Magnetic and electronic properties of Cr,Mn, and Fe adatoms on Si(001): A first-principles study

The magnetic and electronic properties of TM (TM=Cr, Mn, and Fe) adatoms adsorption on Si(001) surface are studied by means of the first-principles method. For the adsorption of a single TM atom on Si(001), we obtain decreasing spin moments and increasing adsorption energies as TM varies from Cr to Fe. In the case of TM dimers adsorption, the calculated results show that the spin coupling changes from antiferromagnetic (AFM) to ferromagnetic (FM) as the 3d electrons increased. AFM coupling is found to be preferred for Cr, while FM coupling is energetically favorable for Mn and Fe. In the case of TM wires, we find that the FM state is energetically preferred for Mn and Fe atoms on the Si(001) surface, while for Cr wires, the up–down–up state for P–M–M site Cr atoms seems to be more energy favorable. We also find that the silicon surfaces become metallic for the adsorption of TM wires.     

Structural,electronic and magnetic properties of hcp Fe,Co and Ni nanowires encapsulated in zigzag carbon nanotubes

The structural, electronic and magnetic properties of hcp transition metal (TM = Fe, Co or Ni) nanowires TM₄ encapsulated inside zigzag nanotubes C(m, 0) (m = 7, 8, 9, 10, 11 or 12), along with TM _n (n = 4, 10 or 13) encapsulated inside C(12, 0), have been systematically investigated using the first-principle calculations. The results show that the TM nanowires can be inserted inside a variety of zigzag carbon nanotubes (CNTs) exothermically, except from the systems TM₄@(7, 0) and TM₁₃@(12, 0) which are endothermic. The charge is transferred from TM nanowires to CNTs, and the transferred charge increases with decreasing CNT diameter or increasing nanowire thickness. The magnetic moments of hybrid systems are smaller than those of the freestanding TM nanowires, especially for the atoms on the outermost shell of the nanowires. The magnetic moment per TM atom of TM/CNT system increases with increasing CNT diameter or decreasing nanowire thickness. Both the density of states and spin charge density analysis show that the spin polarization and the magnetic moments of all hybrid systems mainly originate from the TM nanowires, implying these systems can be applied in magnetic data storage devices.     

多壳层铜纳米线结构和电子特性的第一性原理研究

基于密度泛函理论框架下的第一性原理计算,系统地研究了多壳层Cu纳米线的稳定结构和电子特性.得到不同线径多壳层Cu纳米线的平衡态晶格常数相差不大,都表现出金属特性,且其单原子平均结合能和量子电导随着纳米线直径的增加而增加.纳米线中内壳层Cu原子表现出体相结构Cu原子相似的电子特性,而表面壳层由于配位数的减少,其3d态能量范围变窄且整体向费米能级发生移动.电荷密度分析表明,相对于体相Cu晶体中原子间的相互作用,纳米线表面壳层Cu原子与其最近邻原子间的相互作用明显增强.     

Cr掺杂ZnO纳米线的电子结构和磁性

采用自旋极化密度泛函理论系统研究了Cr掺杂ZnO纳米线的电学、磁学以及光学属性.计算结果显示,Cr原子沿[0001]方向替代ZnO纳米线中的Zn原子时体系一般呈现铁磁耦合,沿[1010]和[0110]方向替代Zn原子时体系呈现反铁磁耦合,且磁性耦合状态在费米能级附近出现了明显的自旋劈裂现象,发生了强烈的Cr 3d和O 2p杂化效应.自旋态密度计算结果显示,磁矩主要来源于Cr原子未成对3d态电子的贡献,磁矩的大小与Cr原子的电子排布有关.光学性质计算结果显示,Cr掺杂ZnO纳米线在远紫外和近紫外都具有明显的吸收峰,吸收峰发生了明显的红移.这些结果都表明Cr掺杂ZnO纳米线也许是一种很有前途的稀磁半导体材料. 关键词： ZnO 纳米线 第一性原理 磁性     

First-Principles Study of Magnetic Properties of TM_(13) and TM_(13)@Au_(32) Clusters(TM = Mn,Co)

The structural and magnetic properties of TM_(13 )and TM_(13)@Au_(32 )clusters(TM=Mn,Co)are studied by firstprinciples calculations.We find that the Au_(32 )cluster can tune not only the magnetic moment but also the magnetic coupling properties between the TM atoms of the TM cluster.The Au_(32 )cluster can increase the net magnetic moment of Mn_(13 )clusters while reducing that of Co_(13 )clusters.The interaction between Au and Mn atoms induces more Mn atoms to form spin parallel coupling,resulting in an increase of the total magnetic moment of Mn_(13 )clusters,while for the Co_(13 )clusters,the interaction between Au and Co atoms does not change the magnetic coupling states between the Co atoms,but reduces the magnetic moment of the Co atoms,leading to a decrease of the total magnetic moment of this system.Our findings indicate that the encapsulation of Au_(32 )clusters can not only raise the chemical stability of TM clusters,but also can tune their magnetic coupling properties and magnetic moment,which enables such systems to be widely applied in fields of spintronics and medical science.     

Magnetism in transition-metal-doped silicon nanotubes

Using first-principles density functional calculations, we show that hexagonal metallic silicon nanotubes can be stabilized by doping with 3d transition metal atoms. Finite nanotubes doped with Fe and Mn have high local magnetic moments, whereas Co-doped nanotubes have low values and Ni-doped nanotubes are mostly nonmagnetic. The infinite Si24Fe4 nanotube is found to be ferromagnetic with nearly the same local magnetic moment on each Fe atom as in bulk iron. Mn-doped nanotubes are antiferromagnetic, but a ferrromagnetic state lies only 0.03 eV higher in energy with a gap in the majority spin bands near the Fermi energy. These materials are interesting for silicon-based spintronic devices and other nanoscale magnetic applications.     

3d过渡金属Co掺杂核壳结构硅纳米线的第一性原理研究

基于密度泛函理论的第一性原理计算,研究了横截面为五边形和六边形的核壳结构硅纳米线的过渡金属Co原子替代掺杂.通过比较形成能发现,核心位置掺杂、壳层单链掺杂以及外壳层全替代掺杂的硅纳米线都具有稳定性,其中核心位置掺杂结构的稳定性最高.掺杂体系均呈现金属性,随着掺杂浓度的增加,电导通道数增加.Co原子掺杂的硅纳米线呈现铁磁性,具有磁矩.Bader电荷分析表明,电荷从Si原子转移至过渡金属Co原子.与自由态时过渡金属Co原子的磁矩相比,体系中Co原子的磁矩有所降低,这主要是由Co原子4s轨道向3d/4p轨道的电荷转移以及4s,3d,4p的上自旋电子转移至下自旋导致的.     

First-principles study of the stability,magnetic and electronic properties of Fe and Co monoatomic chains encapsulated into copper nanotube

By using first-principles calculations based on density-functional theory, the stability, magnetic and electronic properties of Fe and Co monoatomic chains encapsulated into copper nanotube are systematically investigated. The binding energies of the hybrid structures are remarkably higher than those of corresponding freestanding TM chains, indicating the TM chains are significantly stabilized after encapsulating into copper nanotube. The formed bonds between outer Cu and inner TM atoms show some degree of covalent bonding character. The magnetic ground states of Fe@CuNW and Co@CuNW hybrid structures are ferromagnetic, and both spin and orbital magnetic moments of inner TM atoms have been calculated. The magnetocrystalline anisotropy energies (MAE) of the hybrid structures are enhanced by nearly fourfold compared to those of corresponding freestanding TM chains, indicating that the hybrid structures can be used in ultrahigh density magnetic storage. Furthermore, the easy magnetization axis switches from that along the axis in freestanding Fe chain to that perpendicular to the axis in Fe@CuNT hybrid structure. The large spin polarization at the Fermi level also makes the hybrid systems interesting as good potential materials for spintronic devices.     

β-碳化硅/碳纳米管核壳结构的第一性原理研究

采用基于密度泛函理论的第一性原理方法研究了β-碳化硅/(15, 0) 碳纳米管和β-碳化硅/(16, 0)碳纳米管核壳结构的电子结构特性. 结果表明, 两种核壳异质结构都呈现出金属性, 它们的金属性主要是由碳纳米管和碳化硅纳米线表面的原子所贡献的. 碳化硅纳米线表面呈现的金属性由其结构本身决定, 而对于金属性的 (15, 0) 和半导体性的 (16, 0) 碳纳米管在填充碳化硅纳米线之后都表现出金属性, 主要是由于碳纳米管和碳化硅纳米线之间的电荷转移导致的, 而并不是由于碳纳米管形变造成的. 关键词： 核壳结构 电子结构 第一性原理     

First principles study on the electronic structure and effect of vanadium doping of BN nanowires

The electronic structure and effect of vanadium doping of BN nanowires are studied by first principles calculations. For the pure nanowires, it can be found that B atoms move inwards whereas N atoms move outwards, and BN nanowires have a constant band gap about 4.08 eV with larger diameter. The above-mentioned features are in agreement with those of BN nanotubes. We also find that the pure nanowires become more and more stable with increasing diameter. For V-doped BN nanowires, the V atoms move outwards, and the total energies of pair V-doped BN nanowires indicate that the ferromagnetic ground state, and the electronic structures show half-metallicity. The majority of total spin magnetic moments originate from V atoms, and B atoms which near dopant have a little contribution, while N atoms provide a little reverse magnetic moment. This study may be useful in spintronics and nanomagnets.     

面心立方单晶镍纳米线稳定性及磁性的第一性原理计算

本文采用第一性原理方法,研究了轴向为低指数晶向的面心立方(fcc)单晶镍纳米线的稳定性和磁性.计算表明,[110] 是fcc镍纳米线最容易出现的取向,[111] 取向次之,而 [001] 取向则很难出现,这一结果与实验事实符合.镍纳米线按照原子位置和磁性强弱的不同,可以分成简单的芯-壳结构,在纳米线芯部,原子的磁矩大小与块体基本一致.在纳米线表面,镍原子的磁矩比芯部原子有所增加.表面原子磁矩与轴向的取向相关,[110] 为轴向的纳米线表面原子磁矩最低,而[001] 为轴向的纳米线表面原子磁矩最高. 关键词： 镍 纳米线 第一性原理 原子磁矩     

Manipulating electronic and magnetic properties of black phosphorene with 4d series transition metal adsorption

We carry out first-principles calculations within density-functional theory to investigate the structural, electronic and magnetic properties of 4d transition metal (TM) decorated monolayer black phosphorene (BP). The results indicate that the TM adsorption on BP can have dilute magnetic semiconductor (DMS) properties. The spin polarized semiconducting state is realized in BP by adsorption of Y, Nb and Ru, while a half-metal state is obtained by Tc adsorption. In the case of two same types of TMs adsorption on BP, only [email protected] shows DMS state. In particular, two different types of TMs decorated BP can induce magnetic moments, localized mainly on the 4d TMs and the neighboring P atoms. Furthermore, the 4d TMs may enrich the electronic properties of BP, such as half-metallic, metallic and semiconducting features. These findings suggest that the 4d TM adsorbed BP can be used as a potential next-generation spintronics and magnetic storage material.     

First-principles studies of BN sheets with absorbed transition metal single atoms or dimers: stabilities, electronic structures, and magnetic properties

BN sheets with absorbed transition metal (TM) single atoms, including Fe, Co, and Ni, and their dimers have been investigated by using a first-principles method within the generalized gradient approximation. All of the TM atoms studied are found to be chemically adsorbed on BN sheets. Upon adsorption, the binding energies of the Fe and Co single atoms are modest and almost independent of the adsorption sites, indicating the high mobility of the adatoms and isolated particles to be easily formed on the surface. However, Ni atoms are found to bind tightly to BN sheets and may adopt a layer-by-layer growth mode. The Fe, Co, and Ni dimers tend to lie (nearly) perpendicular to the BN plane. Due to the wide band gap of the pure BN sheet, the electronic structures of the BN sheets with TM adatoms are determined primarily by the distribution of TM electronic states around the Fermi level. Very interesting spin gapless semiconductors or half-metals can be obtained in the studied systems. The magnetism of the TM atoms is preserved well on the BN sheet, very close to that of the corresponding free atoms and often weakly dependent on the adsorption sites. The present results indicate that BN sheets with adsorbed TM atoms have potential applications in fields such as spintronics and magnetic data storage due to the special spin-polarized electronic structures and magnetic properties they possess.     

Electronic structure effects on stability and quantum conductance in 2D gold nanowires

In this study, we have investigated the stability and conductivity of unsupported, two-dimensional infinite gold nanowires using ab initio density functional theory (DFT). Two-dimensional ribbon-like nanowires with 1–5 rows of gold atoms in the non-periodic direction and with different possible structures have been considered. The nanowires with >2 rows of atoms exhibit dimerization, similar to finite wires, along the non-periodic direction. Our results show that in these zero thickness nanowires, the parallelogram motif is the most stable. A comparison between parallelogram- and rectangular-shaped nanowires of increasing width indicates that zero thickness (111) oriented wires have a higher stability over (100). A detailed analysis of the electronic structure, reveals that the (111) oriented structures show increased delocalization of s and p electrons in addition to a stronger delocalization of the d electrons and hence are the most stable. The density of states show that the nanowires are metallic and conducting except for the double zigzag structure, which is semiconducting. Conductance calculations show transmission for a wide range of energies in all the stable nanowires with more than two rows of atoms. The conductance channels are not purely s and have strong contributions from the d levels, and weak contributions from the p levels.     

Metallization of DNA on silicon surface

New simple way for silver deoxyribonucleic acid (DNA)-based nanowires preparation on silicon surface was developed. The electrochemical reduction of silver ions fixed on DNA molecule provides the forming of tightly matched zonate silver clusters. Highly homogeneous metallic clusters have a size about 30 nm. So the thickness of nanowires does not exceed 30–50 nm. The surface of n-type silicon monocrystal is the most convenient substrate for this procedure. The comparative analysis of DNA metallization on of n-type silicon with a similar way for nanowires fabrication on p-type silicon, freshly cleaved mica, and glass surface shows the advantage of n-type silicon, which is not only the substrate for DNA fixation but also the source of electrons for silver reduction. Images of bound DNA molecules and fabricated nanowires have been obtained using an atomic force microscope and a scanning ion helium microscope. DNA interaction with silver ions in a solution was examined by the methods of ultraviolet spectroscopy and circular dichroism.     

Cr掺杂ZnO纳米线电子性质和磁性质

本文采用第一性原理密度泛函理论系统的研究了Cr原子单掺杂和双掺杂两种尺寸ZnO纳米线的电子性质和磁性质.所有掺杂纳米线的形成能都比纯纳米线的形成能低,表明掺杂增强了纳米线的稳定性.研究发现Cr原子趋于替代纳米线表面的Zn原子.所有掺杂纳米线都显示了金属性.纳米线的总磁矩主要来源于Cr原子3d轨道的贡献.由于杂化,相邻的O原子和Zn原子也产生了少量自旋.在超原胞内,Cr和O原子磁矩反平行排列,表明它们之间是反铁磁耦合.表面双掺杂纳米线铁磁态能量比反铁磁态能量低149 meV,表明Cr掺杂ZnO纳米线可能获得室温铁磁性.     

离子径迹模板法制备纳米线

重离子辐照的高分子有机膜,经过适当的处理,可以作为模板制备金属和可溶性盐纳米线,此方法称为离子径迹模板法。介绍了用电化学沉积方法和过饱和溶液法制备金属纳米线和可溶性盐纳米线的基本原理和制各实例,同时还展望了离子径迹模板法制备纳米线的一些可能的应用。The polymer foils irradiated by heavy ions can be used as temptates to prepai nanowires and some inorganic salt nanowires. It is called ＂ion-track template method＂. Compared to other templates, such as AAO template and porous silicon, etched ion-track template is more convenient and flexible. The density of the pores can be easily controlled by changing the ion fluences and the diameter of the pores can be altered through changing the etching condition. The pores of the etched ion-track template are well aligned. We present some examples of preparing metallic nanowires and inorganic salt wires by electrochemical deposition and by supersaturation solution method, respectively. We also introduce some applications of nanowires prepared with ion-track template method.     

硅和锗纳米线的原子排布和电荷分布的密度泛函紧束缚方法研究

低维硅锗材料是制备纳米电子器件的重要候选材料,是研发高效率、低能耗和超高速新一代纳米电子器件的基础材料之一,有着潜在的应用价值。采用密度泛函紧束缚方法分别对厚度相同、宽度在0.272 nm~0.554 nm之间的硅纳米线和宽度在0.283 nm~0.567 nm之间的锗纳米线的原子排布和电荷分布进行了计算研究。硅、锗纳米线宽度的改变使原子排布,纳米线的原子间键长和键角发生明显改变。纳米线表层结构的改变对各层内的电荷分布产生重要影响。纳米线中各原子的电荷转移量与该原子在表层内的位置相关。纳米线的尺寸和表层内原子排列结构对体系的稳定性产生重要影响。     

Spin resonance transport properties of a single Au atom in S–Au–S junction and Au–Au–Au junction

The spin transport properties of S–Au–S junction and Au–Au–Au junction between Au nanowires are investigated with density functional theory and the non-equilibrium Green's function. We mainly focus on the spin resonance transport properties of the center Au atom. The breaking of chemical bonds between anchor atoms and center Au atom significantly influences their spin transmission characteristics. We find the 0.8 eV orbital energy shift between anchor S atoms and the center Au atom can well protect the spin state stored in the S–Au–S junction and efficiently extract its spin state to the current by spin resonance mechanism, while the spin interaction of itinerant electrons and the valence electron of the center Au atom in the Au–Au–Au junction can extract the current spin information into the center Au atom. Fermi energy drift and bias-dependent spin filtering properties of the Au–Au–Au junction may transform information between distance, bias,and electron spin. Those unique properties make them potential candidates for a logical nanocircuit.     

Structural and magnetic properties of MoS2 monolayer zigzag nanoribbon doped by Ti,V, Cr,and Mn

In order to find new functions of monolayer MoS₂ in nanoelectronics or spin electronic devices, using spin-polarized density functional theory (DFT) calculations with on-site coulomb interaction (U), we investigated substitutional doping of Mo atoms of monolayer zigzag MoS₂ nanoribbon (ZZ-MoS₂ NR) by transition metals (TM) (where TM = Ti, V, Cr, Mn) at the Mo-edge, S-edge, and the middle of the NRs. The results of this study indicate the NR widened irrespective of the doped TM position and type, and the Mo-edge was found as the easiest substitutional position. For ZZ-MoS₂ NR doped by Mn, Cr or V atoms, the preferred magnetic coupling state is the edge atoms of S at the S-edge, exhibiting the same spin polarization with TM (named the FM1 state), attributing the NR with metallic magnetism. For Ti-doped monolayer ZZ-MoS₂ NR, in addition to the FM1 state, other preferred magnetic coupling state was observed in which the edge atoms of S at the S-edge exhibit the opposite spin polarization with that of Ti (named the FM2 state). Thus, the NR doped by Ti atom possesses metallic (FM1 state) or half-metallic (FM2 state) magnetism. The total magnetic moments of the ZZ-MoS₂ NR doped by TM follows a linear relationship as a function of the TM dopants (Mn, Cr, V, and Ti). Under $>4\text{\%}$ applied strain, the NR doped by Ti atom only presents the characteristics of half-metallic magnetism as the initial one in the FM2 state, and its total magnetic moment always remained 0 μB, i.e., it was not affected by the width of the NR. This study provides a rational route of tuning the magnetic properties of ZZ-MoS₂ NRs for their promising applications in nanoelectronics and spin electronic devices.