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。     

Magnetoadsorptive Particles Enabling the Centrifugation‐Free,Preparative‐Scale Separation,and Sorting of Single‐Walled Carbon Nanotubes

A novel magnetic composition of the high surface area particles with amide chemical functionality, Sephacryl S‐200, is reported enabling the preparative‐scale (1 L, ≈5–10 mg) separation of metallic and semiconducting single‐walled carbon nanotubes (SWNT) from completely unpurified and uncentrifuged nanotube stocks. Sephacryl S‐200 has previously been utilized in separating semiconducting SWNT (s‐SWNT) on the laboratory scale. Significantly, use of these magnetic derivative particles in absorptive separation of SWNT allows the unprecedented and industrially scalable purification of both metallic SWNT (m‐SWNT) as well as s‐SWNT directly from uncentrifuged, ultrasonicated surfactant‐based SWNT solutions by simple and scalable magnetic separation. These particles also allowed for the systematic study on the effect of SWNT–polymer interaction time on the resulting SWNT “payloads.” Ultimately, high ‐purity m‐SWNT and s‐SWNT products are independently achieved by controlling the SWNT–polymer interaction time and relative concentrations, as well as SWNT sonication conditions. Furthermore, by controlling these factors, single‐chirality (6,5) s‐SWNT can be isolated with 92% purity directly from unpurified stocks. Thermogravimetric analysis indicates a total process SWNT yield of 1.2% and 1.7% for m‐SWNT and s‐SWNT, respectively. These results demonstrate the potential for a preparative method for separating carbon nanotubes based on electronic properties.     

金属纳米结构表面吸附的CO分子在外电场中的相互作用

建立金属纳米颗粒在外电场中的排列结构模型，用经典理论分析纳米结构金属表面上吸附的CO分子在外电场中的相互作用能，包括有效偶极子间的相互作用和与局域电场的相互作用，并讨论和计算了纳米颗粒表面附近的局域电场. 用Monte-Carlo方法进行数值计算和模拟，具体给出纳米颗粒表面CO分子的分布和相互作用能，表明金属表面纳米结构使CO产生凝聚，并使分子相互作用能增加，为解释异常红外吸收效应提供依据. 关键词： 纳米结构金属 吸附分子 相互作用 局域电场     

Doping effects on metallic and semiconductor single-wall carbon nanotubes

In this paper we investigate nitrogen- and boron-doped zigzag and armchair single-wall carbon nanotubes (SWNTs) with theoretical models based on the density functional theory. We take into account nitrogen and boron doping for two isomers in which substitutive atoms are on opposite sides of the tube, but only in one isomer the impurity sites are symmetrical with respect to the diameter. The band structures show a strong hybridization with impurity orbitals that change the original band structure. Although the two isomers of armchair SWNT exhibit the same formation energy, their band structures are different. Indeed asymmetrical isomers are gapless and exhibit a crossing of valence and conduction bands at k?=?π/c, leading to metallic SWNTs. Band structures of symmetrical isomers, on the other hand, exhibit an energy gap of 0.4?eV between completely filled valence and empty conduction bands. We use density of charge in order to understand this difference. In zigzag SWNT an impurity band is introduced in the energy gap and for N doping this band is just partially occupied in such a way that the electronic behaviour is reversed from semiconductor to metallic. Whereas for a given isomer armchair SWNT shows similar behaviours of N- and B-doped structures, B-doped zigzag SWNTs present different band structure and occupation compared to the N-doped case.     

First-principles calculations of carbon nanotubes adsorbed on Si(001)

We report first-principles calculations on the adsorption of a metallic (6,6) single-walled carbon nanotube (SWCN) on the Si(001) surface. We find stable geometries for the nanotube between two consecutive dimer rows where C-Si chemical bonds are formed. The binding energy in the most stable geometry is found to be 0.2 eV/A. Concerning the electronic properties, the most stable structure shows an increase in the density of states near the Fermi level due to the formation of C-Si bonds enhancing the metallic character of the nanotube by the contact with the surface. These properties may lead one to consider metallic SWCNs adsorbed on Si substrates for interconnections and contacts on future nanoscale devices. Finally, the nature of the nanotube-surface interaction for nanotubes of larger diameters is also discussed.     

Single‐wall carbon nanotube interactions with copper‐oxamato building block of molecule‐based magnets probed by resonance Raman spectroscopy

The electronic interactions between the [Cu(opba)]²⁻ anions (where opba is orthophenylenebis (oxamato)) and single‐wall carbon nanotubes (SWCNTs) were investigated by resonance Raman spectroscopy. The opba can form molecular magnets, and the interactions of opba with SWCNTs can produce materials with very different magnetic/electronic properties. It is observed that the electronic interaction shows a dependence on the SWCNT diameter independent of whether they are metallic or semiconducting, although the interaction is stronger for metallic tubes. The interaction also is dependent on the amount of complex that is probably adsorbed on the carbon surface of the SWCNTs. Some charge transfer can be also occurring between the metallic complex and the SWCNTs. Copyright © 2012 John Wiley & Sons, Ltd.     

锯齿型碳纳米管的结构衍生及电子特性

利用密度泛函理论研究锯齿型单、双壁碳纳米管从核到管状团簇直至纳米管的逐层结构衍生.研究结果表明五边形结构在管状团簇生长中发挥关键作用.此外,基于管状团簇的研究,运用周期性边界条件得到锯齿型单、双壁碳纳米管,并通过计算能带和态密度研究其电子特性.对单壁(n,0)和双壁(n,0)@(2n,0)碳纳米管,当n=3q(q为整数)时,具有金属或窄带隙半导体特性;n?=3q时,具有较宽带隙半导体特性,且带隙随管径的增加而减小.然而,小管径碳纳米管受曲率效应的明显影响,n?=3q的(4,0),(4,0)@(8,0)和(5,0)@(10,0)均呈现金属性;n=3q的(6,0)@(12,0)则表现出明显的半导体特性.     

Passivation at semiconductor/electrolyte interface: Role of adsorbate solvation and reactivity in surface atomic and electronic structure modification of III-V semiconductor

These studies are focused on understanding the role played by a solvent in chemical and electronic processes occurred in the course of semiconductor surface passivation at semiconductor/electrolyte interface. It is shown that the chemical reactivity of the ionic adsorbate at a semiconductor/electrolyte interface can be changed considerably through interaction with solvent molecules. The reactivity of anions depends essentially on the solvating solvent: hydrated ions could be either slightly electrophilic or slightly nucleophilic, whereas the ions solvated by alcohol molecules are always strongly nucleophilic. Mechanism of interaction of such solvated ions with the semiconductor surface atoms depends on the solvent, as is demonstrated by the example of processes occurred at GaAs(1 0 0)/sulfide solution interfaces. It is found that on adsorption of HS⁻ ions from different solvents the AsS bonds with solvent-dependent ionic character are formed on a GaAs(1 0 0) surface. The surface obtained in such a way possesses different ionization energy and exhibit different electronic properties dependent on the solvent.     

Interaction of hydrogen molecules on Ni-doped single-walled carbon nanotube

Adsorption of hydrogen molecules on an Ni-doped (8,0) single-walled carbon nanotube (SWNT) is investigated by using first-principles density functional calculations. The result shows that a single Ni atom adsorbed on the bridge site of the tube could cannot dissociate the H₂, however it can chemisorb three H₂ at most, with the average binding energy per H₂ suitable for the hydrogen storage at the room temperature. More H₂ would physisorb around an Ni atom weakly. As for the SWNT with an Ni dimer adsorbed, we find that when the H₂ approaches the Ni--Ni bond, it dissociates without overcoming any barrier and makes bonds with Ni atom.     

Tuning the magnetic and electronic properties of strontium titanate by carbon doping

The magnetic and electronic properties of strontium titanate with different carbon dopant configurations are explored using first-principles calculations with a generalized gradient approximation (GGA) and the GGA+U approach. Our results show that the structural stability, electronic properties and magnetic properties of C-doped SrTiO₃ strongly depend on the distance between carbon dopants. In both GGA and GGA+U calculations, the doping structure is mostly stable with a nonmagnetic feature when the carbon dopants are nearest neighbors, which can be ascribed to the formation of a C–C dimer pair accompanied by stronger C–C and weaker C–Ti hybridizations as the C–C distance becomes smaller. As the C–C distance increases, C-doped SrTiO₃ changes from an n-type nonmagnetic metal to ferromagnetic/antiferromagnetic half-metal and to an antiferromagnetic/ferromagnetic semiconductor in GGA calculations, while it changes from a nonmagnetic semiconductor to ferromagnetic half-metal and to an antiferromagnetic semiconductor using the GGA+U method. Our work demonstrates the possibility of tailoring the magnetic and electronic properties of C-doped SrTiO₃, which might provide some guidance to extend the applications of strontium titanate as a magnetic or optoelectronic material.     

Co stretching vibration of carbon monoxide adsorbed on nickel(111) studied by high resolution electron loss spectroscopy

The frequency of the v-CO stretching vibration measured by HRELS has been followed as a function of the CO coverage and in the presence of coadsorbed hydrocarbons on the Ni(111) face. The v-CO frequency shifts continuously from 225 meV (1814 cm^?1) to 237 meV (1911 cm^?1) when the CO coverage increases from 0 to 0.41. Coadsorption of electron donor molecules, such as ethylene and benzene, generates a significant lowering of the v-CO frequency. Results are discussed in terms of the back donation of metallic electrons into the 2π ¹ antibonding orbitals of CO, the dipole-dipole coupling and the coordination number of the CO adsorbed molecules. The back donation is found to play the major role in the range of coverage explored but we cannot exclude some contribution of a dipole-dipole coupling effect.     

Novel single-walled carbon nanotubes periodically embedded with four- and eight-membered rings

Based on experimental results, we obtain five types of single-walled carbon nanotube (SWNT) clusters with different chirality indices and diameters using density functional theory (DFT). We then obtain the corresponding SWNTs by using periodic boundary conditions. Studies of the stability and electronic properties show that the stability of the novel SWNTs is independent of the chirality index and relates only to the tube diameter; larger diameters correspond to more stable SWNTs. The electronic properties all show metallic characteristics independent of the chirality indices and tube diameters, thereby promoting the application of metallic-type SWNTs.     

The interaction of a gold atom with carbon nanohorn and carbon nanotube tips and their complexes with a CO molecule: A first principle calculation

The interactions of a gold atom with: (a) a single-wall carbon nanohorn (SWNH) conic tip; (b) with a single-wall carbon nanotube (SWNT) tip; and (c) their complexes with a CO molecule were studied using first-principle calculations based on density functional theory. The analysis of the pyramidalization angle (θ_p) as well as the π-orbital misalignment angles indicate that there should be many reactive carbon sites on the tips of SWNH and SWNT. It was found that SWNH provides reactive sites that can more selectively interact with the target atom. We identified five sites on both the SWNT tip and the nanohorn where attachment of a gold atom leads to a stable complex. This metal is found to be bi-coordinated with the tip of SWNH, while it is mono-coordinated with the SWNT tip. The largest interaction energies are –10.75 kcal/mol and –16.17 kcal/mol, respectively. The CO probe molecule binds to Au on the Au/SWNH or Au/SWNT tips with interaction energies of –22.34 and –18.29 kcal/mol, respectively. The main contributions of the interaction with both carbon nanostructures stems from σ-donation and π-backbonding. The results suggest that SWNHs could be one of the promising candidates for the development of high-specifity nanosensors.     

First principles modeling of boron-doped carbon nanotube sensors

We investigated the interactions between two different geometrical configurations of single-walled carbon nanotubes and boron atoms using first-principle calculations within the framework of the density functional theory. With the aid of ab initio calculations, we introduced a new type of toxic gas sensor that can detect the presence of CO, NO and H₂ molecules. We proved that the dopant concentration on the surface of the nanotube plays a crucial role in the sensitivity of this device. Furthermore, we showed that small concentrations of dopants can modify the transport and electronic properties of the single-walled carbon nanotube and can lend metallic properties to the nanotube. Band-gap narrowing occurs when the nanotube is doped with boron atoms. The emerged new energy level near the Fermi level upon boron doping clearly indicates the coupling between the p orbital of the boron atom and the large p bond of the carbon nanotube. We also predicted a weak hybridization between the boron atoms and the nanotube for the valence-band edge states; this weak coupling leads to conducting states around the band gap.     

Titanium-decorated carbon nanotubes as a potential high-capacity hydrogen storage medium

We report a first-principles study, which demonstrates that a single Ti atom coated on a single-walled nanotube (SWNT) binds up to four hydrogen molecules. The first H2 adsorption is dissociative with no energy barrier while the other three adsorptions are molecular with significantly elongated H-H bonds. At high Ti coverage we show that a SWNT can strongly adsorb up to 8 wt % hydrogen. These results advance our fundamental understanding of dissociative adsorption of hydrogen in nanostructures and suggest new routes to better storage and catalyst materials.     

Large scale highly organized single-walled carbon nanotube networks for electrical devices

Large-scale room-temperature liquid-phase directed assembly of highly organized single-walled carbon nanotubes (SWNT) over large areas is demonstrated. The presented process utilizes lithographically patterned template to guide the fluidic self-assembly of SWNTs on a silicon-dioxide substrate. The width of these highly organized SWNT structures are in the micron range while their heights are in orders of nanometers. Room temperature electrical I–V characterization of these fabricated high coverage SWNT wires show linear ohmic behavior. The resistivity of these assembled SWNT network is in the order of 10⁻⁶ Ω m demonstrating their metallic characteristics during conductance. Scaling of the assembly processes on a wafer level with high yield is demonstrated. Our developed assembly process is compatible with complimentary metal oxide semiconductor (CMOS) processes and provides a simple and flexible way of building SWNT nanotube-based electronics in a large scale.     

Effects of various defects on the electronic properties of single-walled carbon nanotubes: A first principle study

The geometries,formationenergies and electronic band structures of （8, 0） and （14, 0） singlewailed carbon nanotubes （SWCNTs） with various defects, inehlding vaeaney, Stone-Wales defect, and octagon pentagon pair defect, have been investigated within the framework of the density- huictional theory （DFT）, and the influence of the concentration within the same style of deflect on the physical and chenfical properties of SWCNTs is also studied. The results suggest that the existeilcc of vacancy and octagon-pentagon pair deflect both reduce the band gap, whereas the SW- defect induces a band gap opening in CNTs. More int, erestingly, the band gaps of （8, 0） and （14, 0） SWCNTs eonfigurations with two octagon pentagon pair defect presents 0.517 eV and 0.163/eV, which arc a little smaller than the perfectt CNTs. Furthermore, with the concentration of defects increasing, there is a decreasing of band ga.p making the two types of SWCNTs change from a semiconductor to a metallic conductor.     

CO2在中性及带负电Be（n=4, 7, 10, 12, m=0, -1）团簇表面的吸附与解离

运用密度泛函理论,对中性及带负电的BeCO2 (n=4, 7, 10, 12, m=0, -1) 团簇进行了构型优化,稳定性和电子性质分析。结果表明：CO2吸附于Ben和Ben-1团簇表面时,C-O键长均有不同程度的伸长。其中Be4CO2-1,Be12CO2-1中CO2分子的一个C-O键自然断裂(伸长量达到了134%和156%),为典型的解离性吸附。Be团簇表现出了较好的吸附CO2分子的能力,特别是带负电以后,吸附能明显增大(约为3.16eV--5.965eV)。电子性质分析表明,带负电升高了相应团簇的前线轨道能级,使轨道杂化发生在费米能级处附近,从而增强了CO2分子与相应团簇的成键能力。     

Structural,electronic and catalytic performance of single-atom Fe anchored 3Si-doped graphene

By density functional theory (DFT) calculations, it is found that the single-atom Fe anchored three Si modified defective graphene (3Si-graphene-Fe) exhibits the high stability, and this system is semiconducting property and has non-magnetic moment. Besides the most stable configurations, electronic structures and magnetic properties of adsorbed species (O₂, CO, 2CO and CO/O₂) on 3Si-graphene-Fe systems are comparably discussed. The adsorption of O₂ is more stable than that of CO molecule and the coadsorption of 2CO and CO/O₂ has the larger adsorption energy than that of the isolated one. The adsorbed O₂, CO and CO/O₂ can induce the change in magnetic properties of 3Si-graphene-Fe system, and the coadsorbed CO/O₂ on system exhibits the metallic property. Among the reaction mechanisms, the CO oxidation reactions through Eley–Rideal (ER) reactions have lower energy barriers (<0.5?eV) than those of the Langmuir–Hinshelwood (LH) and new termolecular Eley–Rideal (TER) mechanisms, indicating that the ER reaction as starting step is an energetically favourable process. These results provide an important guidance on validating the catalytic activity of single atom on graphene-based materials.     

Adsorption of carbon oxide and nitrogen oxide molecules on the surface of the Ni/MgO(111) system

The coadsorption of carbon oxide (CO) and nitrogen oxide (NO) molecules on the surface of nickel nanoclusters formed on a thin magnesium oxide MgO(111) film grown on the Mo(110) face in an ultrahigh vacuum is studied by reflective infrared spectroscopy and thermodesorption spectroscopy (TDS). The adsorption of NO molecules is found to substantially change the state of the initially adsorbed CO molecules. The TDS and IR spectra suggest that the adsorption of NO molecules stimulates the surface migration of CO molecules from the surface of metallic clusters to the cluster-oxide interface, which is accompanied by a decrease in the angle of inclination of the molecular axis to the surface.