half-metallic ferromagnet with a graphene-like structure. To demonstrate the possible spintronic applications, herein, we designed spintronic devices based on the half-metallic YN monolayer, and found perfect dual spin filtering and dual spin diode effects when a bias voltage was applied.

Thermoelectric properties of monolayer MSe2 (M = Zr, Hf): low lattice thermal conductivity and a promising figure of merit.

Monolayer transition-metal dichalcogenides (TMDCs) MX2 (M = Mo, W, Zr, Hf, etc; X = S, Se, Te) have become well-known in recent times for their promising applications in thermoelectrics and field effect transistors. In this work, we perform a systematic study on the thermoelectric properties of monolayer ZrSe2 and HfSe2 using first-principles calculations combined with Boltzmann transport equations. Our results point to a competitive thermoelectric figure of merit (close to 1 at optimal doping) in both monolayer ZrSe2 and HfSe2, which is markedly higher than previous explored monolayer TMDCs such as MoS2 and MoSe2.

The spin-dependent transport properties of zigzag α-graphyne nanoribbons and new device design.

By performing first-principle quantum transport calculations, we studied the electronic and transport properties of zigzag α-graphyne nanoribbons in different magnetic configurations. We designed the device based on zigzag α-graphyne nanoribbon and studied the spin-dependent transport properties, whose current-voltage curves show obvious spin-polarization and conductance plateaus. The interesting transport behaviours can be explained by the transport spectra under different magnetic configurations, which basically depends on the symmetry matching of the electrodes' bandstructures.