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.     

金基纳米管AunSi12 (n=25-60)的奇异结构与电磁特性预测

应用相对论效应的密度泛函理论,系统研究了一系列稳定的中空类管状Au_nSi₁₂(n=25, 30, 35, 40, 45, 50, 55, 60)团簇. Au_nSi₁₂可以通过在不同长度的单壁Au纳米管(5, 5)的两端戴帽由二十面体Au₂₀Si₁₂平分的两个相同半球构建而成.计算结果显示,Si原子的掺杂使得Au_nSi₁₂的结构变得更加紧密且加强了相应的类管状Au团簇的稳定性.最高占据分子轨道(HOMO)和最低未占据分子轨道(LUMO)之间的能隙值在0.041 eV至0.138 eV区间,表明Au_nSi₁₂具有较高的化学活性.电子结构分析显示,Si原子和Au原子之间的p-d轨道杂化在形成和维持Au_nSi₁₂的类管状结构方面发挥了重要作用.Hirshfeld电荷分析显示,电荷从Au原子转移到Si原子上,Au_n...     

Structural,electronic and magnetic properties of hydrogenated BC2N

Density functional theory has been used to study the electronic and magnetic properties as well as the stability on the hydrogenated BC₂N sheets. It is found that two different structures (BC₂NH-I and BC₂NH-II) with the ferromagnetic ground states can be formed when removing the H atoms from one side of semi-hydrogenated BC₂N sheet. By applying tensile strain, both of their magnetisms are robust to 2.0 μ_B. However, the magnetisms are sensitively changed by compressive strain larger than ?6%. The BC₂NH-I system can be transitioned from semiconductor to half-metal and then to metal when the compressive strain is changed from ?6% to ?8%. And the BC₂NH-II system can be changed into half-metal by applying the compressive strain between ?6% and ?7.5%. Our calculation results suggest a possible way to tune the electronic and magnetic properties by choosing the appropriate structural type and the external strain, which would have potential applications in spintronics and nanodevices.     

Electronic and magnetic properties of free and supported transition metal clusters

The spin-polarized relativistic version of the multiple scattering or the Korringa–Kohn–Rostoker method for electronic structure calculations has been used to study the electronic and magnetic properties of free and supported transition metal clusters. Corresponding results are presented for the spin- and spin–orbit-induced orbital magnetic moments in free Fe and FePt clusters. For both systems a pronounced enhancement is found for the spin as well as for the orbital moments compared with the corresponding bulk value which diminishes in an oscillatory fashion with increasing cluster size. Corresponding investigations on small Co clusters deposited on a Pt (111) surface also revealed a strong dependence of the magnetic properties on the cluster size and shape. A comparison of our theoretical results with available experimental data led to rather satisfying agreement.     

Electronic band structure,stability, structural,and elastic properties of IrTi alloys

The structural properties and mechanical stabilities of B2-IrTi have been investigated using first-principle calculations. The elastic constants calculations indicate that the B2-IrTi is unstable to external strain and the softening of C₁₁−C₁₂ triggers the B2-IrTi (cubic) to L1₀-IrTi (tetragonal) phase transformation. Detailed electronic structure analysis revealed a Jahn–Teller-type band split that could be responsible for elastic softening and structure phase transition. The cubic–tetragonal transition is accompanied by a reduction in the density of states (DOS) at the Fermi level and the d-DOS of Ti at Fermi level plays a decisive role in destabilizing the B2-IrTi phase.     

Structural and electronic properties of boron-doped double-walled silicon carbide nanotubes

The effects of boron doping on the structural and electronic properties of (6,0)@(14,0) double-walled silicon carbide nanotube (DWSiCNT) are investigated by using spin-polarized density functional theory. It is found that boron atom could be more easily doped in the inner tube. Our calculations indicate that a Si site is favorable for B under C-rich condition and a C site is favorable under Si-rich condition. Additionally, B-substitution at either single carbon or silicon atom site in DWSiCNT could induce spontaneous magnetization.     

Electronic properties of single-molecule junction: Effect of the molecular distortion

For a model system consisting of a benzenedithio (BDT) molecule sandwiched between two Au plates, the electronic properties as a function of different BDT geometry are investigated using density functional theory. The distorted BDT structures are got through stretching the electrode distance. The corresponding electronic properties, including the spatial distribution of the frontier orbits, the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital levels and density of states at the Fermi energy are determined. It reveals that the molecular distortion essentially determines electronic structures. The result should be beneficial to understand the stress-dependent or structure-dependent transport mechanism of electrons of the BDT junction.     

Electronic structure and magnetic properties of BaTi1-xMnxO3

The electronic structure and magnetic properties of polycrystalline BaTi_1-xMn_xO₃ (x = 0–0.1) compounds prepared by solid-state reactions were studied. The results revealed that the increase in Mn content (x) did not change the oxidation numbers of Ba (+2) and Ti (+4) in BaTi_1-xMn_xO₃. However, there is the change in Mn valence that Mn^3+,4+ ions coexist in the samples with x = 0.01–0.04 while Mn⁴⁺ ions are almost dominant in the samples with x = 0.06–0.1. We also point out that Mn³⁺ and Mn⁴⁺ ions substitute for Ti⁴⁺ and prefer locating in the tetragonal and hexagonal BaTiO₃ structures, respectively, in which the hexagonal phase constitutes soon as x = 0.01. Particularly, all the samples exhibit room-temperature ferromagnetism. Ferromagnetic order increases with increasing x from 0 to 0.02, but decreases as x ≥ 0.04. We think that ferromagnetism in BaTi_1-xMn_xO₃ is related to lattice defects and/or exchange interactions between Mn³⁺ and Mn⁴⁺ ions.     

Electronic structure and optical properties of non-metallic modified graphene: a first-principles study

In this paper, the electronic structure and stability of the intrinsic, B-, N-, Si-, S-doped graphene are studied based on first-principles calculations of density functional theory. Firstly, the intrinsic, B-, N-, Si-, S-doped graphene structures are optimized, and then the forming energy, band structure, density of states, differential charge density are analyzed and calculated. The results show that B- and Si-doped systems are p-type doping, while N is n-type doping. By comparing the forming energy, it is found that N atoms are more easily doped in graphene. In addition, for B-, N-, Si-doped systems, it is found that the doping atoms will open the band gap, leading to a great change in the band structure of the doping system. Finally, we systematically study the optical properties of the different configurations. By comparison, it is found that the order of light sensitivity in the visible region is as follows: S-doped> Si-doped> pure > B-doped > N-doped. Our results will provide theoretical guidance for the stability and electronic structure of non-metallic doped graphene.     

Electronic and optical properties of V doped AlN nanosheet: DFT calculations

Electronic and optical properties of pure and V-doped AlN nanosheet have been investigated using density functional theory, and the dielectric tensor is calculated using the random phase approximation (RPA). The results of structural calculations show that the V atoms tend to replace instead of aluminum atoms with the lowest formation energy. In addition, study of the electronic properties shows that pure AlN nanosheet is a p-type semiconductor that by increasing one V atom, it possesses the metallic properties and magnetic moment becomes Zero. Moreover, by replacing two V atoms, the half-metallic behavior with 100% spin polarization can be found, and each supercell gains a net magnetic moment of 3.99 µ_B. Optical properties like the dielectric function, the energy loss function, the absorption coefficients, the refractive index are calculated for both parallel and perpendicular electric field polarizations, and the results show that the optical spectra are anisotropic.     

Electronic and magnetic properties of pristine and hydrogenated borophene nanoribbons

The groundbreaking works in graphene and graphene nanoribbons (GNRs) over the past decade, and the very recent discovery of borophene naturally draw attention to the yet-to-be-explored borophene nanoribbons (BNRs). We herein report a density functional theory (DFT) study of the electronic and magnetic properties of BNRs. The foci are the impact of orientation (denoted as BxNRs and ByNRs with their respective periodic orientations along x- and y-axis), ribbon width (N_x, N_y=4–15), and hydrogenation effects on the geometric, electronic and magnetic properties of BNRs. We found that the anisotropic quasi-planar geometric structure of BNR and the edge states largely govern its electronic and magnetic properties. In particular, pristine ByNRs adopt a magnetic ground state, either anti-ferromagnetic (AFM) or ferromagnetic (FM) depending on the ribbon width, while pristine BxNRs are non-magnetic (NM). Upon hydrogenation, all BNRs exhibit NM. Interestingly, both pristine and hydrogenated ByNRs undergo a metal-semiconductor-metal transition at N_y=7, while all BxNRs remain metallic.     

Structural and electronic properties of the TiC nanotubes: Density functional-based tight binding calculations

Atomic models of the hypothetical single- and multi-walled cylindrical- and prismatic-like TiC nanotubes have been constructed and their structural and electronic properties have been studied by means of density functional-based tight binding (DFTB) method. The electronic bands, densities of states and binding energies are analyzed as a function of the TiC tubes sizes. Our calculations showed that TiC nanotubes are semiconducting, in contrary to the metallic-like crystalline TiC, and the band gaps tend to vanish as the number of tube walls increase.     

氧化钨纳米线-单壁碳纳米管复合型气敏元件的室温NO2敏感性能与机理

利用溶剂热法合成了一维的氧化钨纳米线, 通过掺入适量单壁碳纳米管(SWNT)制备了基于氧化钨纳米线-SWNT 复合结构的室温气敏元件并评价了其对NO₂气体的室温敏感性能. 利用X射线与扫描电子显微镜表征了材料的微结构, 结果表明, 合成的氧化钨纳米线具有单斜的W₁₈O₄₉结构, 复合材料中SWNT被包埋在氧化钨纳米线中间. 气敏性能测试结果表明, 氧化钨纳米线-SWNT复合结构气敏元件在室温下对NO₂气体表现出了高的灵敏度和超快的响应特性; 较低的SWNT掺入量对获得好的气敏性能有利. 分析了基于复合结构材料气敏元件的可能的气敏机理, 认为元件良好的室温敏感性能与SWNT掺入在复合结构材料中引入大量的贯穿气孔和p-n异质结有关.     

First-principles study of the electronic and optical properties of ZnO nanowires

The geometric, energetic, electronic structures and optical properties of ZnO nanowires (NWs) with hexagonal cross sections are investigated by using the first-principles calculation of plane wave ultra-soft pseudo-potential technology based on the density functional theory (DFT). The calculated results reveal that the initial Zn-O double layers merge into single layers after structural relaxations, the band gap and binding energies decrease with the increase of the ZnO nanowire size. Those properties show great dimension and size dependence. It is also found that the dielectric functions of ZnO NWs have different peaks with respect to light polarization, and the peaks of ZnO NWs exhibit a significant blueshift in comparison with those of bulk ZnO. Our results gives some reference to the thorough understanding of optical properties of ZnO, and also enables more precise monitoring and controlling during the growth of ZnO materials to be possible.     

Structural stability and electronic properties of GaSb nanowires

The structural stability and electronic properties of four different shapes of GaSb nanowire have been studied by ab-initio method using the generalized gradient approximations. The different structures were two atom linear wire, two atom zigzag wire, four atom square wire and six atom hexagonal wire. The geometry optimization and the stability of all nanowires were investigated. We explore the minimum energy atomic configuration for all the considered shapes. We find that four atom square wire configuration has greater stability in comparison to other shapes. The analysis of density of states and band structures of optimized nanowires predicts that semiconducting nanowires may be metallic or semiconducting. The behavior entirely depends upon the geometrical structure.     

3d过渡金属掺杂对Cd12O12纳米线电子和磁性能的影响

采用基于密度泛函理论的第一性原理计算方法,系统研究了3d过渡金属元素(Sc、Ti、Cr、Mn、Co、Cu和Zn)掺杂Cd12O12纳米线的几何结构,电子结构和磁性。结果表明：所有掺杂体系均是热力学稳定的;掺杂Ti或Zn时体系保留了原有的非磁半导体特性,掺杂Mn、Co或Cu时能够实现磁性半导体态,而在掺杂Sc（Cr）时体系转变为非磁性金属态（磁性金属态）。研究结果表明,掺杂3d过渡金属元素的Cd12O12纳米线在电子、光电和自旋电子学领域具有潜在的应用价值。     

Electronic structure and magnetic properties of the compound CeCuIn

Magnetization, magnetic susceptibility, electrical resistivity, thermoelectric power and X-ray photoemission measurements were performed on a polycrystalline sample of CeCuIn. This compound crystallizes in a hexagonal structure of the ZrNiAl type. The magnetic data indicate that CeCuIn remains paramagnetic down to 1.9 K with a paramagnetic Curie temperature of −13 K and an effective magnetic moment equal to 2.5 μ_B. The electrical resistivity has metallic character, yet in the entire temperature range studied here, it is a strongly nonlinear function of temperature. The temperature dependence of the thermoelectric power is dominated by a small positive maximum near 76 K and a deep negative minimum at about 16 K. Above 150 K the thermopower exhibits a Mott's type behavior. The positive sign of the Seebeck coefficient in this temperature region indicates that the holes are dominant charge and heat carriers. The structure of Ce 3d_5/2 and Ce 3d_3/2 XPS spectra has been interpreted in terms of the Gunnarsson-Schönhammer theory. Three final-state contributions f⁰, f¹ and f² are clearly observed, which exhibit a spin-orbit splitting Δ_SO≈18.7 eV. The appearance of the 3d⁹f⁰ component is a clear evidence of the intermediate valence behavior of Ce. From the intensity ratio I(f⁰)/[I(f⁰)+I(f¹)+I(f²)] the 4f-occupation number is estimated to be 0.95. In turn, the ratio I(f²)/[I(f¹)+I(f²)]=0.08 yields a measure of the hybridization energy that is equal to 45 meV.     

The structural, electronic, and magnetic properties of Fe-Ir, Co-Ir and Ni-Ir linear and zigzag nanowires: First-principles calculations

The magnetic and electronic properties of both linear and zigzag bimetallic chains of Fe-Ir, Co-Ir and Ni-Ir have been calculated based on density functional theory and using the generalized gradient approximation. It is found that all considered zigzag chains form a twisted two-legged ladder, look like a corner-sharing triangle ribbon, and have a lower total energy than the corresponding linear chains. All the Fe-Ir, Co-Ir and Ni-Ir linear and zigzag chains have stable or metastable ferromagnetic (FM) states. The bond lengths in bimetallic Fe-Ir, Co-Ir and Ni-Ir at ferromagnetic state are larger than those in the corresponding structures at nonmagnetic state. Interestingly, the Ni-Ir zigzag nanowire has two energy minimum states, both ferromagnetic and nonmagnetic (NM), indicating a possible stable condition for mechanically controllable break-junction experiments.     

Tuning the electronic properties of single-walled SiC nanotubes by external electric field

The electronic properties of SiC nanotubes (SiCNTs) under external transverse electric field were investigated using density functional theory. The pristine SiCNTs were semiconductors with band-gaps of 2.03, 2.17 and 2.25 eV for (6,6), (8,8) and (10,10) SiCNTs, respectively. It was found the band gaps was reduced with the external transverse electric filed applied. The (8,8) and (10,10) SiCNTs changed from semiconductor to metals as the intensity of electric field reached 0.7 and 0.5 V/Å. The results indicate that the electronic properties of SiCNTs can be tuned by the transvers electric field with integrality of the nanotubes.