Search

The effects of various vacancies and group‐VIB and VIIB transition metal substitutional doping on the structural, electronic, and magnetic properties of monolayer HfS2 are studied by first‐principles calculations. The results show that pristine monolayer HfS2 is a nonmagnetic semiconductor; it becomes a metal on creating a single V1Hf or V1S vacancy, whereas it is still a semiconductor on creating V1Hf+1S divacancy or V1Hf+2S trivacancy. The V1Hf single vacancy and V1Hf+1S divacancy induce magnetic moments of 3.265 and 2.000 μB, respectively, whereas the V1S single vacancy and V1Hf+2S trivacancy do not induce any magnetic moments. One of the group‐VIB and VIIB transition metal atoms substituting for one Hf atom in the monolayer HfS2 induces magnetic moments of about 2.000 and 3.000 μB, respectively. Furthermore, the spin‐polarized band structures show that the Cr‐doped monolayer HfS2 is a magnetic metal, whereas the Mn‐, Tc‐, and Re‐doped monolayer HfS2 are magnetic semiconductor. The Mo‐ and W‐doped monolayer HfS2 are magnetic half metal with wide spin‐down bandgaps of 0.975 and 1.074 eV, respectively, and thus can be used in nanoelectronics and spintronics devices. [ABSTRACT FROM AUTHOR]

First-principles calculations are used to investigate the electronic and magnetic properties of substitutional doping of transition metal (TM) atoms (V, Cr, Mn, Co, Ni, Cu and Zn) on marcasite FeS2 (m-FeS2). It is energetically favorable to combine TM atoms into m-FeS2 under S-rich condition. The electronic properties of m-FeS2 are changed significantly due to the introduced impurity states by TM atoms. Simultaneously, TM atoms doping can induce magnetism in m-FeS2 except Cu and Zn. The magnetism stem from the localized unpaired 3d electrons of TM atoms, a small amount of magnetic moments are induced in the neighboring Fe and S atoms due to the p-d hybridization mechanism. V-, Mn- and Ni-doped m-FeS2 compounds exhibit magnetic semiconducting character, Cr-doped compound display a half-metallic property, while Cu-doped compound shows non-magnetic metallic property, Zn-doped compound behavior as a non-magnetic semiconductor. More interestingly, a single Co-doped compound shows magnetic semiconducting but double Co-doped compound shows half metallic character. In addition, Co- and Cr-doped compounds prefer ferromagnetic state which is important for spintronics. [ABSTRACT FROM AUTHOR]

The structural, elastic, electronic, magnetic and optical properties of the Zn0.75V0.25X (X = S, Se or Te) have been investigated by the spin-polarized first-principles calculations. The optimized lattice constant increases with the increasing anions radius of S2−, Se2− and Te2−. All the Zn0.75V0.25X systems show the ductile and half-metallic characters. The spin exchange splitting energy Δx(d) increases but the absolute value of the exchange splitting energy Δx(pd) decreases for Zn0.75V0.25S, Zn0.75V0.25Se and Zn0.75V0.25Te successively, and the p-d exchange constant N0β is greater than s-d exchange constant N0α. The static dielectric constants ε1(0), the maximum value of ε2(ω), static refractive indexes n(0) and the maximum value of k(ω) get the biggest values for Zn0.75V0.25Se among Zn0.75V0.25X (X = S, Se or Te). Compared with pure ZnX, the new absorption peaks occur in the energy range of 0-1.4 eV for Zn0.75V0.25X systems. The results provide a certain degree of helpful theoretical guidance for the application of the Zn0.75V0.25X in spintronics devices and optical detectors. [ABSTRACT FROM AUTHOR]

The effects of the kinds (M=V, Cr, Mn, Fe, Co, and Ni) and separation distances (d=3.252, 4.600, 5.635, 6.504, 7.273, and 8.607Å for (0, i=1–6) configurations, respectively) of two identical 3d transition metal (TM) atoms M doping on the structural, electronic and magnetic properties of ZnO have been investigated by using spin-polarized first-principles calculations. The formation energies of two identical M atoms doped ZnO systems are lower under O-rich condition than under Zn-rich condition and the formation energy minimization shows the Mn-doped ZnO system is the easiest to form and there exists a clustering trend for two identical M dopants. The ferromagnetic coupling between two identical M atoms under double-exchange mechanism leads to V (0, i=1–6), Cr (0, i=1–6), Fe (0, 2), and Ni (0, i=4–6) cases to be half-metal with integer total magnetic moments of 6, 8, 8, and 4μB, respectively. Whereas, the antiferromagnetic coupling between two identical M atom under superexchange mechanism leads to Mn (0, i=1–6) and Co (0, i=1–6) cases as well as Fe (0, i ≠ 2) and Ni (0, i=1–3) cases to be nonmagnetic semiconductor as well as nonmagnetic metal, respectively. [ABSTRACT FROM AUTHOR]

The structural, electronic and magnetic properties of the quaternary Heusler alloy TiZrCoSn have been investigated firstly by using the first-principles calculations within GGA and GGA+U methods. The structural study shows the Y-type (I) is the most stable configuration among three possible configurations of the TiZrCoSn alloy in FM phase. The GGA calculation shows the TiZrCoSn alloy at its equilibrium lattice constant 6.536 Å is HM ferromagnet with an indirect band gap of 1.043 eV and a HM gap of 0.353 eV in the spin-down channel. The formation energy of −1.041 eV and the cohesion energy of 24.402 eV indicate the stability of the TiZrCoSn alloy. The Curie temperature of the TiZrCoSn alloy is higher than room temperature shows the TiZrCoSn alloy is suitable for spintronic applications. The band gap in the spin-down channel is formed by the bonding ( t 2g ) states and nonbonding ( t u ) states created from the d states hybridisation of transition metal atoms Ti, Zr and Co. The TiZrCoSn alloy has an integer total magnetic moment of 3 μ B / f .u . , satisfying the Slater-Pauling rule μ t = Z t − 18 . In addition, the HM character is kept as hydrostatic strain ranges from −10.3% to 8.4% and tetragonal strain ranges from −16.3% to 20.8%. The similar results are also obtained by GGA+U calculation. [ABSTRACT FROM AUTHOR]

The spin-polarized first-principles calculations are performed to study the structural, electronic and magnetic properties of a single and two identical transition metal (TM) atoms X (X = V, Cr, Mn, Fe, Co and Ni) doped ZnS dilute magnetic semiconductors (DMS). The single V-, Cr-, Fe- and Ni-doped ZnS systems exhibit the magnetic half-metallic (HM) characters, while Mn- and Co-doped ZnS systems display magnetic semiconducting characters. For two identical TM atoms doped ZnS systems, the two identical V, Cr and Ni atoms are in a ferromagnetic (FM) coupling under the double-exchange (DE) mechanism, leading V-, Cr- and Ni-doped ZnS systems to be HM with FM coupling. While two identical Mn- and Co-doped ZnS systems are semiconductors with antiferromagnetic (AFM) coupling consisting with the superexchange (SE) mechanism. Specifically, two identical Fe atoms display a competition between the SE and DE mechanisms. The Zn 70 Fe 2 S 72 system is metal with AFM coupling at the nearest separation of two Fe atoms while HM with FM coupling at the farther separations of two Fe atoms. [ABSTRACT FROM AUTHOR]

The spin-polarized first-principles calculations are performed to study the electronic structures and magnetic properties of a single or double identical transition metal (TM) atoms X (X = Mn, Fe, Co and Ni) doped monolayer WS 2 systems. Although the pristine monolayer WS 2 system is a nonmagnetic semiconductor with a direct band gap of 1.820 eV, a single Mn, Fe, Co or Ni doped WS 2 systems exhibit the magnetic half-metallic (HM) characters with the total magnetic moments M tot of 1, 2, 3 and 4 μ B and the smaller spin-down gaps E g of 1.262, 1.154, 1.407 and 1.073 eV, respectively. For double identical TM atoms doped monolayer WS 2 systems, except for the cases of two Ni atoms doped at the first (0,1), second (0,2) and third (0,3) nearest-neighbor cation configuration which are antiferromagnetic (AFM), ferromagnetic (FM) and FM metals, respectively, the other cases are all HM ferromagnets, and the total magnetic moment M tot increases not only for double identical TM dopants Mn, Fe, Co and Ni (except for (0,1) AFM case) successively at the same nearest-neighbor cation configuration but also for each of the double identical TM dopants at the first (0,1), second (0,2) and third (0,3) nearest-neighbor cation configurations successively. These results provide a theoretical guide to choose new two-dimensional HM ferromagnetic materials in spintronic applications. [ABSTRACT FROM AUTHOR]

We have performed the first-principles calculations on the structural, electronic, and magnetic properties of 3d transition-metal™ (Cr, Mn, Fe, Co, and Ni) atoms doped 2D GaN nanosheet. The results show that 3d TM atom substituting one Ga leads to a structural reconstruction around the 3d TM impurity compared to the pristine GaN nanosheet. The doping of TM atom can induce magnetic moments, which are mainly located on the 3d TM atom and its nearest-neighbor N atoms. It is found that Mn- and Ni-doped GaN nanosheet with 100% spin polarization characters seem to be good candidates for spintronic applications. When two Ga atoms are substituted by two TM dopants, the ferromagnetic (FM) ordering becomes energetically more favorable for Cr-, Mn-, and Ni-doped GaN nanosheet with different distances of two TM atoms. On the contrary, the antiferromagnetic (AFM) ordering is energetically more favorable for Fe-doped GaN nanosheet. In addition, our GGA + U calculations show the similar results with GGA calculations. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The structural, electronic, magnetic and optical properties of 4d transition metal adatoms (Tc, Ru, Rh and Cd) adsorbed on blue phosphorene (blue P) monolayer have been systematically investigated by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA) as well as taking into account the on-site Coulomb repulsive interactions (GGA + U). The pristine blue P monolayer is a nonmagnetic semiconductor, but adatom-doping with these 4d transition metals is an effective way to modify its electronic, magnetic and optical properties and thus expands its applications in spintronics, magnetoelectronics and optoelectronics. Except for the close-filled Cd adatom is unadsorbed, the Tc and Ru adatom-adsorbed blue P monolayers change to bipolar magnetic semiconductor, while the Rh adatom-adsorbed blue P monolayer turns into magnetic spin-gapless semiconductor. The binding energy and optical absorption results confirm that, the Tc, Ru and Rh adatom-adsorbed blue P monolayers are not only fabricable experimentally but also have enhanced absorption for visible and infrared lights. The structural, electronic, magnetic and optical properties of 4d transition metal adatoms (Tc, Ru, Rh and Cd) adsorbed on blue phosphorene monolayer have been systematically investigated. The improvement of optical absorption property for blue phosphorene monolayer will be beneficial to its potential applications towards photovoltaics. [Display omitted] • Tc and Ru adatom-adsorbed blue P monolayers change to bipolar magnetic semiconductor. • Rh adatom-adsorbed blue P monolayer turns into magnetic spin-gapless semiconductor. • Close-filled Cd adatom is unadsorbed on blue P monolayer. • Absorptions of infrared and visible light are enhanced in Tc, Ru and Rh adatom-adsorbed blue P monolayers. [ABSTRACT FROM AUTHOR]

The electronic structure and magnetic and optical properties of a 3 d transition metal M (M = V, Cr, Mn, Fe) doped (5,5) boron nitride (BMN) nanotube are investigated by using the first-principles projector augmented wave potential within density functional theory under the generalized gradient approximation. It is found that BVN and BMnN systems are ideal candidates for spintronic applications, and the BCrN system seems to be a promising diluted magnetic semiconductor. The analyses of optical dielectric functions show that BCrN exhibits a new main peak at about 0.3 eV, and thus may be utilized in fields that are associated with infrared technology, such as infrared detectors, infrared masers, and so on. [ABSTRACT FROM AUTHOR]

Abstract: Structural, electronic and magnetic properties of six 3d transition metals (TM=V, Cr, Mn, Fe, Co and Ni) linear monoatomic chains adsorbed on the (5,5) boron nitride nanotube (BNNT) at five different sites have been investigated by first-principle calculations. The results indicate all TM chains can be spontaneously adsorbed on the outer surface of the BNNT. The stable adsorption sites are different for different TM chains. All TM chains can be adsorbed on the N site, while the adsorption on the Z site is unstable. The dispersion character occurs in energy band curves of stable TM/BNNT systems and bring about the band gap disappearance in comparison with that of pure (5,5) BNNT. Interestingly, the TM/BNNT systems with nearly half-filled 3d metals V and Cr at H and N sites, as well as Mn at A site show a half-metal character and are usable in spintronics devices. The different electronic properties of BNNT can also be achieved through decorations of the same TM chain on different sites. The TM chain adsorbed BNNT systems exhibit high stability, promising electronic properties and high magnetic moments, which may be useful for a wide variety of next-generation nanoelectronic device components. [Copyright &y& Elsevier]

Abstract: The substitution of a single boron atom or two atoms boron and nitrogen in (4,4) and (8,0) boron nitride nanotubes (BNNTs) by 3d transition metal (TM=V, Cr or Mn) atom has been systemically studied using first-principle calculations. All optimized TM-doped BNNT systems have obvious local deformation of the nanotubes, and almost all TM atoms protrude to the exterior of the wall. The substitution of TM atoms induces some impurity states within the band gaps of the pure BNNTs. The B site V-doped (4,4) BNNT system is half-metal while the BN1 site TM-doped (4,4) BNNT systems are metallicity. All the TM-doped (8,0) BNNT systems are still semiconductor. Overall charges are transferred from the TM atoms to more electronegative BNNTs. The substituted doping of TM atoms gives rise to magnetic moments which mainly stem from TM atoms. Therefore, the substitution of doping by TM enhances the chemical reactivity and significantly increases the conductivity of pure BNNT, and renders the TM-doped BNNT systems have larger magnetic moments. All these show the TM-doped BNNT systems have potential applications in hydrogen storage, gas sensing, catalysts, spintronics and magnetic data storage devices. [ABSTRACT FROM AUTHOR]

Combining the modified analytic embedded atom method (MAEAM) with lattice dynamics theory, the phonon dispersion along five symmetry directions have been calculated for three transition metals V, Nb and Ta. A good agreement between calculations and experiments along three high symmetry directions [q00], [qqq] and [qq0] implies that the predicted phonon dispersion along the other two directions [1qq] and $[\frac{1}{2}\frac{1}{2}q]$ are well behaved. Along each direction, the phonon frequency decreases for V, Nb and Ta successively may be related to the ratio of the cohesive energy to atomic mass. [ABSTRACT FROM AUTHOR]

Abstract: The structure, electronic and magnetic properties of transition metals M9 (M=Fe, Co or Ni) nanowires encapsulated inside armchair (8,8) beryllium oxygen nanotube (BeONT) [M9@(8,8)] have been investigated by first-principles calculations. Due to strong interaction between inner M9 nanowire and outer BeONT, not only a near square cross-section shape is formed for outer BeONT but also a counter-clockwise rotation about their common axis takes place for the M9 nanowire. The charge density accumulated strongly around the O atom implies a large charge transfer from Fe atom (as well as from Be atom) to O atom and thus the ionic-binding characters exist among them. The negative values of the binding energies for all three M9@(8,8) hybrid systems indicate the combining processes of all three M9@(8,8) hybrid systems are exothermic. Therefore, the stable insulator (8,8) BeONT can be used to shield the M9 nanowire. Although (8,8) BeONT is non-magnetic and a decrease in the magnetic moments is found after M9 nanowires are encapsulated inside (8,8) BeONT, less than ten percent reduction in the magnetic moments shows all three M9@(8,8) hybrid systems can be utilized in spin transport devices. [ABSTRACT FROM AUTHOR]

Abstract: The surface relaxation and surface energy of both the mixed AuCu and pure Cu terminated Cu3Au (001) surfaces are simulated and calculated by using the modified analytical embedded-atom method. We find that the mixed AuCu termination is energetically preferred over the pure Cu termination thereby the mono-vacancy diffusion is also investigated in the topmost few layers of the mixed AuCu terminated Cu3Au (001) surface. In the mixed AuCu terminated surface the relaxed Au atoms are raised above Cu atoms for 0.13Å in the topmost layer. All the surface atoms displace outwards, this effect occurs in the first three layers and changes the first two inter-layer spacing. For mono-vacancy migration in the first layer, the migration energies of Au and Cu mono-vacancy via two-type in-plane displace: the nearest neighbor jump (NNJ) and the second nearest neighbor jump (2NNJ), are calculated and the results show that the NNJ requires a much lower energy than 2NNJ. For the evolution of the energy requirements for successive nearest neighbor jumps (SNNJ) along three different paths: circularity, zigzag and beeline, we find that the circularity path is preferred over the other two paths due to its minimum energy barriers and final energies. In the second layer, the NN jumps in intra- and inter-layer of the Cu mono-vacancy are investigated. The calculated energy barriers and final energies show that the vacancy prefer jump up to a proximate Cu site. This replacement between the Cu vacancy in the second layer and Cu atom in the first layer is remunerative for the Au atoms enrichment in the topmost layer. [Copyright &y& Elsevier]

Abstract: The structural stability and theoretical strength of BCC transition metals Cr, Mo and W under hydrostatic loading have been investigated by combining the modified analytical embedded atom method (MAEAM) with modified Born stability criteria. For all three BCC transition metals Cr, Mo and W, the stable regions are controlled by shear modulus μ only. Determined stable regions are 0.917–1.079, 0.907–1.090, 0.904–1.095 in the relative deformation a/a 0 and corresponding compressive and tensile theoretical strengths are 161.0 and 28.15, 162.3 and 34.56, 198.8 and 41.60GPa for Cr, Mo, W, respectively. The calculated stresses are consistent well with the results of ab initio calculation. [Copyright &y& Elsevier]

Abstract: The formation energies, the intra- and inter-layer migration and diffuse activation energies of a single vacancy in W(001) surface have been investigated with the modified analytical embedded-atom method (MAEAM). The results show that the effect of the surface on the vacancy is only down to the fourth-layer. It is easier for a vacancy to form and to migrate in the first layer. For inter-layer migration, a single vacancy in the second atomic layer is favorable to migrate to the first layer via the 1NN jump, that in the third atomic layer is favorable to migrate to the first layer via the 2NN jump, and that in the fourth atomic layer is favorable to migrate to the second layer via the 2NN jump. However, a single vacancy in the fifth or sixth layer is not easy to migrate to the upper layer due to its slightly higher migration energy than that of the vacancy migrating to lower layer. [Copyright &y& Elsevier]

Abstract: Combining MAEAM with the lattice dynamics, the atomic force constants and phonon dispersion curves have been obtained along five symmetry directions [00 ζ], [0 ζ ζ], [ζ ζ ζ], and [ζ ζ 1] for three BCC transition metals Ta, W and Mo within interactions out to the sixth neighbors. The calculated results that are nearly in agreement with available experimental results along [00 ζ], [0 ζ ζ] and [ζ ζ ζ] directions implies that the predicted phonon dispersion curves along and [ζ ζ 1] directions are well behaved. Along each symmetry direction, the vibration frequency that increases for Ta, W and Mo successively may be related to the ratio of cohesive energy E c to mass M. [Copyright &y& Elsevier]

Abstract: The energy during the process of self-diffusion in BCC transition metals Fe, W, Mo, Cr, Ta, Nb and V has been calculated by using modified analytic embedded-atom method (MAEAM). For each kind of three diffusion mechanisms nearest-neighbor (NN), next-nearest-neighbor (NNN) and third-nearest-neighbor (TNN), the energy curve is symmetric and the maximum value of the energy appears at the middle point of the diffusion path. Determined mono-vacancy formation energy , migration energy and activation energy Q 1v for self-diffusion agree well with available experimental data of NN diffusion and are better than those obtained by the analytic embedded-atom method (AEAM) and Finnis–Sinclair models. Compared the energies corresponding to three diffusion mechanisms, the NN diffusion needs the lowest activation energy (and thus the lowest migration energy). So that, the NN mono-vacancy diffusion is favorable in BCC transition metals. [Copyright &y& Elsevier]

Abstract: The general expressions for the compliance , Young''s modulus E(hkl) and Poisson''s ratio υ(hkl) along an arbitrary direction [hkl] are given for cubic crystals. The representation surfaces, for which the length of the radius vector in the [hkl] direction equals to E(hkl) or υ(hkl), are constructed for seven BCC transition metals Cr, Fe, Mo, Nb, Ta, V and W. Neglecting W, which is isotropic, both representation surfaces of Young''s modulus and Poisson''s ratio are spherical surfaces. The remaining BCC transition metals may be grouped into two classes. In the first group (Cr, Mo, Nb and V) with negative values of s A, Young''s modulus surface has eight depressed corners and six rounded protuberances at the centers of the faces. In the second group (Fe and Ta) with positive values of s A, on the contrary, Young''s modulus surface has eight rounded protuberance corners and six depressions at the centers of the faces. The contrary conclusions are obtained for Poisson''s ratio. [Copyright &y& Elsevier]

Abstract: The formation energies of isolated vacancy and adatom–vacancy pair (where the two are separated by a large distance) at low-index surfaces of fcc metals calculated by using the modifies analytical embedded atom method (MAEAM). The results predict the prevailing formation of vacancies on the surfaces (111), (100) (but Pd), Cu and Ni on the (110) surfaces at low temperature, and the defect formation energies consistently create in the sequence (110)→(100)→(111). With good accuracy, the calculated energy values coincide with those obtained by the embedded atom methods (EAM) and from experiments. The correctness of the method by which calculated the formation energies of point defects on the surface was proved. [Copyright &y& Elsevier]

Abstract: The surface energies for 24 surfaces of all bcc transition metals Fe, Cr, Mo, W, V, Nb and Ta have been calculated by using the second nearest–neighbor modified embedded atom method. The results show that, for all bcc transition metals, the order among three low-index surface energies E (110) < E (100) < E (111) is in agreement with experimental results and E (110) is also the lowest surface energy for various surfaces. So that from surface energy minimization, the (110) texture should be favorable in the bcc films. This is also consistent with experimental results. The surface energy for the other surfaces increases linearly with increasing angle between the surfaces (h k l) and (110). Therefore, a deviation of a surface orientation from (110) can be used to estimate the relative values of the surface energy. [Copyright &y& Elsevier]

Abstract: The energies of the ideal, missing row (MR) and missing column (MC) (110) surfaces have been calculated by using modified embedded atom method (MEAM) for seven face centered cubic (FCC) transition metals Au, Pt, Ag, Pd, Rh, Cu and Ni. The results, that the MC reconstruction can not be formed for all metals, while the MR reconstruction can be formed naturally for Au and Pt, inductively for Ag, Pd, Rh and Cu and difficultly for Ni, are better than EAM calculated results in comparing with experimental results. In addition to the surface energy explanation, the results are also related to the surface topography and valence electron structure. [Copyright &y& Elsevier]

We investigate mechanical, structural and electronic properties of CO2 adsorbed graphitic carbon nitride (g-C3N4) system under biaxial tensile strain via first-principles calculations. The results show that the stress of CO2 adsorbed g-C3N4 system increases and then decreases linearly with the increasing biaxial strain, reaching maximum at 0.12 strain. This is primarily caused by the plane N–C stretching of the g-C3N4. Furthermore, both the Perdew-Burke-Ernzerhof (PBE) and Heyd- Scuseria-Ernzerhof screened hybrid functional (HSE06) band gaps show direct-indirect transitions under biaxial tensile strain and have the maximum also at 0.12 strain. It is found that there is large dipole transition matrix element around Γ point, leading high optical absorption coefficients of the deformed adsorption system, which would be of great use for the applications of new elastic nanoelectronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

• Electronic structure and magnetic properties of doped PtTe 2 monolayer are studied by first-principles calculation. • Long-range ferromagnetic ordering is introduced in the V-, Cu- and Zn-doped PtTe 2 monolayers. • The Mn- and Fe- doped PtTe 2 monolayers have antiferromagnetic ordering in ground state. • The group VA atom N, P and As doped monolayers exhibit ferromagnetic ground state. Most of the two-dimensional layered materials discovered so far are intrinsically nonmagnetic. Introducing ferromagnetism into these materials will expand their application greatly in the field of spintronics. Here we study the introduction of ferromagnetism into the PtTe 2 monolayer via doping the 3d transition metal atoms and the group VA and VIIB atoms by means of the first-principles calculations. Results show that the magnetic order can be introduced in the V-, Mn-, Fe-, Cu- and Zn-doped PtTe 2 monolayers, among which the V-, Cu- and Zn-doped monolayers have ferromagnetic ground state, and the Mn- and Fe-doped monolayers have antiferromagnetic ordering in ground state. Among the group VA atom doped systems, N-, P- and As-doped monolayers exhibit ferromagnetic, and Sb doped monolayer is a nonmagnetic metal. All the VIIB atom doped PtTe 2 monolayers are nonmagnetic, while the doping makes the PtTe 2 monolayer transit from an indirect bandgap semiconductor to metal. The findings obtained in this work may initiate new experimental exploration and expand the application of the layered transition-metal ditellurides in spintronics. [ABSTRACT FROM AUTHOR]

• Ferromagnetism of M Te 2 monolayers are studied by first-principles calculation. • M Te 2 (M = V, Mn, Fe) monolayers are founded to be ferromagnetic. • Curie temperature of VTe 2 monolayer is near the room temperature. • Ferromagnetism origin and the magnetocrystalline anisotropy are discussed theoretically. We study the electronic structure and magnetism of monolayer 3 d transition-metal ditellurides M Te 2 (M = Ti, V, Cr, Mn, Fe, Co and Ni) in trigonal prismatic H- and/or octahedral T-phase by means of the first-principles calculations. The results show that H-VTe 2 , T-VTe 2 , H-FeTe 2 and T-MnTe 2 monolayers exhibit intrinsic ferromagnetism, and the others have no ferromagnetism. The exchange splitting of V, Mn and Fe 3d orbitals is responsible for ferromagnetism. The exchange constant and the Curie temperature are estimated by using 2D Ising model and mean field theory. Among the four ferromagnetic monolayers, the H-VTe 2 monolayer has the largest exchange constant and the corresponding Curie temperature is near room temperature. Calculations also show that the T-VTe 2 , H-VTe 2 and H-FeTe 2 monolayers have in-plane easy magnetization direction, while the easy direction of the T-MnTe 2 monolayer is perpendicular to the layer. Moreover, we analyze the relative exchange strength of the four ferromagnetic monolayers based on the competition between the through-bond ferromagnetic interaction and the through-space antiferromagnetic interaction according to the Goodenough–Kanamori rules. The magnetocrystalline anisotropy is explained qualitatively based on the second-order perturbation theory from the spin-orbit coupling between 3d orbitals of M atoms. [ABSTRACT FROM AUTHOR]

• It is easily to dope 5d TM atoms into monolayer SnS 2 under S-rich condition. • W, Re, Os, Ir, Pt, Au, Hg-doped monolayer SnS 2 have moments 2, 3, 2, 1, 0, 1, 2µ B. • W, Re, Hg-doped monolayer SnS 2 systems are magnetic semiconductors. • Os, Ir, Au-doped monolayer SnS 2 are magnetic half-metallic useable in spintronics. We explore the structural, electronic and magnetic properties of the monolayer SnS 2 systems doped with 5d transition metals (TM) atoms X (X = W, Re, Os, Ir, Pt, Au or Hg) using first-principles approach. The formation energies show that these materials can be easily fabricated under the S-rich experimental condition. The spin-polarized phases are more favorable than non spin-polarized phases. The pristine monolayer SnS 2 is a nonmagnetic semiconductor with an indirect band gap of 1.579 eV, the 5d TM atoms X (X = W, Re, Os, Ir, Pt, Au or Hg) doped monolayer SnS 2 systems have the total magnetic moments of 2, 3, 2, 1, 0, 1, 2 µ B , respectively, because the octahedral coordinated six S ligands bring in a larger crystal field splitting than exchange splitting onto the 5d TM atoms X. Furthermore, the spin-polarized band structures show that the W, Re or Hg-doped monolayer SnS 2 systems are magnetic semiconductors, but the Os, Ir or Au-doped monolayer SnS 2 systems are magnetic half-metallic with the wider band gaps of 1.509, 1.632 or 1.383 eV respectively in one of the two spin channels, and thus are useable in spintronic fields. [ABSTRACT FROM AUTHOR]

Inspired by the unique properties and potential applications especially in spintronics, here we investigate the structure and electronic properties of the bulk TiZrIrZ (Z = Al, Ga or In) quaternary Heusler alloys and their (001)-oriented thin films by using first-principles calculations. The results show that all the bulk TiZrIrZ alloys are half-metallic ferromagnets with a total magnetic moment μ t of 2 μ B /f. u., satisfying the Slater-Pauling rule μ t = Z t − 18. Their spin-down band gaps are resulted from the d-d hybridizations between the transition metal elements Ti, Zr and Ir. The large absolute values of both positive cohesive energies and negative formation energies indicate these three alloys are thermodynamically stable and can be fabricated experimentally. The nonappearances of negative phonon frequency demonstrate their dynamic stability. Furthermore, their (001)-oriented thin films with natural ZrZ (Z = Al, Ga or In) terminations are still half-metallic ferromagnets and thus useable in spintronics and magnetoelectronics fields. • The bulk TiZrIrZ (Z = Al, Ga or In) alloys are stable in type-I configuration ferromagnetic phase. • The bulk TiZrIrZ alloys are thermodynamically, dynamically and mechanically stable. • Magnitude of B, G, Y, V m and Θ D varies as TiZrIrGa>TiZrIrAl>TiZrIrIn. • The bulk TiZrIrZ alloys are all half-metallic ferromagnets (HM-FM). • The TiZrIrZ (001)-oriented thin films with ZrZ (Z = Al, Ga or In) terminations are still HM-FM. [ABSTRACT FROM AUTHOR]

Abstract: The energetics, electronic and magnetic properties of 3d transition-metal (TM) atoms adsorbed low-dimensional Ge honeycomb structures have been systematically investigated from the spin-polarized density-functional theory calculations. For the two-dimensional Ge honeycomb structure, all TM atoms considered prefer to adsorb on the hollow site of the buckled hexagon in both single-sided and double-sided adsorption cases, with binding energies ranging between 3.27 and 5.92eV. Upon adsorption, the semimetallic 2D honeycomb Ge can change to either ferromagnetic or antiferromagnetic metals depending on both TM species and coverage density. For the one-dimensional structure, we found binding of TM atoms to hollow site of the edge hexagon yields the minimum energy state for all TM species considered and in all three AGeNRs examined which belong to different families. Depending on ribbon width, adsorbed TM species and adsorption concentration, most of the TM decorated AGeNRs can either be metals or semiconductors with ferromagnetic or antiferromagnetic spin alignment, except for Co-adsorbed ones which remain to be nonmagnetic. Interestingly, Cr or Mn adsorption can make certain AGeNRs to be half-metallic with a 100% spin-polarization at Fermi level which can be good candidates for future application in spintronic fields. Furthermore, the effect of the on-site Coulomb interaction on the stability of these half-metallic ribbons is also considered by performing L(S)DA+ U calculations, and the results show that the half-metallic ground state of the Cr-adsorbed ribbons is more robust than that of the Mn-adsorbed one. [Copyright &y& Elsevier]

Abstract: Using density-functional theory calculations, we investigate the energetic, electronic and magnetic properties of 3d transition metals adsorption on hydrogen-passivated germanium nanowire along [001] direction. It is found that most of the adatoms prefer to bind on the HH site, while the Sc adatom prefers to the Top site. The atoms of good conducting metals, such as Cu and Zn form weak bonding with the wire, however, those such as Ti, V, Fe, Co, and Ni have relative larger binding energies. In addition, various types of wires can be obtained depending on the adatom species, including nonmagnetic metals (Sc or Cu adsorption) and semiconductors (Ni or Zn adsorption), weak-ferromagnetic metals (Ti or V adsorption), ferromagnetic semiconductor (Cr adsorption), and more interesting the ferromagnetic half-metals (Mn, Fe or Co adsorption) with 100% spin-polarization at the Fermi level. These ferromagnetic wires should have potential applications in the fields of quasi-one-dimensional spintronics devices. Detail analysis of the density of states indicates that the ferromagnetism originates mainly from spin-split of the TM-3d states. Furthermore, the effect of on-site Coulomb interaction on the stability of the three ferromagnetic half-metallic wires is also examined, and it is found that the half-metallic ground state of Mn- or Co-adsorbed wire is more robust than that of Fe-adsorbed wire. [ABSTRACT FROM AUTHOR]

Using the first-principles calculations based on density functional theory (DFT-D2 method), we systematically study the structural, energetic, electronic and magnetic properties of toxic gas molecules (H 2 S, NH 3 and SO 2) adsorbed on pristine and transition metal (TM) atom (Fe, Mn) doped GaN monolayer (GaN-ML). The results show that the H 2 S and NH 3 are physisorbed on pristine GaN-ML with small adsorption energy, charge transfer, and long adsorption distance. While chemical adsorption character of SO 2 on GaN-ML can be obtained, which means that the pristine GaN-ML is sensitive to SO 2. We find that the adsorption ability of pristine GaN-ML can be improved by introducing TM dopants. TM (Fe, Mn) doping can increase adsorption energy and charge transfer of the adsorbed systems, except for SO 2 adsorbed Fe doped GaN-ML. The enhancing interaction between adsorbed molecules and the TM doped GaN-ML can dramatically induce electrical conductivity changes. Therefore, the TM doped GaN-ML is more suitable for gas molecules detection compared with the pristine GaN-ML. These present properties of gas molecules adsorbed on the pristine and TM doped GaN-ML will help to guide scientists to develop better two-dimensional GaN-based gas sensors in the future. • Adsorptions of toxic gas molecules on pristine and TM doped GaN-ML are studied by DFT-D2 method. • The H 2 S and NH 3 are physisorbed on pristine GaN-ML, while chemical adsorption character of SO 2 on GaN-ML can be obtained. • TM doping is promising to improve gas molecules adsorption ability of pristine GaN-ML. • The enhancing interaction between gas molecules and TM doped GaN-ML can induce electrical conductivity changes. [ABSTRACT FROM AUTHOR]

Abstract To explore the novel application of graphene nanomaterials, we investigate the structural, electronic and magnetic properties of transition metals (TM = V, Cr, Mn, Fe, Co and Ni) monatomic chains intercalated AA stacked bilayer graphene nanoribbons ([GTMG] w) using first-principles calculations. The combining processes of all the [GTMG] w compounds are exothermic except the [GCuG] w (w = 5, 6, 7, 8, 9) compounds, accompanying with larger formation energies and charges transfer. The formed TM–C ionic bonds are contributed to enhancing the stability of [GTMG] w compounds. The most stable intercalated structures, are the [GVG] w compounds for the different TM chain, and are the [GTMG] 4 compounds for the different widths of bilayer graphene nanoribbons (w = 4, 5, 6, 7, 8, 9). The [GMnG] w compounds have the maximum magnetic moment, but the [GVG] w , [GNiG] w and [GCuG] w compounds have magnetic quenching phenomenon with zero magnetic moment. There are different magnetic properties for the even (w = 4, 6, 8) and odd (w = 5, 7, 9) widths of bilayer graphene nanoribbons in [GTMG] compounds. Therefore, the TM chains intercalated bilayer graphene nanoribbons exhibit tunable magnetic properties for potential spintronics applications. Highlights • The most stable structures are the [GVG] w compounds for the different TM chain. • The most stable structures are [GMG] 4 compounds for the different width nanoribbons. • The Mn chains intercalated BGR have the maximum magnetic moment. • The V, Ni and Cu chains intercalated BGR have magnetic quenching phenomenon. • The magnetic moments are different for the even and odd width of BGR in [GMG] compounds. [ABSTRACT FROM AUTHOR]

Using first-principles calculations based on density-functional theory, the effects of adsorbates (CO molecule, O and N atoms) and defects (an adhered atom and a monovacancy) on structural and electronic properties of the smallest (4, 4) AgNT have been systematically investigated. For CO adsorption on energetically preferred top site, the donation–backdonation process between the CO and Ag states leads to the formation of bonding/antibonding pairs, 5σ b /5σ a and 2π b ∗ /2π a ∗ , and the quantum conductance of AgNT decreases by 1 G 0 after CO adsorption. Both O and N atoms strongly interact with AgNT after adsorption, leading to a 3 G 0 and 2 G 0 of drop in quantum conductance, respectively, for the AgNT. High adsorption energy of adhesion of one Ag atom and relatively low formation energy of a monovacancy suggest that these two types of defects are likely to occur in the fabrication of AgNT. The quantum conductance of the AgNT remains unchanged for adhesion of one Ag atom, but decreases by 1 G 0 when a monovacancy is present. [ABSTRACT FROM AUTHOR]

Using first-principles calculations based on density functional theory (DFT-D2 method), the adsorption behavior of pristine and transition metal (TM) atoms (Fe, Ni, Pd and Pt) doped α -AsP monolayer for toxic H 2 S, CO and NO molecules are systematically studied. The results show that TM dopants prefer to substitute As atoms with lower binding energy. TM doping significantly enhances the adsorption ability of the α -AsP monolayer for H 2 S, CO and NO molecules. Furthermore, there is a significant change in work function (WF) after H 2 S, CO and NO adsorption, meaning that the TM doped α -AsP monolayer is sensitive to gas molecules. Double NO can be stably adsorbed on the TM doped substrate plane, indicating that they are suitable for reversible sensor applications under practical circumstances. Our calculations can provide theoretical guidance to develop promising novel two dimensional V–V binary AsP-based gas sensors. • The adsorption behavior of H 2 S, CO and NO molecules on pristine and TM doped α -AsP monolayer are studied by DFT-D2 method. • TM doping can significantly enhance the adsorption ability of the α -AsP monolayer for H 2 S, CO and NO molecules. • TM doped α -AsP monolayer could be promising candidate for better adsorption or detection the toxic H 2 S, CO and NO molecules. [ABSTRACT FROM AUTHOR]

Abstract: We have performed first-principles calculations on the structural, electronic and magnetic properties of seven different 3d transition-metal (TM) impurity (V, Cr, Mn, Fe, Co, Ni and Cu) doped armchair (5,0) and zigzag (8,0) gallium nitride nanotubes (GaNNTs). The results show that there is distortion around 3d TM impurities with respect to the pristine GaNNTs for 3d TM-doped (5,5) and (8,0) GaNNTs. The change of total magnetic moment follows Hund’s rule for 3d TM-doped (5,5) and (8,0) GaNNTs, respectively. The total density of states (DOS) indicates that Cr-, Mn-, Fe- and Ni-doped (5,5) GaNNTs as well as Cr-, Mn-, Ni- and Cu-doped (8,0) GaNNTs are all half-metals with 100% spin polarization. The study suggests that such TM-doped nanotubes may be useful in spintronics and nanomagnets. [Copyright &y& Elsevier]

Abstract: We have performed the first-principles calculations onto the adsorption behaviors of 12 transition-metal (TM) atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd and Pt) on the surface of the pristine zigzag (8,0) gallium nitride nanotube (GaNNT). The results show that, for Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Pd and Pt, the most stable adsorption sites are all on the top site of the nitrogen atom (N), whereas Ni prefers slightly to the hollow site above the Ga3N3 hexagon ring (H). The binding energies can vary significantly with different TM atoms. This may be related to their number of d electrons. The almost zero binding energy of Zn atom means it can only be physically adsorbed above the N site. The binding energy of Cr is negative (–0.32eV), indicating the adsorption process is endothermal. The adsorption of TM atoms generally induces some impurity states within the band gap of the pristine GaNNT, except weaker metallic adatom Pd with fully filled 4d electrons of 10. For Cu-adsorbed (8,0) GaNNT, only one type of bands (minority spin) crosses the Fermi level implying the Cu-adsorbed (8,0) GaNNT is half-metal. The certain amount of charge is transferred from the TM atoms to the (8,0) GaNNTs. The Sc-, V-, Cr-, Mn-, Fe-, Co- and Cu-adsorbed (8,0) GaNNT systems have a net magnetic moment from 0.60 (for Cu) to 4.98 (for Mn). These net magnetic moments are located mainly on the TM atoms. [ABSTRACT FROM AUTHOR]

To explore the novel properties and applications of two-dimensional black phosphorene, we perform a first-principles study on the modulation of the structure and electronic properties of bilayer phosphorene nanoribbons (BPNRs) by using transition metal (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) atoms. For one-dimensional zigzag-edge AA-stacked bilayer phosphorene nanoribbons with hydrogen passivation, we find that the atomic stacking of the BPNRs reorders from the AA to the AE stacking. The AE-stacked structure is the most stable structure for one-dimensional zigzag BPNRs. All the BPNRs with widths N = 4–10 exhibit semiconductor character with indirect band gaps (1.17, 1.01, 0.92, 0.84, 0.75, 0.74, and 0.72 eV), which gradually decrease with increasing nanoribbon width. The adsorption energies show that all the TM atom-adsorbed 4-BPNR compound systems [PTMP] can form stable structures, however, the most stable structures have different adsorption energies (−9.38, −10.73, −13.19, −8.26, −13.68, −9.73, −10.41, −10.33, and −5.98 eV) for different TM (Sc, Ti, V, Cr, Mn, Fe, Co, Ni and Cu) atoms. The calculated bond lengths, charge transfer, and difference charge density of [PMnP] systems indicate that there are strong chemical interactions between the TM atoms and their adjacent P atoms in the BPNRs, resulting in the formation of TM-P ionic bonds. The adsorption of TM atoms induces various electronic structures in 4-BPNR. The [PTMP] 1 systems exhibit metallic properties with the adsorption of Sc, Co, and Cu atoms, and semiconductor properties with the adsorption of Ti, V, Cr, Mn, Fe, and Ni atoms with band gaps of 0.30, 0.18, 0.19, 0.20, 0.61, and 0.08 eV, respectively. The Ni and Cu adsorption systems show magnetic quenching with no magnetic moments in all the compound systems [PTMP]. The [PCrP] 1 has the maximum magnetic moment of approximately 3.62 μ B amongst all the [PTMP] 1 systems, while the [PVP] 1 and [PMnP] 1 systems have magnetic moments of 1.66 μ B and 1.84 μ B , respectively. Our results show that TM atom-adsorbed bilayer phosphorene nanoribbons exhibit tunable electronic structures and magnetic properties for potential applications in nanoelectronics. • The atomic stacking of the BPNRs reorder from the AA to the AE stacking. • All the BPNRs are semiconductive with indirect bandgaps which gradually decreases with increasing nanoribbon width. • There are strong chemical interactions and TM-P ionic bond between TM atoms and their adjacent P atoms in the BPNRs. • The adsorption of TM atoms induces various electronic structures in 4-BPNR. [ABSTRACT FROM AUTHOR]

The adsorption of hydrogen sulfide molecules onto bilayer graphene (BG) doped with transition metals (TM), such as V, Cr, Mn, Fe, Co, and Ni, was studied using external electric fields and density functional theory calculations. The adsorption of H 2 S onto TM-doped BG was significantly improved compared with adsorption onto pristine BG. An external electric field can promote the adsorption of H 2 S onto BG, and the stability of this adsorption increases with the intensity of the electric field. Typically, this stability is independent of the direction of the electric field (upward or downward). However, H 2 S is sensitive to the direction of the electric field, and a downward (negative value) electric field is more favorable for H 2 S adsorption onto TM-doped BG. The desorption of H 2 S molecules from TM-doped BG was achieved using an upward (positive value) electric field, and the maximum desorption effect occurred at an electric field intensity of approximately 0.2 V/Å. The adsorption of gas molecules was also observed to modify the electronic structures of the TM/BG systems. All the TM/BG-H 2 S systems demonstrated semiconductive characteristics with different band gaps, except for the V/BG-H 2 S system. Overall, the results of this study showed that TM-doped BG has potential applications to methods for the adsorption, storage, and detection of H 2 S gas. • The TM/BG systems can significantly improve the adsorption stability of H 2 S compared with pristine bilayer graphene. • The external electric field promotes the adsorption of H 2 S onto bilayer graphene. • The adsorption of H 2 S is sensitive to the direction of the electric field. • The desorption of H 2 S gas molecules from TM-doped bilayer graphene can be achieved using an upward electric field. • The adsorption of gas molecules modifies the electronic structures of the TM/BG systems. [ABSTRACT FROM AUTHOR]

First-principles calculations within the density functional theory (DFT-D2 method) is carried out to systematically investigate the structural, energetic, electronic and magnetic properties of toxic CO and NO gas molecules on pristine and transition metal (TM) atom (Fe, Co, Ni, Pd, Ag and Pt) doped blue phosphorene. Our calculations show that the CO and NO molecules are physisorbed on pristine blue phosphorene due to small adsorption energies, charge transfer, and large adsorption distances of the adsorbed systems. TM doping can significantly enhance the interaction between the gas molecules and the blue phosphorene, leading to the CO and NO molecules absorbed on TM doped blue phosphorene belong to chemisorption with relatively large adsorption energies and charge transfer, except for CO adsorbed on Ag doped blue phosphorene. Meanwhile, the enhancing interaction between the gas molecules and TM doped blue phosphorene can dramatically induce magnetism and electrical conductivity changes. These results indicate that TM doped blue phosphorene is a potential candidate to develop novel two-dimensional phosphorene-based gas sensors. • Adsorptions of CO and NO gas molecules on pristine and TM doped blue phosphorene are studied by DFT-D2 method. • The chemical adsorption character of CO and NO molecules on TM doped blue phosphorene can be obtained. • TM atom doping can improve the gas molecules adsorption ability of pristine blue phosphorene. • The enhancing interaction between gas molecules and TM doped blue phosphorene can induce magnetism and conductivity changes. [ABSTRACT FROM AUTHOR]

The gap-strain curves of 2H-SnS 2 , 1T-SnS 2 and 1T-SnSe 2 are similarly parabolas, while SnO 2 decreases linearly with increasing strain. Notably, the slope of the band gap variation of the biaxial strained 1T-SnO 2 reaches up to −0.16 eV/1%. • The stiffness of 2H-SnX 2 is much higher. • The band gap of SnO 2 decreases linearly with increasing strain. • The gap-strain curves of 2H-SnS 2 , 1T-SnS 2 and 1T-SnSe 2 are similarly parabolas. • Small (1%) deformations can results in semiconductor-metal transitions. Based on first-principles calculations, we investigate the structural, mechanical and electronic properties of monolayer tin dioxides and dichalcogenides SnX 2 (X O, S, Se, Te) under uniaxial and biaxial strains. Our results show that monolayer 1T-SnX 2 is energetically more stable than 2H-SnX 2 , while the stiffness of 2H-SnX 2 is much higher. The unstrained SnX 2 is thermodynamically and dynamically more stable than the strained ones. We also show that when external strain is applied, the band gaps of both 2H- and 1T-SnO 2 decrease linearly with increasing strain, which is contributed by the strain induced orbital redistribution of the decomposition of the p orbital of X atom and s, p orbitals of Sn atom. Notably, the slope of the band gap variation of the biaxial strained 1T-SnO 2 reaches up to -0.16 eV/1%. In our calculations, strain can result in a semiconductor–metal transition of 2H-SnX 2 , while it only affects the band gap of 1T-SnX 2. [ABSTRACT FROM AUTHOR]