铜基二元合金纳米线稳定性、电子结构和磁性的第一性原理研究

By using first-principles projected-augmented wave (PAW) potential within the density functional theory (DFT) framework, the stability, electronic structure and electronic transport properties of the ultrathin Cu1-xMx (M=Au, Pt, Ag, Pd, Zn, Mg) binary alloy nanowires will be investigated. And the ways for the formation of stable copper-based binary alloy nanowires will be explored. The factors (such as the orbital hybridization, charge transfer, the bonding energy differences between the mono-elements and hetero-elements and string tension) which affect the formation mechanism and stability of the alloy nanowires will be theoretically analyzed. The relationship between the alloy concentration and the stability as well as the properties of the alloy nanowires will also be illuminated. At the same time we will systematically investigate the magnetic properties and electronic structures of one-dimensional Co/Cu、Ni/Cu and Fe/Cu multilayered nanowires. As the width of the nonmagnetic Cu spacer varies, the interlayer exchange coupling (IEC), giant magnetoresistance (GMR) and the magnetic moment of the multilayered nanowires will be studied. A mechanism based on the relaxed structure as well as multistep electron transfer between the layers and spin flip within the layer will be proposed to explain the magnetic-moment enhancement of the atoms at the interface. The direct exchanges interaction, indirect RKKY exchange interaction and superexchange interaction between atom layers as well as the electronic structure of the multilayered nanowire will be proposed to explain the nonmonotonous feature in IEC. These numerical studies in this research might stimulate further experimental studies in the nanoalloy area, and also may be useful for guiding the manufacture and application for stable copper-based binary alloy nanowires and multilayered nanowires.

应用基于密度泛函理论框架下的第一性原理投影缀加波计算方法，对超细Cu1-xMx (M=Au, Pt, Ag, Pd, Zn, Mg)二元合金纳米线的稳定性、电子结构和电子输运性质进行研究。探索形成稳定Cu基二元合金纳米线的途径，从轨道杂化、电荷转移、键能差异和弦张力等方面分析合金纳米线的形成机制和稳定性成因，明确合金浓度与纳米线稳定性和特性间的关系；同时研究Co/Cu、Ni/Cu和Fe/Cu多层纳米线的磁性和电子结构，考察Cu分割层厚度对多层纳米线层间交换耦合(IEC)和巨磁阻(GMR)以及系统磁矩的影响，从弛豫结构、层间电子转移和层内自旋反转等角度揭示界面原子磁矩变化机制，结合原子层间的多种交换相互作用和纳米线系统的电子结构等因素阐明IEC随非磁性层厚度变化而变化的机理，为实验制备稳定的Cu基二元合金纳米线和磁性可控的多层纳米线提供思路和理论依据。

随着电子和机械器件尺寸的不断缩小，一维金属纳米线由于具有优良的电学、磁学、力学和光学特性以及其在纳米科技中的潜在应用而备受关注。本项目采用第一性原理计算方法，对超细Cu基二元合金纳米线的结构稳定性、电子结构和磁性进行了研究。对Au-Ag、Au-Cu和Ag-Cu合金单原子链和合金纳米管的研究表明，Au-Ag和Au-Cu合金单原子链和纳米管结构稳定性较高，且其稳定性随着Au浓度的增加而增强，而Ag-Cu合金单原子链和纳米管的稳定性较差；分析表明Au元素的相对论性效应和两尖端电极间弦张力的共同作用可以有效抑制纳米材料中的“自净效应”，从而导致稳定Au-Ag和Au-Cu合金单原子链和纳米管的形成。此外，碳纳米的包裹能够有效地提升了合金纳米线的力学性能。研究了轴向应力作用下Cu-Fe和Cu-Co合金单原子链以及Fe/Co线性单原子链填充Cu纳米管所形成合金纳米线的结构稳定性和磁性，均匀交替构型Cu-Fe和Cu-Co合金单原子链在较大的原子间距范围内能够稳定存在，Cu纳米管的包裹使Fe或Co单原子链的稳定性显著增强；电子结构的分析表明Cu原子和Fe/Co原子间的轨道杂化和电荷转移导致了Cu-Fe、Cu-Co合金纳米线的高稳定性；相对于Fe/Co单原子链的磁晶各向异性能，Cu-Fe和Cu-Co合金纳米线结构的磁晶各向异性能增加了约4倍，因此可应用于超高密度磁存储中。研究了非磁性分隔层厚度对Fe/Cu多层纳米线磁性和电子特性的影响，其层间交换耦合随非磁性Cu分隔层厚度的增加呈现出振荡衰减的特性，且其振荡周期为两个Cu原子层，且多层纳米线的电导依赖于Cu分隔层的厚度，使得Fe/Cu多层纳米线也可应用于磁电子学和自旋电子学领域。上述研究结果为实验制备稳定的Cu基二元合金纳米线和磁性可控的多层纳米线提供了理论依据。最后，研究了碱土金属Ca原子修饰缺陷氮化硼低维纳米材料的储氢性能和储氢机理，结果表明Ca原子的修饰大大提高了缺陷氮化硼低维纳米材料的储氢能力。