Micro-Raman and Tip-Enhanced Raman Spectroscopy of Carbon Allotropes

Summary: Raman spectroscopic data are obtained on various carbon allotropes like diamond, amorphous carbon, graphite, graphene and single wall carbon nanotubes by micro-Raman spectroscopy, tip-enhanced Raman spectroscopy and tip-enhanced Raman spectroscopy imaging, and the potentials of these techniques for advanced analysis of carbon structures are discussed. Depending on the local organisation of carbon the characteristic Raman bands can be found at different wavenumber positions, and e.g. quality or dimensions of structures of the samples quantitatively can be calculated. In particular tip-enhanced Raman spectroscopy allows the investigation of individual single wall carbon nanotubes and graphene sheets and imaging of e.g. local defects with nanometer lateral resolution. Raman spectra of all carbon allotropes are presented and discussed.     

激光辐照对二茂铁掺杂单壁碳纳米管的影响

以单壁碳纳米管和二茂铁为原料, 采用气相扩散法合成填充率较高的二茂铁掺杂单壁碳纳米管(Fc@SWNTs)的复合材料. 考察激光辐射对样品的影响, 结果表明, 当激光功率达到20 mW时, 对样品进行10 s辐照, 样品的拉曼光谱出现了稳定的新峰. 对比分析发现, 二茂铁在激光辐照后形成了碳化铁, 同时部分碳源转化成碳管形成了双层碳管. 表明碳化铁是二茂铁裂解向内层碳管转化的中间产物.     

Evolution of the molecular structure of metallic and semiconducting carbon nanotubes under laser irradiation

The temperature dependence of the morphology of single wall carbon nanotubes (SWNTs) has been studied by Raman spectroscopy at different temperatures by changing the incident laser power. It is shown that a high power laser irradiation treatment of as-grown samples anneals the SWNTs, improving their structural order and perhaps also removing adsorbed gases. As a result, a significant increase in the Raman cross-section of the nanotubes upon laser irradiation can be observed, for both metallic or semiconducting tubes. The investigation of the power level dependence of the Raman spectra also reveals that smaller diameter nanotubes are burned off first, increasing the mean diameter of the nanotubes in the sample.     

气凝胶催化剂上甲烷裂解制备的碳纳米管结构特征

采用XRD、TGA、SEM、TEM、 Raman光谱等多种表征手段,考察了Al2O3气凝胶催化剂上甲烷裂解生长的碳纳米管的结构特征.制得的碳纳米管形态单一,为管径均匀、管壁光滑的中空纳米管,平均直径在10～20 nm.碳纳米管的比表面积较大,具有较强的抗氧化能力,其结构的长程有序度较石墨低.由碳纳米管的Raman光谱分析可知,碳纳米管存在碳层缺陷和无定形碳.当反应温度升高或甲烷浓度下降时,碳纳米管石墨化程度逐渐提高.     

Covalent assembly of shortened multiwall carbon nanotubes on polyelectrolyte films and relevant electrochemistry study

A significant and versatile approach was developed for perpendicularly aligning multiwall carbon nanotubes on diverse substrates suitable for layer-by-layer self-assembly. The multiwall carbon nanotubes (s-MWNTs) used were shortened with oxidation under ultrasonic and functionalized with acyl chloride in thionyl chloride (SOCl2). The monolayer of s-MWNTs perpendicularly grafted to the substrate was obtained by dipping the polyelectrolyte modifying substrate into a tetrahydrofuran suspension of the functionalized s-MWNTs. The interaction proved to be stable and not liable to be affected by the ambience. Transmission electron microscopy and atomic force microscopy were used to examine the morphology of the MWNTs and s-MWNTs grafted on the substrates. Raman spectroscopy was applied to verify the existence of s-MWNTs for assembly, and Fourier transform infrared absorption spectra were used to investigate the interaction pattern between s-MWNTs and polyelectrolyte. The electrochemistry properties of the monolayer of s-MWNTs when the substrate was indium-tin oxide were studied.     

Synthesis and characterization of nanocarbon having different morphological structures by chemical vapor deposition over Fe-Ni-Co-Mo/MgO catalyst

Catalytic chemical vapor deposition (CCVD) is one of the most promising synthesis methods for economically producing large quantities of different nanocarbon structures. Here we report a systematic study of the synthesis conditions for the preparation of different nanocarbon morphological structures via acetylene decomposition over the surface of quaternary-metallic catalyst (Fe-Ni-Co-Mo) supported on MgO (Fe-Ni-Co-Mo/MgO). In particular, the effect of temperature, and the reaction time were investigated to optimize the yield, quality, size and graphitic crystallinity of the deposited carbon. The study showed a successful synthesis of: (i) a high-yield and quality bamboo-like multiwalled carbon nanotubes (b-CNT), (ii) hybrid graphene/carbon nanotubes (G/CNT), and (iii) multilayer graphene (MLG). The structures of the obtained products were characterized by HR-TEM, TGA, Raman spectroscopy, FTIR and X-ray diffraction. The results found seem essential for realizing the role of different synthesis parameters on the yield, quality, and morphology of the synthesized product.     

Thermoelectric properties of nanocomposite thin films prepared with poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) and graphene

Carbon nanotubes (CNTs), either single wall carbon nanotubes (SWNTs) or multiwall carbon nanotubes (MWNTs), can improve the thermoelectric properties of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT?:?PSS), but it requires addition of 30-40 wt% CNTs. We report that the figure of merit (ZT) value of PEDOT?:?PSS thin film for thermoelectric property is increased about 10 times by incorporating 2 wt% of graphene. PEDOT?:?PSS thin films containing 1, 2, 3 wt% graphene are prepared by solution spin coating method. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy analyses identified the strong π-π interactions which facilitated the dispersion between graphene and PEDOT?:?PSS. The uniformly distributed graphene increased the interfacial area by 2-10 times as compared with CNT based on the same weight. The power factor and ZT value of PEDOT?:?PSS thin film containing 2 wt% graphene was 11.09 μW mK(-2) and 2.1 × 10(-2), respectively. This enhancement arises from the facilitated carrier transfer between PEDOT?:?PSS and graphene as well as the high electron mobility of graphene (200,000 cm(2) V(-1) s(-1)). Furthermore the porous structure of the thin film decreases the thermal conductivity resulting in a high ZT value, which is higher by 20% than that for a PEDOT?:?PSS thin film containing 35 wt% SWNTs.     

Vibrational Spectroscopic and Mechanical Investigation of Carbon Nanotube-Reinforced Styrene-Butadiene Rubbers

This paper reports investigations carried out on elastomeric matrices based on a styrene-butadiene copolymer filled with multiwall carbon nanotubes. Stress-strain measurements of the composites demonstrate that carbon nanotubes bring significantly improvements in the mechanical properties with regard to the pure polymer. Raman spectroscopy, which is one of the most extensively employed methods for the characterization of carbon materials, has been applied for the analysis of the dependence of the Raman spectra on the nanotube content and on application of an uniaxial deformation. The results reveal a negligible stress transfer suggesting a weak interface between the tubes and the polymer chains.     

The adsorption kinetics of cadmium by three different types of carbon nanotubes

Oxidized nitrogen-doped multiwall carbon nanotubes (ox-N-MWCNTs), oxidized multiwall carbon nanotubes (ox-MWCNTs), and oxidized single-wall carbon nanotubes (ox-SWCNTs) were evaluated via batch adsorption kinetic experiments to determine the effect of nanotube morphology on the adsorption rate of cadmium. The nanotubes were characterized by HRTEM, XRD and Raman spectroscopy. Cadmium adsorption isotherms were determined at pH 6. Analyses of the kinetic data with an external mass transport model and an intraparticle diffusion model considered two cases: (1) single nanotubes suspended in aqueous solution and (2) agglomerates of nanotubes suspended in aqueous solution. The intraparticle diffusion model produced the best fit to the experimental data. However, only the diffusivity coefficients for single nanotubes suspended in solution were similar to literature values: about 4×10(-9), 1×10(-9) and 2.4×10(-11) cm(2)/s for ox-N-MWCNTs, ox-MWCNTs and ox-SWCNTs, respectively. The morphology of the various carbon nanotubes might determine cadmium diffusivity. The high amount of sidewall pores observed in the single-walled carbon nanotubes could limit cadmium diffusion and account for the slow diffusion rate of 180 min. Conversely, the short length, small surface area and bamboo-type morphology observed with nitrogen-doped multiwall carbon nanotubes may account for the relatively fast adsorption rate of 15 min as this morphology prevents cadmium diffusion through the internal tubular space of these nanotubes.     

Potential dependent surface Raman spectroscopy of single wall carbon nanotube films on platinum electrodes

The analysis of the resonance Raman spectra of single-walled carbon nanotubes in an electrochemically controlled aqueous H₂SO₄ environment using different laser excitation energies shows major reversible and irreversible differences in the main vibrational features regarding their intensities, lineshapes, and frequencies for different applied potentials. These differences arise from the electrochemically induced changes in the occupation of electronic states for metallic and semiconducting nanotubes.     

Multilayer films of carbon nanotubes and redox polymer on screen-printed carbon electrodes for electrocatalysis of ascorbic acid

Multilayer films containing multiwall carbon nanotubes and redox polymer were successfully fabricated on a screen-printed carbon electrode using layer-by-layer (LBL) assembled method. UV-vis spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy and electrochemical method were used to characterize the assembled multilayer films. The multilayer films modified electrodes exhibited good electrocatalytic activity towards the oxidation of ascorbic acid (AA). Compared with the bare electrode, the oxidation peak potential negatively shifted about 350 mV (versus Ag/AgCl). Furthermore, the modified screen-printed carbon electrodes (SPCEs) could be used for the determination of ascorbic acid in real samples.     

Carbon black,multiwall carbon nanotubes,expanded graphite and functionalized graphene flame retarded polypropylene nanocomposites

Herein, we examine the influence of adding functionalized graphene (FG), distinct expanded graphites and carbon nanofillers such as carbon black and multiwall carbon nanotubes on mechanical properties, morphology, pyrolysis, response to small flame and burning behavior of a V‐2 classified flame‐retarded polypropylene (PP). Among carbon fillers, FG and multilayer graphene (MLG) containing fewer than 10 layers are very effectively dispersed during twin‐screw extrusion and account for enhanced matrix reinforcement. In contrast to the other fillers, no large agglomerates are detected for PP‐FR/FG and PP‐FR/MLG, as verified by electron microscopy. Adding FG to flame‐retardant PP prevents dripping due to reduced flow at low shear rates and shifts the onset of thermal decomposition to temperatures 40°C higher. The increase in the onset temperature correlates with the increasing specific surface areas (BET) of the layered carbon fillers. The reduction of the peak heat release rate by 76% is attributed to the formation of effective protection layers during combustion. The addition of layered carbon nanoparticles lowers the time to ignition. The presence of carbon does not change the composition of the evolved pyrolysis gases, as determined by thermogravimetric analysis combined with online Fourier‐transformed infrared measurements. FG and well‐exfoliated MLG are superior additives with respect to spherical and tubular carbon nanomaterials. Copyright © 2013 John Wiley & Sons, Ltd.     

催化裂解CH4制备碳纳米管的影响因素

以柠檬酸法制备的Fe-MgO、Co-MgO和Ni-MgO为催化剂,CH4为碳源气,H2为还原气,在873、973和1073 K制备出碳纳米管,通过TEM和拉曼光谱表征,讨论了催化剂、制备温度、反应时间等因素对碳纳米管形貌、产率和内部结构的影响.结果表明:不同的催化剂在相同的温度下制备的碳纳米管的形态和内部结构有很大的差异.其中Fe-MgO催化剂制备的碳纳米管管径粗,且大小不均匀,而Ni-MgO催化剂制备的碳纳米管管径较细、较均匀.碳纳米管的产率随着裂解温度的变化而改变.Fe-MgO催化剂制备碳纳米管的产率随制备温度的升高而提高,而Ni-MgO催化剂制备碳纳米管的产率随制备温度的升高而降低.Fe-MgO催化剂制备碳纳米管,在1073K甚至更高的制备温度才能达到其最高产率.Co-MgO催化剂制备碳纳米管的产率在973 K左右产率较高,而用Ni-MgO催化剂制备碳纳米管,则在873 K甚至更低的制备温度就能达到最高产率.反应时间与碳纳米管的产率不成正比,有一最佳反应时间,如Ni-MgO催化剂的最佳反应时间为2 h.     

Effects of carbon nanotube functionalization on the agglomeration and sintering of supported Pd nanoparticles

The size of carbon nanotube supported Pd and PdO nanoparticles was investigated on oxidatively functionalized multiwall carbon nanotubes. All samples were characterized by transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy and Raman spectroscopy. The average particle diameter calculated from TEM image analysis was found to be inversely proportional with the duration of the oxidation in nitric acid. Crystallite sizes determined from XRD patterns confirmed this general tendency.     

Bulk synthesis of linear carbon chains confined inside single-wall carbon nanotubes by vacuum discharge

Carbyne, an infinite carbon chain, has attracted much interest and induced significant controversy for many decades. Recently, the presence of linear carbon chains (LCCs), which were confined stably inside double-wall carbon nanotubes (DWCNTs) and multiwall carbon nanotubes (MWCNTs), has been reported. In this study, we present a novel method to produce LCCs in a film of carbon nanotubes (CNTs). Our transmission electron microscopy and Raman spectroscopy revealed the formation of a bulk amount of LCCs after electric discharge of CNT films, which were used as field emission cathodes. The LCCs were confined inside single-wall CNTs as well as DWCNTs. Furthermore, two or three LCCs in parallel with each other are encapsulated when the inner diameter of CNT is larger than approximately 1.1 nm.     

Mechanical, electrical and spectroscopic investigations of carbon nanotube-reinforced elastomers

This paper reports investigations carried out on elastomeric matrices filled with multiwall carbon nanotubes. A comparison with carbon black-filled polymers is also made. The state of dispersion of the fillers in the polymer matrix is evaluated through transmission electron and atomic force microscopies. Stress–strain measurements of the composites demonstrate that carbon nanotubes bring significant improvements in the mechanical properties with regard to the pure polymer. Infrared and Raman spectroscopies are shown to bring molecular insights into the structure/property correlations. Electrical properties of the filled materials are also analyzed in order to determine the so-called percolation threshold and the insulator–conductor transition corresponding to the formation of an interconnected filler network throughout the matrix.     

Real‐time electro‐diffusion method to discriminate carbon nanomaterials

We report both the experimental and theoretical insights of differential electro‐diffusion behavior of carbon nanomaterials (e.g. single wall, multiwall carbon nanotubes, and graphene). We thus discriminate one from the other in a soft gel system. The differential mobility of such material depends on their intrinsic properties, both extend and rate of migration bearing the discriminatory signature. The mobility analysis is made by a real time monitoring of the respective bands.     

Controllable preparation of triple-walled carbon nanotubes and their growth mechanism

Triple-walled carbon nanotubes (TWNTs) with three concentric cylindrical graphene layers have been selectively synthesized for the first time from decomposition of ferrocene encapsulated inside double-walled carbon nanotubes, and were identified by high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy; HRTEM observations reveal that the formation of inner tubes of TWNTs follows a base-growth mechanism.     

Growth and characterization of ultrathin carbon films on electrodeposited Cu and Ni

Ultrathin carbon films were grown on different types of metallic substrates. Free‐standing foils of Cu and Ni were prepared by electroforming, and a pure Ni film was obtained by galvanic displacement on a Si wafer. Commercial foil of Ni 99.95% was used as a reference substrate. Carbon films were grown on these substrates by chemical vapour deposition in a CH₄‐H₂ atmosphere. Obtained films were characterized by Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, and ultraviolet photoemission spectroscopy. The XPS at grazing collection angle was used to determine the thickness of carbon films. Depending on the deposition parameters, the films of graphene or graphite were obtained on the different substrates. The uniformity of graphene and its distribution over the sample area were investigated from Raman data, optical images, and XPS chemical maps. The presence of graphene or graphite in the films was determined from the Raman spectra and Auger peak of C KVV. For this purpose, the D parameter, which is a fingerprint of carbon allotropes, was determined from C KVV spectra acquired by using X‐rays and electron beam. A formation of an intermediate layer of metal hydroxide was revealed in the samples with graphene overlayer.     

Multiwall carbon nanotubes and their applications

The chemical, electrophysical, magnetic, tribological, and physicomechanical properties of multiwall carbon nanotubes (MWCNTs), as well as the characteristics of new nanocomposites and instruments thereof were discussed. These MWCNTs are produced by unique technology and are free from impurities of other carbon modifications. Advantages of multiwall over single-wall carbon nanotubes were demonstrated for applications in electronic devices and preparation of nanocomposites (as filling agents).