层数调控磷烯能带与光学性质的研究

近年来,黑磷作为兼具石墨烯和过渡金属硫化物之长的新型二维材料而倍受关注.本文基于密度泛函理论,研究了不同厚度黑磷的电子结构与光学性质.结果表明,黑磷的性质与其厚度密切相关,可通过厚度调整实现能带与光学性质的可调控性.层间相互作用导致费米能级附近价带和导带的劈裂,是造成黑磷带隙随层数减小的根本原因.黒磷的静态折射率和静态反射率的大小均随层数的增大有增大的趋势,并且各层黑磷的反射峰均位于紫外光波段.黑磷对光的吸收涵盖了可见光到紫外光区域,对光的损失范围小于4eV.本文基于能带图和分波态密度图,从电子跃迁的角度分析了黑磷各项光学性质的变化情况,旨在为黑磷的带隙及光学性质层数可调控性提供理论依据.     

碱金属在磷烯表面吸附，迁移行为的第一性原理研究

利用基于密度泛函理论的平面波赝势方法研究了碱金属（Li、Na、K）−磷烯体系,分析了体系的吸附性质、电学性质和迁移行为. 结果表明：碱金属在磷烯表面的最稳定吸附位都是H位.吸附过程中电荷由碱金属原子转移到磷烯,碱金属−磷烯体系表现出一定的离子性. 碱金属−磷烯体系的吸附能从大到小为ΔELi−磷烯大于ΔEK−磷烯大于ΔENa−磷烯. Li→Na→K,随着原子序数的递增,体系的离子性逐渐增强;碱金属原子越来越容易在磷烯表面迁移.     

Ballistic thermal transport in black and blue phosphorene nanoribbons and in-plane heterostructures

The thermal transport properties of black and blue phosphorene nanoribbons and in-plane heterostructures are systematically investigated by non-equilibrium Green's-function method. Both edge shape and width have a sensitive influence on the thermal conductance of pristine black and blue phosphorene nanoribbons and they all exhibit a clear anisotropic thermal performance. Interestingly, the in-plane heterostructures possess a tunable thermal conductance which depends on the percentage of black phosphorene nanoribbons and the way how they are linked. These findings will provide new applications in nanoelectronic and thermoelectric devices based on phosphorene.     

Superconductivity of bilayer phosphorene under interlayer compression

According to first-principles calculations, it is our prediction that bilayer phosphorene(BLP) will become a quasitwo-dimensional superconductor under a certain degree of interlayer compression. A decreasing interlayer distance may realize the transition in the BLP from a semiconducting phase to a metallic phase. On the other hand, a severe vertical compression may make the BLP lattice become dynamically unstable. It is found that in the stable metallic phase of the BLP, interlayer phonon modes dominate the electron-phonon coupling λ. The obtained λ can be greater than 1 and the superconducting temperature T_c can be higher than 10 K.     

A density-functional-theory-based finite element model to study the mechanical properties of zigzag phosphorene nanotubes

In this paper, the density functional theory calculations are used to obtain the elastic properties of zigzag phosphorene nanotubes. Besides, based on the similarity between phosphorene nanotubes and a space-frame structure, a three-dimensional finite element model is proposed in which the atomic bonds are simulated by beam elements. The results of density functional theory are employed to compute the properties of the beam elements. Finally, using the proposed finite element model, the elastic modulus of the zigzag phosphorene nanotubes is computed. It is shown that phosphorene nanotubes with larger radii have larger Young's modulus. Comparing the results of finite element model with those of density functional theory, it is concluded that the proposed model can predict the elastic modulus of phosphorene nanotubes with a good accuracy.     

Defect engineering on the electronic and transport properties of one-dimensional armchair phosphorene nanoribbons

We investigate the electronic and transport properties of one-dimensional armchair phosphorene nanoribbons(APNRs) containing atomic vacancies with different distributions and concentrations using ab initio density functional calculations. It is found that the atomic vacancies are easier to form and detain at the edge region rather than a random distribution through analyzing formation energy and diffusion barrier. The highly local defect states are generated at the vicinity of the Fermi level, and emerge a deep-to-shallow transformation as the width increases after introducing vacancies in APNRs.Moreover, the electrical transport of APNRs with vacancies is enhanced compared to that of the perfect counterparts. Our results provide a theoretical guidance for the further research and applications of PNRs through defect engineering.     

First-principles study on the influence of biaxial strain on the electronic and magnetic properties of defective blue phosphorene

Regulating the magnetic state of 2D materials is becoming increasingly important for the next generation of spintronic devices. In this study, the first-principles calculation method is used to study the synergistic modulating effect of biaxial strain and vacancy defects on the magnetic properties of blue phosphorene. Results show that only Single Vacancy (SV) doping magnetizes the intrinsic blue phosphorene, Double Vacancy-1 (DV-1), Double Vacancy-2 (DV-2) and Double Vacancy-3 (DV-3) doped blue phosphorene are magnetized under biaxial strain. The magnetic states of SV, DV-1, DV-2 and DV-3 systems change with the intensity of biaxial strain. In some cases, the magnetic moment of the system can be changed from 0 μB to 4 μB. The biaxial strain affects the partially bonding structure near the defects, changes the position of the dangling bond, and thereby adjusts the magnetic state. Our research provides positive guidance for the future application of blue phosphorene in the semiconductor field.     

碳、氧、硫掺杂二维黑磷的第一性原理计算

基于密度泛函理论的第一性原理平面波赝势方法,研究了二维黑磷中的碳原子(C P)、氧原子(C P)、硫原子(S P)掺杂的几何结构、磁学性质和电子结构.发现掺杂体系结构稳定,C P和O P体系形变较大,而S P体系形变较小;二维黑磷本身无磁矩,掺杂后都具有1μB的总磁矩.由于掺杂体系具有稳定的铁磁性,使其在自旋电子器件方面可发挥重要的作用.     

离子辐照对磷烯热导率的影响及其机制分析

通过离子辐照产生缺陷,可以非常有效地调控磷烯诸多物理性质.本文应用分子动力学方法模拟离子辐照磷烯的过程,给出了缺陷的形成概率与入射离子能量、离子种类以及离子入射角度之间的关系,并且应用非平衡态分子动力学计算辐照后磷烯热导率的变化.以缺陷形成概率为切入点,系统地研究了辐照离子的能量、辐照剂量、离子的种类以及离子的入射角度对磷烯热导率的影响.应用晶格动力学方法研究了空位缺陷对磷烯声子参与率的影响,并计算了声子局域模式的空间分布.基于量子微扰和键弛豫理论,指出空位缺陷明显降低磷烯热导率的最重要物理机制是空位缺陷附近的低配位原子对声子强烈散射.本文研究可为缺陷工程调控磷烯的热输运性质提供理论参考.     

过渡金属原子掺杂的锯齿型磷烯纳米带的磁电子学特性

利用基于密度泛函理论的第一性原理方法,研究了掺杂铁、钴和镍原子的锯齿型磷烯纳米带(ZPNR)的磁电子学特性.研究表明,掺杂和未掺杂ZPNR的结构都是稳定的.当处于非磁态时,未掺杂和掺杂钴原子的ZPNR为半导体,而掺杂铁或者镍原子的ZPNR为金属.自旋极化计算表明,未掺杂和掺杂钴原子的ZPNR无磁性,而掺杂铁或者镍原子的...     

Computationally predicting spin semiconductors and half metals from doped phosphorene monolayers

First-principles computations are performed to investigate phosphorene monolayers doped with 30 metal and nonmetal atoms. The binding energies indicate the stability of all doped configurations. Interestingly, the magnetic atom Co doping induces the absence of the magnetism while the magnetism is realized in phosphorene with substitutional doping of nonmagnetic atoms (O, S, Se, Si, Br, and Cl). The magnetic moment of transition metal (TM)-doped systems is suppressed in the range of 1.0-3.97 μ_B. The electronic properties of the doped systems are modulated differently; O, S, Se, Ni, and Ti doped systems become spin semiconductors, while V doping makes the system a half metal. These results demonstrate potential applications of functionalized phosphorene with external atoms, in particular to spintronics and dilute magnetic semiconductors.     

Edge-functionalization of blue phosphorene nanoribbons: Studied from first-principle methods

Through density functional theory calculations, the impact of edge functionalization with O, OH, and alternate termination of them (OHO) on the structural stabilities, electronic and magnetic properties of blue phosphorene nanoribbons (BPNR) are mainly investigated. The formation energies demonstrate that the O-termination on the BPNRs is the most stable, and OHO-termination is more stable than OH-termination, besides the ab initio dynamic simulation show that they are all thermal dynamically stable at room temperature. Both the ground structures of O- and OH-BPNRs are spin-polarized semiconductors, while OH-functionalized BPNRs are nonmagnetic semiconductors. As the ribbon width increasing, the band gaps of O-aBPNRs tend to 1.04 eV, but that of OH-aBPNRs tend to 1.97 eV, comparable with the band gap of single-layer blue phosphorene, since it is dominated by pz electrons of the inner P atoms. In contrast, the influence of OHO-termination on GNRs, SiNRs, and black PNRs are also studied. Our results demonstrate that OHO-terminated GNRs and SiNRs are not a simple summation of O- and OH-terminated GNRs and SiNRs, and they are nonmagnetic stable both with zigzag and armchair edges, presenting metallic properties. While the OHO-terminated black PNRs present similar electronic and magnetic properties with OHO-terminated blue PNRs, and both the OHO-terminated zigzag and armchair edges are spin-polarized stable. These results provide potential help in the fields of band gap engineering and the designing of phosphorus-based spin devices with control over spin in spintronics.     

Defective phosphorene for highly efficient formaldehyde detection: Periodic density functional calculations

The exfoliation of black phosphorene has spurred a great deal of research interest in improved sensors and electronic devices in the past few years. This article has dealt with the sensing of formaldehyde (CH₂O) molecule over the pristine (BP) and vacancy-doped (DP) phosphorene layers at the HSE06/TZVP level of theory. The lowest-energy configurations of formaldehyde preferred a planar form, which was oriented perpendicular to the surface of the defective sensor. The defect engineering provided improved sensitivities (by about 200% and 20% higher) in terms of work function and electronic conductivity. Meanwhile, the defect engineering preserved the regeneration ability of formaldehyde with a 0.22 ns recovery time at room temperature. Therefore, DP provided higher CH₂O sensitivity and reusability compared to BP. Moreover, the selectivity coefficient of formaldehyde was found to be 11.6 in air. These improvements open new insights into the rational design of capable reusable nanosensors for the CH₂O molecule.     

Van der Waals heterostructure of phosphorene and hexagonal boron nitride: First-principles modeling

We have studied the structural and electronic properties of a hybrid hexagonal boron nitride with phosphorene nanocomposite using ab initio density functional calculations. It is found that the interaction between the hexagonal boron nitride and phosphorene is dominated by the weak van der Waals interaction, with their own intrinsic electronic properties preserved. Furthermore, the band gap of the nanocomposite is dependent on the interfacial distance. Our results could shed light on the design of new devices based on van der Waals heterostructure.     

非对称结构对黑磷烯器件电子输运的影响

利用不同宽度的锯齿型黑磷烯纳米带构建了非对称结构的纳米器件.第一性原理计算结果表明,非对称结构器件I-V曲线展现表现出整流效应,最大整流比达到1.01×10~6.器件的不同非对称结构导致了不同整流行为.我们通过传输谱和透射本征态讨论得到,器件中心区域和电极的耦合变化导致了本征态的变化,从而产生不同的电子输运性质.结果为基于黑磷烯二维材料异质结整流器件的设计提供了一种可行性方案.     

Electronic and transport properties of zigzag-edge monolayer/bilayer phosphorene nanoribbon junctions under a perpendicular electric field

We study the electronic and transport properties of monolayer/bilayer/bilayer (ML/BL/BL) and monolayer/bilayer/monolayer (ML/BL/ML) zigzag-edge phosphorene nanoribbon (ZPNR) junctions modulated by a perpendicular electric field (PEF). Within the tight-binding model Hamiltonian and by adopting the nonequilibrium Green's function, it is demonstrated that some oscillating conductance plateaus appear for the junctions, and the conductances are suppressed by the applied PEF. Interestingly, the direction of the PEF has different influence on the conductance of both junctions. We further present separately the band structures of the left lead, the central region and right lead, to reveal the reason for different conductance behavior in detail. Our results show that the ML/BL/BL ZPNR junction may be more suitable for the usage of field effect transistor than the ML/BL/ML ZPNR one under a PEF. Moreover, a PEF can be applied to distinguish the bottom−bottom and bottom−up configurations for the ML/BL/ML ZPNR junction.     

Metal adsorption on monolayer blue phosphorene: A first principles study

We investigated the electronic structure, adsorption energies, magnetic properties, dipole moment and work function of metal adatoms (Mg, Cr, Mo, Pd, Pt, and Au) adsorption on a blue phosphorene monolayer. For Mg, Pt and Au metals, the most stable state was found in hollow site while for Cr, Mo and Pd metals we found an adsorption in valley site. We suggest that the Pd and Pt atoms prefer 2D growth mode while the Mg, Cr, Mo and Au atoms prefer 3D island growth mode on monolayer phosphorene. The electronic band structures and magnetic properties were dependent on the doping site and dopant materials. For instance, the semiconducting features were preserved in Mg, Pd, Pt, and Au doped systems. However, the Cr and Mo doped systems displayed half-metallic band structures. The total magnetic moment of 4.05, 2.0 and $0.77{\text{μ}}_B/\text{impurity}$ atom were obtained in Cr, Mo and Au doped systems whereas the Mg, Pd and Pt doped systems remained nonmagnetic. We also investigated the magnetic interaction between two transition metal impurities. We observed ferromagnetic coupling between two transition metal impurities in Cr and Mo doped systems while the Au doped system displayed almost degenerated magnetic state. For Mg, Cr, and Mo adsorptions, we found relatively large values of dipole moments compared to those in the Pd, Pt and Au adsorptions. This resulted in a significant suppression of the work function in Mg, Cr and Mo adsorptions. Overall, adsorption can tune the physical and magnetic properties of phosphorene monolayer.     

First‐principles prediction of a novel hexagonal phosphorene allotrope

Phosphorus prefers three‐connected configurations due to its inequivalent sp³‐hybridization. In the past year, many quasi two‐dimensional three‐connected networks were proposed as possible phosphorene allotropes. In this Letter, a new quasi two‐dimensional three‐connected network is proposed as a new potential phosphorene allotrope (Hex‐star). Based on first‐principles method calculations, the structure, stability and electronic properties of Hex‐star were systematically investigated. Our results indicate that Hex‐star is dynamically stable and it is a semiconductor with quasi‐direct band gap of 1.81 eV based on HSE06 method. Perspective top view (left) and Magen–David‐like orthographic top view (right) of Hex‐star phosphorene.

     

二维材料的磁性研究

二维材料在自旋电子学器件中具有良好的应用潜力,高磁化强度、室温铁磁性二维材料的制备与研究,成为近年来自旋电子学领域的研究热点.文章简要回顾了二维材料磁性研究的背景,主要介绍了几种具有代表性的二维材料磁性研究的现状,并对二维材料的磁性研究进行了展望.