功能化单壁碳纳米管的热导率

采用基于BrennerⅡ势的非平衡态分子动力学方法,模拟研究了300K温度下经氢化学修饰的(10,0)单壁碳纳米管的热导率.研究显示功能化后碳管的热导率有明显减小,当有一列碳原子被氢化后（功能化程度为5%）,碳管的热导率减小了大约1/3,为了进一步解释这种功能化对碳纳米管热导率的影响,计算了不同功能化程度下碳纳米管的声子谱.     

功能化单壁碳纳米管的热导率

采用基于BrennerⅡ势的非平衡态分子动力学方法,模拟研究了300K温度下经氢化学修饰的(10,0)单壁碳纳米管的热导率.研究显示功能化后碳管的热导率有明显减小,当有一列碳原子被氢化后（功能化程度为5%）,碳管的热导率减小了大约1/3,为了进一步解释这种功能化对碳纳米管热导率的影响,计算了不同功能化程度下碳纳米管的声子谱.     

Strain-induced metal to semiconductor transition in ultra-small diameter single-wall carbon nanotubes

Under a large tensile strain near fracture limit, the band structures of single-wall carbon nanotubes (SWCNTs) with diameter less than 0.5 nm begin a metal to semiconductor transition and these ultra-small SWCNTs can normally maintain their metallicities. The band gap behavior of these SWCNTs intrinsically originates from the long axial direct bond lengths and the severe curvature. The gap opening comes mainly from the transfer of pπ electrons. And the localized π and σ states can result in a lower electrical conductivity. This band gap behavior suggests that it has potential to find applications in nano-electromechanical system.     

Adsorption on the carbon nanotubes

Adsorption on single walled carbon nanotubes (SWCNTs) is a subject of growing experimental and theoretical interest. The possible adsorbed patterns of atoms and molecules on the single-walled carbon nanotubes vary with the diameters and chirality of the tubes due to the confinement. The curvature of the carbon nanotube surface enlarges the distance of the adsorbate atoms and thus enhances the stability of high coverage structures of adsorbate. There exist two novel high-coverage stable structures of potassium adsorbed on SWCNTs, which are not stable on graphite. The electronic properties of SWCNTs can be modified by adsorbate atoms and metal-semiconductor and semiconductor-semi-conductor transitions can be achieved by the doping of alkali atoms.     

Electron transport in armchair single-wall carbon nanotubes

The rates of electron scattering via phonons in the armchair single-wall carbon nanotubes were calculated by using the improved scattering theory within the tight-binding approximation. Therefore, the problem connected with the discrepancy of the scattering rates calculated in the framework of the classical scattering theory and ones predicted by experimental data was clarified. Then these results were used for the solving of the kinetic Boltzmann equation to describe electron transport properties of the nanotubes. The equation was solved numerically by using both the finite difference approach and the Monte Carlo simulation procedure.     

非共振条件下单壁碳纳米管拉曼散射强度的计算

利用非共振情况下的键极化模型理论，对单壁碳纳米管的拉曼光谱强度进行了研究.考察了碳纳米管结构、入射光和散射光的偏振方向以及管轴的取向对散射光强度的影响.计算结果表明，光的偏振方向对拉曼散射强度影响较大，而手性对拉曼光谱的影响较小.针对碳管样品的实际情况，给出了无规取向碳管的拉曼散射光谱. 关键词： 碳纳米管 拉曼散射 声子 键极化     

Chromatographic size separation of single-wall carbon nanotubes

Received: 18 May 1998/Accepted: 22 May 1998     

单壁碳纳米管中电子的有效质量

解析研究了单壁碳纳米管中电子的有效质量，以及导带底的电子有效质量与其管径和螺旋度的关系.结果表明，单壁碳纳米管的几何结构对其电子有效质量有重要的影响.特别是锯齿形窄隙半导体管，发现其导带底的电子有效质量与管径的平方成反比. 关键词： 单壁碳纳米管 电子有效质量     

Photocurrent in single walled carbon nanotubes

Carbon based nanomaterials have received a lot of attention due to their unique structural and physical properties. In this study, photoresponse in semiconducting single-walled carbon nanotubes is investigated using density functional theory. The photocurrent generated is found to increase with the increasing electrode voltage at a constant flux. In all models the current increases uniformly with applied voltage and maximum value of current is found in the pristine CNT model, however the magnitude of photocurrent decreases in the homogenously nitrogen and boron doped models. Moreover, the photocurrent increases with increase in flux showing photoresistive property in CNTs. The spectral peaks appear at different wavelengths in the three models paving way for wide range of applications in the futuristic optoelectronic devices.     

Structural and electronic properties of chiral single-wall copper nanotubes

The structural,energetic and electronic properties of chiral(n,m)(3≤n≤6,n/2≤m≤n)single-wall copper nanotubes(CuNTs)have been investigated by using projector-augmented wave method based on density-functional theory.The(4,3)CuNT is energetically stable and should be observed experimentally in both free-standing and tip-suspended conditions,whereas the(5,5)and(6,4)CuNTs should be observed in free-standing and tip-suspended conditions,respectively.The number of conductance channels in the CuNTs does not always correspond to the number of atomic strands comprising the nanotube.Charge density contours show that there is an enhanced interatomic interaction in CuNTs compared with Cu bulk.Current transporting states display different periods and chirality,the combined effects of which lead to weaker chiral currents on CuNTs.     

单壁碳纳米管的高压拉曼研究

采用金刚石对顶砧装置对直径分布在1.3 nm左右的单壁碳纳米管进行了高压拉曼光谱研究.实验结果表明随压力的增加碳管的截面形状发生了由圆到椭圆再到扁平的变化,这和我们之前的研究结果一致.从31 GPa卸压至常压后碳管的结构得到了较好的保持,这个压力值明显高于传统的Sp2键结构的碳材料所能稳定存在的压力范围(20 GPa以...     

Coherent transport through intramolecular junction of single-wall carbon nanotubes

We have constructed four types single-wall carbon nanotube intramolecular junctions (IMJs) of (5,5)/(8,0), (5,5)/(10,0), (5,5)/(9,0)A, and (5,5)/(9,0)B along a common axis, and calculated their electronic and transport properties using a tight binding-based Green's function approach that is particular suitable for realistic calculation of electronic transport property in extended system. Our results show that quasi-localized states can appear in the metal/semiconductor heterojunctions ((5,5)/(8,0) and (5,5)/(10,0)junctions), which is desirable for the design of a quantum device; and the conductance of M-M IMJs is very sensitive to the connectivity of the matching tubes, certain configurations of connection completely stop the flow of electron, while others permit the transmission of the current through the interface. These results may have implications for the device assembly and manipulation process of all carbon nanotubes-based microelectronic elements. Received 14 January 2003 / Received in final form 25 February 2003 Published online 4 June 2003 RID="a" ID="a"e-mail: lfyzz@yahoo.com.cn     

单壁碳纳米管杂化轨道计算

根据轨道杂化理论以及碳纳米管的几何结构,计算了(n,0),(n,n)和(n,m)三种单壁碳纳米管的杂化轨道,给出了杂化轨道s轨道成分和p轨道成分的解析式.对于管径较小的纳米管,锯齿型(n<40),扶手椅型(n<20),手性型(n<30,m相似文献   

STM morphology study of ropes of single-wall carbon nanotubes

Received: 10 February 1998     

Correlated transport and non-Fermi-liquid behavior in single-wall carbon nanotubes

We derive the effective low-energy theory for single-wall carbon nanotubes including the Coulomb interactions among electrons. The generic model found here consists of two spin-fermion chains which are coupled by the interaction. We analyze the theory using bosonization, renormalization-group techniques, and Majorana refermionization. Several experimentally relevant consequences of the breakdown of Fermi liquid theory observed here are discussed in detail, e.g., magnetic instabilities, anomalous conductance laws, and impurity screening profiles. Received: 12 December 1997 / Revised: 9 March 1998 / Accepted: 12 March 1998     

模拟研究碳纳米管的热稳定性质

运用分子动力学方法具体模拟研究单个碳纳米管（CNTs）在加热过程中的结构变化．选择多组不同结构的单壁碳纳米管（SWCNTs）和双壁碳纳米管（DWCNTs）作为研究对象,加热温度从室温开始到4000 K,压强保持为1 atm．结果表明单壁碳管中手性型结构热稳定性最好,其次是扶手椅型和锯齿型,当手性角相同时,直径大的热稳定性更高;对于双壁碳管,研究表明当双壁中至少之一为手性结构时其热稳定好,而内外壁均为锯齿结构的稳定性最差,该结果进一步支持了有关单壁碳管的结论;还从理论上探索了描述结构热稳定性的方式,并在键层 关键词： 单壁碳纳米管 双壁碳纳米管 分子动力学方法 热稳定性能     

Growth mechanisms for single-wall carbon nanotubes in a laser-ablation process

Mechanisms proposed in the literature are compared with a current scenario for the formation of single-wall carbon nanotubes in the laser-ablation process that is based on our spectral emission and laser-induced fluorescence measurements. It is suggested that the carbon which serves as feedstock for nanotube formation not only comes from the direct ablation of the target, but also from carbon particles suspended in the reaction zone. Fullerenes formed in the reaction zone may be photo-dissociated into C₂ and other low molecular weight species, and also may serve as feedstock for nanotube growth. Confinement of the nanotubes in the reaction zone within the laser beam allows the nanotubes to be ‘purified’ and annealed during the formation process by laser heating. Received: 2 November 2000 / Accepted: 3 November 2000 / Published online: 23 March 2001     

The separation single-wall carbon nanotubes on length by sepharose gel

The separations of single-wall carbon nanotubes on length by sepharose gel were investigated in this work. The solutions of sodium dodecyl sulfate and sodium deoxycholate were applied as the eluent in sequence. SEM and Raman were used to characterize the length of nanotube bundles. The results show that the longer nanotubes were eluted out first, and then the shorter tubes were followed by the sodium dodecyl sulfate. However, the separated order was totally reversed by the sodium deoxycholate. By this method, the process generated nanotube fractions not only were narrower in length distributions, but also could control the separation orders by changing the eluents. Moreover, the separation principle was also discussed.     

Exploring the simultaneous existence of Stone-Wales and carbon ad-dimer defects in the zigzag single-walled carbon nanotubes

We have applied density functional calculations to investigate simultaneous existence of Stone–Wales (SW) and carbon ad-dimer (CD) defects in the zigzag (n, 0) n=5, 6, 7, 8, 9, and 10 SWCNTs, with an extensive search by considering two different orientations of defects. According to our results, the adsorption of a carbon dimer on a hexagonal ring of SWCNTs is easier than the rotation of a C–C bond trough the SW rearrangement. Moreover, the formation of a carbon dimer on the exterior sidewalls of an SW defective SWCNT or the rotation of a C–C bond of a CD defective SWCNT is more favorable than those on the perfect ones. Defect formation energy shows a strong dependence on the both SWCNT radius and defect orientation. The reactivity of SW–CD defective SWCNTs through chemisorption of hydrogen atoms on the central bonds of defect sites shows the thermodynamically lower preference of additions for the CD defective sites in comparison to SW defective sites. Histograms of the ¹³C NMR chemical shifts of SW–CD defective SWCNTs exhibit individual signals for defect sites, which can be attributed to azupyrene- and pentalelene-like structures for SW and CD defect sites, respectively.     

Periodic resonance excitation and intertube interaction from quasicontinuous distributed helicities in single-wall carbon nanotubes

Photoselective resonance Raman scattering from laser ablation grown single-wall carbon nanotubes is demonstrated to be consistent with a response from tubes with all geometrically allowed helicities. This information is drawn from an analysis of the resonance scattering by combining ab initio calculations for the mode frequencies with evaluations of the resonance cross sections for isolated tubes. The resonance excitation was found to exhibit an oscillatory behavior. To match the experiments and the calculations, the frequencies obtained from the latter must be up-shifted by 8.5% on the average. This stiffening is ascribed to the tube-tube interaction in the carbon nanotube bundles.