Electronic and magnetic properties of Fe-, Co-, and Ni-decorated BC3: A first-principles study

The electronic and magnetic properties of Fe-, Co-, and Ni-decorated two dimensional (2D) BC₃ are systematically investigated by first-principles calculations. We find that the Fe, Co, and Ni atoms can be strongly adsorbed on the hollow sites of 2D BC₃. Fe and Co adatoms are more stable when adsorbed on the hollow sites of the carbon rings in the 2D BC₃, while the hollow sites of boron-carbon rings in the 2D BC₃ are the most stable sites for the adsorption of Ni adatoms. These proposed metal–BC₃ complexes exhibit interesting electronic and magnetic behaviors. In particular, the Fe–BC₃ and Co–BC₃ complexes are metals with magnetic ground states , while the Ni–BC₃ complex behaves as a nonmagnetic semiconductor with a direct bandgap. Furthermore, our magnetic analysis reveals that induced magnetism in the Fe–BC₃ and Co–BC₃ complexes arises from their local magnetic moments. Functionalization of 2D BC₃ through these metal–adatom adsorption appears to be a promising way to extend its applications.     

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.     

非金属与金属原子共掺杂石墨烯体系的气敏特性研究

采用基于密度泛函理论的第一性原理方法研究了非金属N原子和金属原子(M=Mo,Al,Co,Fe,Au和Pt)共掺杂石墨烯体系(M-GN4)的电子结构和表面活性.研究发现:单个金属原子掺杂的GN4体系表现出不同的稳定性,相比掺杂的Au原子,其它的金属原子都具有很高的稳定性( 6. 0 e V).掺杂的金属原子失去电荷显正电性将有助于调控气体分子的吸附特性. Mo-GN4和Al-GN4衬底对吸附的O_2表现出较高的灵敏性,单个CO和O_2分子在Co-GN4和Fe-GN4衬底的吸附能差别较小.此外,吸附不同的气体分子能够有效地调控M-GN4体系的电子结构和磁性变化.     

Spin splitting of s and p states in single atoms and magnetic coupling in dimers on a surface

Electronic states of magnetic atoms (Mn, Fe, and Co) and artificially assembled dimers (Mn2, Fe2, and Co2) on a NiAl(110) surface were probed by scanning tunneling spectroscopy at 17 K. Resonance peaks characteristic of each adsorbed species were observed in the unoccupied density of states. Comparison of the measured spectra with calculations by density functional theory revealed spin splitting in the unoccupied states with s and p characters for the single magnetic adatoms and addimers. The magnitude of the resonance splitting for the adatoms increased with the calculated values of magnetic moments. The resonance structures for the addimers exhibited signatures of their internal magnetic coupling.     

表面吸附对单层黑磷砷结构、电子性质和磁性调控的第一性原理研究

基于第一性原理，系统研究了11种不同原子吸附在单层AsP上的几何结构、吸附能、磁矩和电子结构性质. 使用的吸附原子包括轻质非金属(C、N、O)原子，第三周期金属原子(Na、Mg、Al)和过渡金属原子(Ti、V、Cr、Mn和Fe). 研究结果表明，吸附原子引起了AsP多样的结构、磁性和电子性质改变. AsP与所研究的吸附原子都能紧密结合，并且所有系统的吸附能都比吸附原子在石墨烯、SiC、BN以及MoS₂上的吸附能强得多. AsP的半导体特性受到吸附原子的影响，其可以诱导产生中间能隙态或引起n型掺杂. 此外，表面吸附产生了不同的自旋电子特性，具体而言，吸附N、Ti和Fe的AsP成为双极半导体；Mn修饰的AsP成为双极自旋无间隙半导体.     

First-principles study of transition metal linear monoatomic chains adsorption on boron nitride nanotube

Structural, electronic and magnetic properties of six 3d transition metals (TM=V, Cr, Mn, Fe, Co and Ni) linear monoatomic chains adsorbed on the (5,5) boron nitride nanotube (BNNT) at five different sites have been investigated by first-principle calculations. The results indicate all TM chains can be spontaneously adsorbed on the outer surface of the BNNT. The stable adsorption sites are different for different TM chains. All TM chains can be adsorbed on the N site, while the adsorption on the Z site is unstable. The dispersion character occurs in energy band curves of stable TM/BNNT systems and bring about the band gap disappearance in comparison with that of pure (5,5) BNNT. Interestingly, the TM/BNNT systems with nearly half-filled 3d metals V and Cr at H and N sites, as well as Mn at A site show a half-metal character and are usable in spintronics devices. The different electronic properties of BNNT can also be achieved through decorations of the same TM chain on different sites. The TM chain adsorbed BNNT systems exhibit high stability, promising electronic properties and high magnetic moments, which may be useful for a wide variety of next-generation nanoelectronic device components.     

Structural,electronic,and magnetic properties of transition-metal atom adsorbed two-dimensional GaAs nanosheet

By using first-principles calculations within the framework of density functional theory,the electronic and magnetic properties of 3d transitional metal(TM) atoms(from Sc to Zn) adsorbed monolayer Ga As nanosheets(Ga As NSs) are systematically investigated.Upon TM atom adsorption,Ga As NS,which is a nonmagnetic semiconductor,can be tuned into a magnetic semiconductor(Sc,V,and Fe adsorption),a half-metal(Mn adsorption),or a metal(Co and Cu adsorption).Our calculations show that the strong p–d hybridization between the 3d orbit of TM atoms and the 4p orbit of neighboring As atoms is responsible for the formation of chemical bonds and the origin of magnetism in the Ga As NSs with Sc,V,and Fe adsorption.However,the Mn 3d orbit with more unpaired electrons hybridizes not only with the As 4p orbit but also with the Ga 4p orbit,resulting in a stronger exchange interaction.Our results may be useful for electronic and magnetic applications of Ga As NS-based materials.     

The influence of hydrogen on the electronic and magnetic structures of TM(0 0 1) (TM=Fe, Co, Ni, and Cu) surfaces and interfaces: Ab-initio calculations

We present ab-initio investigation of the electronic and magnetic structure of TM(0 0 1) surfaces and TM/Cu(0 0 1) systems (TM=Fe, Co, Ni, Cu) with and without hydrogen adsorbed layer. The adsorption energy of hydrogen atom is found to be energetically more stable above the surface layer of Ni(0 0 1) surface than other TM(0 0 1) surfaces. The adsorption energies of hydrogen on TM/Cu(0 0 1) systems are larger than those on TM(0 0 1) surfaces. The relaxed geometries show that hydrogen has a strong influence on the interlayer distance. Furthermore, a marked reduction of Fe, Co, and Ni surface magnetic moments to 2.54, 1.41 and 0.25 μ_B, respectively, is obtained due to the presence of hydrogen.     

钴原子及其团簇在Rh(111)和Pd(111)表面的扫描隧道显微学研究

利用扫描隧道显微镜和扫描隧道谱(STM/STS)及单原子操纵,系统研究了单个钴原子(Co) 及其团簇在Rh (111)和Pd (111)两种表面的吸附和自旋电子输运性质. 发现单个Co原子在Rh (111)上有两种不同的稳定吸附位,分别对应于hcp和fcc空位, 他们的高度明显不同,在针尖的操纵下单个Co原子可以在两种吸附位之间相互转化. 在这两种吸附位的单个Co原子的STS谱的费米面附近都存在很显著的峰形结构, 经分析认为Rh (111)表面单个Co原子处于混价区,因此这一峰结构是d轨道共振 和近藤共振共同作用的结果.对于Rh (111)表面上的Co原子二聚体和三聚体, 其费米面附近没有观测到显著的峰,这可能是由于原子间磁交换相互作用 和原子间轨道杂化引起的体系态密度改变所共同导致.与Rh (111)表面不同, 在Pd (111)表面吸附的单个Co原子则表现出均一的高度.并且对于Pd (111)表面所有 单个Co原子及其二聚体和三聚体,在其STS谱的费米面附近均未探测到显著的电子结构, 表明Co原子吸附于Pd (111)表面具有与Rh (111)表面上不同的原子-衬底相互作用与自旋电子输运性质.     

Ab initio study of magnetic properties in the adsorption of transition-metal atoms on arsenene

The magnetic properties of adsorption of different transition-metal (TM) atoms (Co, Cu, Mn, Fe, and Ni) on arsenene are investigated using density functional theory (DFT). Magnetism appears in the cases of Co, Mn, and Fe. Among all the magnetic cases, the TM atom prefers the same adsorption site. Then, we further study the interaction in two-TM-adsorbed system and different magnetic states are observed. Our results show that both nonmagnetic and ferromagnetic states exist in two-Co-adsorbed system and the p-d hybridization mechanism results in its ferromagnetic state. However, for two Mn and two Fe adsorbed systems, an AFM interaction is found, which could be reasonably explained by the superexchange mechanism. Such multiple magnetic properties may suggest promising applications of TM-adsorbed arsenene in the future.     

Modulation of magnetic properties of bilayer SnSe with transition-metals doping in the interlayer

We investigate the spin-polarized electronic and magnetic properties of bilayer SnSe with transition-metal (TM) atoms doped in the interlayer by using a first-principles method. It shows that Ni dopant cannot induce the magnetism in the doped SnSe sheet, while the ground state of V, Cr, Mn, Fe and Co doped systems are magnetic and the magnetic moment mainly originates from 3d TM atom. Two types of factors, which reduce the magnetic moment of TM atoms doped in bilayer SnSe, are identified as spin-up channel of the 3d orbital loses electrons to SnSe sheet and spin-down channel of the 3d orbital gains electrons from 4s orbital. The spin polarization is found to be 100% at Fermi level for the Mn and Co atoms doped system, while the Ni-doped system is still a semiconductor with a gap of 0.26 eV. These results are potentially useful for development of spintronic devices.     

Observing spin polarization of individual magnetic adatoms

We have used spin-polarized scanning tunneling spectroscopy to observe the spin polarization state of individual Fe and Cr atoms adsorbed onto Co nanoislands. These magnetic adatoms exhibit stationary out-of-plane spin polarization, but have opposite sign of the exchange coupling between electron states of the adatom and the Co island surface state: Fe adatoms exhibit parallel spin polarization to the Co surface state while Cr adatoms exhibit antiparallel spin polarization. First-principles calculations predict ferromagnetic and antiferromagnetic alignment of the spin moment for individual Fe and Cr adatoms on a Co film, respectively, implying negative spin polarization for Fe and Cr adatoms over the energy range of the Co surface state.     

气体分子在类石墨烯材料负载单个金属原子表面的吸附特性

采用密度泛函理论方法研究了不同种类和数量的气体小分子在类石墨烯材料(graphenylene)衬底支撑的金属原子(M=Co, Mo和Pd, gra-M)表面的吸附特性,系统地分析了吸附不同数量的NO和CO分子的稳定构型,吸附能,电荷转移量以及引起的体系电子结构和磁性变化.研究结果表明:1) NO、CO气体小分子的稳定吸附位在金属原子顶位,吸附物与衬底间的电荷转移量表明负载不同的金属原子能够有效地调制类石墨烯材料的气敏特性;2)单个和两个气体分子吸附能够引起gra-M体系的自旋电荷密度分布发生变化,进而使得气体吸附体系表现出不同磁矩大小.     

Spectrally controlled atom-by-atom photoassembly of silver clusters on the surface of ionic-covalent crystals

The fundamental possibility of implementing light-controlled atom-by-atom assembly of silver clusters beginning with dimers and trimers via photostimulated diffusion of individual atoms initially adsorbed on the surface of AgCl and ZnS single crystals by mass-spectrometric ion deposition is shown. Possible mechanisms of this process are discussed, including the charge exchange in adatoms via alternating capture of holes and electrons accompanied by the transition to neighboring, energetically more favorable adsorption sites; hopping displacements of adatoms over the surface by gaining kinetic energy upon nonradiative recombination of photocarriers from their levels; and low-barrier diffusion of short-lived negatively charged adatoms with a captured electron.     

单层GaSe表面Fe原子吸附体系电子自旋性质调控

Ⅲ族金属单硫化物因其优越的光电和自旋电子特性而备受关注,实现对其自旋性质的有效调控是发展器件应用的关键.本文采用密度泛函理论系统地研究了GaSe表面Fe原子吸附体系的几何构型及自旋电子特性.Fe/GaSe体系中Fe吸附原子与最近邻Ga,Se原子存在较强的轨道耦合效应,使体系呈现100%自旋极化的半金属性.其自旋极化贡献主要来源于Fe-3d电子的转移及Fe-3d,Se-4p和Ga-4p轨道杂化效应.对于Fe双原子吸附体系,两Fe原子之间的自旋局域导致原本从Fe转移至GaSe的自旋极化电荷量减少,从而费米能级附近的单自旋通道转变为双自旋通道,费米能级处的自旋极化率转变为0.研究结果揭示了Fe_n/GaSe吸附体系自旋极化特性的形成和转变机制,可为未来二维自旋纳米器件的设计与构建提供参考.     

硫化锌纳米管稳定性、电子性质和磁性质的比较研究

用第一性原理方法系统地研究硫化锌纳米管的稳定性、电子性质和掺杂磁性质.比较三种纳米管的稳定性.研究表明,六边形截面的双壁管的稳定性最高,相同截面的单壁管稳定性次之,而圆截面的之字形和扶手椅纳米管稳定性最低.电子能带结构计算表明它们都是直接带隙半导体.纳米管表面氢吸附后,六边形截面的单壁管转变为间接带隙半导体.研究了磁性原子掺杂六边形截面管的磁性质.发现掺杂纳米管的形成能比纯纳米管的形成能低,说明掺杂过程是一个放热反应.纳米管的总磁矩等于掺杂的磁性原子的磁矩.这些单掺杂纳米管在可调磁的新材料方面有潜在的应用价值.     

First-principles studies of Fe atoms adsorption on hydrogen-terminated boron nitride nanoribbons

By using density functional theory (DFT), we have studied the adsorption of Fe atoms on boron nitride nanoribbons (BNNRs). The stabilities of Fe atoms adsorption on BNNRs for the inner sites are very weakly dependent on the adsorption sites and Fe atoms energetically prefer to be adsorbed on the edge boron sites. The analysis of electronic structures shows that the most of the stable systems are the interesting spin gapless semiconductors. The magnetism of the Fe adatom is preserved well on the BNNRs, very close to that of the corresponding isolated atom for all the considered adsorption sites.     

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.     

Structural,electronic and magnetic properties of the 3d transition metal atoms adsorbed on boron nitride nanotubes

Adsorption configurations for a series of transition metal (TM) 3d atoms adsorbed on the zigzag (8, 0) BNNT at five different sites have been investigated using the first-principles PAW potential within DFT under GGA. The most stable adsorption sites are different for different TM atoms. Partially filled 3d metals V, Cr and Mn can bind strongly with zigzag (8, 0) BNNT, and Sc, Ti, Co and Ni can be chemically adsorbed on the (8, 0) BNNT. The binding between the Fe or Cu atom and the BNNT is only marginal. One unusual case is Zn. Its zero binding energy independent of the adsorption sites implies it can only physically adsorbed on the BNNT mainly stemmed from the van de Waals interaction. Electronic structure analyses show that: (1) for each TM atom adsorbed at five different sites, the total DOS curves of both majority and minority spins make a slightly relative shift along the energy axis, and for each site the total DOS of the minority spin shifts slightly in high energy direction with respect to that of the majority spin lead to a exchange splitting, except fully filled 3d metals Cu and Zn; (2) total DOS curves of both the majority and minority spins for the adsorbed systems shift to the lower energy region compared with that of the pristine (8, 0) BNNT. And the smaller 3d electrons number of the TM atom, the larger shift to the lower energy region of its DOS curves; (3) for V-, Mn- and Fe-adsorbed (8, 0) BNNT, only one type of electrons (either majority spin or minority spin) passes through the Fermi level implies these adsorbed systems are all half-metals.