碳纳米管网络导电特征的导电型原子力显微镜研究

利用导电型原子力显微镜对大范围碳纳米管（CNT）网络的导电性能进行成像观察.研究发现：在几十微米的成像范围内,每根CNT本身的电阻远小于CNT之间的接触电阻,以致于在电压偏置的网络中不同的CNT呈现电位不同的等位体;CNT的导电性能虽不因与其他CNT的交叠接触而改变,但是如果缠绕成束,则半导体性CNT趋于呈现金属性CNT的导电特征. 关键词： 导电型原子力显微镜 碳纳米管网络 碳管纳米电导     

Structural and vibrational properties of deformedcarbon nanotubes

The fantastic variation of the physical properties of carbon nanotubes (CNTs) and their bundles under mechanical strain and hydrostatic pressure makes them promising materials for fabricating nanoscale electromechanical coupling devices or transducers. In this paper, we review the recent progress in this field, with much emphasis on our first-principles numerical studies on the structural and vibrational properties of the deformed CNTs under uniaxial and torsional strains, and hydrostatic pressure. The nonresonant Raman spectra of the deformed CNTs are also introduced, which are calculated by the first-principles calculations and the empirical bond polarizability model.     

Effect of boron and nitrogen co-doping on CNT's electrical properties: Density functional theory

In this work, we have theoretically studied the changes in electrical properties of three different geometrical structures of carbon nanotubes upon co-doping them with boron and nitrogen atoms. We applied different doping mechanisms to study band structure variations in the doped structures. Doping carbon nanotubes with different atoms will create new band levels in the band structure and as a consequence, a shift in the Fermi level occurs. Whereas, filling up the lowest conduction/ upper valence bands created an up/ downshift in the Fermi level. Moreover, dopants concentration and dopants position play a critical rule in defining the number of new band levels. These new band levels in the band gap region represented as new peaks appeared in the density of states. These new bands are solely attributed to co-doping carbon nanotubes with boron and nitrogen atoms.     

Blume–Emery–Griffiths纳米管的热力学与相变性质

利用有效场理论研究了圆柱形纳米管上Blume-Emery-Griffiths系统的热力学与相变性质,得到了系统的磁化强度、磁化率、比热和相图.讨论了四次交换作用与二次交换作用的比值 与晶格场对系统热力学量和相图的影响.研究发现:系统存在三临界点,且三临界点由参数 和晶格场共同决定,即若确定了参数 ,则三临界点所对应的晶格场也能确定.随着参数 的增加,系统出现三临界点时所对应的温度和晶格场也相应增大.     

Sonochemical modification of carbon nanotubes for enhanced nanocomposite performance

Multi-walled carbon nanotubes (CNTs) have been treated using 20 kHz ultrasound in combination with dilute nitric and sulfuric acids at much lower concentrations than previously reported. The measurements revealed an optimum set of sonication conditions (in this case 30 min at 12 W cm⁻²) exists to overcome aggregation of the nanotubes and to allow efficient dispersion in ethanol or in chitosan. Transmission electron microscopy and Raman spectroscopy suggested the removal of amorphous material and reduction of the CNT diameter as well as modifications to their defect structures. The surface oxidation was determined by FTIR spectroscopy. At longer times or higher ultrasound intensities, degradation such as nanotube shortening and additional defect generation in the graphitic network occurred and the benefits of using ultrasound decreased. The modified CNTs were used as fillers for chitosan films and gave a tenfold increase in tensile strength and integrity of the films. The methodology was combined with sonochemical generation of gold or iron oxide nanoparticles to produce a range of functional membranes for catalytic reductive hydrogenation or dye degradation under conditions that are more environmentally benign than those previously used. Our results further add to the usefulness of sonochemistry as a valuable tool in preparative materials chemistry but also illustrate the crucial importance of careful control over the experimental conditions if optimum results are to be obtained.     

六方氮化硼的振动光谱与立方氮化硼的合成

 以X射线衍射分析作参比，分析了高度三维有序到近乱层结构的9种六方氮化硼的红外和拉曼光谱，并进行了立方氮化硼的高温高压合成。光谱分析表明，随着晶性的降低，六方氮化硼的低频红外吸收峰的位置及拉曼谱线等基本振动光谱发生明显的特征性的变化，并伴随出现各自不同的次级光谱结构。合成结果表明，在触媒作用下，立方氮化硼的形成需要六方氮化硼原料有一定的结晶度，但立方氮化硼合成效果与六方氮化硼结晶度并非是简单的单调关系。对振动光谱和合成试验的结果进行了讨论。     

Theoretical investigation of encapsulation processes of C60 into single-wall carbon nanotubes

The encapsulation of C₆₀ into single-wall carbon nanotubes is systematically studied by tight-binding molecular dynamics method with an appropriate long-range Lennard-Jones potentials. For a (16,0) nanotube, it is impossible to encapsulate C₆₀ into the tube because of a much larger energy barrier with the relaxation of the open end.     

Effect of sp-hybridized defects on the oscillatory behavior of carbon nanotube oscillators

Using molecular dynamics simulations, we investigate the oscillatory behaviors of carbon nanotube oscillators containing sp³-hybridized defects formed by hydrogen chemisorption. It is found that the presence of these defects significantly affects the kinetic and potential energies of the nanotube systems, which in turn affects their oscillation periods and frequencies. We have also studied the oscillatory characteristics of the oscillators containing sp³-hybridized Stone-Wales defects. Our results show that it is possible to control the motion of the inner nanotube by introducing sp³-hybridized defects on the outer nanotube, which provides a potential way to tune the oscillatory behavior of nanotube oscillators.     

Effects of electromigration on copper atoms in carbon nanotube channels

The effects of electromigration on copper in carbon nanotube (CNT) channels are investigated using molecular dynamics simulations. The study shows that the potential energy of copper and the resistive forces on copper are dependent on the shape of the CNT junction, and the increase in bias voltages magnifies these effects. Bias voltages affect the density of copper in the downstream CNT. The velocity of copper in the downstream CNT is relatively lower than that in the upstream CNT when the biased voltage is high.     

Transparent titania nanotubes of micrometer length prepared by anodization of titanium thin film deposited on ITO

Transparent TiO₂ nanotube arrays of micrometer lengths were prepared by anodization of titanium thin film RF sputtered on indium tin oxide (ITO) which was coated on glass substrate. The sputtering process took place at elevated temperature of 500 °C. The structures of the films were studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD) while the optical properties of the films were investigated using UV-visible spectroscopy. Two types of electrolytes were used in this work: an aqueous mixture of acetic acid and HF solution and a mixture of NH₄F and water dissolved in ethylene glycol. The concentration of NH₄F, voltage and the thickness of the sputtered titanium film were varied to study their effect on the formation of TiO₂ nanotube arrays. It is demonstrated in this work that the nanoporous layer is formed on top of the ordered array of TiO₂ nanotubes. Furthermore, the optical transmittance of TiO₂ nanotubes annealed at 450 °C is much lower than the non annealed TiO₂ nanotubes in the visible wavelength region.