Carbon nanotubes and nanostructures grown from diamond-like carbon and polyethylene

We report a simple way to synthesize carbon nanotubes and nanostructures from the solid phase. Vacuum annealing of diamond-like carbon (DLC) films or polyethylene mixed with catalyst in argon atmosphere leads to the formation of nanotubes and nanostructures. High-resolution transmission electron microscopy studies reveal highly graphitized multi-walled nanotubes (MWNTs) or amorphous fibre-like structures, depending on the catalyst amount. This synthesis process may give a new approach to understanding the phase transition of different carbon allotropes into nanotubes or nanostructures. Received: 3 July 2001 / Accepted: 3 July 2001 / Published online: 2 October 2001     

Structure comparison of nanotubes produced by different processes

Several methods used for the synthesis of carbon nanotubes have been developed in the last decade. The preparation techniques used, and their associated parameters, have an ultimate effect on the structure of the resulting nanotubes. Consequently, it is of great interest to compare the structure of carbon nanotubes synthesized by different techniques. We investigated a range of nanotubes of different origin by scanning probe microscopy (TM-AFM), and by scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS). Three different types of nanotubes have been investigated: commercial SWNT and MWNT, MWNT (synthesized using a CCVD process) and its SiO₂ coated variant, and nanostructures produced using an electrochemical method. A preparative technique is described and different tube parameters are measured. The quality of coated MWNT-s is investigated and nano-structured rings are revealed in samples obtained by electrolysis of molten salts on graphite electrodes.     

Electronic and optoelectronic nano-devices based on carbon nanotubes

The discovery and understanding of nanoscale phenomena and the assembly of nanostructures into different devices are among the most promising fields of material science research. In this scenario, carbon nanostructures have a special role since, in having only one chemical element, they allow physical properties to be calculated with high precision for comparison with experiment. Carbon nanostructures, and carbon nanotubes (CNTs) in particular, have such remarkable electronic and structural properties that they are used as active building blocks for a large variety of nanoscale devices. We review here the latest advances in research involving carbon nanotubes as active components in electronic and optoelectronic nano-devices. Opportunities for future research are also identified.     

PREPARATION OF NANOWIRES AND MICROARRAYS

We report on the synthesis of one-dimensional (1D) solid nanostructures and ordered microarrays consisting of nanowires and carbon nanotubes. For 1D nanostructures, several synthesis methods, such as, carbothermal reduction of silica xerogels containing carbon nanoparticles, chemical vapor deposition on mesoporous active carbon with transition metal catalyst nanoparticles inside the pores, and simple physical evaporation with the help of transition metal nanoparticles as catalysts, have been used. For microarrays, anodic alumina membranes (AAMs) with highly ordered honeycomb structure were used as templates, chemical vapor reaction inside the nanochannels, Sol-gel technique, and selective electrodeposition in the channels, have been used to prepare microarrays embedded in AAMs.     

Preparation of carbon nanosheets deposited on carbon nanotubes by microwave plasma-enhanced chemical vapor deposition method

Carbon nanosheets were synthesized by microwave plasma-enhanced chemical vapor deposition method on carbon nanotubes substrate which was treated by hydrogen plasma. The results showed that the diameters of carbon nanotubes first got thick and then “petal-like” carbon nanosheets were grown on the outer wall of carbon nanotubes. The diameters of carbon nanotubes without and with carbon nanosheets were 100-150 and 300-500 nm, respectively. Raman spectrum indicated the graphite structure of carbon nanotubes/carbon nanosheets. The hydrogen plasma treatment and reaction time greatly affected the growth and density of carbon nanosheets. Based on above results, carbon nanosheets/carbon nanotubes probably have important applications as cold cathode materials and electrode materials.     

Microscopic model of the optical absorption of carbon nanotubes functionalized with molecular spiropyran photoswitches

The adsorption of molecules to the surface of carbon nanostructures opens a new field of hybrid systems with distinct and controllable properties. We present a microscopic study of the optical absorption in carbon nanotubes functionalized with molecular spiropyran photoswitches. The switching process induces a change in the dipole moment leading to a significant coupling to the charge carriers in the nanotube. As a result, the absorption spectra of functionalized tubes reveal a considerable redshift of transition energies depending on the switching state of the spiropyran molecule. Our results suggest that carbon nanotubes are excellent substrates for the optical readout of spiropyran-based molecular switches. The gained insights can be applied to other noncovalently functionalized one-dimensional nanostructures in an externally induced dipole field.     

离子辐照与碳纳米结构体的合成

阐述了在离子辐照下生成各种碳纳米结构体研究的发展现状,探讨了相应的生长机制和一些相变机理 ,提出了一些有待解决的问题 ,并对其发展方向作了展望. The synthesis of carbon nanostructures, such as fullerenes, nanotubes, onions and diamond, by using ion irradiation, has been reviewed and the growth mechanisms of these carbon nanostructures as well as their phase transitions are simply discussed. It shows that high density plasma engendered by ion irradiation plays an important role in the growing of carbon nanostructures. In addition, it indicates that ion irradiation, due to its great flexibility of experimental parameters, is enormously convenient in...     

Raman scattering from one-dimensional carbon systems

Although the Raman effect was discovered nearly 80 years ago, it is only recently that the special characteristics of Raman scattering for one-dimensional systems have been seriously considered. This review focuses on the special interest of the Raman effect for one-dimensional systems that is of particular relevance to carbon nanostructures. Two examples of Raman scattering in one-dimensional systems are given. The first illustrates the use of Raman spectroscopy to reveal the remarkable structure and properties of carbon nanotubes arising from their one-dimensionality. Some of the recent advances in using Raman spectroscopy to study doping and intercalation to modify nanotube properties are reviewed, in the context of a one-dimensional system. The second example is the Raman spectra of a linear chain of carbon atoms and the special properties of this interesting system. New approaches toward applying Raman spectroscopy to carbon nanostructures are also emphasized.     

Optical studies of carbon nanotubes and nanographites

Resonance Raman and photoluminescence excitation (PLE) spectroscopies are used to study the optical properties of different types of carbon nanostructures such as carbon nanotube, nanoribbons, nanographites and graphite edges. In the resonance Raman experiments of carbon nanotubes, the (n,m) assignment is obtained by comparing the experimental and theoretical diameter and chirality dependence of the optical transitions. The influence of the environment on the optical transitions of the nanotubes is also obtained in the Raman experiments. The PLE measurements in different samples of carbon nanotubes show both direct and phonon-assisted optical transitions, and the results give new evidences that the optical transitions in nanotubes have an excitonic character, which is very strong for the low energy transitions. We also analyze the Raman spectra of nanoribbons and nanographites, showing that this technique is an important tool for defect characterization in graphitic materials, and can be used to distinguish the atomic structure of the graphite edges.     

Biophysical and electrochemical properties of Self-assembled noncovalent SWNT/DNA hybrid and electroactive nanostructure

DNA self-assembled hybrid nanostructures are widely used in recent research in nanobiotechnology. Combination of DNA with carbon based nanoparticles such as single-walled carbon nanotube (SWNT), multi-walled carbon nanotube (MWNT) and carbon quantum dot were applied in important biological applications. Many examples of biosensors, nanowires and nanoelectronic devices, nanomachine and drug delivery systems are fabricated by these hybrid nanostructures. In this study, a new hybrid nanostructure has been fabricated by noncovalent interactions between single or double stranded DNA and SWNT nanoparticles and biophysical properties of these structures were studied comparatively. Biophysical properties of hybrid nanostructures studied by circular dichroism, UV–vis and fluorescence spectroscopy techniques. Also, electrochemical properties studied by cyclic voltammetry, linear sweep voltammetry, square wave voltammetry, choronoamperometry and impedance spectroscopy (EIS). Results revealed that the biophysical and electrochemical properties of SWNT/DNA hybrid nanostructures were different compare to ss-DNA, ds-DNA and SWNT singly. Circular dichroism results showed that ss-DNA wrapped around the nanotubes through π-π stacking interactions. The results indicated that after adding SWNT to ss-DNA and ds-DNA intensity of CD and UV–vis spectrum peaks were decreased. Electrochemical experiments indicated that the modification of single-walled carbon nanotubes by ss-DNA improves the electron transfer rate of hybrid nanostructures. It was demonstrated SWNT/DNA hybrid nanostructures should be a good electroactive nanostructure that can be used for electrochemical detection or sensing.     

Carbon Nanostructures

An overview of the various carbon structures with characteristic sizes in the nanoscale region is presented, with special attention devoted to the structures and properties of ‘nanodiamond’ and carbon nanotubes. The term ‘nanodiamond’ is used broadly for a variety of diamond-based materials at the nanoscale ranging from single diamond clusters to bulk nanocrystalline films. Only selected properties of carbon nanotubes are discussed, with an aim to summarize the most recent discoveries. Current and potential applications of carbon nanostructures are critically analyzed.     

Nickel-containing carbon nanotubes and nanoparticles prepared in a high-frequency arc plasma

This paper presents the results of an investigation of nickel-containing carbon nanostructures prepared by plasma-chemical synthesis in a carbon-helium plasma jet at atmospheric pressure with the arc fed by a high-frequency current. It is demonstrated that, under these conditions, the conversion of graphite into a carbon condensate reaches 98 wt % and the contents of carbon nanotubes and nickel in this condensate are 72 and 10 wt %, respectively. Sequential treatment with nitric and hydrochloric acids has made it possible to extract purified carbon nanotubes and nickel nanoparticles coated with a carbon shell (approximately 50 nm thick) in which the nickel content is 4 wt %. Data are presented on the diameters of the prepared nanotubes and on the state of carbon in the samples.     

Separating weak-localization and electron-electron-interaction contributions to the conductivity of carbon nanostructures

The effect of the modification of curvilinear carbon nanostructures (nanotubes) on their electrical properties has been studied. The samples were prepared using a special method of synthesis, which excluded the formation of amorphous carbon particles in multiwalled carbon nanotubes and in expanded graphite. Such materials exhibit a quadratic growth in the positive magnetoconductivity in the fields of up to B ～ 1 T, which is not observed in the samples synthesized by usual methods.     

Tip-induced distortions in STM imaging of carbon nanotubes

By means of STM measurements and fully self-consistent transport calculations we analyze how STM trajectories for the mapping of nanostructures on surfaces are affected by the atomic structure of the tip. For the particular case of carbon nanotubes we show that considerable distortions of the STM trajectory with respect to the actual structure, position and diameter of the nanotube can occur for certain tip geometries. Comparison between theory and experiment can allow to characterize and correct these distortions.     

纳米结构中的量子问题

文章讨论了纳米器件发展方向和近期的研究成果，指出是子效应和纳米结构是将来的纳米器件的两大基础，以碳纳米管和各种电极组成的纳米结构为代表，论述了不同的量子效应及其在纳米器件中的可能应用。     

Reactor with activated hydrogen for carbon nanotube synthesis

A reactor for synthesis of carbon nanostructures with hydrogen activated during diffusion through an incandescent metallic partition is proposed and implemented. Multiwall carbon nanotubes and nanorods synthesized in this reactor are described.     

Highlighting the mechanisms of the titanate nanotubes to titanate nanoribbons transformation

Titanate nanorods, nanoribbons, and nanofibers synthesized by hydrothermal treatment are being investigated by several groups. Similar to titanate nanotubes, with average diameter of 9 nm, there is a strong controversy regarding the composition and microscopic formation mechanism of these non-hollow nanostructures (nanoribbons). In this article, we report the synthesis and characterization of the titanate nanostructures by exploiting some aspects that were not exploited so far. By using X-ray diffraction, FT-infrared and Raman spectroscopies and electron microscopy, we have studied the intermediate structure and morphology between nanotubes and the non-hollow nanostructures. Our findings give further evidence that the transformation of nanotubes into non-hollow nanostructures is induced by a sequence of both oriented attachment and Ostwald rippening cooperative mechanisms.     

Nonequilibrium Green's function approach to phonon transport in defective carbon nanotubes

We have developed a new theoretical formalism for phonon transport in nanostructures using the nonequilibrium phonon Green's function technique and have applied it to thermal conduction in defective carbon nanotubes. The universal quantization of low-temperature thermal conductance in carbon nanotubes can be observed even in the presence of local structural defects such as vacancies and Stone-Wales defects, since the long wavelength acoustic phonons are not scattered by local defects. At room temperature, however, thermal conductance is critically affected by defect scattering since incident phonons are scattered by localized phonons around the defects. We find a remarkable change from quantum to classical features for the thermal transport through defective carbon nanotubes with increasing temperature.