Ab-Initio Study of Cobalt Impurity Effects on Phonon Spectra,Mechanical and Thermal Properties of Single Wall Carbon Nanotube （5,0）

We use density functional perturbation theory based on the pseudo-potential to calculate the phonon spectrum, phonon density of states, specific heat capacity and mechanical properties of pristine and cobalt doped （5,0） single wall carbon nanotube （CNT）. In the calculations, we consider one Co atom in the center of the unit cell of the tube and it is shown that the pristine （5~0） CNT is nonmagnetic while the Co-doped tube becomes magnetic. Young＇s modulus for both systems is about 1 TPa （＇after Co-doping it goes slightly higher） and the Poisson ratio for the pristine tube becomes quite a bit larger than the doped one. On the other hand, the calculated value of radial breath mode for the pristine CNT is in good agreement with the experimental reports while after Co-doping it is increased. In addition, heat capacity of the doped CNT is reduced, which leads to some important empirical applications.     

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.     

Electronic Transport in Molecular Junction Based on C20 Cages

Choosing closed-ended armchair （5, 5） single-wall carbon nanotubes （CCNTs） as electrodes, we investigate the electron transport properties across an all-carbon molecular junction consisting of C20 molecules suspended between two semi-infinite carbon nanotubes. It is shown that the conductances are quite sensitive to the number of C20 molecules between electrodes for both configuration CF1 and double-bonded models： the conductances of C20 dimers are markedly smaller than those of monomers. The physics is that incident electrons easily pass the C20 molecules and are predominantly scattered at the C20-C20 junctions. Moreover, we study the doping effect of such molecular junction by doping nitrogen atoms substitutionally. The bonding property of the molecular junction with configuration CF1 has been analysed by calculating the Mulliken atomic charges. Our results have revealed that the C atoms in N-doped junctions are more ionic than those in pure-carbon ones, leading to the fact that N-doped junctions have relatively large conductance.     

Phonon spectrum boron nitrideof single-wallednanotubes

Based on a force constant model, we investigated the phonon spectrum and then specific heat of single-walled boron nitride nanotubes. The results show that the frequencies of Raman and infrared active modes decrease with increasing diameter in the low frequency, which is consistent with the results calculated by density functional theory. The fitting formulae for diameter and chirality dependence of specific heat at 300K are given.     

Low-temperature charged impurity scattering-limited conductivity in relatively high doped bilayer graphene

Based on semiclassical Boltzamnn transport theory in random phase approximation, we develop a theoretical model to investigate low-temperature carrier transport properties in relatively high doped bilayer graphene. In the presence of both electron–hole puddles and band gap induced by charged impurities, we calculate low-temperature charged impurity scattering-limited conductivity in relatively high doped bilayer graphene. Our calculated conductivity results are in excellent agreement with published experimental data in all compensated gate voltage regime of study by using potential fluctuation parameter as only one free fitting parameter, indicating that both electron–hole puddles and band gap induced by charged impurities play an important role in carrier transport. More importantly, we also find that the conductivity not only depends strongly on the total charged impurity density, but also on the top layer charged impurity density, which is different from that obtained by neglecting the opening of band gap, especially for bilayer graphene with high top layer charged impurity density.     

Modification of Band Gap of -SiC by N-Doping

The geometrical and electronic structures of nitrogen-doped β-SiC are investigated by employing the first principles of plane wave ultra-soft pseudo-potential technology based on density functional theory. The structures of SiC1-xNx （x = 0, 1/32, 1/16, 1/8, 1/4） with different doping concentrations are optimized. The results reveal that the band gap of β-SiC transforms from an indirect band gap to a direct band gap with band gap shrinkage after carbon atoms are replaced by nitrogen atoms. The Fermi level shifts from valence band top to conduction band by doping nitrogen in pure β-SiC, and the doped β-SiC becomes metallic. The degree of Fermi levels entering into the conduction band increases with the increment of doping concentration; however, the band gap becomes narrower. This is attributed to defects with negative electricity occurring in surrounding silicon atoms. With the increase of doping concentration, more residual electrons, more easily captured by the 3p orbit in the silicon atom, will be provided by nitrogen atoms to form more defects with negative electricity.     

First-Principles Study on Magnetic Properties of V-Doped ZnO Nanotubes

Electronic and magnetic properties of V-doped ZnO nanotubes in which one of Zn^2＋ ions is substituted by V^2＋ ions are studied by the first-principles calculations of plane wave ultra-soft pseudo-potential technology based on the spin-density function theory. The computational results reveal that spontaneous magnetization in Vdoped （9,0） ZnO nanotubes can be induced without p-type or n-type doping treatment, and the ferromagnetism is isotropic and independent of the chirality and diameter of the nanotubes. It is found that V-doped ZnO nanotubes have large magnetic moments and are ferromagnetic half-metal materials. Moreover, the ferromagnetic coupling among V atoms is generated by O 2p electron spins and V 3d electron spins localized at the exchanging interactions between magnetic transitional metal （TM） impurities. The appearance of ferromagnetism in V-doped ZnO nanotubes gives some reference to fabrication of a transparent ferromagnet which may have a great impact on industrial applications in magneto-optical devices.     

Stability and electronic structure of InN nanotubes from first-principles study

The stability and electronic structure of hypothetical InN nanotubes were studied by first-principles density functional theory. It was found that the strain energies of InN nanotubes are smaller than those of carbon nanotubes of the same radius. Single-wall zigzag InN nanotubes were found to be semiconductors with a direct band gap while the armchair counterparts have an indirect band gap. The band gaps of nanotubes decrease with increasing diameter, similar to the case of carbon nanotubes.     

Surface optical phonon—assisted electron Raman scattering in a semiconductor quantum disc

We have carried out a theoretical calculation of the differential cross section for the electron Raman scattering process associated with the surface optical phonon modes in a semiconductor quantum disc.electron states are considered to be confined within a quantum disc with infinite potential barriers.The optical phonon modes we have adopted are the slab phonon modes by taking into consideration the Frohlich interaction between an electron and a phonon.The selection rules for the Raman process are given.Numerical results and a discussion are also presented for various radii and thicknesses of the disc,and different incident radiation energies.     

Growth of small diameter multi-walled carbon nanotubes by arc discharge process

Multi-walled carbon nanotubes （MWCNTs） are grown by arc discharge method in a controlled methane environment. The arc discharge is produced between two graphite electrodes at the ambient pressures of 100 tort, 300 torr, and 500 torr. Arc plasma parameters such as temperature and density are estimated to investigate the influences of the ambient pressure and the contributions of the ambient pressure to the growth and the structure of the nanotubes. The plasma temperature and density are observed to increase with the increase in the methane ambient pressure. The samples of MWCNT synthesized at different ambient pressures are analyzed using transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. An increase in the growth of MWCNT and a decrease in the inner tube diameter are observed with the increase in the methane ambient pressure.     

Doping in carbon nanotubes probed by Raman and transport measurements

In situ Raman experiments together with transport measurements have been carried out on carbon nanotubes as a function of gate voltage. In metallic tubes, a large increase in the Raman frequency of the G(-) band, accompanied by a substantial decrease of its linewidth, is observed with electron or hole doping. In addition, we see an increase in the Raman frequency of the G(+) band in semiconducting tubes. These results are quantitatively explained using ab initio calculations that take into account effects beyond the adiabatic approximation. Our results imply that Raman spectroscopy can be used as an accurate measure of the doping of both metallic and semiconducting nanotubes.     

铬银氧共掺n型，p型特性氮化硼纳米管第一性原理研究

基于第一性原理的平面波超软赝势法对(6, 0)单壁氮化硼纳米管、Cr掺杂、Ag掺杂、以及Cr-O共掺纳米管进行电子结构和光学性质的计算。结果表明：Cr掺杂和Cr-O共掺体系相比于本征体系的带隙值均减小,掺杂体系的导带底穿过费米能级从而实现了氮化硼纳米管的n型掺杂。Ag掺杂实现了纳米管的p型掺杂。本征氮化硼纳米管、Ag掺杂、Cr掺杂、以及Cr-O共掺纳米管的静态介电常数分别为1.17、1.61、1.32和1.48,相对于本征体系静介电性能有所提高。     

Electro-optical properties of planar nematic cells impregnated with carbon nanosolids

We report electro-optical effects in planar-aligned liquid-crystal cells of pristine and doped calamitics in the presence of dc voltage. The doped cells comprise both a nematic host and a minute amount of either buckminsterfullerene or multiwalled carbon nanotubes. The voltage–transmittance and voltage–capacitance hystereses were observed from the sample cells in the range of applied dc voltage up to 8 V. Experimental evidence indicates that a nanoscale carbon dopant can affect the behavior of a nematic in terms of ion-charge effects and that doping with nanotubes can effectively reduce the driving voltage.     

Effect of uniaxial tensile strength on the electrical properties of doped carbon nanotubes: Density functional theory

We investigated the effect of uniaxial tensile strength on a pristine carbon nanotube, boron-doped carbon nanotube, nitrogen-doped carbon nanotube and co-doped carbon nanotube with boron and nitrogen atoms. To achieve our goal, we performed our calculations with the aid of density functional theory. We studied the changes in the electrical properties after the atomic substitution of a carbon atom by boron, nitrogen, and boron and nitrogen in pristine carbon nanotubes. We also applied uniaxial tensile strength to doped structures as well as pristine one. In addition to studying the band gap, we studied the changes in the Fermi energy, valence bands, and conduction bands. We found that defects as well as stress and strain play a crucial rule on modifying the electrical properties of carbon nanotubes.     

掺杂对碳纳米管拉曼光谱及场发射性能的影响

采用高温热解法在860℃分别制备出了镓、氮以及硼和氮掺杂的碳纳米管,提纯后利用丝网印刷工艺分别将它们制备成薄膜,并测试了它们的拉曼光谱与场发射性能。测试结果表明,掺杂纳米管的缺陷密集度比纯碳纳米管明显增大,而它们的场致电子发射性能则与掺杂元素的性质密切相关。镓和氮掺杂的纳米管均具有非常优异的场发射性能,而硼和氮共掺杂的纳米管的场发射性能很差。掺杂引起碳纳米管费米能级附近能态密度的变化及功函数的降低是其具有优异场致电子发射性能的主要原因。     

Amphoteric and controllable doping of carbon nanotubes by encapsulation of organic and organometallic molecules

By using first principles calculations, we show that fine tuning of both p- and n-type doping can be realized on single-wall carbon nanotubes (SWNTs) by tuning the electron affinity or ionization potential of the organic and organometallic molecules encapsulated inside SWNTs. This novel type of SWNT-based material offers great promise for molecular electronics because of its air stability, synthetic simplicity and the abundance of organic and organometallic molecules.     

重碳掺杂p型GaAs中纵光学声子与等离振子耦合模的Raman散射特性

对用MOMBE法生长的重C掺杂p型GaAs进行了Raman散射研究,结合理论分析,较好地解释了p型GaAs中纵光学(LO)声子与空穴等离振子耦合(LOPC)模的Raman散射特性,证明它具有与n型状态不同的特点,根据实验结果讨论了重掺杂对Raman散射谱的影响,发现LOPC模的散射峰特征(位置和宽度)与重掺杂效应程度具有很大关系。     

Nonadiabatic Kohn anomaly in a doped graphene monolayer

We compute, from first principles, the frequency of the E(2g), Gamma phonon (Raman G band) of graphene, as a function of the charge doping. Calculations are done using (i) the adiabatic Born-Oppenheimer approximation and (ii) time-dependent perturbation theory to explore dynamic effects beyond this approximation. The two approaches provide very different results. While the adiabatic phonon frequency weakly depends on the doping, the dynamic one rapidly varies because of a Kohn anomaly. The adiabatic approximation is considered valid in most materials. Here, we show that doped graphene is a spectacular example where this approximation miserably fails.     

拉曼光谱研究掺杂与非掺杂碳纳米管电子性质的新进展(英文)

本文综述了非掺杂和掺杂碳纳米管拉曼光谱研究的新进展,特别注意到了悬浮液中单个分散的单壁纳米管、硼和氮掺杂的纳米管、碱金属插入的纳米管以及用化学方法功能化的单壁纳米管的拉曼光谱与其电子性质的相关性。讨论了所存在的问题,展望了可能的发展方向。     

Influence of Electron–Phonon Interaction on the Lattice Thermal Conductivity in Single-Crystal Si

Lattice thermal conductivity can be reduced by introducing point defect, grain boundary, and nanoscale precipitates to scatter phonons of different wave-lengths, etc. Recently, the effect of electron–phonon (EP) interaction on phonon transport has attracted more and more attention, especially in heavily doped semiconductors. Here the effect of EP interaction in n-type P-doped single-crystal Si has been investigated. The lattice thermal conductivity decreases dramatically with increasing P doping. This reduction on lattice thermal conductivity cannot be explained solely considering point defect scattering. Further, the lattice thermal conductivity can be fitted well by introducing EP interaction into the modified Debye–Callaway model, which demonstrates that the EP interaction can play an important role in reducing lattice thermal conductivity of n-type P-doped single-crystal Si.