铂掺杂扶手椅型石墨烯纳米带的电学特性研究

本文采用基于密度泛函理论(DFT)的第一性原理计算了铂原子填充扶手椅型石墨烯纳米带(AGNR)中双空位结构的电学性能.计算结果表明: 通过控制铂原子的掺杂位置, 可以实现纳米带循环经历小带隙半导体—金属—大带隙半导体的相变过程; 纳米带边缘位置是铂原子掺杂的最稳定位置, 边缘掺杂纳米带的带隙值随宽度的变化与本征AGNR一样可用三簇曲线表示, 但在较大宽度时简并成两条曲线, 一定程度上抑制了带隙值的振荡; 并且铂原子边缘掺杂导致宽度系数N_a = 3p和3p + 1(p是一个整数)的几个较窄纳米带的带隙中出现杂质能级, 有效地降低了其过大的带隙值. 此外, 铂掺杂AGNR的能带结构对掺杂浓度不是很敏感, 从而降低了对实验精度的挑战. 本文的计算有利于推动石墨烯纳米带在纳米电子学方面的应用.     

Modification of the electronic structure of graphene by intercalation of iron and silicon atoms

The ab initio calculations of the electronic structure of low-dimensional graphene–iron–nickel and graphene–silicon–iron systems were carried out using the density functional theory. For the graphene–Fe–Ni(111) system, band structures for different spin projections and total densities of valence electrons are determined. The energy position of the Dirac cone caused by the p _z states of graphene depends weakly on the number of iron layers intercalated into the interlayer gap between nickel and graphene. For the graphene–Si–Fe(111) system, the most advantageous positions of silicon atoms on iron are determined. The intercalation of silicon under graphene leads to a sharp decrease in the interaction of carbon atoms with the substrate and largely restores the electronic properties of free graphene.

     

Electronic properties of BN-doped bilayer graphene and graphyne in the presence of electric field

In the present paper, we have used density functional theory to study electronic properties of bilayer graphene and graphyne doped with B and N impurities in the presence of electric field. It has been demonstrated that a band gap is opened in the band structures of the bilayer graphene and graphyne by B and N doping. We have also investigated influence of electric field on the electronic properties of BN-doped bilayer graphene and graphyne. It is found that the band gaps induced by B and N impurities are increased by applying electric field. Our results reveal that doping with B and N, and applying electric field are an effective method to open and control a band gap which is useful to design carbon-based next-generation electronic devices.     

新型超导材料MgCNi3的电子结构与超导电性研究

用MS-Xα方法研究了非氧化物超导材料MgCNi₃的电子结构. 研究结果显示, 态密度分布曲线的主峰靠近Fermi面, 主要来自于Ni的d电子的贡献. 用T(T=Co，Mn，Cu)替代MgCNi₃中的部分Ni形成化合物MgCNi₂T，替代使Ni的价电子数减小, 价态发生变化, Fermi面处态密度N(E_F)减小. 计算结果表明：无论是电子掺杂（Cu）还是空穴掺杂（Co，Mn），MgCNi₃的超导电 关键词： 电子结构 态密度 超导电性     

Sulfur dioxide adsorbed on graphene and heteroatom-doped graphene: a first-principles study

The adsorption of sulfur dioxide (SO₂) on intrinsic graphene and heteroatom-doped (B, N, Al, Si, Cr, Mn, Ag, Au, and Pt) graphene samples was theoretically studied using first-principles approach based on density functional theory to exploit their potential applications as SO₂ gas sensors. The structural and electronic properties of the graphene-molecule adsorption adducts are strongly dependent on the dopants. SO₂ molecule is adsorbed weakly on intrinsic graphene, and B-, N-doped graphene; in general, strong chemisorption is observed on Al-, Si-, Cr-, Mn-, Ag-, Au-, and Pt-doped graphene. The adsorption mechanisms are discussed from charge transfers and density of states. This work reveals that the sensitivity of graphene-based chemical gas sensors for SO₂ can be drastically improved by introducing appropriate dopant, and Cr, as well as Mn, may be the best choices among all the dopants.     

Influence of electronic structures of doped TiO2 on their photocatalysis

The modification of bandgap of TiO₂ was intensively studied for decades to improve its visible light absorbance efficiency. The practical application potential of TiO₂ as photocatalysts for water splitting and water purification has motivated enduring experimental and theoretical research of the doping effects in bulk and nanosized TiO₂ using transition metals, rear earths, p‐block metals and metalloids, and non‐metal elments as dopants to decrease the bandgap of TiO₂. This review summarized the typical theoretical results of the dopant induced variation in electronic structure, bandgap, and density of states of TiO₂. The codoping effects of metal/metal, metal/non‐metal combinations were also introduced briefly to display the modification of electronic structures. Some results were accompanied by experimental results to demonstrate the influence of improved light absorbance efficiency on the photocatalytic performance. The doping effects on the density of states of surface were also summarized briefly. The metal dopants show clear influences on the 3d electrons of titanium to elevate or depress the minimum of conduction band, while the non‐mental dopants mainly interact with the 2p electrons of oxygen to change the position of the maximum of the valence band. The review also noticed the theoretical development of the doping effect with the establishment of novel models, such as the water–TiO₂surface interaction. It should be noted that the theoretical models rarely consider the doping induced variation of defect types and concentration, Fermi level position, surface active sites, and charge transport due to the ground state simulation and shortcoming of density functional theory (DFT). The phenomenological explanations of the experimental results are arbitrary in most of the reports. A universal model is required to explain the complex dependence of the process of photocatalysis on the semiconducting properties, such as bandgap, Fermi level, charge transport, and surface states. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

First-principles calculations of the monoclinic transition-metal doped NaMnO2 cathode material

ABSTRACT

Using spin-polarised generalised gradient approximation (GGA?+?U), I successfully investigate the electronic properties of the monoclinic NaMnO₂ doped with Cr, Fe and V atom to enhance the electrochemical performance. The expansion of volumes is induced by the dopants. The lowest conduction band and highest valence band are mostly from d orbital of Mn atom and transition-metal dopants which are responsible for the electronic conductivity. Na(Mn, Fe)O₂ is a semiconductor with the reduced band gap. Cr and V doping in NaMnO₂ compound reveal the half-metallic performance. The enhancement of the insertion potentials is induced by transition-metal dopants. The electronic conductivity of NaMnO₂ cathode material is improved by Cr-doping scheme. Finally, this research presents the new horizons for the expenditure of transition-metal doping for designing and improving the NaMnO₂ cathode materials in Na-ion rechargeable batteries.     

双空位掺杂氟化石墨烯的电子性质和磁性

基于密度泛函理论,计算了外来原子X(Al,P,Ga,As,Si)双空位替代掺杂氟化石墨烯的电子特性和磁性.通过对计算结果分析发现,与石墨烯的双空位掺杂类似,氟化石墨烯的双空位掺杂也是一种较为理想的掺杂方式.通过不同原子掺杂,氟化石墨烯的电子性质与磁性均发生很大变化:Al和Ga掺杂使氟化石墨烯由半导体变为金属,并且具有磁性;P和A8掺杂使氟化石墨烯变为自旋半导体;Si掺杂氟化石墨烯仍是半导体,只改变带隙且没有磁性.进一步讨论磁性产生机制获得了掺杂原子浓度与磁性的关系,并且发现不同掺杂情况的磁性是由不同原子的不同轨道电子引起的.双空位掺杂不仅丰富了氟化石墨烯的掺杂方式,其不同电磁特性也使此类掺杂结构在未来的电子器件中具有潜在应用.     

Ab initio study of the (2 × 2) phase of barium on graphene

We present a first-principles density functional theory study on the structural, electronic and dynamical properties of a novel barium doped graphene phase. Low energy electron diffraction of barium doped graphene presents clear evidence of (2 × 2) spots induced by barium adatoms with BaC₈ stoichiometry. First principles calculations reveals that the phase is thermodynamically stable but unstable to segregation towards the competitive BaC₆ monolayer phase. The calculation of phonon spectrum confirms the dynamical stability of the BaC₈ phase indicating its metastability, probably stabilized by doping and strain conditions due to the substrate. Barium induces a relevant doping of the graphene π states and new barium-derived hole Fermi surface at the M-point of the (2 × 2) Brillouin zone. In view of possible superconducting phase induced by foreign dopants in graphene, we studied the electron–phonon coupling of this novel (2 × 2) obtaining λ = 0.26, which excludes the stabilization of a superconducting phase.     

Electronic structure and optical properties of boron-sulfur symmetric codoping in 4 × 4 graphene systems

The electronic structure and optical properties of boron-doped, sulfur-doped, andboron-sulfur-codoped graphene systems have been studied by using first-principlescalculations. Energy band structure and density of states are presented to describe theelectronic properties. The doping can open the band gap and change the optical propertiesof graphene. For all optical properties of doped graphene systems, parallel(E _∥) polarization and perpendicular(E _⊥) polarization are presented. Theoptical properties under two kinds of polarizations are reflected in the range of peakheight and the change of some extraordinary features.     

DFT investigation of the geometrical and electronic structures of (X = B, N and Si) clusters

Geometrical and electronic structures of C₃₅X fullerenes with , N and Si as substitutional dopants have been studied. Three non-equivalent sites in the D_6h structure of C₃₆ have been considered for the substitution. We have found that the dopant has a strong tendency to substitute at sites where the carbon atom contributes significantly to the frontier orbitals of C₃₆ and has the weakest interaction with its nearest-neighbor atoms. The relative stability of C₃₅Si and C₃₅B (C₃₅N) has been investigated and high chemical reactivity of C₃₅Si has been predicted. Received 8 July 1999 and Received in final form 4 October 1999     

Effect of C doping on the structural and electronic properties of LiFePO4: A first-principles investigation

Using first-principles calculations within the generalized gradient approximation （GGA） ＋U framework, we inves- tigate the effect of C doping on the structural and electronic properties of LiFePO4. The calculated formation energies indicate that C doped at O sites is energetically favoured, and that C dopants prefer to occupy 03 sites. The band gap of the C doped material is much narrow than that of the undoped one, indicating better electro- conductive properties. To maintain charge balance, the valence of the Fe nearest to C appears as Fe3＋, and it will be helpful to the hopping of electrons.     

Influence of oxygen impurities on the electronic properties of graphene nanoflakes

Controlled chemical doping with oxygen impurities is a promising approach for the electronic band engineering of graphene nanoflakes (GNFs). Based on the first-principles of the density functional theory (DFT) calculations, we investigated the effect of various consternations of substitutional impurities from oxygen atoms on the electronic properties of GNFs. Our results show that the electronic properties of GNFs do not only depend on the oxygen impurity concentrations, but also depend on the geometrical pattern of oxygen impurities in the GNFs. Additionally, we also found interesting electronic properties of GNFs structure, which significantly contribute to that oxygen dopants cause a decreased energy gap. So, our results suggest that substitutional impurities are the best viable option for enhancement of desired electronic properties of GNFs.     

Delta doping in silicon

Two-dimensional doping sheets (“δ-doping”) are integral parts of many novel semiconductor device concepts. Their practical realization in silicon (Si), however, was long delayed by the difficulty to introduce dopants into Si in a well-controlled way during epitaxial growth. Recent advances in the understanding of epitaxial growth and the incorporation of dopants in Si have overcome these difficulties and opened a new field in Si materials and device research. In this article, we review the growth, processing, and characterization of epitaxially grown 5-doped Si. Furthermore, we discuss the electronic subband states of such structures. Finally, we give an overview of device concepts that use 5-doping and analyze their properties.     

First principles study of the electronic properties and Schottky barrier in Cu2Si/C2N van der Waals heterostructures

Based on the first principles calculations, we have systematically investigated the electronic structures of Cu₂Si/C₂N van der Waals (vdW) heterostructures. We discovered that the electronic structures of Cu₂Si and C₂N monolayers are preserved in Cu₂Si/C₂N vdW heterostructures. There is a transition from the n-type Schottky contact to Ohmic contact when the interfacial distance decreases from 4.4 to 2.7 Å, which indicates that the Schottky barrier can be tuned effectively by the interfacial distance. Meanwhile, we find that the carrier concentration between the Cu₂Si and C₂N interfaces in the vdW heterostructures can be tuned. These findings suggest that the Cu₂Si/C₂N vdW heterostructure is a promising candidate for application in future nanoelectronics and optoelectronics devices.     

Formation and lithium doping of graphene on the surface of cobalt silicide

The intercalation of silicon under graphene on the Co(0001) surface, which is accompanied by the formation of a silicon solid solution in cobalt and by the formation of a surface crystalline Co₂Si phase, has been investigated using photoelectron spectroscopy. It has been shown that the formation of cobalt silicide leads to a substantial weakening of the hybridization of electronic states of graphene and cobalt and to the recovery of the Dirac spectrum of electronic states of graphene near the Fermi level. This has made it possible to investigate the electron doping of graphene on the cobalt silicide substrate upon deposition of lithium on its surface. It has been found that doping with lithium leads to a significant charge transfer onto graphene, and the electron concentration reaches 3.1 × 10¹⁴ cm^?2. Moreover, the specific form of the Fermi surface creates favorable conditions for the enhancement of the electron-phonon coupling. As a result, the formed system can be considered as a candidate for the creation of superconductivity in single-layer graphene.     

Ab initio study of Ru-terminated and Ru-doped armchair graphene nanoribbons

We investigate the effects of ruthenium (Ru) termination and Ru doping on the electronic properties of armchair graphene nanoribbons (AGNRs) using first-principles methods. The electronic band structures, geometries, density of states, binding energies, band gap information, and formation energies of related structures are calculated. It is well founded that the electronic properties of the investigated AGNRs are highly influenced by Ru termination and Ru doping. With Ru termination, metallic band structures with quasi-zero-dimensional, one-dimensional and quasi-one-dimensional density of states (DOS) behavior are obtained in addition to dominant one-dimensional behavior. In contrast to Ru termination, Ru doping introduces small but measurable (12.4 to 89.6?meV) direct or indirect band gaps. These results may present an additional way to produce tunable band gaps in AGNRs.     

First-principles calculations on TiO2 doped by N, Nd, and vacancy

First-principles density functional theory calculations have been carried out to investigate electronic structures of anatase TiO₂ with substitutional dopants of N, Nd, and vacancy, which replace O, Ti, and O, respectively. The calculation on N-doped TiO₂ with the local density approximation (LDA) demonstrates that N doping introduces some states located at the valence band maximum and thus makes the original band gap of TiO₂ smaller. Examining the effect of the strong correlation of Nd 4f electrons on the electronic structure of Nd-doped TiO₂, we have obtained the half-metallic ground state with the LDA and the insulating ground state with the LDA+U (Hubbard coefficient), respectively. In addition, the calculation on vacancy-doped TiO₂ with the LDA shows that a vacancy can induce some states in the band-gap region, which act as shallow donors.     

n-type conductivity in Si-doped amorphous AlN: an ab initio investigation

We report the electronic structure and topology of a heavily Si-doped amorphous aluminium nitride (Al_37.5Si_12.5N₅₀) using ab initio simulations. The amorphous Al_37.5Si_12.5N₅₀ system is found to be structurally similar to pure amorphous aluminium nitride. It has an average coordination number of about 3.9 and exhibits a small amount of Si–Si homopolar bonds. The formation of Si–Al bonds is not very favourable. Electronic structure calculations reveal that the Si doping has a negligible effect on the band gap width but causes delocalization of the valence band tail states and a shift of the Fermi level towards the conduction band. Thus, amorphous Al_37.5Si_12.5N₅₀ alloys show n-type conductivity.     

F掺杂SnO2电子结构的模拟计算

采用基于密度泛函理论的平面波赝势方法对SnO₂:F体系的电子结构进行了第一性原理模拟计算.用广义梯度近似方法优化SnO₂:F体系的晶胞结构，计算了体系基态总能.通过确定F掺杂对O的优先替代位置，计算了SnO₂:F的能带结构、态密度、分波态密度.分析了F掺杂对SnO₂晶体的电子结构和晶体性质及光学吸收边的影响，从理论上得出光学吸收边发生蓝移.对不同掺杂量的体系电子结构进行了分析. 关键词： F掺杂 2')" href="#">SnO₂ 电子结构 态密度