Preferentially oriented vanadium nitride films deposited by magnetron sputtering

Because of solid state lubricious properties of vanadium oxides, wear resistant coatings based on nitrides and carbides of that metal are still of interest for research teams. The aim of this report is to show phase composition evolution from metallic vanadium through intermediate phases up to δ-VN phase supersaturated with nitrogen in thin films deposited by reactive, pulsed magnetron sputtering from vanadium target. This analysis is completed by remarks on preferential orientation, lattice constant and crystallite size. Presented work is a part of research on composite hard coatings for woodworking tools where vanadium nitrides and carbides are considered as a component reducing friction.     

Facile synthesis of boron nitride coating on carbon nanotubes

Boron nitride (BN) coating on the surface of carbon nanotubes (CNTs) was synthesized by the direct reaction of NaBH₄ and NH₄Cl in the temperature range of 500–600 °C. X-ray diffraction, field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) confirm the formation of BN coating. It is revealed that the BN coating follows the shape of CNTS without damaging the surface of CNTs, and the elements B and N distribute homogenously along the whole CNTs without chemical bonds between carbon and BN layers. Besides, the oxidation resistance of the CNTs improved a lot after being coated with BN.     

Removal of vanadium from wastewater by multi-walled carbon nanotubes

Nitric acid heating reflux modified multi-walled carbon nanotubes (HMWCNTs) were used for the removal of vanadium(V) in aqueous solution. The removal rate of vanadium(V) decreased with the increase of the initial vanadium(V) concentration and the solution pH, and increased with the increase of reaction time, HMWCNTs amount and solution temperature. The adsorption equilibrium and dynamic kinetics fitted the Langmuir adsorption isotherm and pseudo-second order models. The results obtained by scanning electron micrography and Fourier transform infrared spectroscopy analysis revealed that the hydroxyl and carboxyl functional groups are mainly responsible for the vanadium adsorption. This study showed that the HMWCNTs proved to be a considerable adsorbent for the removal of vanadium from wastewater.     

Growth of carbon nanotubes on diatomite

We report the formation of vertical carbon nanotubes utilizing diatomite as a substrate. This new material combines the advantages of carbon nanotubes and diatomite in one material. The SEM investigations showed that the average diameter of the carbon nanotubes was 60 nm and the growth was through the tip growth mechanism. Raman spectroscopy was also used for the carbon nanotubes characterization and showed two intensive peaks around 1350 cm⁻¹ and 1580 cm⁻¹ and several peaks at low frequency range from 100 cm⁻¹ to 500 cm⁻¹ which are assigned to the radial breathing mode (RBM) and used as a characteristic of single wall carbon nanotubes. The photoluminescence measurements at the room temperature showed two very narrow intensive overlapping peaks near the ultraviolet range at energy of about 3 eV. And there are two peaks with lower intensity in the infrared region at 830 nm and at 940 nm (or 1.49 eV, 1.3 eV respectively).     

碳纳米管的改性与应用

本文主要介绍对碳纳米管不同位置的修饰以及其应用等方面的研究进展,并对今后的研究方向进行展望.     

Thermal stability of magnetron sputtering amorphous carbon nitride films

Magnetron sputtered amorphous carbon nitride films were annealed at different temperatures (450-900°C) and time (30-120 min). Compositional, bonding structural and surface morphological modifications of the films were characterized by Fourier transformation infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy. The as-deposited film was found to have nitrogen content of 30 at%, and the carbon atoms were bonded to nitrogen atoms in the chemical structure state of CN, CN and CN bonds. The FTIR and XPS results showed that the films were thermally stable without an obvious change in the films as annealing temperature was lower than 600°C. The relative intensity ratio of CN over CN bonds reached a maximum at annealing temperature of 750°C, and then decreased gradually at annealing temperature up to 900°C. The CN bonds in the films decreased with the increase of annealing temperature and eliminated completely at annealing temperature of 900°C. These results revealed that annealing caused a substantial decrease in the number of weak bonds between carbon and nitride atoms. The CN bonds have higher thermal stability than CN bonds and CN bonds in the films. Simultaneously annealing also led to the formation of a large fraction graphitic-like carbon in the films while nitrogen escaped from the film. Besides, the surface roughness of the films increased with annealing temperature. However, when annealing time was increased from 30 to 120 min at annealing temperature of 750°C, only a slight effect of the annealing time on composition, bonding structure and the surface roughness of the films was observed.     

Coating of carbon nanotubes with amorphous carbon nitride thin films and characterization of long-term emission stability

The effects of amorphous carbon nitride (CN) thin films that were coated on carbon nanotubes (CNTs) and their thermal treatment were investigated, in terms of the chemical bonding and morphologies of the CNTs and their field emission properties. CNTs were directly grown on conical tip-type tungsten substrates via the inductively coupled plasma-chemical vapor deposition (ICP-CVD) system, and the CNTs were coated with CN films using the RF magnetron sputtering system. The CN-coated CNTs were thermally treated using the rapid thermal annealing (RTA) system by varying the temperature (300-700 °C). The morphologies, microstructures, and chemical compositions of the CN-coated CNTs were analyzed as a function of the thickness of the CN layers and the RTA temperatures. The field emission properties of the CN/CNT hetero-structured emitters, and the fluctuation and long-term stability of the emission currents were measured and compared with those of the conventional non-coated CNT-emitter. The results showed that the electron emission capability of CNT was noticeably improved by coating a thin CN layer on the surface of the CNT. This was attributed to the low work function and negative electron affinity nature of the CN film. The CN-coated CNT-emitter had a more stable emission characteristic than that of the non-coated one. In addition, the long-term emission stability of the CN-coated emitter was further enhanced by thermal treatment, which was verified by x-ray photoelectron spectroscopy (XPS) analysis.     

Curved carbon nanotubes: From unique geometries to novel properties and peculiar applications

Incorporating pentagons and heptagons into the hexagonal networks of pristine carbon nanotubes （CNTs） can form various CNT-based nanostructures, as pentagons and heptagons will bend or twist the CNTs by introducing positive and negative curvature, respectively. Some typical so-made CNT-based nanostructures are reviewed in this article, including zero-dimensional toroidal CNTs, and one-dimensional kinked and coiled CNTs. Due to the presence of non-hexagonal rings and curved geometries, such nanostructures possess rather different structural, physical and chemical properties from their pristine CNT counterparts, which are reviewed comprehensively in this article. Additionally, their synthesis, modelling studies, and potential applications are discussed.     

Improved conductivity and capacitance of interdigital carbon microelectrodes through integration with carbon nanotubes for micro-supercapacitors

In the last decade,pyrolyzed-carbon-based composites have attracted much attention for their applications in micro-supercapacitors.Although various methods have been investigated to improve the performance of pyrolyzed carbons,such as conductivity,energy storage density and cycling performance,effective methods for the integration and mass-production of pyrolyzed-carbonbased composites on a large scale are lacking.Here,we report the development of an optimized photolithographic technique for the fine micropatterning of photoresist/chitosan-coated carbon nanotube (CHIT-CNT) composite.After subsequent pyrolysis,the fabricated carbon/CHIT-CNT microelectrode-based micro-supercapacitor has a high capacitance (6.09 mF.cm-2) and energy density (4.5 mWh.cm-3) at a scan rate of 10 mV.s-1.Additionally,the micro-supercapacitor has a remarkable long-term cyclability,with 99.9％ capacitance retention after 10,000 cyclic voltammetry cycles.This design and microfabrication process allow the application of carbon microelectromechanical system (C-MEMS)-based micro-supercapacitors due to their high potential for enhancing the mechanical and electrochemical performance of micro-supercapacitors.     

W doped vanadium oxide nanotubes: Synthesis and characterization

W doped vanadium oxide nanotubes (VONTs) were prepared via a rheological phase reaction followed by self-assembling process. The nanotubes were characterized by elemental analysis, IR, XRD, SEM, TEM, HRTEM, SAED and XPS. Elemental analysis, IR, XRD, SAED and XPS could confirm the crystalline characteristic of the W doped VONTs, while the SEM, TEM, and HRTEM confirmed their morphology and microstructure.     

Growth of long aligned carbon nanotubes on amorphous hydrogenated silicon nitride by thermal chemical vapor deposition

Vertically aligned long carbon nanotubes in the range of 80-100 µm have been synthesized on amorphous hydrogenated silicon nitride (a-SiN_x:H) coated silicon substrate by thermal chemical vapor deposition of ferrocene and xylene. It is observed that high temperature annealing in oxygen ambient results in formation of crystalline silicon dioxide in the matrix of amorphous silicon nitride due to out diffusion of hydrogen. It is suggested that active sites created on silicon dioxide and a-SiN_x:H clusters provide mechanical support for the alignment of long carbon nanotubes. It is proposed that a thin layer of a-SiN_x:H prevents silicide formation between the catalyst (Fe) and silicon thus lengthening the catalyst life.     

Direct growth of carbon nanotubes on hydroxyapatite using MPECVD

For the first time carbon nanotubes (CNTs) have been successfully grown directly on hydroxyapatite (HA) by using microwave plasma enhanced chemical vapor deposition (MPECVD). Such integration has potential to capitalize on the merits of both HA and CNTs. This type of coating could be useful to improve the interface between bone and the implant. Scanning electron microscope SEM investigations show that; the surface of the CNTs is relatively clean and free of amorphous carbon. The CNTs diameters lie in the range 30-70 nm. In addition HA encapsulation by carbon was observed at a growth temperature 750 °C. Raman spectroscopy indicates that the CNTs are of high quality and the I_G/I_D ratio lies between 1.243 and 1.774. The changes in the X-ray diffraction (XRD) patterns give an indication that during the plasma deposition the HA-substrate surface is subjected to a temperature sufficient for partial conversion to the β-tricalcium phosphate via dehydroxylation.     

碳纳米管的等离子体功能化及其聚苯胺复合材料的制备

采用等离子体技术对碳纳米管(CNTs)功能化,而后与苯胺原位聚合制备CNTs/聚苯胺(PANI)复合材料。电导测试结果表明:相对于CNTs的强酸氧化法(0.936S/cm),等离子体处理更易获得高电导率的复合材料(2.86S/cm)。相应的最佳等离子体工艺参数为:处理功率50W、时间5min、压力0.08Torr、温度110℃、磁场线圈电流0.08A及电极距离5cm。SEM观察发现:聚合后,CNTs的光滑表面转变成粗糙结构,同时管径增加了80nm。XRD、FTIR及Raman结果均证实:PANI被均匀包覆于CNTs的表面。     

Carbon nanotubes growth on silicon nitride substrates

Carbon nanotubes were synthesized on silicon nitride substrates by thermal chemical vapour deposition using an iron precursor catalyst. The nanotubes were characterized by AFM, FESEM, TEM and micro-Raman spectroscopy. The surface topography of the substrate, dense and flat or porous and rough, controlled the catalyst distribution and carbon nanotubes growth. Flat surfaces led to the synthesis of single-walled carbon nanotubes, whereas the porous ones promoted the growth of multi-walled carbon nanotubes of 60 nm diameter. These nanotubes preferentially grew on the porous sites, exhibiting a good substrate-nanotube interface.     

An effective precursor for growth of bubble-chain boron nitride nanotubes

Large amounts of bubble-chain boron nitride nanotubes were synthesised by annealing an effective precursor. The porous precursor was produced by self-propagation high-temperature synthesis method using Mg, B₂O₃, amorphous B and Fe₂O₃ as the starting materials, which played an important role in synthesis of BN nanotubes in large quantities. Samples were characterised by SEM, TEM, HRTEM, X-ray powder diffraction and Raman and Fourier transform infrared spectroscopy. The as-synthesised BN nanotubes revealed periodical bubble-chain structures, having diameters of range 20–200?nm?and an average length of more than 5?µm. The effects of temperature, time and the possible mechanism of the growth of the BN nanotubes were also discussed.     

Deformation mechanisms for carbon and boron nitride nanotubes

Molecular dynamics simulation in the density functional tight-binding approximation is used to assess the energetics and atomic mechanisms of the bending and twisting of carbon and boron nitride nanotubes.     

Supported Pt-particles on multi-walled carbon nanotubes with controlled surface chemistry

Multi-walled carbon nanotubes (MWCNTs) were functionalized by HNO₃ hydrothermal oxidation at 200 °C. The degree of surface functionalization was described by an exponential function in terms of HNO₃ concentration. Very small Pt particles, with mean particle size of 1.7 ± 0.3 nm, could be supported on the surface of pristine MWCNTs and also on MWCNTs treated with HNO₃ concentrations up to 0.20 mol L^− 1, while a broader range of particle sizes, and larger Pt particles (3.4 ± 1.3 nm) were obtained on the MWCNTs treated with a higher HNO₃ concentration (0.30 mol L^− 1). Therefore, the amounts of surface groups and Pt particle sizes can be selected by tuning the HNO₃ concentration used in the hydrothermal treatment.     

An ultra-sensitive room temperature toluene sensor based on molten-salts modified carbon nitride

In this work, two-dimensional crystalline C₃N₄ (CCN) was obtained by promoting the self-condensation reaction of dicyandiamide in an air atmosphere via the molten salt method. Studies show that compared with polymer-C₃N₄ (PCN) ((9.8 m²/g)), CCN has a larger specific surface area (77.1 m²/g)) and better crystallinity. Additionally, the resistance of CCN in the air is 40 MΩ, 1250 times lower than that of polymer-C₃N₄ (PCN) (∼50000 MΩ). Secondly, when 50 ppm toluene gas analysis flows into the CCN based gas sensor at room temperature, the gas response value is 350. The CCN based gas sensor works for 60 days, or after 25 cycles continuously, the gas response value remains at about 350 (R_g/R_a), which is due to the excellent crystallinity, optimized π conjugate system, and enhanced interlayer van der Waals of CCN. Additionally, the critical effect of crystallinity on the gas sensitivity of carbon nitride is also discussed in detail.     

Multi-scale electrical response of silicon nitride/multi-walled carbon nanotubes composites

Dense silicon nitride (Si₃N₄) composites with various amounts (0-8.6 vol%) of multi-walled carbon nanotubes (MWCNTs) are electrically characterised by combining macroscopic dc-ac and nanoscale conductive scanning force microscopy (C-SFM) measurements. In this way, a coherent picture of the dominant charge transport mechanisms in Si₃N₄/MWCNTs composites is presented. A raise of more than 10 orders of magnitude in the electrical dc conductivity compared to the blank specimen is measured for MWCNTs contents above 0.9 vol%. Semiconductor and metallic-like behaviours are observed depending on both the temperature and the MWCNTs content. Macroscopic measurements are further supported at the nanoscale by means of C-SFM. The metallic-type conduction is associated to charge transporting along the nanotube shells, whereas the semiconductor behaviour is linked to hopping conduction across nanotube-nanotube contacts and across intrinsic defect clusters within the nanotubes.     

氮化碳薄膜的电化学沉积及其电阻率研究

在ITO导电玻璃基底上,采用二氰二胺分散在DMF(N,N-二甲基甲酰胺)中形成的溶液做沉积液,阴极电化学沉积了CNx薄膜。X射线光电子能谱(XPS)和傅立叶转换红外光谱(FTIR)的分析结果表明,沉积的CNx薄膜的N/C比为0.7左右,碳和氮主要以C-N、C=N的形式成键,有少量的碳和氮以C≡N的形式成键。拉曼光谱测试发现其存在多个吸收峰,对其进行分析的结果表明薄膜样品中含有α-C3N4和β-C3N4相的成分。电阻率测试表明,氮化碳薄膜的电阻率值达到1012～1013Ω·cm。