Boron/nitrogen pairs Co-doping in metallic carbon nanotubes: a first-principle study

By using the first-principles calculations, the electronic structure and quantum transport properties of metallic carbon nanotubes with B/N pairs co-doping have been investigated. It is shown that the total energies of metallic carbon nanotubes are sensitive to the doping sites of the B/N pairs. The energy gaps of the doped metallic carbon nanotubes decrease with decreasing the concentration of the B/N pair not only along the tube axis but also around the tube. Moreover, the I--V characteristics and transmissions of the doped tubes are studied. Our results reveal that the conducting ability of the doped tube decreases with increasing the concentrations of the B/N pairs due to symmetry breaking of the system. This fact opens a new way to modulate band structures of metallic carbon nanotubes by doping B/N pair with suitable concentration and the novel characteristics are potentially useful in future applications.     

Negative differential resistance behaviour in N-doped crossed graphene nanoribbons

By using first-principles calculations and nonequilibrium Green’s function technique, we study elastic transport properties of crossed graphene nanoribbons. The results show that the electronic transport properties of molecular junctions can be modulated by doped atoms. Negative differential resistance (NDR) behaviour can be observed in a certain bias region, when crossed graphene nanoribbons are doped with nitrogen atoms at the shoulder, but it cannot be observed for pristine crossed graphene nanoribbons at low biases. A mechanism for the negative differential resistance behaviour is suggested.     

Antiferromagnetic ferromagnetic transition in zigzag graphene nanoribbons induced by substitutional doping

Using first-principles calculations based on density functional theory, we show that the ground state of zigzag-edged graphene nanoribbons(ZGNRs) can be transformed from antiferromagnetic(AFM) order to ferromagnetic(FM) order by changing the substitutional sites of N or B dopants. This AFM–FM transition induced by substitutional sites is found to be a consequence of the competition between the edge and bulk states. The energy sequence of the edge and bulk states near the Fermi level is reversed in the AFM and FM configurations. When the dopant is substituted near the edge of the ribbon, the extra charge from the dopant is energetically favorable to occupy the edge states in AFM configuration. When the dopant is substituted near the center, the extra charge is energetically favorable to occupy the bulk states in FM configuration. Proper substrate with weak interaction is necessary to maintain the magnetic properties of the doped ZGNRs. Our study can serve as a guide to synthesize graphene nanostructures with stable FM order for future applications to spintronic devices.     

First-principles study on with nitrogen and anatase TiO2 codoped praseodymium

<正>The crystal structures,electronic structures and optical properties of nitrogen or/and praseodymium doped anatase TiO₂ were calculated by first principles with the plane-wave ultrasoft pseudopotential method based on density functional theory.Highly efficient visible-light-induced nitrogen or/and praseodymium doped anatase TiO₂ nanocrystal photocatalyst were synthesized by a microwave chemical method.The calculated results show that the photocatalytic activity of TiO₂ can be enhanced by N doping or Pr doping,and can be further enhanced by N+Pr codoping.The band gap change of the codoping TiO₂ is more obvious than that of the single ion doping,which results in the red shift of the optical absorption edges.The results are of great significance for the understanding and further development of visible-light response high activity modified TiO₂ photocatalyst.The photocatalytic activity of the samples for methyl blue degradation was investigated under the irradiation of fluorescent light.The experimental results show that the codoping TiO₂ photocatalytic activity is obviously higher than that of the single ion doping.The experimental results accord with the calculated results.     

Electronic structure and optical property of boron doped semiconducting graphene nanoribbons

We present a system study on the electronic structure and optical property of boron doped semiconducting graphene nanoribbons using the density functional theory. Energy band structure, density of states, deformation density, Mulliken popular and optical spectra are considered to show the special electronic structure of boron doped semiconducting graphene nanoribbons. The C—B bond form is discussed in detail. From our analysis it is concluded that the Fermi energy of boron doped semiconducting graphene nano...     

Electronic Transport of the Adsorbed Trigonal Graphene Flake： A First Principles Calculation

In recent years, electronic transport through molecular devices has attracted much attention due to the progress in experimental techniques for ma- nipulating individual molecules and the availabil- ity of the first-principles method to describe the elec- trical properties of devices. Graphene, a two- dimensional （2D） network of sp2 hybridized carbon atoms, has stimulated great research interest due to its unique electronic transport properties and its pro- found potential for future device applications. Chemical doping with foreign atoms is generally cho- sen to modify the electronic transport properties of carbon materials. The possibility of functionalizing graphene with radicals such as O, F, and H atoms has been experimentally demonstrated. One- dimensional GNRs and zero-dimensional graphene quantum dots （GQDs）, including triangular, rectangular and hexagonal shapes, which can be ob- tained through the geometry cutting method, pro- vide the possibility to explore low-dimensional trans- port properties for carbon-based nanoelectronics. The trigonal graphene flake （TGF）, a kind of representa- tive zero-dimensional GQD, is prominent in electronic and magnetic properties due to its n-fold degenerated half-filled zero-energy states. This novel property was revealed by both experimental and theoretical studies.     

Thermoelectric-transport in metal/graphene/metal hetero-structure

We investigate the thermoelectric-transport properties of metal/graphene/metal hetero-structure. We use a single band tight-binding model to present the two-dimensional electronic band structure of graphene. Using the Landauer--Butticker formula and taking the coupling between graphene and the two electrodes into account, we can calculate the thermoelectric potential and current versus temperature. It is found that in spite of metal electrodes, the carrier type of graphene determines the electron motion direction driven by the difference in temperature between the two electrodes, while for n type graphene, the electrons move along the thermal gradient, and for p type graphene, the electrons move against the thermal gradient.     

First-principles study of La and Sb-doping effects onelectronic structure and optical properties of SrTiO3

The effects of La and Sb doping on the electronic structure and optical properties of SrTiO 3 are investigated by first-principles calculation of the plane wave ultra-soft pseudo-potential based on density functional theory. The calculated results reveal that corner-shared TiO 6 octahedra dominate the main electronic properties of SrTiO 3 , and its structural stability can be improved by La doping. The La 3+ ion fully acts as an electron donor in Sr 0.875 La 0.125 TiO 3 and the Fermi level shifts into the conduction bands (CBs) after La doping. As for SrSb 0.125 Ti 0.875 O 3 , there is a distortion near the bottom of the CBs for SrSb 0.125 Ti 0.875 O 3 after Sb doping and an incipient localization of some of the doped electrons trapped in the Ti site, making it impossible to describe the evolution of the density of states (DOS) within the rigid band model. At the same time, the DOSs of the two electron-doped systems shift towards low energies and the optical band gaps are broadened by about 0.4 and 0.6 eV for Sr0.875La0.125TiO3 and SrSb0.125Ti0.875O3 , respectively. Moreover, the transmittance of SrSb0.125Ti0.875O3 is as high as 95% in most of the visible region, which is higher than that of Sr0.875La0.125TiO3 (85%). The wide band gap, the small transition probability and the weak absorption due to the low partial density of states (PDOS) of impurity in the Fermi level result in the significant optical transparency of SrSb0.125 Ti0.875 O3 .     

Quantum diffusion in bilateral doped chains

In this paper,we quantitatively study the quantum diffusion in a bilateral doped chain,which is randomly doped on both sides.A tight binding approximation and quantum dynamics are used to calculate the three electronic characteristics:autocorrelation function C(t),the mean square displacement d(t) and the participation number P (E) in different doping situations.The results show that the quantum diffusion is more sensitive to the small ratio of doping than to the big one,there exists a critical doping ratio q 0,and C(t),d(t) and P (E) have different variation trends on different sides of q 0.For the self-doped chain,the doped atoms have tremendous influence on the central states of P (E),which causes the electronic states distributed in other energy bands to aggregate to the central band (E=0) and form quasi-mobility edges there.All of the doped systems experience an incomplete transition of metal-semiconductor-metal.     

Magnetic properties of AlN monolayer doped with group 1A or 2A nonmagnetic element: First-principles study

The electronic structure, magnetic properties, and mechanism of magnetization in two-dimensional(2D) aluminum nitride(AlN) monolayer doped with nonmagnetic elements of group 1A(Li, Na, K) or group 2A(Be, Mg, Ca) were systematically investigated using first-principles studies. Numerical results reveal that the total magnetic moments produced by group 1A and group 2A nonmagnetic doping are 2.0μB and 1.0μB per supercell, respectively. The local magnetic moments of the three N atoms around the doping atom are the primary moment contributors for all these doped AlN monolayers. The p orbital of the dopant atom contributes little to the total magnetic moment, but it influences adjacent atoms significantly, changing their density of states distribution, which results in hybridization among the p orbitals of the three closest N atoms, giving rise to magnetism. Moreover, the doped AlN monolayer, having half-metal characteristics,is a likely candidate for spintronic applications. When two group 1A or group 2A atoms are inserted, their moments are long-range ferromagnetically coupled. Remarkably, the energy of formation shows that, if the monolayer has been grown under N-rich conditions, substitution of a group 2A atom at an Al site is easier than substitution of a group 1A atom.     

Magnetism induced by Mn atom doping in SnO monolayer

The structural, magnetic properties, and mechanism of magnetization of SnO monolayer doped with 3 d transition metal Mn atom were studied using first-principles calculations. The calculated results show that the substitution doping is easier to realize under the condition of oxygen enrichment. Numerical results reveal that the spin-splitting defect state of the Mn doped system is produced in the band gap and the magnetic moment of 5.0 μB is formed. The induced magnetic moment by Mnsubis mostly derived from the 3 d orbital of the doped Mn atom. The magnetic coupling between magnetic moments caused by two Mn atoms in SnO monolayer is a long-range ferromagnetic, which is due to the hole-mediated p–p and p–d interactions. The calculated results suggest that room-temperature ferromagnetism in a SnO monolayer can be induced after substitutional doping of a Mn atom.     

Comparative study on transport properties of N-, P-, and As-doped SiC nanowires: Calculated based on first principles

According to the one-dimensional quantum state distribution, carrier scattering, and fixed range hopping model, the structural stability and electron transport properties of N-, P-, and As-doped SiC nanowires(N-SiCNWs, P-SiCNWs, and As-SiCNWs) are simulated by using the first principles calculations. The results show that the lattice structure of NSiCNWs is the most stable in the lattice structures of the above three kinds of doped SiCNWs. At room temperature,for unpassivated SiCNWs, the doping effect of P and As are better than that of N. After passivation, the conductivities of all doped SiCNWs increase by approximately two orders of magnitude. The N-SiCNW has the lowest conductivity. In addition, the N-, P-, As-doped SiCNWs before and after passivation have the same conductivity–temperature characteristics,that is, above room temperature, the conductivity values of the doped SiCNWs all increase with temperature increasing.These results contribute to the electronic application of nanodevices.     

Edge effect and interface confinement modulated strain distribution and interface adhesion energy in graphene/Si system

In order to clarify the edge and interface effect on the adhesion energy between graphene(Gr)and its substrate,a theoretical model is proposed to study the interaction and strain distribution of Gr/Si system in terms of continuum medium mechanics and nanothermodynamics.We find that the interface separation and adhesion energy are determined by the thickness of Gr and substrate.The disturbed interaction and redistributed strain in the Gr/Si system induced by the effect of surface and interface can make the interface adhesion energy decrease with increasing thickness of Gr and diminishing thickness of Si.Moreover,our results show that the smaller area of Gr is more likely to adhere to the substrate since the edge effect improves the active energy and strain energy.Our predictions can be expected to be a guide for designing high performance of Grbased electronic devices.     

Effect of heat treatment on electronic phase in underdoped La2-xSrxCuO4 single crystal

Superconducting La1.937Sr0.063CuO4 crystals grown by the travelling-solvent floating-zone technique were thermally treated under various temperatures and oxygen pressures for moderately adjusting the oxygen content. The response of intrinsic electronic property of the crystals to the change of hole density in La2-xSrxCuO4 in the vicinity of the magic doping of x= 1/16 （= 0.0625） is studied in detail by magnetic measurements under various fields up to 1 T. It is found that when the superconducting critical temperature （Tc） increases with the oxygen content, there appears also a new subtle electronic state that can be detected from the differential curves of diamagnetic susceptibility dx/dT of the crystal sample. In contrast with the intrinsic state, the new subtle electronic state is very fragile under the magnetic fields. Our results indicate that a moderate change in oxygen doping does not significantly modify the intrinsic electronic state originally existing at the magic doping level.     

Optoelectronic Properties for Armchair-Edge Graphene Nanoribbons

We study theoretically the electronic and transport property for an armchair-edge graphene nanoribbon （GNR.） with 12 and 11 transversal atomic lines, respectively. The ONR. is irradiated under an external longitudinal polarized high-frequency electromagnetic field at low temperatures. Within the framework of linear response theory in the perturbative regime, we examine the joint density of states and the real conductance of the system. It is demonstrated that, by numerical examples, some new photon-assisted intersubband transitions over a certain range of field frequency exist with different selection rules from those of both zigzag-edge GNR. and single-walled carbon nanotube. This opto-electron property dependence of armchair-edge GNR. on field frequency may be used to detect the high-frequency electromagnetic irradiation.     

Electronic structure and optical properties of In-doped SrTiO3 by density function theory

The effect of In doping on the electronic structure and optical properties of SrTiO3 is investigated by the first-principles calculation of plane wave ultra-soft pseudo-potential based on the density function theory （DFT）. The calculated results reveal that due to the hole doping, the Fermi level shifts into valence bands （VBs） for SrTi1-x InxO3 with x = 0.125 and the system exhibits p-type degenerate semiconductor features. It is suggested according to the density of states （DOS） of SrTi0.875In0.125O3 that the band structure of p-type SrTIO3 can be described by a rigid band model. At the same time, the DOS shifts towards high energies and the optical band gap is broadened. The wide band gap, small transition probability and weak absorption due to the low partial density of states （PDOS） of impurity in the Fermi level result in the optical transparency of the film. The optical transmittance of In doped SrTiO3 is higher than 85% in a visible region, and the transmittance improves greatly. And the cut-off wavelength shifts into a blue-light region with the increase of In doping concentration.     

Modulating magnetism of nitrogen-doped zigzag graphene nanoribbons

We present a study of electronic properties of zigzag graphene nanoribbons （ZGNRs） substitutionally doped with nitrogen atoms at a single edge by first principle calculations. We find that the two edge states near the Fermi level sepa- rate due to the asymmetric nitrogen-doping. The ground states of these systems become ferromagnetic because the local magnetic moments along the undoped edges remain and those along the doped edges are suppressed. By controlling the charge-doping level, the magnetic moments of the whole ribbons are modulated. Proper charge doping leads to interest- ing half-metallic and single-edge conducting ribbons which would be helpful for designing graphene-nanoribbon-based spintronic devices in the future.     

Impact of nitrogen doping on growth and hydrogen impurity incorporation of thick nanocrystalline diamond films

A much larger amount of bonded hydrogen was found in thick nanocrystalline diamond(NCD) films produced by only adding 0.24% N2 into 4% CH4 /H2 plasma,as compared to the high quality transparent microcrystalline diamond(MCD) films,grown using the same growth parameters except for nitrogen.These experimental results clearly evidence that defect formation and impurity incorporation(for example,N and H) impeding diamond grain growth is the main formation mechanism of NCD upon nitrogen doping and strongly support the model proposed in the literature that nitrogen competes with CH x(x=1,2,3) growth species for adsorption sites.     

Tuning the Water Desalination Performance of Graphenic Layered Nanomaterials by Element Doping and Inter-Layer Spacing

Through atomic molecular dynamics simulations, we investigate the performance of two graphenic materials,boron(BC3) and nitrogen doped graphene(C3 N), for seawater desalination and salt rejection, and take pristine graphene as a control. Effects of inter-layer separation have been explored. When water is filtered along the transverse directions of three-layered nanomaterials, the optimal inter-layer separation is 0.7–0.9 nm, which results in high water permeability and salt obstruction capability. The water permeability is considerably higher than porous graphene filter, and is about two orders of magnitude higher than commercial reverse osmosis(RO)membrane. By changing the inter-layer spacing, the water permeability of three graphenic layered nanomaterials follows an order of C3 N ≥ GRA BC3 under the same working conditions. Amongst three nanomaterials, BC3 is more sensitive to inter-layer separation which offers a possibility to control the water desalination speed by mechanically changing the membrane thickness. This is caused by the intrinsic charge transfer inside BC3 that results in periodic distributed water clusters around the layer surface. Our present results reveal the high potentiality of multi-layered graphenic materials for controlled water desalination. It is hopeful that the present work can guide design and fabrication of highly efficient and tunable desalination architectures.     

Structure and electronic structure of S-doped graphitic C3N4 investigated by density functional theory

The structures of the heptazine-based graphitic C3N4 and the S-doped graphitic C3N4 are investigated by using the density functional theory with a semi-empirical dispersion correction for the weak long-range interaction between layers.The corrugated structure is found to be energetically favorable for both the pure and the S-doped graphitic C3N4.The S doptant is prone to substitute the N atom bonded with only two nearest C atoms.The band structure calculation reveals that this kind of S doping causes a favorable red shift of the light absorption threshold and can improve the electroconductibility and the photocatalytic activity of the graphitic C3N4.