Characterisation of carbonaceous materials using Raman spectroscopy: a comparison of carbon nanotube filters,single‐ and multi‐walled nanotubes,graphitised porous carbon and graphite

Multi‐walled carbon nanotube (MWCNT) filters have been recently synthesised which have specific molecular filtering capabilities and good mechanical strength. Optical and scanning electron microscopy (SEM) reveals the formation of highly aligned arrays of bundles of carbon nanotubes having lengths up to 500 µm. The Raman spectra of this material along with four other carbonaceous materials, commercially available single‐walled carbon nanotubes (SWCNTs) and MWCNTs, graphitised porous carbon (Carbotrap) and graphite have been recorded using two‐excitation wavelengths, 532 and 785 nm, and analysed for band positions and shape with special emphasis paid to the D‐, G‐ and G′‐bands. A major difference between the different MWCNT varieties analysed is that G‐bands in the MWCNT filters exhibit almost no dispersion, whereas the other MWCNTs show a noticeable dispersive behaviour with a change in the excitation wavelength. Spectral features similar to those of the MWCNT filter varieties were observed for the Carbotrap material. From the line shape analysis, the intensity ratio, I_D/I_G, of the more ordered MWCNT filter material using the integral G‐band turns out to be two times lower than that of the less ordered MWCNT filter product at both excitation wavelengths. This parameter can, therefore, be used as a measure of the degree of MWCNT alignment in filter varieties, which is well supported also by our SEM study. Copyright © 2008 John Wiley & Sons, Ltd.     

Electrical conductivity and electromagnetic interference shielding characteristics of multiwalled carbon nanotube filled polyacrylate composite films

Multiwalled carbon nanotubes (MWCNTs) were homogeneously dispersed in pure acrylic emulsion by ultrasonication to prepare MWCNT/polyacrylate composites applied on building interior wall for electromagnetic interference (EMI) shielding applications. The structure and surface morphology of the MWCNTs and MWCNT/polyacrylate composites were studied by field emission scanning microscopy (FESEM) and transmission electron microscopy (TEM). The electrical conductivity at room temperature and EMI shielding effectiveness (SE) of the composite films on concrete substrate with different MWCNT loadings were investigated and the measurement of EMI SE was carried out in two different frequency ranges of 100-1000 MHz (radio frequency range) and 8.2-12.4 GHz (X-band). The experimental results show that a low mass concentration of MWCNTs could achieve a high conductivity and the EMI SE of the MWCNT/polyacrylate composite films has a strong dependence on MWCNTs content in both two frequency ranges. The SE is higher in X-band than that in radio frequency range. For the composite films with 10 wt.% MWCNTs, the EMI SE of experiment agrees well with that of theoretical prediction in far field.     

Observation of the diameter-dependent Raman dispersion effect in chemically oxidized multiwalled carbon nanotubes

Chemical oxidation of multiwalled carbon nanotubes (MWCNTs) using H₂SO₄/HNO₃ solution has been monitored by micro-Raman spectroscopy and X-ray absorption spectroscopy. The diameter distribution variation in MWCNTs due to chemical oxidation has been measured by scanning electron microscopy and transmission electron microscopy. The Raman dispersion behaviors of the intensity ratio and the band positions of the D, G, and G′ bands were found to be correlated with the MWCNT diameter distribution. It was also found that, during the nanotube unzipping process, defect formation complicates the observation of the diameter-dependent Raman dispersion effect. The curvature effect plays an important role in the intensity ratio trend. On the other hand, defect formation dominates the band position trend.     

Preparation, characterization and photocatalytic activity of multi-walled carbon nanotube-supported tungsten trioxide composites

Multi-walled carbon nanotube (MWCNT)-supported tungsten trioxide (WO₃) composite catalysts were prepared by liquid-phase process. WO₃ nanoparticles grew on the inner and outer surface of MWCNTs. Their photocatalytic activities in the degradation of the Rhodamine B Dye were studied. The effects of mass ratio of MWCNTs to WO₃ were discussed. X-ray diffraction, field emission transmission electron microscopy, thermogravimetric-differential thermal analysis and ultraviolet-visible light absorption spectra were carried out to characterize the composite catalysts. The results indicated that the optimum mass ratio of MWCNTs to WO₃ is 5:100.     

Ternary semiconductor compounds CuInS2 (CIS) thin films synthesized by electrochemical atomic layer deposition (EC-ALD)

In this paper the formation and characterization of the I-III-VI₂ semiconductor compound CuInS₂ (CIS) on gold substrate at room temperature by electrochemical atomic layer deposition (EC-ALD) method are reported. Optimum deposition potentials for each element are determined using cyclic voltammetry (CV) technique and Amperometric I-t method is used to prepare the semiconductor compound. These thin films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared spectroscopy (FT-IR). XRD results indicate that the CIS thin films have a (1 1 2) preferred orientation. The XPS analyses of the films reveal that Cu, In and S are present in an atomic ratio of approximately 1:1:2. And their semiconductor band gaps are found to be 1.50 eV by FT-IR.     

A comparison of the magnetic and microwave absorption properties of Mn–Sn–Ti substituted strontium ferrite with and without multi-walled carbon nanotube

In this work, a comparison of magnetic and microwave properties between Mn–Sn–Ti substituted SrM ferrite and nanocomposite of Mn–Sn–Ti substituted SrM ferrite–20% volume multi-walled carbon nanotube (MWCNT) has been done. Phase characterization and crystal structure of the synthesized nanoparticles were tested by X-ray diffraction (XRD). Field emission scanning electron microscopy (FESEM), Fourier transform infrared spectrometry (FTIR) analysis approved that the SrFe_12−x(MnSn_0.5Ti_0.5)_x/2O₁₉ nanoparticles were attached on the external surfaces of the MWCNTs. Mӧssbauer spectroscopy (M_S) showed the occupancy by non-magnetic Mn²⁺–Sn⁴⁺–Ti⁴⁺ cations into the hexagonal lattice structure. Magnetic properties were evaluated by a vibrating sample magnetometer (VSM). The results also indicated that saturation magnetization and coercivity were decreased with an increase in x content and also MWCNTs addition. Microwave absorption properties were investigated by a vector network analyzer (VNA). It was found that with an addition of 20 volume percentage of MWCNTs, the saturation magnetization coupled with coercivity decrease, but reflection loss (RL) increase broadly. Also it proved that with an increase in the thickness of absorption the frequency band shifts from K_u (12–18 GHz) to X (8–12 GHz) band.     

Vitamin C functionalized multi-walled carbon nanotubes and its reinforcement on poly(ester-imide) nanocomposites containing L-isoleucine amino acid moiety

The aim of this research was to prepare poly(ester–imide) (PEI)-based nanocomposites (NCs) through the functionalization of carboxylated-multiwalled carbon nanotubes (MWCNT)s with ascorbic acid, in order to ensure better filler dispersion and good interfacial adhesion between filler and matrix. Chiral and biodegradable PEI was synthesized from amino acid-based diacid with 4,4′-thiobis(2-tert-butyl-5-methylphenol) by a direct polycondensation method. Using the solution mixing technique, the NCs containing modified MWCNTs with different loading levels of 5,10, 15 wt% were produced and examined in terms of chemical structure, morphology, and thermal stability by FT-IR spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction, transmission electron microscopy (TEM), and field emission scanning electron microscopy (FE-SEM). TEM and FE-SEM photographs of the obtained NCs indicated well-dispersed morphologies and strong interaction between the functionalized MWCNTs and the polymer matrix. TGA results revealed that the addition of MWCNT resulted in a significant increase of the thermal stability and char yields of the NCs compared to those of the neat PEI.     

Synthesis of modified multi-walled carbon nanotube poly(benzimidazole-imide) composites: assessment of morphological and thermo-mechanical properties

A fully aromatic poly(benzimidazole-imide) (PBI) containing triazole side units and amine-modified multi-wall carbon nanotube (MWCNT)/PBI composites were fabricated via a polymerization process of monomer reactants and solution mixing with ultrasonication excitation. The polymer and composites were characterized by field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction. According to the microscopic characterizations, the MWCNTs homogeneously dispersed in the composites. The mechanical properties of the composite films were also measured by tensile test. The test results evidently indicated that the Young’s modulus increased by about 60.0% at 1 wt% CNT loading, and further modulus growth was observed at higher filler loading. The composite films hold preferable thermal stability the same as the pure PBI. The improvement of the mechanical and thermal properties was attributed to the incorporation of the surface modified CNTs. For CNT-reinforced polymer composites, strong interfacial adhesion and uniform dispersion of CNTs are more crucial factors for improving such properties.     

Influence of plasma pressure on the growth characteristics and ferroelectric properties of sputter-deposited PZT thin films

PZT thin films of thickness (320-1040) nm were synthesized on Si/SiO₂/Ti/Pt multilayered substrates by radio frequency magnetron sputtering. The influence of plasma pressure in the range of (0.24-4.9) Pa, during deposition, on the structural, electrical and ferroelectric properties of the PZT films was systematically studied. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and cross-sectional transmission electron microscopy (XTEM) were employed for structural study. Nano-probe Energy Dispersive (EDX) line scanning was employed to investigate the elemental distribution across the film-bottom electrode interface. I-V characteristics and polarization-electric field (P-E) hysteresis loop of the films were measured. The study reveals that the plasma pressure has a strong influence on the evolution and texture of the ferroelectric perovskite phase and microstructure of the films. At an optimum plasma pressure of 4.1 Pa, PZT films are grown with 93% perovskite phase with (1 1 1) preferred orientation and uniform granular microstructure. These films show a saturation polarization of 67 μC/cm², remnant polarization of 30 μC/cm² and coercive field of 28 kV/cm which, according to the literature, seem to be suitable for device applications.Transmission electron microscopy (TEM) study shows that at a plasma pressure of 4.1 Pa, the PZT/bottom Pt interface is sharp and no amorphous interlayer is formed at the interface. At a higher plasma pressure of 4.9 Pa, poor I-V and P-E hysteresis loop are observed which are interpreted as due to an amorphous interlayer at the film-bottom electrode interface which is possibly enriched in Pb, Zr, O and Pt.     

Remarkable influence of carbon nanotubes on microwave absorption characteristics of strontium ferrite/CNT nanocomposites

In this research work, magnetic multi-walled carbon nanotube (MWCNT) nanocomposites have been created by the assembly of Zn-Sn substituted strontium ferrite film onto the surface of MWCNTs. X-ray diffraction and transmission electron microscopy were used to demonstrate the successful attachment of ferrite films to MWCNTs. Mössbauer spectroscopy indicates that the Zn-Sn ions preferentially occupy the 2b and 4f₂ sites. Vibrating sample magnetometry confirms the relatively strong dependence of saturation magnetization with the volume percentage of MWCNTs. Microwave absorption of the MWCNTs/doped strontium ferrite nanocomposites is evidently enhanced compared to that of pure MWCNTs and ferrite. The maximum reflection loss increased significantly with an increase in volume percentage of MWCNTs in nanocomposites. Reflection loss evaluations indicated that the nanocomposites display a great potential application as wide-band electromagnetic wave absorbers.     

Synthesis of carbon nanotubes on diamond-like carbon by the hot filament plasma-enhanced chemical vapor deposition method

Carbon nanotubes (CNTs) have attracted considerable attention as possible routes to device miniaturization due to their excellent mechanical, thermal, and electronic properties. These properties show great potential for devices such as field emission displays, transistors, and sensors. The growth of CNTs can be explained by interaction between small carbon patches and the metal catalyst. The metals such as nickel, cobalt, gold, iron, platinum, and palladium are used as the catalysts for the CNT growth. In this study, diamond-like carbon (DLC) was used for CNT growth as a nonmetallic catalyst layer. DLC films were deposited by a radio frequency (RF) plasma-enhanced chemical vapor deposition (RF-PECVD) method with a mixture of methane and hydrogen gases. CNTs were synthesized by a hot filament plasma-enhanced chemical vapor deposition (HF-PECVD) method with ammonia (NH₃) as a pretreatment gas and acetylene (C₂H₂) as a carbon source gas. The grown CNTs and the pretreated DLC films were observed using field emission scanning electron microscopy (FE-SEM) measurement, and the structure of the grown CNTs was analyzed by high resolution transmission scanning electron microscopy (HR-TEM). Also, using energy dispersive spectroscopy (EDS) measurement, we confirmed that only the carbon component remained on the substrate.     

类富勒烯纳米晶CNx薄膜及其场致电子发射特性

利用微波等离子体增强化学气相沉积技术制备出了CN_x薄膜,并利用x射线光电子能谱、x射线衍射、扫描电子显微镜和Raman光谱等测试手段对所制备的CN_x薄膜的微结构和成分进行了分析.研究了其场致电子发射特性.发现薄膜的结构和场发射特性与反应系中的甲烷、氮气及氢气的流量比有关,当甲烷、氢气及氮气流量比为8/50/50 sccm时,制备的薄膜具有弯曲层状的纳米石墨晶体结构（类富勒烯结构）和很好的场发射特性.场发射阈值电场降低至1.1V/μm.当电场为5.9V/μm时,平 关键词： 类富勒烯 x薄膜')" href="#">CN_x薄膜 场致电子发射 微波等离子体增强化学气相沉积     

Efficient field emission from well-oriented Cu2O film

Well-oriented Cu₂O films comprising of octahedral-shaped crystals were grown directly on copper foil via an hydrothermal treatment. The well-oriented films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Field emission from the film showed good emission properties, and, the electron emission turn-on field (E_to) and threshold field (E_thr) are about 9.6 and 13.4 V/μm respectively, which is similar to the values reported for CuO nanofiber, although the latter has a much larger size. The corresponding Fowler-Nordheim (F-N) plots showed a linear behavior. The sharp corners of the tips are considered as main electron emitters and account for its good performance.     

Photoconductivity and photoluminescence in chemically deposited films of CdSSe:CdCl2,Ho

Results of the scanning electron microscopy (SEM), X-ray diffraction (XRD), optical absorption, photoconductivity (PC), and photoluminescence (PL) studies for the CdSSe:CdCl₂,Ho films are presented in this paper. The SEM studies of different CdSSe films show a layered growth structure. A crystalline nature of the films is observed in the XRD studies. The regions with stacking fault were also observed in the X-ray diffractograms. The optical absorption spectra of these films show variations corresponding to the band gaps and the grain-sizes obtained under various deposition conditions and also with annealing. The effect of flux, impurities and annealing on the saturated photo to dark current ratio I_pc/I_dc is observed in the PC rise and decay studies. The maximum value of I_pc/I_dc ∼10⁷ is obtained for the impurity doped annealed films. The PL emission spectra of CdSSe films show two emission peaks associated with the annihilation of free excitons and the transitions between shallow donor and deep acceptor states. In CdSSe:CdCl₂,Ho films, two PL emission peaks are observed at 495 nm and 545 nm corresponding to the transitions ⁵S₂→⁵I₈ and ⁵F₃→⁵I₈, respectively, in Ho. The effect of pH on PL and grain size is also included in the present studies.     

Temperature dependence and the effect of hydrogen peroxide on ITO/poly-ZnO Schottky diodes fabricated by laser evaporation

Transparent and efficient poly-ZnO ultraviolet Schottky diodes grown at different temperatures with indium-tin-oxide (ITO) as the metallic contact layer were fabricated with hydrogen peroxide (H₂O₂) applied as a surface treatment at 70 °C for 20 min. Analysis via field-emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS) demonstrated that the ZnO films underwent gradual oxidation and that H₂O₂ treatment resulted in an interfacial ZnO₂ layer that covered the ZnO surface. I–V measurements indicated that the ideality factor and the Schottky barrier height improved with increasing shunt resistance, and the trade-off between film quality and the degree of oxidation revealed that films grown at 400 °C exhibited the best diode characteristics.     

Morphology controlled solvothermal synthesis of Cd(OH)2 and CdO micro/nanocrystals on Cd foil

Cadmium hydroxide (Cd(OH)₂) and cadmium oxide (CdO) nano and micro crystals were synthesized in ethanol-water medium using cadmium foil both as a source and substrate under solvothermal condition. Different concentrations of ammonium hydroxide, hydrazine hydrate, sodium hydroxide and potassium hydroxide were added to study the structural and morphological variations in the products. Synthesis was carried out at different temperatures to study the growth stages of the nano/microstructures. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The as-prepared Cd(OH)₂ products were transformed to CdO by thermal treatment in air. The possible growth mechanism for the formation of different morphologies at different basic medium has been proposed. The optical absorption measurement was carried out to determine the values of the band gap of CdO.     

Assessment of the Microstructure and Mechanical Properties of Polycarbonate (PC)/Acrylonitrile Butadiene Rubber (NBR) Blends Reinforced with Multi-wall Carbon Nanotubes

Abstract

A series of polycarbonate (PC)/acrilonitrile butadiene rubber (NBR)/multi-wall carbon nanotube (MWCNT) nanocomposites were prepared via melt compounding in an internal mixer. The effect of the MWCNT content on the morphology and the thermal and mechanical properties of the prepared nanocomposites were studied. The morphologies of the samples were investigated by field-emission scanning electron microscopy (FESEM) and the thermal properties by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The tensile mechanical results of the nanocomposites showed a decrease in elongation at break with an increase of only 2?wt% of MWCNT content in the PC/NBR blends, and an increasing value in elastic modulus and tensile strength of the nanocomposites. The FESEM images showed that the MWCNTs had good affinity with the polymers and no compatibilizer was needed for making the nanocomposites. The DSC and TGA results showed an increase in thermal stability with addition of MWCNTs because of the more thermally stable carbon nanotubes particles which was uniformly dispersed within the nanocomposites.     

不同氮源制备CNx纳米管薄膜及其低场致电子发射性能

采用高温热解法，分别以氯化铵(NH₄Cl)和乙二胺(C₂H₈N₂)为氮源在洁净的硅片上沉积生长CN_x纳米管薄膜.利用扫描电子显微镜、高分辨率透射电子显微镜和拉曼光谱对CN_x纳米管进行形貌观察和表征.结果显示不同氮源制备出的CN_x纳米管薄膜的洁净度、有序度以及纳米管的结构明显不同.热解乙二胺(C₂H₈N₂)/二茂铁(C₁₀H₁₀Fe)制备出的结晶度较低的“竹节状” 结构CN_x纳米管平行基底表面有序生长，而且低场致电子发射性能优越,开启电场1.0V/μm，外加电场达到2.89V/μm时发射电流密度为860μA/cm². 关键词： x纳米管')" href="#">CN_x纳米管 高温热解 “竹节状”结构 场致发射     

Columnar growth of crystalline silicon films on aluminium-coated glass by inductively coupled plasma CVD at room temperature

Silicon films were grown on aluminium-coated glass by inductively coupled plasma CVD at room temperature using a mixture of SiH₄ and H₂ as the source gas. The microstructure of the films was evaluated using Raman spectroscopy, scanning electron microscopy and atomic force microscopy. It was found that the films are composed of columnar grains and their surfaces show a random and uniform distribution of silicon nanocones. Such a microstructure is highly advantageous to the application of the films in solar cells and electron emission devices. Field electron emission measurement of the films demonstrated that the threshold field strength is as low as ～9.8V/μm and the electron emission characteristic is reproducible. In addition, a mechanism is suggested for the columnar growth of crystalline silicon films on aluminium-coated glass at room temperature.     

Multiwalled carbon nanotubes decorated with nitrogen, palladium co-doped TiO2 (MWCNT/N, Pd co-doped TiO2) for visible light photocatalytic degradation of Eosin Yellow in water

Multiwalled carbon nanotube (MWCNT/N), Pd co-doped TiO₂ nanocomposites were prepared by calcining the hydrolysis products of the reaction of titanium isopropoxide, Ti(OC₃H₇)₄ containing multiwalled carbon nanotubes with aqueous ammonia. The prepared samples were characterised by Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, diffuse reflectance UV?CVis spectrophotometry (DRUV?CVis), XRD, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). DRUV?CVis analysis confirmed the red shift in the absorption edge at lower MWCNT percentages. SEM and TEM images showed the complete coverage of the MWCNTs with clusters of anatase TiO₂ at low MWCNT percentages. Higher MWCNT levels led to their aggregation and consequently poor coverage by N, Pd co-doped TiO₂. The photocatalytic activities of the nanocomposites were monitored by photodegradation of Eosin Yellow under simulated solar and visible light irradiation (???>?450?nm). Irradiation with simulated solar radiation gave higher dye-degradation rates compared to visible radiation. The optimum MWCNT weight percentage in the composites was found to be 0.5. High degradation-rate constants of 3.42?×?10^?2 and 5.18?×?10^?3?min^?1 were realised for the 0.5% MWCNT/N, Pd co-doped TiO₂ composite, using simulated solar light and visible light, respectively.