多壁纳米碳管环的成环机理研究

利用连续介质模型和弹性能理论,分析了多壁纳米碳管环的形成过程.发现弯曲纳米碳管成形自由能为零的条件决定了多壁纳米碳管环的形成;并存在使直纳米碳管变弯的阈值条件,纳米碳管环是诸多弯曲构型中的一种稳定构型.此模型导出的多壁纳米碳管环半径与实测值符合.说明了连续介质弹性能理论在原子尺度下仍能使用及多壁纳米碳管环的形成是一个成形自由能为零的自组织过程.     

小直径螺旋型单壁碳纳米管电子结构的计算

针对结构参数（m,n）为（4,1）、（4,2）和（5,2）等小直径螺旋型单壁碳纳米管的电子结构,采用密度泛函理论、第一性原理以及ABINIT软件进行了理论计算,得到了上述管的电子能带及其态密度曲线,并分析了这些管的导电性能.计算结果表明：（4,1）和（5,2）这两种单壁碳纳米管无能量禁带,均属于金属型;而（4,2）管有能量禁带,属于半导体型.此结论与用金属型单壁碳纳米管的判据|m-n|=3J（J=0,1,2,3,…）给出的结果一致.     

含氮复合缺陷改性单壁碳纳米管的电学性能

基于第一性原理的密度泛函理论,利用非平衡格林函数方法本文研究了氮原子与SW（Stone-Wales）缺陷组成的复合缺陷对碳纳米管几何结构及电子透射系数的影响。结果显示SW缺陷和掺杂都对单壁管的几何结构和电子性能有显著的影响。对于半导体性（8,0）碳纳米管,复合缺陷增强了体系的输运性能,但是输运特性明显受到杂质原子的位置的影响。     

碳纳米管的电学性质

依据碳纳米管中电子-声子相互作用的原理,采用哈密顿量、量子化理论推导了二聚化对应能隙和相变温度,在紧束缚近似、量子理论和能带理论的基础上,利用周期性边界条件对碳纳米管Π电子进行了分析,讨论了碳纳米管的导电性,预测了室温下碳纳米管碳管中载流子输运方向.     

Mn掺杂c-ZrO2电子和光学性质的第一性原理研究

基于DFT+U第一性原理计算,预测了过渡金属锰（Mn）掺杂立方氧化锆（c-ZrO₂）体系的电子和光学性质。当c-ZrO₂中的Zr原子被Mn原子取代后,体系的电子态密度图表明体系的带隙减小,同时价带顶的电子密度明显增加使得价带展宽约5%。在自旋向上通道中,费米面附近的电子密度源于Mn 3d电子与O 2p电子的强烈混合,使得掺杂体系具有半金属铁磁性能,这也可能是引起体系带隙减小的原因。本研究还表明,通过Mn掺杂,体系折射率明显增加,在约为2.8 eV 低能区域形成新的坡度陡峭的光吸收峰,这一发现使Mn掺杂c-ZrO₂用作光吸收材料成为可能。通过Zener双交换机制解释了体系的铁磁性能,该理论也曾用于解释其他化合物;同时也探讨了体系的电子结构和光学性质之间的联系。     

形变小直径扶手椅型碳纳米管的电子性质

在紧束缚近似下,解析地推导了轴向拉伸和扭转形变下小直径单壁碳纳米管（SWNT）的能量色散关系．分析了拉伸和扭转形变对小直径扶手椅型SWNT的电子性质的影响．结果表明,在拉伸形变下扶手椅型SWNT仍然是导体,但其费米速度随拉伸比的变大而变大;在拉伸比不变的情况下,考虑曲率效应后其费米速度变大．在扭转形变下,扶手椅型SWNT变成了半导体,其能隙随扭转度的变大而变大;在扭转度不变的情况下,考虑曲率效应后能隙变化不大．     

反钙钛矿晶体Sc3AlN电子结构和光学性质的第一性原理研究

采用基于密度泛函理论的第一性原理的分子动力学方法,对立方反钙钛矿Sc3AlN的电子结构和光学性质进行了计算．系统分析了Sc3AlN电子结构和成键情况,并利用计算的能带结构和态密度分析了Sc3AlN的介电函数实部和虚部以及由它们派生出来的光学常数,即折射率、反射谱、吸收谱、光电导率和能量损失函数等．计算结果表明Sc3AlN属于导体材料,其价带主要由Al的2s2p,Sc的3d态电子构成,导带主要由Sc的3d态电子构成,静态介电常数ε1（O）=22．1,折射率n（0）=4．7．     

Molecular dynamics simulation of the test of single-walled carbon nanotubes under tensile loading

Molecular dynamics (MD) simulations were performed to do the test of sin-gle-walled carbon nanotubes (SWCNT) under tensile loading with the use of Bren-ner potential to describe the interactions of atoms in SWCNTs. The Young’s modulus and tensile strength for SWCNTs were calculated and the values found are 4.2 TPa and 1.40―1.77 TPa, respectively. During the simulation, it was found that if the SWCNTs are unloaded prior to the maximum stress, the stress-strain curve for unloading process overlaps with the loading one, showing that the SWCNT’s de-formation up to its fracture point is completely elastic. The MD simulation also demonstrates the fracture process for several types of SWCNT and the breaking mechanisms for SWCNTs were analyzed based on the energy and structure be-havior.     

First-Principles Studies the Lattice Constants and the Electronic Structures of Diluted Magnetic Semiconductors （In,Mn）As

Lattice constants and electronic structures of diluted magnetic semiconductors （ In, Mn ） As were investigated using the first principles LMTO-ASA band calculation by assuming supercell structures. Three concentrations of the 3 d impurities were studied （ x = 1/2, 1/4, 1/8）. The effect of varying Mn coucentrations on the lattice constants and the electronic structures are shown.     

碳纳米管超晶格结构的第一性原理

针对掺杂N、B、Si的碳纳米管超晶格的电子结构及拉伸性能,运用第一性原理进行了相关研究.结果表明,碳纳米管超晶格会形成类似管状结构.不同掺杂元素导致碳纳米管超晶格的结构稳定性有所不同.碳纳米管经掺杂后,能带中的能隙由半导体性转变为金属性,且费米能级处的态密度值增大,表明碳纳米管超晶格的物理化学活性增强,而结构稳定性降低.对于碳纳米管超晶格而言,结构稳定性从高至低依次为3×1碳氮、1×1碳硼和3×1碳硼纳米管超晶格.     

B/Al掺杂ZnS电子结构的第一性原理研究

用第一性原理的赝势方法,计算了B和Al掺杂ZnS的电子结构差异.根据计算,掺杂时B原子p态在导带底附近形成高度局域态,而Al原子p态则较为离域;B和Al原子的s态均具有较好的离域性.以上结果表明,从获得n型导电性的角度而言,Al掺杂优于B掺杂.     

沉积法掺金改善碳纳米管电接触特性

研究了沉积法在碳纳米管中掺杂金属金对碳纳米管与金属电极间的电接触特性的影响。首先,采用酸回流方式在碳纳米管表面构造缺陷及亲水官能团并配制碳纳米管分散液;然后,采用柠檬酸钠和氯金酸配制金溶胶溶液,再将配制好的碳纳米管分散液滴入金溶胶溶液中,经震荡沉积得到掺杂金纳米粒子的碳纳米管样品。扫描电子显微图片及红外吸收光谱表明,酸回流成功地在碳纳米管管壁及端部构造了一些缺陷及亲水官能团。形貌表征及X射线光电子谱表明,在碳纳米管表面及端部成功地掺杂了金纳米粒子。掺金后碳纳米管拉曼光谱的G带波数增大,表明该掺杂类型为p型。最后,采用介电电泳法将原样与掺金碳纳米管分别组装到金电极之间,并实时测量接触电阻。结果表明,沉积法掺金可降低碳纳米管与金电极间的接触电阻,其阻值平均降幅高达71.49%。     

Effect of Co-polyester antistatic agent modified by carbon nanotubes on the properties of polypropylene fibers

Antistatic polymer fibers were investigated by using carbon nanotubes (CNTs) to enhance the antistatic ability of inner antistatic agents based on the mechanism of attracting moisture by polar radical groups. It is indicated that the antistatic ability of the fibers filled with composite antistatic agents that contain CNTs and organic antistatic agents was superior to that of the fibers filled either with pure organic antistatic agents or pure CNTs. The antistatic ability of the composite antistatic agent fabricated by an in situ process was superior to that of the composite antistatic agent fabricated by direct dispersing CNTs in the antistatic agent carrier. Moreover, the heat-treated CNTs could further enhance the antistatic effect compared with the initial CNTs. The antistatic effect is significantly influenced by the content of CNTs in the composite antistatic agent.     

掺氮3C-SiC电子结构的第一性原理研究

采用广义梯度近似方案处理电子间相互作用的交换关联能量泛函,电子波函数采用平面波基矢展开,并采用超软赝势近似离子实与价电子间相互作用,对掺氮(3×3×3)3C-SiC超晶胞电子结构进行了第一性原理研究．对不同掺氮浓度3C-SiC超晶胞的能带结构和态密度进行计算,结果表明氮原子的2p态和2s态分别占据价带顶和导带底,随着掺杂浓度的增加,导带底和价带顶的位置逐渐向低能端移动,导带底移动速度要大于价带顶,导致禁带宽度减小．     

Development of supercapacitors based on carbon nanotubes

Block-type electrodes made of carbon nanotubes were fabricated by different processes. The volumetric specific capacitance based on such electrodes reached 107 F/cm3, which proves carbon nanotubes to be ideal candidate materials for supercapacitors. The composite electrodes consisting of carbon nanotubes and RuO2 ·xH2O were developed by the deposition of RuO2 on the surface of carbon nanotubes. Supercapacitors based on the composite electrodes show much higher specific capacitance than those based on pure carbon nanotube ones. A specific capacitance of 600 F/g can be achieved when the weight percent of RuO2· xH2O in the composite electrodes reaches 75% . In addition , supercapacitors based on the composite electrodes show both high energy density and high power density characteristics.     

Research on the electronic transport characteristics of the three-dimensional graphene/carbon nanotube composite structure

According to the actual growth way of graphene presence of the carbon source, four kinds of 3d grapheme-carbon nanotubes composite T structure are built, and their electron transport properties studied by combining density functional theory and the non-equilibrium green's function method. First the double probe model is built and the structure optimization is designed in ATK software, and then their transmission spectrums and electronic state density spectrum lines are analyzed. These research results can provide the reference for the 3d interconnect based on carbon nanomaterials.     

The electronic structure and grain boundary segregation by boron addition

The electronic structure and grain boundary segregation caused by boron addition to Ni₃Al have been studied by X-ray photoelectron spectroscopy and Auger electron spectroscopy, respectively. The obtained results show that the Ni2p_3/2 electron binding energy rises gradually in the sequence of pure Ni<Ni₇₆Al₂₄<Ni₇₄Al₂₆<Ni₇₅Al₂₅, while it reduces monotonously with an increase in boron addition to Ni₃Al. Besides, it is found that the grain boundary segregation of boron occurring in Ni₃Al is a combined equilibrium and non-equilibrium type in nature. Based on the concept of the bonding environmental inhomogeneity, measured by the shift in Ni2p_3/2 electron binding energy from the nickel atoms in the simple substance nickel to those in the intermetallic compound Ni₃Al (ΔE _B), being responsible for the brittle behavior of the alloy, a binding energy shifting criterion for the brittle-ductile fracture transition in Ni₃Al is presented; when ΔE _B>0, the brittle failure occurs in Ni₃Al; when δE _B<0, the ductile one appears. Combined with the above experimental rules, the criterion predicts that pure Ni₃Al is brittle, and there exist the stoichiometric effect and concentration effect in the ductilization process for Ni₃Al by boron addition. Hence the criterion can be taken as a theoretical guide to alloy design in developing ductile intermetallics. Project supported by the National Natural Science Foundation of China.     

立方SrZrO3电子结构和光学性质的研究

采用基于密度泛函理论（DFT）框架下广义梯度近似平面波超软赝势法,计算了立方SrZrO3的电子结构和光学性质。计算结果表明立方SrZrO3为间接带隙钙钛矿型复合氧化物,计算得到的最小带隙为3.33eV。计算并分析了立方SrZrO3的复介电函数、复折射率、吸收系数、反射率、损失函数和光电导率,计算得到静态介电常数为3.40,折射率为1.86,吸收系数的最大峰值为468431.8cm1,反射峰的最大值为0.472,理论计算结果与其他文献结果基本一致,并利用分子轨道理论解释了立方SrZrO3电子结构和光学性质之间的关系,这为立方SrZrO3的应用提供了理论参考数据。     

First-principles study on electronic structure,magnetic and dielectric properties of Cr-doped Fe_3C

The first-principles calculations were performed to investigate the electronic structure, magnetic and dielectric properties of Cr-doped Fe_3C, in comparison to those of pure Fe_3C and Cr_3C. The obtained results show that the thermodynamic stability of Crdoped Fe_3C becomes weaker in terms of the larger formation enthalpy, on the contrary, the metallicity and covalency are found to strengthen to some extent. The magnetic moments of Fe_3C, Fe_(11)CrC_4(g), and Fe_(11)CrC_4(s) are respectively 21.36 μB/cell, 16.92 μB/cell, and 17.62 μB/cell, and in Fe_(11)CrC4(g) and Fe_(11)CrC_4(s), the Fe of Wyckoff positions of 8d and 4c is substituted by Cr. The local magnetic moment of Cr at 8d site is larger than that at 4c site in the doped structure, which is opposite to that of Fe. In low frequency band, the permittivity follows the ranking of Fe_(11)Cr C_4(s)Cr_3CFe_(11)Cr C_4(g)Fe_3C. Once exceeding a certain frequency, the sequence will be broken. Besides the electron transition, the polarization of atoms also makes a contribution to the dielectric properties.     

First-principle investigation on electronic structures and elastic properties of Al-doped MoSi2

The electronic structures and elastic properties of Al-doped MoSi₂ were calculated using the plane wave pseudo-potential method based on the density functional theory, in which the generalized-gradient approximation (GGA) was used to describe the exchange-correlation potential. Starting from the elastic constants, bulk modulus, shear modulus, elastic modulus and Poisson ratio of Al-doped MoSi₂ were obtained by using the Hill method. The results indicate that conductivity of Al-doped MoSi₂ is improved to some extent in comparison with that of pure MoSi₂ due to the orbit hybridization of Mo 4d, Al 3p and Si 3p electrons. In addition, calculations show that the elastic modulus and the brittleness of Al-doped MoSi₂ are smaller than those of pure MoSi₂, which implies that it is feasible to toughen MoSi₂ by doping Al. The agreement of the conclusion with experiment shows that the present theory is reasonable.