摘要
石墨烯与磁性材料复合是调控其电磁性能的重要方法之一。本文使用基于密度泛函理论的第一性原理方法,研究了石墨烯吸附Fe,Co,Ni磁性原子的稳定吸附结构和电磁性质。通过计算石墨烯穴位、顶位和桥位吸附磁性原子的吸附能,发现3种磁性原子都倾向于石墨烯穴位吸附构型。电子结构分析结果表明,磁性原子d轨道与碳原子p轨道之间轨道杂化,导致费米能级附近态密度增加。在磁性方面,吸附Fe和Co原子后,石墨烯体系呈现磁性特征;吸附Ni原子后,石墨烯体系仍然保持自旋非极化,呈现非磁性特征。在介电性能方面,磁性原子的吸附可以有效改变石墨烯体系介电函数的实部和虚部,实现了石墨烯的极化强度和能量损耗能力的有效调控。此外,通过改变磁性原子吸附浓度,可以调控石墨烯体系的介电性能和电磁波衰减频率范围。本文揭示了吸附磁性原子对石墨烯电磁性质的调控机制,为石墨烯在电磁防护领域的应用提供了一定的理论指导。
The development of electronic devices has led to an increasingly complex electromagnetic interference(EMI)environment,posing potential health risks.Graphene,with its excellent mechanical,electrical,and thermal properties,emerges as a promising candidate for EMI shielding.However,its limited dielectric loss and lack of magnetism restrict its application in microwave absorption.Recent studies have shown that recombination of graphene with magnetic materials can effectively regulate its electromagnetic properties,enhancing microwave absorption performance.Therefore,it is crucial to study the structure of graphene adsorbed with magnetic atoms,as well as the influence of magnetic elements on graphene's electromagnetic properties.In this work,we investigated the crystal structure and electromagnetic properties of graphene adsorbed with three magnetic atoms(Fe,Co,and Ni)using the first-principles method based on density functional theory(DFT).A 4×4×1 supercell was used for the pristine graphene structure,and a 3 nm vacuum layer was introduced in the z-direction to eliminate interlayer interaction.The magnetic atoms were adsorbed onto graphene at three sites:the hollow(H)site at the center of the hexagon,the top(T)site of the carbon atom,and the bridge(B)site between two carbon atoms.The adsorption energy,crystal structure,electronic band structure,magnetic moment,and dielectric constant of graphene adsorbed with Fe,Co,and Ni atoms were calculated using the Vienna Ab initio Simulation Package(VASP)code.Bader charge analysis was performed to reveal electron transfer between the magnetic atoms and graphene,and the adsorption energy was used to assess the stability of the adsorption structures.Our results revealed that the most stable configurations for magnetic atoms Fe,Co,and Ni on graphene were observed at the H site,which exhibited more negative adsorption energy and the lowest adsorption height.Pristine graphene exhibited a unique band structure where the valence band maximum(VBM)and conduction band minimum(CBM)met at the high-symmetry K point,forming a characteristic Dirac point at the Fermi energy level.Upon adsorption of an Fe atom,the band structure of the Fe@graphene system retained the Dirac points,but significant changes occurred near the Fermi level.Notably,the degeneracy of spin-up and spin-down bands was broken,and new flat valence and conduction bands emerged.For Co@graphene,the Fermi level crossed the valence band,inducing spin polarization in the bands.Additionally,new bands formed near the Fermi level.In contrast,the Fermi energy level of Ni@graphene remained located at the Dirac point,with no observed spin polarization.However,some new bands appeared near the Fermi level for Ni@graphene as well.The calculated density of states(DOS)and partial density of states(PDOS)revealed a broken spin-up/down symmetry for graphene adsorbed with Fe and Co atoms,indicating the presence of a magnetic moment.This was further confirmed by our calculations,which showed total magnetic moments of 2.01 and 1.12μB for Fe@graphene and Co@graphene,respectively.The PDOS results indicated that the peaks near the Fermi energy level were mainly attributed to the d orbitals of magnetic atoms and the p orbitals of carbon atoms.In contrast,Ni@graphene exhibited a total magnetic moment of OμB.The PDOS showed three peaks below the Fermi level,arising mainly from the Ni-d orbital.Additionally,the PDOS curves demonstrated that the bands near the Fermi level were dominated by the adsorbed magnetic atoms,while the contributions from carbon atoms became significant below-2.0 eV.Orbital hybridization between the d orbitals of adsorbed magnetic atoms and the p orbitals of carbon atoms occurred near the Fermi level,resulting in new bands.The adsorption of magnetic atoms significantly impacted the electron distribution of graphene.Bader analysis revealed charge transfers of 0.665e,0.57le,and 0.464e from Fe,Co,and Ni to graphene,respectively.This charge transfer was further confirmed by the charge density difference analysis.Additionally,the electron localization function displayed overlap between the charge clouds of adsorbed atoms and carbon atoms,suggesting the presence of covalent bonding.Our investigation further explored how adsorbed magnetic atoms influenced graphene's dielectric properties.The intrinsic static dielectric constant of graphene was 4.45.Affer adsorption of Fe,Co,and Ni atoms,the static dielectric constants increased to 7.52,7.61,and 4.66,respectively.This increase indicated that magnetic atoms could enhance the polarization intensity of graphene.Compared to pristine graphene,both the real and imaginary parts of the dielectric constants were significantly enhanced after adsorption of Fe,Co,and Ni atoms.In the range of 0-0.68 eV,the maximum values of the real part reached 8.12,4.74,and 6.31 for graphene adsorbed Fe,Co,and Ni,respectively.As the energy increased,the real part of the dielectric constant became consistent with graphene.Similarly,the maximum values of the imaginary part of the dielectric constant for graphene adsorbed with Fe,Co,and Ni were 6.25,4.29,and 6.10,respectively.Interestingly,the first peaks of the imaginary parts of the dielectric functions for Co@graphene and Fe@graphene shifted toward the low-energy region,while the first peak for Ni@graphene shifted toward the high-energy region.This behavior could be attributed to the orbital hybridization between the d-orbitals of the magnetic atoms and the p-orbitals of the carbon atoms in graphene.Furthermore,our results showed that the concentration of magnetic atoms was crucial for optimizing the dielectric properties and the range of attenuation frequency.In conclusion,our study demonstrated that the electric,magnetic,and dielectric properties of graphene could be regulated by adsorbing magnetic atoms.This work provided theoretical guidance for the research and application of graphene in the field of electromagnetic shielding.
作者
马江将
胡丽芳
李克训
张均锋
Ma Jiangjiang;Hu Lifang;Li Kexun;Zhang Junfeng(School of Physics and Electronic Engineering,Shanxi Normal University,Taiyuan 030031,China;No.33 Research Institute of China Electronics Technology Group Corporation,China-Belarus Belt and Road Joint Laboratory on Electromagnetic Environment Effect,Taiyuan 030032,China;College of Physics and Electronic Engineering,Hainan Normal University,Haikou 571158,China)
出处
《稀有金属》
北大核心
2025年第9期1353-1362,共10页
Chinese Journal of Rare Metals
基金
国家重点研发计划项目(2023YFB3811305)
中央引导地方科技发展资金项目(YDZJSX2022C035)
山西省重点研发项目(2022ZDYF027)
山西省研究生科研创新项目(2024KY453)资助。
关键词
第一性原理
石墨烯
电磁性质
介电性质
first-principles
graphene
electromagnetic properties
dielectric properties
