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Black phosphorene (BP) have aroused great concern because of its great potential for the application in nanoelectronic devices and high-performance anode materials for alkali metal ion batteries (AIBs). However, the absence of magnetism for an ideal BP limits its wide application in spintronic devices which is one of the important nanoelectronic devices, and its application as a high-performance anode material for AIBs is still to be explored. In this paper, we adopt first-principles calculations to explore the effects of B, C, N, O, F, Al, Si and S atom doping on the magnetic state of monolayer BP and Li or Na atom adsorption and diffusion on the BP. Additionally, the thermal stability of the doped BP systems at room temperature is revealed by the ab initio molecular-dynamics calculations. Our calculated results indicate that O and S doping can make the doped BP become a magnetic semiconductor, C and Si doping makes the doped BP be metallic, and B, N, F and Al doping preserves semiconductor property. Moreover, little structural changes and significant decreases of diffusion barriers in armchair direction and slight increases of diffusion barriers in zigzag direction make B-doped BP beneficial as an anode material for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). It reveals that S-doping is suitable for improving the performance of SIBs rather than LIBs. Interestingly, it is found that magnetic states of O- and S-doped BP disappear when Li or Na atoms adsorb on them, whereas Li or Na adsorption on B- and Al-doped BP induces magnetic states of these systems. The analyses indicate that the distinct electron transfer between the dopant atom, adatom and neighboring P atoms, and specific electron configuration of dopant atoms cause the magnetism of the systems. Our results suggest that selecting appropriate composition to dope can effectively manipulate magnetic state and improve Li/Na adsorption and diffusion on the BP. These results may inspire further theoretical and experimental exploration on doped two-dimensional (2D) materials in spintronics and doped 2D promising anode materials for high-performance metal ion batteries.

In recent years, the discovery of ‘magic angle’ graphene has given new inspiration to the formation of heterojunctions. Similarly, the use of hexagonal boron nitride, known as white graphene, as a substrate for graphene devices has more aroused great interest in the graphene/hexagonal boron nitride heterostructure system. Based on the first principles method of density functional theory, the band structure, density of states, Mulliken population, and differential charge density of a tightly packed model of twisted graphene/hexagonal boron nitride/graphene sandwich structure have been studied. Through the establishment of heterostructure models twisted bilayer-graphene inserting hBN with different twisted angles, it was found that the band gap, Mulliken population, and charge density, exhibited specific evolution regulars with the rotation angle of the upper graphene, showing novel electronic properties and realizing metal–insulator phase transition. We find that the particular value of the twist angle at which the metal–insulator phase transition occurs and propose a rotational regulation mechanism with angular periodicity. Our results have guiding significance for the practical application of heterojunction electronic devices.

In this paper, topological quantum phase transition was reported in the magnetic topological insulator MnBi2Te4 under pressure strain. Electronic and topological properties of the bulk anti-ferromagnetic MnBi2Te4 were investigated by first-principles calculations. We found that the band structure of MnBi2Te4 changes with the strain, resulting in a phase transition between metal and insulator. From the variation of charge-density distribution with strain, it was found that hydrostatic tensile strain is beneficial for increasing the interlayer spacing, thereby reducing the anti-ferromagnetic interaction between layers. On the contrary, the compressive strain promotes the strengthening of the bonding between the Te and Bi atomic layers. It was worth noting that the phase transition occurs at 2.12% strain when the band crossing is observed at Γ point, suggesting that the band gap has just closed. In addition, through the calculation of surface states, it is observed that, after the action of 2.12% strain, the bulk band gap of the system closes with the surface band gap reopens, achieving an intrinsic mechanism of strain modulation of the MnBi2Te4 antiferromagnetic bulk structure to undergoes a topological quantum phase transition. Our results provide feasible guidance not only for pressure-strain engineering of MnBi2Te4 experimentally but also for developing a meaningful strain-control mechanism for the electronic structures of other potential intrinsic magnetic insulators.

Two-dimensional heterostructures formed by stacking layered materials play a significant role in condensed matter physics and materials science due to their potential applications in high-efficiency nanoelectronic and optoelectronic devices. In this paper, the structural, electronic, and optical properties of SiC/CrS2 van der Waals heterostructure (vdWHs) have been investigated by means of density functional theory calculations. It is confirmed that the SiC/CrS2 vdWHs is energetically and thermodynamically stable indicating its great promise for experimental realization. We find that the SiC/CrS2 vdWHs has a direct-band gap and type-II (staggered) band alignment, which can effectively separate the photo-induced electrons and holes pairs and extend their life time. The carrier mobilities of electrons and holes along the armchair and zigzag directions are as high as 6.621 × 103 and 6.182 × 104 cm2 V−1 s−1, respectively. Besides, the charge difference and potential drop across the interface can induce a large built-in electric field across the heterojunction, which will further hinder the electron and hole recombination. The SiC/CrS2 vdWHs has enhanced optical absorption capability compared to individual monolayers. This study demonstrates that the SiC/CrS2 vdWHs is a good candidate for application in the nanoelectronic and optoelectronic devices.

Contacts between black phosphorene (BP) and metal electrodes are critical components of BP-based devices and can dramatically affect device performance. In this paper, we adopted first-principles calculations to explore binding energies, electronic structures, spatial potential distribution of monolayer BP–Ni interfaces in surface contact and edge contact types, and used density functional theoretical coupled with nonequilibrium Green’s function method to investigate the electrical transport properties for transport systems of monolayer BP with Ni electrodes. Our calculated results indicate that contact type between monolayer BP and metal Ni electrodes may much affect the transport properties of monolayer BP–Ni devices. Interfacial interaction between Ni and monolayer BP in edge contact type is stronger than that in surface contact type. The potential distributions indicate that edge contact type is more beneficial for reducing contact resistance of monolayer BP–Ni contacts and conducive to improve the performance of BP–Ni electrode device.

Thin films with stable half-metallic (HM) character and 100% spin-polarization (SP) are required to be used in spintronic devices. The HM character has been predicted theoretically in many Heusler alloys thin films and confirmed by experiments. Full-Heusler alloy Ti2FeSn has been studied extensively. It has been reported that their (001)-oriented thin films with TiFe or TiSn terminations preserve 100% SP, but the HM character is unstable because the edge of the bandgap is closed to the Fermi level E F. Therefore, we investigate the effects of the Co-doping on the structural, electronic and magnetic properties of the bulk full-Heusler alloys Ti2Fe1-x Co x Sn (x = 0.00, 0.25, 0.50, 0.75 or 1.00) and their (001)-oriented thin films. The bulk Ti2Fe1-x Co x Sn (x = 0.00, 0.25, 0.50, 0.75 or 1.00) alloys are all HM ferromagnets. We investigate twelve possible terminations and show that five of them preserve HM character with 100% SP at the Fermi level E F, while in the remaining seven, surface states emerge in the spin-down channel at the Fermi level E F, significantly reducing their SP. The Co-doping significantly increases the stability of the TiSn slab, also increases its spin-down bandgap [Formula: see text] and HM gap [Formula: see text] at x = 0.50. The stable HM character makes it is a slab of maximum benefit in the applications of spintronic devices, especially in magnetic tunnel junctions.

Layered transition metal oxide PbPdO2 has great potential application in electronic devices because of its unique electronic structure and large thermoelectric power at room temperature. In this work, strain effect on the electronic structure of PbPdO2 slab with preferred (0 0 2) orientation was systematically investigated using first-principles calculation. The calculated results indicate that PbPdO2 ultrathin slab possesses a small indirect gap while an indirect-direct band gap transition occurs when a moderate 2% compression or tensile strain is applied on the slab. Moreover, this strain induced indirect-direct band gap transition was analyzed in detail using the charge density difference at different point of valence band. The charge transfer and energy barrier with charge polarization resulting from the changes of bond length and angle for Pd-O bonding under the strain, have been accounted for this transition. Remarkablely, for the (0 0 2) preferred orientation PbPdO2 slab, the predicted carrier mobilities of electrons and holes are 11 645.31 and 694.60 cm2 V-1 s-1 along the x-axis direction, 935.05 and 16.05 cm2 V-1 s-1 along the y -axis direction, respectively. These calculated mobilities of electrons along the x-axis direction are larger than those for 2D MoS2 (~400 cm2 V-1 s-1), and being comparable to those for InSe (103 cm2 V-1 s-1) and black phosphorene (103-104 cm2 V-1 s-1). It is strong suggested that the (0 0 2) orientated PbPdO2 slab with high mobility should be an ideal candidate material for the application of electronics devices.

Magnetic doping in topological insulator Sbalt;subagt;2alt;/subagt;Tealt;subagt;3alt;/subagt; can produce very novel physical phenomena such as quantum anomalous Hall effect (QAHE). However, experimental observations of QAHE in the magnetic atoms doped Sbalt;subagt;2alt;/subagt;Tealt;subagt;3alt;/subagt; have encountered significant challenges due to the complexity of the electronic structure and the relatively small band gap. Generally, mechanical strain can effectively modulate the band structure, thus we theoretically investigate the electronic structures of Cr-doped Sbalt;subagt;2alt;/subagt;Tealt;subagt;3alt;/subagt; under mechanical strain using first-principles calculations within density functional theory (DFT). The band gap of Cr-doped Sbalt;subagt;2alt;/subagt;Tealt;subagt;3alt;/subagt; is 0.031eV. When the compressive strain η becomes as -2%, the band gap will be further enlarged to 0.045eV, which is 45% larger than that of the unstrained material. However, as the compressive strain η exceed -2%, strong hybridization between Cr and Te atoms will cause the overlap of bands, which leads to the closure of band gap. In addition, when tensile strain are applied to Cr-doped Sbalt;subagt;2alt;/subagt;Tealt;subagt;3alt;/subagt;, the decrease in the spacing between quintuple layers (QLs) can enhance the coupling between Te and Sb atoms, which can also result in the closing of the band gap. Finally, we used HSE06 to calculated the band gaps. The band gaps may be underestimated, but HSE06 and GGA have the same band structures evolution tendency under mechanical strain. Our calculated results provide a guideline for the modulation of band structure by mechanical strain, which pave the way for the observation of QAHE in Cr-doped Sbalt;subagt;2alt;/subagt;Tealt;subagt;3alt;/subagt;.

Using first-principles calculations, we present a potential new way to improve the photocatalytic efficiency of the g-C3N4 sheet by coupling with the g-ZnO sheet to form heterojunction nanostructure followed by the addition of N atom at an atomic level. The result indicates the g-C3N4/g-ZnO heterojunction is a staggered band alignment (type II) structure and a polarized field is generated by the electrons transfer across the interface simultaneously, which facilitate the separation of e--h+ pairs and promote the photocatalytic activity. Furthermore, a great difference in energy levels between redox potentials and band edges of the C3N4/g-ZnO nanocomposite ensures that the water splitting/CO2 reduction reaction is energetically favored. In addition, through the incorporation of nitrogen dopant, the g-C3N4/N-g-ZnO nanocomposite displays desirable properties. The N-derived doping peak causes a decrease of the band gap width of the g-C3N4/g-ZnO nanocomposite, resulting in the enhanced optical absorption from UV into visible light. This theoretical predictions provide insightful outlooks in understanding the effects of interface and doping on the enhanced photocatalytic property of the g-C3N4/g-ZnO nanocomposites, which will assist in engineering highly efficient g-C3N4-based photocatalysts.

Tuning band gaps of semiconductors in terms of defect control is essential for the optical and electronic properties of photon emission or photon harvesting devices. By using first-principles calculations, we study the stability condition of bulk CuInS2 and formation energies of point and complex defects in CuInS2 with hybrid exchange-correlation functionals. We find that at Cu-rich and In-poor conditions, 2Cui??+??CuIn is the main complex defect, while InCu??+??2VCu is the main complex defect at In-rich and Cu-poor conditions. Such stable complex defects provide the feasibility of tuning band gaps by varying the [Cu]/[In] molar ratios. These results present how the off-stoichiometry CuInS2 crystal structures, and electronic and optical properties can be optimized by tuning the [Cu]/[In] ratio and Fermi level, and highlight the importance of complex defects in achieving better photoelectric performance in CuInS2. Such band gap tuning in terms of complex defect engineering is a general approach and thus applicable to other photo-harvest or light-emission semiconductors.

Using first-principles calculations based on density-functional theory, we systematically investigate the structural and electronic properties of hydrogen (hydrogen atoms and H2 molecule) doped Cu chain nanowires and nanocontacts. Various possible configurations of Cu chain nanowires and nanocontacts doped with hydrogen impurities are considered. These Cu chain nanowires and nanocontacts are stabilized by hydrogen impurities beyond their classical breaking point. The formed metal-impurity bond is much stronger than the metal–metal bond. Upon elongation, the doped Cu chain nanowire tends to break from the remote metal–metal bond and the doped Cu nanocontact will break from metal–metal chain bond. The interaction between hydrogen impurities and Cu atoms alters the interatomic bonding and hybridization of electronic states in Cu chain nanowires and nanocontacts. Additionally, the dissociation of H2 molecule is observed when H2 molecule doped in Cu nanocontact, which can be used in catalytic application.

We use first-principles calculations to investigate the half-metallicity of pure , doped and systems. The results show that the conduction bands minimum (CBM) of pure is mainly contributed by the low intensity state of S in the spin-down channel. The S state extends below the Fermi level (E F) and destroys the half-metallicity of , rather than Co- states proposed previously. Replacing sulfur (S) with nitrogen (N) reduces the bandwidth of the S (N) bands and destroys the continuous S network, as a result the bottom of the S band shifts upward above the bottom of the Co- band and makes the a perfect half metal ferromagnet (HMF) and a promising candidate for spintronic devices.

In this paper, we investigated the magnetic topological insulator (MTI) Cr-doped Bi2Se3 film using first principles calculations based on the density functional theory (DFT). The band structure of Cr doped 3QL-Bi2Se3 film was calculated comparing with pure Bi2Se3 film. Our results demonstrate that the doping of Cr atom changes the degenerate surface state of pure Bi2Se3, inducing the ferromagnetism. Under the external electric field, the band gap of pure Bi2Se3 films is determined by the charge transfer and the effect of spin-orbital coupling (SOC). For the MTI, the electric field will redistribute the electrons and enhance the magnetism. Our results will further promote the development of the electronic and spintronic applications of topological insulator.

The electronic structures and magnetic properties of ZnO semiconductors doped with Cu, Co, C, Al and S are studied by first-principles calculation. The electronic transfer among Zn, O and doped atoms, and the differences of the number of electron between spin-up and spin-down, Δs, Δp, Δd for s, p and d orbits of these atoms, are analyzed in detail. It is found that, the ferromagnetic ground state is stabilized by its half-metallic electronic structure, and the strong local magnetic moments in Zn1−xCoxO, Zn1−xCuxO and ZnO1-xCx (x = 5.55%) DMSs originate mainly from the strong hybridizations between Cu-3d and O-2p, Co-3d and O-2p, Zn-3d and C-2p electrons. It is considered that the requirements to give rise to the ferromagnetism in the DMSs are the strong local magnetic moment and the electron transfer. The magnetic coupling in Zn1-xCoxO, Zn1-xCuxO and ZnO1-xCx is also considered to be a RKKY interaction.

In recent years, actuators based on carbon nanotube (CNT) or graphene demonstrate great potential applications in the fields of artificial muscles, smart switches, robotics, and so on. The electrothermal and photothermal bending actuators based on CNT/graphene and polymer composites show large bending actuations, which are superior to traditional thermal-driven actuators. However, the influence of material parameters (thickness, temperature change, etc.) on the actuation performance needs to be further studied, because it is a critical point to the design and fabrication of high-performance actuators. In this work, finite element analysis (FEA) is employed to simulate the actuation performance of CNT/polymer actuator, which has a bilayer structure. The main focus of this work is to design and to optimize material parameters by using computational method. FEA simulation results show that each layer thickness of actuator has an important influence on the actuation deformation. A maximum curvature of 2.7 cm is obtained by simulation, which is much larger than most of the actuator curvature reported in previous experiments. What is more, larger temperature change and larger difference of coefficient of thermal expansion (CTE) between two layers will result in larger bending actuation. This study is expected to provide valuable theoretical reference for the design and realization of CNT-based thermal actuator with ultra-large actuation performance.

The structural, electronic, magnetic and mechanical properties of the quaternary Heusler alloys ZrTiCrZ (Z = Al, Ga, In, Si, Ge, Sn) have been investigated firstly by using the first-principles calculations. The preferred configurations of the ZrTiCrZ alloys are all Y-type (I). At their equilibrium lattice constants, the ZrTiCrZ alloys are half-metallic (HM) ferrimagnets for Z = Al, Ga and In, while spin-gapless semiconductor (SGS) antiferromagnets (AFM) for Z = Si, Ge and Sn. The total magnetic moments of the ZrTiCrZ alloys are −1 for Z = Al, Ga and In, while 0 for Z = Si, Ge and Sn, both linearly scaled with the total number of valence electrons by Slater–Pauling rule . The elastic constants , and of the single crystal and the related elastic moduli , , , and of the polycrystalline aggregates are also calculated and used to study the mechanical stability of these alloys. Although the Curie temperatures of the ZrTiCrZ alloys are overestimated by using the mean field approximation (MFA), they can be better estimated by including the exchange interactions. Finally, the HM stabilities as well as the total and atomic magnetic moments of the ZrTiCrZ alloys (Z = Al, Ga, In) under either hydrostatic strain or tetragonal strain are also discussed.

The influence of oxygen vacancy on the magnetism of Co-doped ZnO has been investigated by the first-principles calculations. It is suggested that oxygen vacancy and its location play crucial roles on the magnetic properties of Co-doped ZnO. The exchange coupling mechanism should account for the magnetism in Co-doped ZnO with oxygen vacancy and the oxygen vacancy is likely to be close to the Co atom. The oxygen vacancy (doping electrons) might be available for carrier mediation but is localized with a certain length and can strengthen the ferromagnetic exchange interaction between Co atoms.