钯金属吸附对半导体性碳纳米管电输运的影响

利用物理蒸发技术,在半导体性的碳纳米管上沉积钯金属,利用导电原子力显微镜检测钯吸附对碳纳米管电输运的影响.结果表明:沉积的钯在碳纳米管上形成纳米颗粒,随着钯颗粒密度的增加,半导体性碳纳米管逐渐向金属性转变.利用第一性原理计算了吸附有钯原子的半导体性单壁碳纳米管的能带结构.研究发现,钯的覆盖率越高,其禁带宽度越窄,直至为零,定性说明了实验结果的合理性. 关键词： 单壁碳纳米管 钯纳米颗粒 导电原子力显微镜 第一性原理计算     

Controllable growth and characterization of isolated single-walled carbon nanotubes catalyzed by Co particles

Discrete Co catalytic nanoparticles with small diameters are obtained by pulsed vacuum arc evaporation on Si/SiO₂ substrates, which are used for the growth of isolated single-walled carbon nanotubes (SWNTs) by an ethanol chemical vapor deposition approach (CVD). The distributions of catalytic nanoparticles change with the number of arc pulses, which allows control of the nanotubes formation. We find that an increase of ethanol pressure during CVD growth can change SWNTs from isolated ones into bundles. A new growth mechanism which combines a tip and base model for SWNT growth has been tentatively proposed. It is suggested that the small size catalytic particles prepared by pulsed arc evaporation have a potential advantage for small diameter SWNT growth. PACS 78.67.Ch; 78.67.Bf; 78.67.-n; 81.07.De; 61.46.-w     

磁场中碳纳米管电子结构的紧束缚法研究

利用石墨平面碳原子轨道作sp2杂化时π电子的紧束缚模型,对磁场中直状单层碳纳米管(SWNTs)的电子结构进行理论推导和分析。磁场对碳纳米管的波矢产生影响,从而使碳纳米管的电子结构及能隙均以磁通量子Φ0(=h/e)为周期随磁通量Φ周期性变化。     

DNA-wrapped carbon nanotubes aligned in stretched gelatin films: Polarized resonance Raman and absorption spectroscopy study

We present the study of DNA-wrapped single-walled carbon nanotubes (SWNTs) embedded in the stretched gelatin film by the polarized resonance Raman spectroscopy and visible-NIR optical absorption. The polarized dependent absorption spectra taken along and normal to the stretching direction demonstrate a comparatively high degree of the alignment of isolated SWNTs in the gelatin matrix. The analysis of Raman spectra of isolated SWNTs in the gelatin stretched films showed that the degree of the alignment of carbon nanotubes along the stretching direction is about 62%. The dependence of the peak position of G⁺-band in Raman spectra on the polarization angle θ between the polarization of the incident light and the direction of the stretching of films was revealed. This shift is explained by the different polarization dependence of the most intensive A and E₁ symmetry modes within the G⁺-band. The performed studies of embedded DNA-wrapped nanotubes in the gelatin film show the simple method for obtaining the controlled ordered biocompatible nanotubes inside a polymer matrix. It can be used for manufacturing sizable flexible self-transparent films with integrated nanoelectrodes.     

碳纳米管晶格振动模及拉曼光谱的研究进展

本文介绍了碳纳米管的结构特征和晶格振动模的理论研究 ,综述了不同方法生长的多壁碳纳米管和单壁碳纳米管拉曼光谱的研究进展。另外 ,还简单描述了单壁碳纳米管的应用前景     

Deformation induced semiconductor-metal transition in single wall carbon nanotubes probed by electric force microscopy

We report the direct experimental observation of the semiconductor-metal transition in single-wall carbon nanotubes (SWNTs) induced by compression with the tip of an atomic force microscope. This transition is probed via electric force microscopy by monitoring SWNT charge storage. Experimental data show that such charge storage is different for metallic and semiconducting SWNTs, with the latter presenting a strong dependence on the tip-SWNT force during injection. Ab initio calculations corroborate experimental observations and their interpretation.     

Surface growth of single-walled carbon nanotubes from ruthenium nanoparticles

In this paper, we report that ruthenium is an active and efficient catalyst for growth of single-walled carbon nanotubes (SWNTs) by a chemical vapor deposition (CVD) process for the first time. High density random and horizontally superlong well-oriented SWNTs on substrate can be fabricated via CH₄ or EtOH as carbon source under suitable conditions. Scanning and transition electron microscopy investigations, Raman spectroscopy and atomic force microscopy measurements show the tubular structure, the high crystallinity, and the properties of the grown nanotubes. The results show that the SWNTs from ruthenium have better structural uniformity with less defects and provides an alternative catalyst for SWNTs growth. The successful growth of SWNTs by Ru catalyst provides new experimental information for understanding the growth mechanism of SWNTs, which may be helpful for their controllable synthesis.     

Nanotube surface arrays: weaving, bending, and assembling on patterned silicon

We report the fabrication of ordered arrays of oriented and bent carbon nanotube on a patterned silicon surface with a micron scale spacing extending over millimeter size surface areas. We suggest that the patterning is controlled by the hydrodynamic behavior of a fluid front and orientation and bending mechanisms are facilitated by the pinned carbon nanotubes trapped by the liquid-solid-vapor contact line. The bending of the pinned nanotubes occurs along the shrinking receding front of the drying microdroplets. The formation of stratified microfluidic layers is vital for stimulating periodic instabilities of the contact line.     

碳纳米管中封装富勒烯的机理

利用经典分子动力学模型,发现C60进入单壁碳纳米管(SWNTs)形成(C60)n@SWNTs的吸入和俘获机理.揭示了吸入和俘获势垒只局域于SWNTs的管口区,而在SWNTs的管内区,C60沿管轴方向的运动几乎不受力.最后,系统地计算了吸入和俘获势垒随SWNTs管径的变化,发现只有当SWNTs的管径大于阈值1238nm时才能吸入C 关键词： 富勒烯相关材料 碳纳米管 类虹吸作用     

Single-wall carbon nanotube chemical attachment at platinum electrodes

Self-assembled monolayer (SAM) techniques were used to adsorb 4-aminothiophenol (4-ATP) on platinum electrodes in order to obtain an amino-terminated SAM as the base for the chemical attachment of single-wall carbon nanotubes (SWCNTs). A physico-chemical, morphological and electrochemical characterizations of SWCNTs attached onto the modified Pt electrodes was done by using reflection-absorption infrared spectroscopy (RAIR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and cyclic voltammetry (CV) techniques. The SWNTs/4-ATP/Pt surface had regions of small, medium, and large thickness of carbon nanotubes with heights of 100-200 nm, 700 nm to 1.5 μm, and 1.0-3.0 μm, respectively. Cyclic voltammetries (CVs) in sulfuric acid demonstrated that attachment of SWNTs on 4-ATP/Pt is markedly stable, even after 30 potential cycles. CV in ruthenium hexamine was similar to bare Pt electrodes, suggesting that SWNTs assembly is similar to a closely packed microelectrode array.     

Polarized raman spectroscopy on isolated single-wall carbon nanotubes

Polarized micro-Raman spectroscopy has been performed on spatially separated single-wall carbon nanotubes (SWNTs) in the form of individual nanotubes or thin ropes of only a few SWNTs. Different from bulk samples, the Raman spectra are composed of well-resolved peaks which allow a direct comparison of experimental data with theoretical calculations. Orientation-dependent measurements reveal maximum intensity of all Raman modes when the nanotubes are aligned parallel to the polarization of the incident laser light. The angular dependences clearly deviate from the selection rules predicted by theoretical studies. These differences are attributed to depolarization effects caused by the strongly anisotropic geometry of the nanotubes and to electronic resonance effects for excitation at 633 nm.     

Single-walled carbon nanotube fibers, films and balls

Well-defined fibers and films of single-walled carbon nanotubes (SWNTs) with high purity and narrow diameter distributions were obtained from the strand-like raw soot produced by a dc arc-discharge method. These architectures made up of SWNTs have very uniform smooth surfaces. When the strand-like product was placed on a silicon substrate, dipped into water, treated ultrasonically, and then dried in air, another interesting architecture, an SWNT ball, was obtained. This ball-like structure could also be found on the surface of purified SWNTs. We propose that the surface tension of water and the interaction between SWNTs and silica sphere played the key role in the ball (SWNTs outside and silica sphere inside) formation process.     

Curvature-induced condensation of lithium confined inside single-walled carbon nanotubes: First-principles calculations

We carry out first-principles calculations to explore the potential energy profiles of Li confined inside single-walled carbon nanotubes (SWNTs) and the subsequent condensation processes. We found that Li has high mobility around tube axis with the energy barrier less than 47 meV, whereas the diffusion barrier along radial direction is as higher as 380 meV. This characterizes the condensation of Li atoms when placed randomly into SWNTs, resulting in nanowires with single or multi-shelled morphologies depending on the diameter of SWNTs. The charge transfer from Li nanowires to SWNTs is significant, indicating stronger couplings between them.     

Optical anisotropy in single-walled carbon nanotubes

Optical anistropy at optical communication wavelength was observed in films of vertically aligned single-walled carbon nanotubes (SWNTs). We report the control of both the polarization state and transmission of incoming light at 1550 nm by azimuthal and axial tilting of SWNT film about its aligned axis. The experiments reveal that the polarization state of light is susceptible to the azimuthal angle of the aligned direction of a SWNT having semiconductor characteristics and the intensity of the output beam after SWNT film shows cosine function dependence on the axial tilting angle.     

Effect of PVA functionalization on hydrophilicity of Y-junction single wall carbon nanotubes

Hydrophilic surface of carbon nanotubes (CNTs) are of great interest for various applications including chemical and biological sensing. Surface functionalization of single wall carbon nanotubes (SWNTs) mats with a biocompatible polymer polyvinyl alcohol (PVA) was studied. PVA modification induced a drastic change in water wettability of the SWNT surface transforming it from hydrophobic to highly hydrophilic. These PVA modified SWNTs mats have also demonstrated increasing impedance variation in relative humidity compared to the pristine nanotubes. An appreciable change in conductivity of Y-junction SWNT mats as a function of relative humidity indicates its potential application as humidity sensor. This higher sensitivity for humidity variation shown in Y-junction SWNT mats could be attributed to the greater portion of semiconducting nanotubes in these mats revealed by Raman analysis. A possible conductance changing mechanism of surface modified SWNTs mats is discussed.     

Fast detection of the metallic state of individual single-walled carbon nanotubes using a transient-absorption optical microscope

In spite of the outstanding properties of single-walled carbon nanotubes (SWNTs), the coexistence of metallic and semiconducting SWNTs as a result of synthesis has hindered their electronic and photonic applications. We demonstrate a pump-probe microscopy method for fast, contact-free mapping of metallicity in individual SWNTs. We employ the phase of transient absorption as a contrast to discriminate metallic and semiconducting SWNTs. Furthermore, we have clarified the phase dependence on the pump or probe wavelengths and the energy structure of SWNTs. Our imaging method holds the potential of serving as a high-speed metallicity-mapping tool to assist the development of SWNT-based nanoelectronics.     

Synthesis,characterization, and electrochemical properties of imidazole derivatives functionalized single‐walled carbon nanotubes

The imidazole derivatives functionalized single‐walled carbon nanotubes (SWNTs) were synthesized by a diazonium‐based reaction. We have designed and synthesized two imidazole derivatives to modify SWNTs. The resulting products were characterized by Fourier transform infrared (FT‐IR) spectroscopy, Raman spectroscopy, ultraviolet visible (UV/Vis) spectroscopy, thermo gravimetric analysis (TGA), energy dispersive X‐ray spectroscopy (EDX), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Electrochemical measurements via a cyclic voltammetry method revealed that the weak intramolecular electronic interactions presented between the attached imidazole derivatives groups and the nanotubes. Copyright © 2008 John Wiley & Sons, Ltd.     

Zinc oxide catalyzed growth of single-walled carbon nanotubes

We demonstrate that zinc oxide can catalyze the growth of single-walled carbon nanotubes (SWNTs) with high efficiency by a chemical vapor deposition process. The zinc oxide nanocatalysts, prepared using a diblock copolymer templating method and characterized by atomic force microscopy (AFM), were uniformly spaced over a large deposition area with an average diameter of 1.7 nm and narrow size distribution. Dense and uniform SWNTs films with high quality were obtained by using a zinc oxide catalyst, as characterized by scanning electron microscopy (SEM), Raman spectroscopy, AFM, and high-resolution transmission electron microscopy (HRTEM).     

Image contrast enhancement in field-emission scanning electron microscopy of single-walled carbon nanotubes

The image contrast enhancement in scanning electron microscopy of single-walled carbon nanotubes (SWNTs) on SiO₂ surfaces was experimentally investigated using a field-emission scanning electron microscope (FESEM) using a wide range of primary electron (PE) voltages. SWNT images of different contrasts were obtained at different PE voltages. Image contrast enhancement of SWNTs was investigated by charging SiO₂ surfaces at different PE voltages. The phenomena are ascribed to the surface potential difference and charge injection between SWNTs and SiO₂ substrates induced by the electron-beam irradiation.     

Resonance Raman spectra of carbon nanotubes by cross-polarized light

Resonance Raman studies on single wall carbon nanotubes (SWNTs) show that resonance with cross polarized light, i.e., with the E(mu,mu+/-1) van Hove singularities in the joint density of states needs to be taken into account when analyzing the Raman and optical absorption spectra from isolated SWNTs. This study is performed by analyzing the polarization, laser energy, and diameter dependence of two Raman features, the tangential modes (G band) and a second-order mode (G' band), at the isolated SWNT level.