Modifying the electronic and magnetic properties of the scandium nitride semiconductor monolayer via vacancies and doping.

In this work, the effects of vacancies and doping on the electronic and magnetic properties of the stable scandium nitride (ScN) monolayer are investigated using first-principles calculations. The pristine monolayer is a two-dimensional (2D) indirect-gap semiconductor material with an energy gap of 1.59(2.84) eV as calculated using the GGA-PBE (HSE06) functional. The projected density of states, charge distribution, and electron localization function assert its ionic character generated by the charge transfer from the Sc atoms to the N atoms. The monolayer is magnetized by a single Sc vacancy with a total magnetic moment of 3.00µB, while a single N vacancy causes a weaker magnetization with a total magnetic moment of 0.52µB. In both cases, the magnetism originates mainly from the atoms closest to the defect site. Significant magnetization is also reached by doping with acceptor impurities. Specifically, a total magnetic moment of 2.00µB is obtained by doping with alkali metals (Li and Na) in the Sc sublattice and with B in the N sublattice. Doping with alkaline earth metals (Be and Mg) in the Sc sublattice and with C in the N sublattice induces a value of 1.00µB. In these cases, either magnetic semiconducting or half-metallicity characteristics arise in the ScN monolayer, making it a prospective 2D spintronic material. In contrast, no magnetism is induced by doping with donor impurities (O and F atoms) in the N sublattice. An O impurity metallizes the monolayer; meanwhile, F doping leads to a large band-gap reduction of the order of 82%, widening the working regime of the monolayer in optoelectronic devices. The results presented herein may introduce efficient methods to functionalize the ScN monolayer for optoelectronic and spintronic applications.

A systematic investigation of chromium and vanadium impurities in a Janus Ga2SO monolayer towards spintronic applications.

Transition metals (TMs) have been employed as efficient sources of magnetism in non-magnetic two-dimensional (2D) materials. In this work, doping with chromium (Cr) and vanadium (V) is proposed to induce feature-rich electronic and magnetic properties in a Janus Ga2SO monolayer towards spintronic applications. The Ga2SO monolayer is a 2D semiconductor material with an energy gap of 1.30 (2.12) eV obtained from PBE(HSE06)-based calculations. Considering the structural asymmetry, different vacancy and doping sites are considered. A single Ga vacancy and pair of Ga vacancies magnetize the monolayer with total magnetic moments between 0.69 and 3.13µB, where the half-metallic nature is induced by the single Ga1 vacancy (that bound to the S atom). In these cases, the magnetism is originated mainly from S and O atoms closest to the vacancy sites. Depending on the doping site, either half-metallicity or diluted magnetic semiconductor natures are obtained by doping with Cr and V atoms with total magnetic moments of 3.00 and 2.00µB, respectively. Herein, 3d TM impurities produce mainly the system magnetism. When substituting a pair of Ga atoms, TM atoms exhibit the antiparallel spin alignment to follow the Pauli exclusion principle, retaining the novel electronic characteristics induced by a single TM dopant. Except for the case of doping with a pair of V atoms, total magnetic moments of 2.00 and 1.00µB are obtained by doping with a pair or Cr atoms and Cr/V co-doping, respectively. The non-zero magnetic moment is derived from the different interactions of each TM atom with its neighboring atoms, which will also be studied by Bader charge analysis. Our results introduce new promising 2D spintronic candidates, which are made by structural modifications at Ga sites of a non-magnetic Janus Ga2SO monolayer.

Antiferromagnetism in GaS monolayer doped with TM-TM atom pairs (TM = V, Cr, Mn, and Fe).

In this work, structural modification at Ga sites of the gallium sulfide (GaS) monolayer is explored to create new two-dimensional (2D) materials towards spintronic applications. GaS monolayer is a non-magnetic indirect-gap semiconductor material with an energy gap of 2.38 (3.27) eV as calculated using the PBE(HSE06) functional. Half-metallicity is induced in this 2D material by creating a single Ga vacancy, where S atoms around the defect site produce mainly the magnetic properties with a total magnetic moment of 1.00µB. In contrast, the non-magnetic nature is preserved under the effects of a pair of Ga vacancies, which metallize the monolayer. V, Mn, and Fe doping leads to the emergence of the diluted magnetic semiconductor nature, while doping with Cr creates a new 2D half-metallic material from the GaS monolayer. In these cases, total magnetic moments between 2.00 and 5.00µB are obtained and the 3d orbital of transition metal (TM) impurities mainly induces the system magnetism. In addition, the effects of doping with a pair of TM (pTM) atoms are also investigated, in which the antiferromagnetism is found to be stable rather than the ferromagnetism to follow the Pauli exclusion principle. Significant magnetization of the GaS monolayer is also achieved with zero total magnetic moment because of the structural mirror-symmetry. pV-, pMn-, and pFe-doped systems are antiferromagnetic semiconductor materials with energy gaps of 1.06, 1.90, and 1.84 eV, respectively. Meanwhile, the monolayer is metallized by doping with a pCr pair. The results presented herein indicate that the defective and doped GaS monolayers are prospective 2D candidates for spintronic applications - which are hindered for the pristine GaS monolayer because of the absence of intrinsic magnetism.

Rich essential properties of silicon-substituted graphene nanoribbons: a comprehensive computational study.

The diverse structural, electronic, and magnetic properties of silicon (Si)-substituted armchair and zigzag graphene nanoribbons (AGNRs and ZGNRs) were investigated using spin-polarized density functional theory (DFT) calculations. Pristine AGNRs belong to a nonmagnetic semiconductor with a direct bandgap of 1.63/1.92 eV determined by PBE/HSE06 functionals. Under various Si substitutions, nonmagnetic bandgaps were tuned at 1.49/1.87, 1.06/1.84, 0.81/1.45, 1.04/1.71, 0.89/1.05, and 2.38/3.0 eV (PBE/HSE06) in the single Si edge-, single Si non-edge-, double Si ortho-, double Si meta-, double Si para-, and 100% Si-substituted AGNR configurations, respectively. Meanwhile, pristine ZGNRs displayed antiferromagnetic semiconducting behavior with a spin degenerate bandgap of 0.52/0.81 eV (PBE/HSE06) and becomes a ferromagnetic semimetal in the single Si configurations or an unusual ferromagnetic semiconductor in the 100% Si configuration. Under the developed first-principles theoretical framework, the formation of quasi π (C-2pz and Si-3pz) and quasi σ (C-2s, -2pxy and Si-3s and -3pxy) bands was identified in the Si-substituted configurations. These quasi π and quasi σ bands showed weak separation, resulting in weak quasi sp2 hybridization in Si-C bonds, in which the identified hybridization mechanism was a strong evidence for the formation of stable planar 1D structures in the Si-substituted configurations. Our complete revelation of the essential properties of Si-substituted GNRs can provide a complete understanding of their chemically doped 1D materials for various practical applications.

Half-metallic and magnetic semiconductor behavior in CdO monolayer induced by acceptor impurities.

In this work, a doping approach is explored as a possible method to induce novel features in the CdO monolayer for spintronic applications. Monolayer CdO is a two-dimensional (2D) non-magnetic semiconductor material with a band gap of 0.82 eV. In monolayer CdO, a single Cd vacancy leads to magnetization of the monolayer with a total magnetic moment of -2µB, whereas its non-magnetic nature is preserved upon creating a single O vacancy. Doping the Cd sublattice with Cu-Ag and Au induces half-metallic character with a total magnetic moment of -1 and 1µB, respectively. Dopants and their neighboring O atoms produce mainly magnetic properties. By contrast, doping with N, P, and As at the O sublattice leads to the emergence of magnetic semiconductor behavior with a total magnetic moment of 1µB. Herein, magnetism originates mainly from the spin-asymmetric charge distribution in the outermost orbitals of the dopants. Bader charge analysis and charge density difference calculations indicate charge transfer from Cu, Ag and Au dopants to the host monolayer, whereas the N, P and As dopants exhibit important charge gains. These results suggest that doping with acceptor impurities is an efficient approach to functionalize the CdO monolayer to generate spin currents in spintronic devices.

Doping-mediated electronic and magnetic properties of graphene-like ionic NaX (X = F and Cl) monolayers.

In this work, the stability, and electronic and magnetic properties of pristine and doped graphene-like ionic NaX (X = F and Cl) monolayers are explored using first-principles calculations. The good stability of NaF and NaCl monolayers is confirmed by phonon dispersion curves and ab initio molecular dynamics simulations. Electronic structure calculations show their insulator nature with large indirect band gaps of 5.43 (7.26) and 5.06 (6.32) eV as calculated with the PBE (HSE06) functional, respectively. In addition, their ionic character is also demonstrated. Furthermore, a doping approach is explored to functionalize NaX monolayers for spintronic applications. For such a goal, IIA- and VIA-group atoms are selected as dopants due to their dissimilar valence electronic configuration as compared with the host atoms. The results indicate the emergence of magnetic semiconductor nature with a total magnetic moment of 1µB. Herein, magnetic properties are produced mainly by the dopant atoms, which induce new middle-gap energy states around the Fermi level. Finally, the effects of codoping the NaF monolayer with Ca and O and NaCl with Ba and O are also examined. Adjacent Ca-O and Ba-O pairs preserve the non-magnetic nature. Further separating dopants leads to the emergence of magnetic semiconductor behavior, with lower magnetization than separate doping. This work introduces new ionic 2D materials for optoelectronic and spintronic applications, contributing to the research effort to find out new 2D multifunctional materials.

Novel germanene-arsenene and germanene-antimonene lateral heterostructures: interline-dependent electronic and magnetic properties.

Seamlessly stitching two-dimensional (2D) materials may lead to the emergence of novel properties triggered by the interactions at the interface. In this work, a series of 2D lateral heterostructures (LHSs), namely germanene-arsenene (Gem-As8-m) and germanene-antimonene (Gem-Sb8-m), are investigated using first-principles calculations. The results demonstrate a strong interline-dependence of the electronic and magnetic properties. Specifically, the LHS formation along an armchair line preserves the non-magnetic nature of the original materials. However, this is an efficient approach to open the electronic band gap of the germanene monolayer, where band gaps as large as 0.74 and 0.76 eV are induced for Ge2-As6 and Ge2-Sb6 LHSs, respectively. Meanwhile, magnetism may appear in the zigzag-LHSs depending on the chemical composition (m = 3, 4, 5, and 6 for germanene-arsenene and m = 2, 3, 4, 5, and 6 for germanene-antimonene), where total magnetic moments between 0.13 and 0.50 µB are obtained. Herein, magnetic properties are produced mainly by the spin-up state of Ge atoms at the interface, where a small contribution comes from As(Sb) atoms. Spin-resolved band structures show a multivalley profile in both the valence band and the conduction band with a topological insulator-like behavior, where the interface states are derived mainly from the interface Ge-pz state. The results introduce new 2D lateral heterostructures with novel electronic and magnetic properties to allow new functionalities, which could be further explored for optoelectronic and spintronic applications.

Introducing the 1H-Na2S monolayer as a new direct gap semiconductor with feature-rich electronic and magnetic properties.

In this work, a new direct gap semiconductor, the Na2S monolayer in the 1H-phase, with good stability and ionic character, has been explored using first-principles calculations. A Γ-Γ energy gap of 0.80 (1.48) eV is obtained using the standard PBE (hybrid HSE06) functional. The studied two-dimensional (2D) material possesses weak dynamical stability under compressive strain due to the sensitivity of the ZA mode. Meanwhile tensile strain has much more positive effects, where the stability is well retained up to a strain strength of 7%. Once external strain is applied, the band gap increases due to switching from lattice compression to lattice tension. Further exploration of defect engineering indicates that significant magnetism with magnetic moment of ±1 is induced by a single Na vacancy. The magnetic properties are mainly produced by S atoms around the defect site. In contrast, the paramagnetic nature is preserved with a single S vacancy. However, large energy gap reduction of up to 93.75% can be achieved with a defect concentration of 25%. This research introduces a new prospective 2D material similar to transition metal dichalcogenides for optoelectronic and spintronic applications, contributing to the continued efforts to develop novel multifunctional low-dimensional materials.

Ferromagnetic half-metallicity of the cubic NaMgO3 perovskite: from bulk to (001) surfaces.

Exploration of new half-metallic materials for spintronic applications has drawn great attention from researchers. In this work, we investigate the structural, electronic, and magnetic properties of the NaMgO3 perovskite in the bulk and (001) surface conformations. The results show the half-metallic nature of bulk NaMgO3 generated by insulator spin-up channels with a large band gap of 6.08 eV and metallic spin-down channels. A total magnetic moment of 3 (µB) is obtained, which is produced mainly by O atoms with a local magnetic moment of 0.94 (µB). Once the bulk is cleaved along the (001) direction, atomic relaxation takes place to reach an equilibrium, where all constituent atoms exhibit an inward movement. Interestingly, the half-metallicity is retained from the bulk to the (001) surface conformation. The effects of slab termination and thickness on the surface energy, stability, band edges, spin-up energy gaps, and magnetic anisotropy will be also analyzed in detail. The results presented herein introduce the NaMgO3 perovskite as a promising half-metallic material to generate spin current in spintronic devices.

Two-dimensional buckled tetragonal cadmium chalcogenides including CdS, CdSe, and CdTe monolayers as photo-catalysts for water splitting.

Pure hydrogen production via water splitting is an ideal strategy for producing clean and sustainable energy. Two-dimensional (2D) cadmium chalcogenide single-layers with a tetragonal crystal structure, namely Tetra-CdX (X = S, Se, and Te) monolayers, are theoretically predicted by means of density functional theory (DFT). Their structural stability and electronic and optical properties are investigated. We find that Tetra-CdX single-layers are thermodynamically stable. Their stability decreases as we go down the 6A group in the periodic table, i.e., from X = S to Se, and Te which also means that the electronegativity decreases. All considered novel monolayers are indirect band gap semiconductors. Using the HSE06 functional the electronic band gaps of CdS, CdSe, and CdTe monolayers are predicted to be 3.10 eV, 2.97 eV, and 2.90 eV, respectively. The impact of mechanical strain on the physical properties was studied, which indicates that compressive strain increases the band gap and tensile strain decreases the band gap. The optical properties of the Tetra-CdX monolayers show the ability of these monolayers to absorb visible light. Due to the suitable band gaps and band edge positions of Tetra-CdX, these newly discovered 2D materials are promising for photocatalytic water splitting.

Two-dimensional Janus semiconductor BiTeCl and BiTeBr monolayers: a first-principles study on their tunable electronic properties via an electric field and mechanical strain.

Motivated by the recent successful synthesis of highly crystalline ultrathin BiTeCl and BiTeBr layered sheets [Debarati Hajra et al., ACS Nano, 2020, 14, 15626], herein for the first time, we carry out a comprehensive study on the structural and electronic properties of BiTeCl and BiTeBr Janus monolayers using density functional theory (DFT) calculations. Different structural and electronic parameters including the lattice constant, bond lengths, layer thickness in the z-direction, different interatomic angles, work function, charge density difference, cohesive energy and Rashba coefficients are determined to acquire a deep understanding of these monolayers. The calculations show good stability of the studied single layers. BiTeCl and BiTeBr monolayers are semiconductors with electronic bandgaps of 0.83 and 0.80 eV, respectively. The results also show that the semiconductor-metal transformation can be induced by increasing the number of layers. In addition, the engineering of the electronic structure is also studied by applying an electric field, and mechanical uniaxial and biaxial strain. The results show a significant change of the bandgaps and that an indirect-direct band-gap transition can be induced. This study highlights the positive prospect for the application of BiTeCl and BiTeBr layered sheets in novel electronic and energy conversion systems.

Effect of adsorption and substitutional B doping at different concentrations on the electronic and magnetic properties of a BeO monolayer: a first-principles study.

The 2D form of the BeO sheet has been successfully prepared (Hui Zhang et al., ACS Nano, 2021, 15, 2497). Motivated by these exciting experimental results on the 2D layered BeO structure, we studied the effect of the adsorption of B atoms on BeO (B@BeO) and substitutional B atoms (B-BeO) at the Be site at different B concentrations. We investigated the structural stability and the mechanical, electronic, magnetic, and optical properties of the mentioned structures using first-principles calculations. We found out that hexagonal BeO monolayers with adsorbed and dopant B atoms have different mechanical stabilities at different concentrations. B@BeO and B-BeO monolayers are brittle structures, and B@BeO structures are more rigid than B-BeO monolayers (at the same B concentration). The adsorption and the formation energy per B atom decrease as the B concentration increases. In comparison, the work function increases when increasing the B concentration. The work function of B@BeO is higher than the corresponding value of B-BeO (at the same B concentration). The magnetic moment linearly increases as the B concentration increases. BeO is a semiconductor with an indirect bandgap of 5.3 eV. The B@BeO and B-BeO structures are semiconductors, except for 3B-BeO (14.2% doped concentration), which is a metal. The bandgap is 1.25 eV for most of the adsorbed atom concentrations. For B-BeO, the bandgap decreases to zero at a concentration of 14.2%. The bandgap of the B-BeO monolayer at different B concentrations is smaller than the corresponding values of the B@BeO monolayer, which indicates that B substitutional doping has a greater effect on the electronic structure of the BeO monolayer than B adsorption doping. We investigated the optical properties, including the dielectric function and absorption coefficient. The results indicate good optical absorption in the range of infrared and ultraviolet energies for the B adsorbed and doped BeO monolayer.

Electronic, optical and thermoelectric properties of a novel two-dimensional SbXY (X = Se, Te; Y = Br, I) family: ab initio perspective.

Recent developments in the synthesis of highly crystalline ultrathin BiTeX (X = Br, Cl) structures [Debarati Hajra et al., ACS Nano 14, 15626 (2020)] have led to the exploration of the atomic structure, dynamical stability, and electronic, optical, and thermoelectric properties of SbXY (X = Se, Te; Y = Br, I) monolayers via density functional calculations. The calculated phonon spectrum, elastic stability conditions, and cohesive energy verified the stability of the studied SbXY monolayers. The mechanical properties reveal that all studied monolayers are stable and brittle. Based on PBE (PBE + SOC) functional calculations, the SbXY monolayers are semiconductors with indirect bandgaps. The calculated bandgaps using HSE (HSE + SOC) for SbSeBr, SbSeI, SbTeBr, and SbTeI monolayers are between 1.45 and 1.91 eV, which are appealing for applications in nanoelectronic devices. The signature of the Rashba effect appears in the SbXY monolayer. The SbXY monolayers are visible-light active. Hole doping can be an efficient way to increase the electricity production of SbXY monolayers from waste heat energy. This study suggests that SbXY (X = Se, Te; Y = Br, I) monolayers represent promising new electronic, optical, and energy conversion systems.

First-principles investigation of nonmetal doped single-layer BiOBr as a potential photocatalyst with a low recombination rate.

Nonmetal doping is an effective approach to modify the electronic band structure and enhance the photocatalytic performance of bismuth oxyhalides. Using density functional theory, we systematically examine the fundamental properties of single-layer BiOBr doped with boron (B) and phosphorus (P) atoms. The stability of the doped models is investigated based on the formation energies, where the substitutional doping is found to be energetically more stable under O-rich conditions than under Bi-rich ones. The results showed that substitutional doping of P atoms reduced the bandgap of pristine BiOBr to a greater extent than that of boron substitution. The calculation of the effective masses reveals that B doping can render the electrons and holes of pristine BiOBr lighter and heavier, respectively, resulting in a slower recombination rate of photoexcited electron-hole pairs. Based on the results of HOMO-LUMO calculations, the introduction of B atoms tends to increase the number of photocatalytically active sites. The top of the valence band and the conduction band bottom of the B doped BiOBr monolayer match well with the water redox potentials in an acidic environment. The absorption spectra propose that B(P) doping causes a red-shift. Overall, the results predict that nonmetal-doped BiOBr monolayers have a reduced bandgap, a slow recombination rate, more catalytically active sites, enhanced optical absorption edges, and reduced work functions, which will contribute to superior photocatalytic performance.

n/p-Doping in a buckled honeycomb InAs monolayer using IVA-group impurities.

In this work, the effects of n/p-doping on the electronic and magnetic properties of a low-buckled honeycomb InAs monolayer are investigated using first-principles calculations. Herein, IVA-group atoms (C, Si, Ge, Sn, and Pb) are selected as impurities for n-doping in the In sublattice and p-doping in the As sublattice. The pristine monolayer is a semiconductor with a band gap of 0.77(1.41) as determined using the PBE(HSE06) functional. A single In vacancy induces magnetic semiconductor behavior with a large total magnetic moment of 2.98 µB, while a single As vacancy preserves the non-magnetic nature. The monolayer is not magnetized by n-doping with C and Si atoms due to the strong ionic interactions, while the magnetic semiconducting nature is induced with Ge, Sn, and Pb impurities. In these cases, magnetic properties are produced by IVA-group impurities and their neighboring As atoms. Furthermore, either a magnetic semiconducting or half-metallic nature is obtained via p-doping, whereas magnetism originates mainly from C, Si, Ge, and Sn dopants, and the As atoms closest to a Pb dopant. Further investigation indicates that the magnetization becomes stronger upon increasing the doping level, with a total magnetic moment of up to 3.92 µB with 25% Sn impurity. In addition, the thermal stability of the doped systems at room temperature is also confirmed by ab initio molecular-dynamics (AIMD) simulations. The results introduce IVA-group-assisted functionalization as an efficient way to make prospective 2D InAs-based spintronic materials.

Vacancy-and doping-mediated electronic and magnetic properties of PtSSe monolayer towards optoelectronic and spintronic applications.

Developing new multifunctional two-dimensional (2D) materials with two or more functions has been one of the main tasks of materials scientists. In this work, defect engineering is explored to functionalize PtSSe monolayer with feature-rich electronic and magnetic properties. Pristine monolayer is a non-magnetic semiconductor 2D material with a band gap of 1.52(2.31) eV obtained from PBE(HSE06)-based calculations. Upon creating single Pt vacancy, the half-metallic property is induced in PtSSe monolayer with a total magnetic moment of 4.00 µ B. Herein, magnetism is originated mainly from S and Se atoms around the defect site. In contrast, single S and Se vacancies preserve the non-magnetic nature. However, the band gap suffers of considerable reduction of the order of 67.11% and 48.68%, respectively. The half-metallicity emerges also upon doping with alkali metals (Li and Na) with total magnetic moment of 1.00 µ B, while alkaline earth impurities (Be and Mg) make new diluted magnetic semiconductor materials from PtSSe monolayer with total magnetic moment of 2.00 µ B. In these cases, magnetic properties are produced mainly by Se atoms closest to the doping site. In addition, doping with P and As atoms at chalcogen sites is also investigated. Except for the half-metallic AsSe system (As doping at Se site), the diluted magnetic semiconductor behavior is obtained in the remaining cases. Spin density results indicate key role of the VA-group impurities in magnetizing PtSSe monolayer. In these cases, total magnetic moments between 0.99 and 1.00 µ B are obtained. Further Bader charge analysis implies the charge loser role of all impurities that transfer charge to the host monolayer. Results presented in this work may suggest promises of the defected and doped Janus PtSSe structures for optoelectronic and spintronic applications.

Controlling the electronic and magnetic properties of the GeAs monolayer by generating Ge vacancies and doping with transition-metal atoms.

Controlling the electronic and magnetic properties of two-dimensional (2D) materials is a key step to make new multifunctional candidates for practical applications. In this work, defects and doping with transition metals (TMs = V, Cr, Mn, and Fe) at Ge sublattices are proposed in order to develop novel features in the hexagonal germanium arsenide (GeAs) monolayer. The pristine GeAs monolayer is a non-magnetic indirect gap semiconductor with an energy gap of 1.20(1.82) eV as provided by PBE(HSE06)-based calculations. A single Ge vacancy metallizes the monolayer, preserving its non-magnetic nature. In contrast, significant magnetization with a total magnetic moment of 1.96 µ B is achieved by a pair of Ge vacancies. Herein, the computed band structures assert the half-metallic behavior of the defective system. Similarly, half-metallicity is also obtained by V, Mn, and Fe doping. Meanwhile, the Cr-doped GeAs monolayer is classified as a diluted magnetic semiconductor 2D system. In these cases, magnetic properties are produced mainly by TM-3d electrons with total magnetic moments between 2.00 and 4.00 µ B. Further, the effects of substituting a pair of Ge atoms with a pair of TM atoms (pTMGe systems) are also investigated. Results indicate the ferromagnetic half-metallicity of the pVGe system, meanwhile antiferromagnetic ordering is stable in the remaining cases. In all cases, TM impurities transfer charge to the host GeAs monolayer since they are surrounded by As atoms, which are more electronegative than dopant atoms. Results presented herein may introduce new 2D systems - made from the non-magnetic GeAs monolayer - for spintronic applications with suitable electronic and magnetic features controlled mainly by transition metals.

Realizing new 2D spintronic materials from the non-magnetic 1T-PdO2 monolayer through vacancy defects and doping.

In this work, vacancy- and doping-based magnetism engineering in a non-magnetic 1T-PdO2 monolayer is explored in order to realize new two-dimensional (2D) spintronic materials. The pristine monolayer is an indirect gap semiconductor with a band gap of 1.45 (3.20) eV obtained using the PBE (HSE06) functional. Half-metallicity with a total magnetic moment of 3.95 µB is induced by creating a single Pd vacancy, where the magnetic properties are produced mainly by O atoms around the vacancy site. In contrast, the non-magnetic nature is preserved under the effects of a single O vacancy, however a band gap reduction in the order of 37.93% is achieved. Further doping with transition metals (TMs = V, Cr, Mn, and Fe) in the Pd sublattice and with non-metals (B, C, N, and F) in the O sublattice is investigated. TM impurities lead to the emergence of a diluted magnetic semiconductor nature, where total magnetic moments of 1.00, 2.00, and 3.00 µB are obtained in the V-, Cr(Fe)-, and Mn-doped systems, respectively. In these cases, the TMs' 3d electrons mainly originate the system's magnetism. Significant magnetization of the PdO2 monolayer is also achieved by doping with B, N, and F atoms, where either half-metallic or diluted magnetic semiconductor natures are induced. Herein, electronic and magnetic properties are regulated mainly by the interactions between the 2p orbital of the dopant, 4d orbital of the first neighbor Pd atoms, and 2p orbital of the second neighbor O atoms. Meanwhile, C impurity induces no magnetism in the PdO2 monolayer because of the strong electronic hybridization with their neighbor atoms. Results presented herein may introduce efficient approaches to engineer magnetism in a non-magnetic PdO2 monolayer, such that the functionalized systems are further recommended for prospective spintronic applications.

Electronic and magnetic properties of GeS monolayer effected by point defects and doping.

In this work, defect engineering and doping are proposed to effectively functionalize a germanium sulfide (GeS) mononolayer. With a buckled hexagonal structure, the good dynamical and thermal stability of the GeS monolayer is confirmed. PBE(HSE06)-based calculations assert the indirect gap semiconductor nature of this two-dimensional (2D) material with a relatively large band gap of 2.48(3.28) eV. The creation of a single Ge vacancy magnetizes the monolayer with a total magnetic moment of 1.99 µB, creating a the feature-rich half-metallic nature. VaS vacancy, VaGeS divacancy, SGe and GeS antisites preserve the non-magnetic nature; however, they induce considerable band gap reduction of the order 47.98%, 89.11%, 29.84%, and 62.5%, respectively. By doping with transition metals (TMs), large total magnetic moments of 3.00, 4.00, and 5.00 µB are obtained with V, Cr-Fe, and Mn impurities, respectively. The 3d orbital of TM dopants mainly regulates the electronic and magnetic properties, which induces either the half-metallic or diluted magnetic semiconductor nature. It is found that the doping site plays a determinant role in the case of doping with VA-group atoms (P and As). The GeS monolayer can be metallized by doping the Ge sublattice, meanwhile both spin states exhibit semiconductor character with strong spin polarization upon doping the S sublattice to obtain a diluted magnetic semiconductor nature with a total magnetic moment of 1.00 µB. In these cases, the magnetism originates mainly from P and As impurities. The obtained results suggest an efficient approach to functionalize the GeS monolayer for optoelectronic and spintronic applications.

Adsorption effects of acetone and acetonitrile on defected penta-PdSe2 nanoribbons: a DFT study.

Using DFT calculations, the structural and electronic properties of the ZZ7 p-PdSe2 nanoribbons (ZZ7) with the four kinds of vacancy defects, including ZZ7-VPd, ZZ7-VSe, ZZ7-VPd+Se, and ZZ7-V2Se are studied, in which their stability, diverse geometries, and altered electronic properties are determined through the formation energies, optimal structural parameters, electronic band structures, and DOSs. Specifically, the formation energies of all studied systems show significant negative values around -3.9 eV, evidencing their good thermal stability. The geometries of four defective structures exhibit different diversification, whereas only the ZZ7-V2Se structure possesses the highly enhanced feature, identified as the most effective substrate for the acetone and acetonitrile adsorption. On the electronic behaviors, the ZZ7 band structure displays the nonmagnetic metallic characteristics that become the ferromagnetic half-metallic band structures for the ZZ7-VPd and ZZ7-VSe and the ferromagnetic semi-metallic band structures for the ZZ7-VPd+Se and ZZ7-V2Se. For adsorption of the acetone and acetonitrile on the ZZ7-V2Se structure, the energetic stability, adsorption sites, adsorption distances, charge transfers, and electronic characteristics of the adsorbed systems are determined by the adsorption energies, optimal adsorption sites, adsorption distances, Mulliken populations, and DOSs. The adsorption energies of the acetone- and acetonitrile-adsorbed ZZ7-V2Se systems display significant values at -1.2 eV and -0.86 eV at the preferable sites of 8 and 11, respectively, indicating their great adsorption ability. The adsorption mechanism of the acetone- and acetonitrile-adsorbed systems belongs to the physisorption owing to absence of chemical bonds, in which the bond lengths of the ZZ7-V2Se substrate show a very small deviation. Under the acetone and acetonitrile adsorptions, the ferromagnetic semi-metallic DOSs of the ZZ7-V2Se become the ferromagnetic half-metallic DOSs for the ZZ7-V2Se-acetone-8 and the ferromagnetic semiconducting DOSs for the ZZ7-V2Se-acetonitrile-11. Our systematic results can provide a complete understanding of the acetone- and acetonitrile adsorptions on the potential ZZ7-V2Se structure, which is very useful for nanosensor application.