Preparation of Sn films deposited on carbon nanotubes

In this work carbon nanotubes were first grown on copper substrate by chemical vapor deposition method. The Sn deposits were then deposited on the surface of as-grown carbon nanotubes by three different methods: electroplating, electroless plating and displacing methods. The Sn deposits on CNTs surface were characterized by both scanning electron microscope and field emission scanning electron microscope. The compositions of Sn deposits were analyzed by energy dispersive X-ray spectroscope. The results showed that both electroless plating and displacing deposits can but the electroplating deposits cannot cover on the surface of CNTs. Besides C, Sn, Ni and Pd, the electroless deposits also contain element of oxygen and the displacing deposits also contain elements of copper and oxygen.     

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.     

Superconductivity in thin films of boron-doped carbon nanotubes

Superconductivity in carbon nanotubes (CNTs) is attracting considerable attention. However, its correlation with carrier doping has not been reported. We report on the Meissner effect found in thin films consisting of assembled boron (B)-doped single-walled CNTs (B-SWNTs). We find that only B-SWNT films consisting of low boron concentration leads to evident Meissner effect with Tc=12 K and also that a highly homogeneous ensemble of the B-SWNTs is crucial. The first-principles electronic-structure study of the B-SWNTs strongly supports these results.     

Nanomagnetic domains of chromium deposited on vertically-aligned carbon nanotubes

The drive to create ever smaller magnetic memory devices has led to the development of new nanomagnetic domains on surfaces. This paper reports the development of nano-chromium magnetic domains obtained using electrodeposition on vertically aligned carbon nanofibers arrays. Attempts to achieve this using conventional aqueous solutions were unsuccessful even after thin nickel underlayers were applied. The use of a novel electrolyte, a deep eutectic solvent, made from choline chloride: chromium (III) chloride enabled highly conformal overcoatings of chromium on individual bare carbon nanotubes to be obtained. Very high aspect ratio metal microstructures could be obtained by this novel technology. Magnetic imaging of the coated nanoarrays showed there to be clear magnetic character to the coating when the thin coatings were applied but this disappeared when the deposits were thicker and more contiguous.     

Growth of carbon nanotubes using nanocrystalline carbon catalyst

The basic growth of carbon nanotubes (CNTs) involves dissociation of hydrocarbon molecules over a metal layer as a catalyst. Generally, the metals used for the catalyst include nickel, cobalt, gold, iron, platinum, and palladium. However, the metal catalyst used with CNTs could have a harmful influence on the electrical properties of electronic devices. Therefore, we propose the use of nanocrystalline carbon (nc-C) as the catalyst for the growth of CNTs. We used a nc-C catalyst layer deposited by the closed-field unbalanced magnetron (CFUBM) sputtering method, and CNTs were grown by the hot filament plasma-enhanced chemical vapor deposition (HF-PECVD) method with ammonia (NH₃) as a pretreatment and acetylene gas (C₂H₂) as a carbon source. The CNTs were grown on the nc-C layers pretreated with a variation of the pretreatment time. The characteristics of the pretreated nc-C layers and the grown CNTs were investigated by field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) measurements. Also, the structural variation of the pretreated nc-C layers was investigated by Raman measurement. We used the nc-C catalyst without metal, and we confirmed that our CNTs were composed with only carbon elements through an EDS measurement. Also, the pretreatment time was attributed to the growth of CNTs.     

Synthesis and characterization of carbon nanotubes on carbon microfibers by floating catalyst method

In this paper, carbon nanotubes were synthesized on carbon microfibers by floating catalyst method with the pretreatment of carbon microfibers at the temperature of 1023 K, using C₂H₂ as carbon source and N₂ as carrier gas. The morphology and microstructure of carbon nanotubes were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The composition of carbon nanotubes was determined by energy dispersive X-ray spectroscopy (EDX). The results showed that the surface of treated carbon microfibers was thickly covered by carbon nanotubes with diameters of about 50 nm. EDX image indicated that the composition of carbon nanotubes was carbon. In comparison with the sample grown on untreated carbon microfibers surface, it was found that after carbon microfibers were boiled in the solution of sulfur acid and nitric acid (VH₂SO₄:VHNO₃ = 1:3) and immersed in the solution of iron nitrate and xylene, carbon nanotubes with uniform density can be grown on carbon microfibers surface. Based on the results, we concluded that the pretreatment of carbon microfibers had great effect on the growth of carbon nanotubes by floating catalyst method.     

CVD synthesis and purification of single-walled carbon nanotubes on aerogel-supported catalyst

Single-walled carbon nanotubes (SWNTs) were synthesized by disproportionation of carbon monoxide on an aerogel-supported Fe/Mo catalyst. A simple acidic treatment followed by an oxidation process produced a high purity (>99%) of SWNTs. The nanotubes obtained are bundled SWNTs and free of amorphous-carbon coating. Several factors that affect the yield and the quality of the SWNTs were also studied. This method shows great promise for large-scale production of SWNTs. Received: 30 August 2001 / Accepted: 3 December 2001 / Published online: 4 March 2002     

Transient studies of carbon monoxide oxidation over platinum catalyst

The applicability of transient techniques to the study of the catalytic oxidation of carbon monoxide is discussed. It is shown that at 100–150°C adsorption and desorption equilibria between the gas phase and catalyst cannot be assumed, and an elementary step formulation may be used to predict both multiple steady states and transient behaviour.     

Temperature dependent photoluminescence properties of needle-like ZnO nanostructures deposited on carbon nanotubes

The structural and optical properties of the needle-like ZnO nanostructure grown on the carbon nanotubes (ZnO/CNTs) have been studied by scanning electron microscope (SEM), X-ray diffraction (XRD), and photoluminescence (PL) spectra. It can be seen that there is about tens of nanometers in diameter of the single ZnO nanorod from the SEM picture. The XRD analysis shows that the prepared film is of typical wurtzite hexagonal phase without impurity. Temperature dependence of electronic transitions in the ZnO/CNTs has been investigated by PL in detail. The emission features in near band gap at 10 K reveal a redshift trend compared to ZnO single crystal, which is associated with the strong interfacial connection between ZnO and CNTs. Moreover, the intensities of all transitions in near band gap and visible regions decrease with increasing the temperature but increase with the excitation power. It can be concluded that the combined effect from ZnO and CNTs plays an important role in the PL response. The emission variations with the temperature for the ZnO/CNTs are the result of the electron–phonon interaction and the lattice thermal expansion.     

Electrical properties of boron-doped diamond-like carbon thin films deposited by femtosecond pulsed laser ablation

We report on electrical measurements and structural characterization performed on boron-doped diamond-like carbon thin films deposited by femtosecond pulsed laser deposition. The resistance has been measured between 77 and 300 K using four probe technique on platinum contacts for different boron doping. Different behaviours of the resistance versus temperature have been evidenced between pure DLC and boron-doped DLC. The a-C:B thin film resistances exhibit Mott variable range hopping signature with temperature. Potential applications of DLC thin films to highly sensitive resistive thermometry is going to be discussed.     

Preparation and characterization of amphiphilic multi-walled carbon nanotubes

Multiwalled carbon nanotubes (MWCNTs, average diameter 8 nm) functionalized by N-vinyl pyrrolidone (NVP) were synthesized by radical polymerization and characterized by Fourier transform infrared and Raman spectroscopies, thermogravimetric analysis and transmission electron microscopy. These NVP–MWCNTs exhibit remarkable solubility in water, ethanol and dimethyl formamide. The polyvinyl pyrrolidone can be attached onto the surface of the MWCNTs and the degree of functionalization is affected by NVP content. The functionalization causes possible grafting reaction and solid physical coating between MWCNTs and PVP.     

Preparation and characterization of biocompatible magnetic carbon nanotubes

Magnetic carbon nanotubes consisting of multi-wall carbon nanotubes (MWNTs) core and Fe₃O₄ shell were successfully prepared by in situ thermal decomposition of Fe(acac)₃ or FeCl₃ or Fe(CO)₅ in 2-pyrrolidone containing acid treated MWNTs at 240 °C with the protection of nitrogen gas. The samples were characterized by TEM, XRD, SEAD, XPS and superconducting quantum interference device. Also, their biocompatibility was compared with naked carbon nanotubes. The results showed that after coated with Fe₃O₄ nanoparticles, the obtained magnetic carbon nanotubes show superparamagnetic characteristic at room temperature, and their blocking temperature is about 80 K. The magnetic properties of the nanotubes are relevant to the content of magnetic particles, increasing content of magnetic nanoparticles leads to higher blocking temperature and saturation magnetization. The results of antimicrobial activities to bacterial cells (Escherichia coli) showed that the MWNTs have antimicrobial activity, while the magnetic nanotubes are biocompatible even with a higher concentration than that of MWNTs.     

采用旋转涂膜法制备基底生长的定向碳纳米管阵列

 采用化学气相沉积技术,利用旋转涂膜法制备催化剂基底材料,通过对涂膜过程中的角速度、旋转时间以及基底还原过程中温度的控制改变催化剂颗粒的分布状态,获得了粒径均匀分布的催化剂基底,该基底上催化剂颗粒集中分布在47～62 nm区间,再利用该基底生长出定向碳纳米管阵列。运用扫描电镜、透射电镜、拉曼光谱仪对样品进行了表征。结果表明旋转涂膜法制备的基底平整性好于普通的滴膜法,且较其它基底制备方法具有简单易控、可使催化剂均匀分散等特点。利用该基底制备的碳纳米管阵列定向性良好。     

强流碳纳米管阴极重复频率发射特性

采用钛氰铁高温催化热解方法可制备发射性能优异的碳纳米管薄膜阴极。当脉冲电场峰值达到30 MV/m时,发射电流密度达kA/cm2以上,对应相对论电子束流强度高达15 kA,等离子体发射机制参与电子束发射过程。以重复频率10 Hz发射模式时,其发射阈值低,束压、束流波形跟随性好,发射稳定性优于石墨阴极。发射发次达到1000后,碳纳米管形态依然完整,界面无脱附。     

Nucleation of catalyst clusters during the growth of carbon nanotubes

The formation of cluster in the course of pyrolysis of ferrocene is studied experimentally and theoretically, and the parameters of the clusters are determined. The thermodynamics of homogeneous formation of catalyst clusters is developed. It is shown that the surface tension and sizes of the clusters substantially depend on the temperature and the properties of the substrate. Surface tension coefficients, as well as the characteristic sizes of clusters, are calculated. The resultant dependences and parameters make it possible to reconstruct the size distribution function for the clusters growing on a certain substrate by setting the temperature in the working zone. This permits the prediction of the cluster size depending on the synthesis conditions.     

强流碳纳米管阴极重复频率发射特性

采用钛氰铁高温催化热解方法可制备发射性能优异的碳纳米管薄膜阴极。当脉冲电场峰值达到30 MV/m时,发射电流密度达kA/cm2以上,对应相对论电子束流强度高达15 kA,等离子体发射机制参与电子束发射过程。以重复频率10 Hz发射模式时,其发射阈值低,束压、束流波形跟随性好,发射稳定性优于石墨阴极。发射发次达到1000后,碳纳米管形态依然完整,界面无脱附。     

Field electron emission form single-walled carbon nanotubes with deposited cesium atoms

It has been found that deposition g of cesium atoms on single-walled carbon nanotubes covered with potassium atoms not only drastically increases emission current but also considerably changes the shape of current-voltage characteristics of field electron emission, namely, the characteristics become nonlinear in Fowler-Nordheim coordinates. It has been assumed that this effect is associated with the fact that field electron emission in these layers comes from single-walled carbon nanotubes, which have p-type conductivity after potassium treatment, while deposition of cesium leads to the formation of p-n junctions near nanotube tips. Part of the applied voltage drops in p-n junction, thus causing a nonlinearity of current-voltage characteristics.     

STM/STS investigation of carbon nanotubes deposited on Bi2Te3 surface

This paper reports our scanning tunneling microscopy and spectroscopy (STM/STS) study of double-walled and multi-walled carbon nanotubes (CNTs) of different diameter deposited on Bi₂Te₃ (narrow gap semiconductor). The approximate diameter of the studied double-walled and multi-walled CNTs was 2 nm and 8 nm, respectively. Crystalline Bi2Te3 was used as a substrate to enhance the contrast between the CNTs and the substrate in the STS measurements performed to examine peculiarities of CNT morphology, such as junctions, ends or structural defects, in terms of their electronic structure.      

Preparation and characterization of carbon nanotubes encapsulated GaN nanowires

A novel two-step catalytic reaction is developed to synthesize gallium nitride nanowires encapsulated inside carbon nanotubes (GaN@CNT). The nanowires are prepared from the reaction of gallium metal and ammonium using metals or metal alloys as a catalyst. After the formation of the nanowires, carbon nanotubes are subsequently grown along the nanowires by chemical vapor deposition of methane. The structural and optical properties of pure GaN nanowires and GaN@CNT are characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy and Raman spectroscopy. The results show that GaN nanowires are indeed encapsulated inside carbon nanotubes. The field emission studies show that the turn-on field of GaN@CNT is higher than that of carbon nanotubes, but substantially lower than that of pure GaN nanowires. This work provides a wide route toward the preparation and applications of new one-dimensional semiconductor nanostructures.