Photoluminescence of multiwalled carbon nanotubes excited at different wavelengths

In this paper the multiwalled carbon nanotubes (MWNTs) were synthesized by a chemical vapour deposition and the SEM graph shows that the sample has good construction. The micro-Raman spectrum shows the characteristic line of the MWNTs and an additional line produced by the defects on the outer surface of MWNTs. The photoluminescence (PL) spectra observed experimentally are variable under different excitation wavelengths and the strong excitation wavelength dependence of luminescence indicates a distribution of emitters which include electron $\pi$ in excited states and the Van Hove singularities. The absorption spectra confirm the transition channels which are consistent with the PL emission.     

Large magnetic moment at sheared ends of single-walled carbon nanotubes

In this work we report that after single-walled carbon nanotubes(SWNTs) are sheared with a pair of titanium scissors,the magnetization becomes larger than that of the corresponding pristine ones. The magnetization increases proportionally with the number of SWNTs with sheared ends, suggesting that there exist magnetic moments at the sheared ends of SWNTs.By using the coefficient of this linear relation, the average magnetic moment is estimated to be 41.5 ± 9.8 μB(Bohr magneton) per carbon atom in the edge state at temperature of 300.0 K, suggesting that ultrahigh magnetic fields can be produced. The dangling sigma and pi bonds of the carbon atoms at sheared ends play important roles in determining the unexpectedly high magnetic moments, which may have great potential applications.     

多壁碳纳米管弯曲导致的扭转

文章介绍了多壁碳纳米管弯曲的分子动力学模拟,从原子尺度上解释了由于屈曲失稳而导致的起皱现象,并发现多壁碳纳米管弯曲时会呈现出非线性的力学响应。同时,在模拟过程中,观察到了弯曲诱发扭转的现象,并揭示出扭转变形的内在起因是曲率诱导的晶格错配。     

多壁碳纳米管弯曲导致的扭转

文章介绍了多壁碳纳米管弯曲的分子动力学模拟,从原子尺度上解释了由于屈曲失稳而导致的起皱现象,并发现多壁碳纳米管弯曲时会呈现出非线性的力学响应。同时,在模拟过程中,观察到了弯曲诱发扭转的现象,并揭示出扭转变形的内在起因是曲率诱导的晶格错配。     

Selective growth of individual multiwalled carbon nanotubes

Growth of individual, vertically aligned multiwalled carbon nanotubes (VACNT) on patterned Si wafers using dc plasma-enhanced CVD is described. The selective growth of individual VACNT within larger holes etched in Si is demonstrated for the first time.     

Excitation energy dependence of Raman bands in multiwalled carbon nanotubes

Vertically aligned multiwalled carbon nanotubes (MWCNTs) were grown on 1‐ and 3‐nm cobalt (Co) films, at various growth times by microwave plasma enhanced chemical vapor deposition technique and their microstructural properties were analyzed with the help of Raman spectra that were obtained from different sources of laser excitation energies (E_L: 2.41, 1.96 and 1.58 eV). The variation of D and G band positions in MWCNTs grown on 1‐ and 3‐nm Co films follows a similar behavior, and an anomalous behavior was observed in the E_L dependence of the D′‐band wavenumber. In the second‐order spectra, the G′ band varied strongly according to structure with the laser excitation energy (E_L). The I_D/I_G ratio decreased with the increase of E_L for all MWCNTs; however, for a fixed E_L, the I_D/I_G dispersion is higher at lower E_L. The crystallite sizes were estimated using I_DI_G and E_L. We have shown that, for all MWCNTs, I_D/I_G ratio is inversely proportional to . Copyright © 2010 John Wiley & Sons, Ltd.     

Fractional conductance quantization in multiwalled carbon nanotubes with disorder

A close relationship is established for describing fractional conductance quantization in multiwalled carbon nanotubes with disorder in the framework of the particle-in-a-box model. Our results agree well with experimental data in the context of nanotubes with defects.     

γ射线辐照下多壁碳纳米管结构转变过程研究

采用60Coγ射线辐照纯净的多壁碳纳米管,用高分辨透射电镜和拉曼光谱,研究了多壁碳纳米管由石墨结构向无定形结构转变的演化过程.发现在γ射线辐照下,碳纳米管的外部石墨层逐渐失去最初的有序结构而向无定形结构转变.而且,随着γ射线辐照剂量的增加,无定形结构不断推进,而石墨层结构则不断减小,直至使整个碳纳米管变为一个中空的无定形纳米线结构.用原子位移理论和溅射机理对这种转变过程进行了分析.γ射线轰击碳纳米管击出碳原子,碳原子停留在晶格的间隙位置上产生间隙原子,在它原来的平衡位置则留下一个空位.当轰击粒子动能足够大时导致碰撞级联效应,无序结构增加.多数空位和间隙原子可能相互复合而彼此退火,但仍有少数原子作为间隙原子而造成晶格进一步缺陷.辐射也可以引起碳原子的溅射,溅射出来的碳原子沉积在碳纳米管的外壁上形成一层无定形碳结构.     

The 1/f noise in multiwalled carbon nanotubes

The $1/f$ noise in multiwalled carbon nanotubes bundles has been investigated between the frequency range of 0.1 to 30 Hz. At room temperature the noise spectrum is standard 1/f, and its level is proportional to the square of the bias voltage. With decreasing temperature the noise level also decreases. At 4.2 K the noise level follows a non-monotonic dependence against the bias voltage, showing a peak at a certain bias voltage, meanwhile its frequency dependence also deviates from the 1/f trend. This anomalous behaviour is discussed within the picture of environmental quantum fluctuation of charge transport in the samples.     

Design of soliton electron lattices in carbon nanotubes by a magnetic field

Electron states in the conduction band of carbon nanotubes are studied in the presence of a constant magnetic field perpendicular to the tube axis within the framework of Hubbard's model. Numerical solutions describing electron density waves corresponding to soliton lattices are obtained. The possibility of control over the electron lattice parameters with the help of a constant magnetic field is established. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 17–23, December, 2008.     

轴向磁场对碳纳米管电子性质的影响

用紧束缚法研究了单壁碳纳米管在轴向磁场下费米能级附近电子性质的变化规律.研究发现：能隙随轴向磁场变化的快慢及磁致能隙峰值都与碳纳米管直径有着紧密联系；对于相同直径的碳纳米管，金属性管的磁致能隙峰值最大.具体计算了锯齿型碳纳米管费米能级附近电子态密度随轴向磁场的变化关系,发现所有碳纳米管的电子态密度和能隙变化都体现出周期性.磁场使得碳纳米管发生绝缘体-金属周期性相转变的根本原因是由于在磁场的作用下范霍夫奇异点出现分裂-移动-融合的周期性变化. 关键词： 磁场 碳纳米管 紧束缚法 范霍夫奇异点     

多壁碳纳米管膜湿敏特性的研究

研究了多壁碳纳米管(MWNTs)薄膜的湿敏特性，实验所用的多壁碳纳米管是用热灯丝化学气相沉积法(CVD)合成的.分别对未修饰和修饰的多壁碳纳米管膜温度和湿度特性进行研究后发现，修饰的多壁碳纳米管对温度和湿度非常敏感，且对湿度的响应时间和恢复时间短，重复性好.而未修饰的多壁碳纳米管对温度和湿度不太敏感.对修饰多壁碳纳米管的湿敏特性进行了理论分析，给出了其理论表示式. 关键词： 多壁碳纳米管 化学修饰 湿敏特性 物理吸附     

Raman study on electrochemical lithium insertion into multiwalled carbon nanotubes

We have carried out in situ Raman studies during the electrochemical insertion of lithium ions (Li⁺) into pristine and thermally treated multiwalled carbon nanotubes (MWNTs). We found an improved structural integrity as well as the removal of defects in the thermally treated tubes. The different Li⁺ insertion behaviors above 0.5 V in as‐grown and thermally treated tubes could be explained by the presence of defects on the outer surface of the tubes. No change of Raman spectra from 2.8 to 0.8 V is characterized by the coverage of Li⁺ on the outer surface of tubes, whereas the upshift of G band and the absence of a separated G band below 0.75 V indicate the formation of diluted graphite intercalation below the stage‐2 phase (LiC₁₂). Copyright © 2008 John Wiley & Sons, Ltd.     

Carbon linear chains inside multiwalled nanotubes

Multiwalled carbon nanotubes have been deposited on graphite cathodes by using an arc discharge technique in He atmosphere, with the insertion of a catalytic Ni-Cr mixture as well as without catalysers. The topography of such deposition has been investigated by SEM, while a parallel micro-Raman study has revealed, in particular regions of the deposited cathodes, strong bands in the range 1780-1860 cm⁻¹, assignable to linear carbon chains inside the nanotubes. The variation of intensity, frequency and bandwidth of such bands has been investigated, in relation with the spectral characters of the host multiwalled carbon nanotube. In the cathode deposited without catalyst a quite ordered configuration of multiwalled carbon nanotubes is obtained in the central zone, while the maximum concentration of linear carbon chains is found in a ring shaped zone just inside the border. In sample obtained with catalyst the deposited multiwalled carbon nanotubes appear always more disordered, and a remarkable concentration of carbon chains appears in some zones, with a more casual distribution.     

Raman evidence of the interaction between multiwalled carbon nanotubes and nanostructured TiO2

Nanocomposites of carbon nanotubes and titanium dioxide (TiO₂) have attracted much attention due to their photocatalytic properties. Although many examples in the literature have visualized these nanocomposites by electron microscopic images, spectroscopic characterization is still lacking with regard to the interaction between the carbon nanotube and TiO₂. In this work, we show evidence of the attachment of nanostructured TiO₂ to multiwalled carbon nanotubes (MWNTs) by Raman spectroscopy. The nanostructured TiO₂ was characterized by both full‐width at half‐maximum (FWHM) and the Raman shift of the TiO₂ band at ca 144 cm⁻¹, whereas the average diameter of the crystallite was estimated as approximately 7 nm. Comparison of the Raman spectra of the MWNTs and MWNTs/TiO₂ shows a clear inversion of the relative intensities of the G and D bands, suggesting a substantial chemical modification of the outermost tubes due to the attachment of nanostructured TiO₂. To complement the nanocomposite characterization, scanning electronic microscopy and X‐ray diffraction were performed. Copyright © 2011 John Wiley & Sons, Ltd.     

磁场辅助热处理金属化碳纳米管场发射性能

利用化学镀方法对多壁碳纳米管(multi-walled carbon nanotubes,MWNTs)表面金属化镀镍(MWNTs/Ni),采用丝网印刷制备MWNTs/Ni场发射阴极,并在磁场辅助下热处理所得阴极,研究磁场辅助热处理对MWNTs/Ni阴极的场发射性能的影响,经300mT磁场辅助热处理的MWNTs/Ni的场发射阴极开启场强约为0.80V·μm~(-1),场增强因子β约为16068,对单根MWNTs/Ni在磁场中的受力情况进行建模分析,实验结果表明:磁场辅助热处理有助于提高MWNTs/Ni在阴极表面的直立分布,提高了MWNTs/Ni的场发射性能。     

Investigation of electrical transport in hydrogenated multiwalled carbon nanotubes

Highly disordered multiwalled carbon nanotubes of large outer diameter (∼60 nm) fabricated by means of chemical vapor deposition process inside porous alumina templates exhibit ferromagnetism when annealed in a H₂/Ar atmosphere. In the presence of an applied magnetic field, there is a transition from positive to negative magnetoresistance. The transition may be explained in terms of the Bright model for ordered and disordered carbon structures. Additionally, temperature dependent electrical transport experiments exhibit a zero-bias anomaly at low temperature.     

单层碳纳米管的磁输运特性

依据磁场中Boltzmann输运方程及单层磁纳米管(SWNTs)的能量色散关系,对单个SWNTs中轴向磁场诱发的低温磁阻进行了数值计算.分析表明:当电子以低能输运时,SWNTs的磁阻有明显的Aharonov-Bohn(A-B)效应,与并SWNTs的能隙相对应.     

The effects of static magnetic field on microwave absorption of hydrogen plasma in carbon nanotubes: A numerical study

We theoretically investigate the microwave absorption properties of hydrogen plasma in iron-catalyzed highpressure disproportionation-grown carbon nanotubes under an external static magnetic field in the frequency range 0.3 GHz to 30 GHz, using the Maxwell equations in conjunction with a general expression for the effective complex permittivity of magnetized plasma known as the Appleton–Hartree formula. The effects of the external static magnetic field intensity and the incident microwave propagation direction on the microwave absorption of hydrogen plasma in CNTs are studied in detail. The numerical results indicate that the microwave absorption properties of hydrogen plasma in iron-catalyzed high-pressure disproportionation-grown carbon nanotubes can be obviously improved when the external static magnetic field is applied to the material. It is found that the specified frequency microwave can be strongly absorbed by the hydrogen plasma in iron-catalyzed high-pressure disproportionation-grown carbon nanotubes over a wide range of incidence angles by adjusting the external magnetic field intensity and the parameters of the hydrogen plasma.