Spectroscopic Studies on Pure and Histidine-Functionalized Multiwalled Carbon Nanotubes

Electron paramagnetic resonance, Fourier transform infrared, and ultraviolet-visible studies were carried out for pure and histidine-functionalized multiwalled carbon nanotubes. Electron paramagnetic resonance absorption spectral data were found to be the best fit for the Gaussian lineshape. The g-values indicate the presence of magnetic impurities in the samples and the interaction between the localized electrons and delocalized electrons in the nanotubes trapped at defects or magnetic ion sites. The electron spin concentration decreases with increasing concentration of histidine, which implies that the unpaired electrons undergo a reduction process in the histidine-functionalized multiwalled carbon nanotubes. Fourier transform infrared study confirms the presence of functional groups in pure and histidine-functionalized multiwalled carbon nanotubes. Ultraviolet-visible study reveals the formation of a charge transfer complex in histidine-functionalized multiwalled carbon nanotubes.     

Determination of the texture of arrays of aligned carbon nanotubes from the angular dependence of the X-ray emission and X-ray absorption spectra

The properties of materials containing carbon nanotubes depend on the degree of alignment and the internal structure of nanotubes. It is shown that the degree of misorientation of carbon nanotubes in samples can be evaluated from the measurements of the angular dependences of the carbon X-ray emission and carbon X-ray absorption spectra. The CK _α emission and CK X-ray absorption spectra of the array of multiwalled carbon nanotubes synthesized by catalytic thermolysis of a mixture of fullerene and ferrocene are measured. A comparison of the calculated model dependences of the relative intensities of the π and σ bands in the spectra with the experimental results makes it possible to evaluate the degree of misorientation of nanotubes in the sample and their internal texture.     

Band structure and CK α emission of ultrathin nanotubes

An attempt is made to calculate the energy bands and spectra of the characteristic CK _α emission of small-diameter carbon nanotubes. The calculated spectra for the nanotubes are compared with similar spectra for graphite monolayers used as a test object and with known experimental results for nanotubes. It is concluded that the x-ray emission spectra can be used to identify thin carbon nanotubes. A classification of solid-phase carbon is proposed which takes into account the position of carbon nanotubes in the family of allotropic carbon forms. The type of hybridization of the electrons in the carbon atom is used as the criterion for classification.     

Mesoscopic thermal and thermoelectric measurements of individual carbon nanotubes

We discuss the mesoscopic experimental measurements of electron energy dissipation, phonon thermal transport, and thermoelectric phenomena in individual carbon nanotubes. The temperature distributions in electrically heated individual multiwalled carbon nanotubes have been measured with a scanning thermal microscope. The temperature profiles along the tube axis in nanotubes indicate the bulk dissipation of electronic energy to phonons. In addition, thermal conductivity of an individual multiwalled nanotube has been measured using a microfabricated suspended device. The observed thermal conductivity is two orders of magnitude higher than the estimation from previous experiments that used macroscopic mat samples. Finally, we present thermoelectric power (TEP) of individual single walled carbon nanotubes using a novel mesoscopic device. A strong modulation of TEP as a function of the gate electrode was observed.     

Effect of the cesium and potassium doping of multiwalled carbon nanotubes grown in an electrical arc on their emission characteristics

The effect of cesium and potassium atoms deposited onto multiwalled carbon nanotubes grown in an electrical arc on their emission characteristics was studied. The current–voltage characteristics of the field electron emission of specimens with cesium or potassium doped multiwalled carbon nanotubes of this type were revealed to retain their linear character in the Fowler–Nordheim coordinates within several orders of magnitude of change in the emission current. The deposition of cesium and potassium atoms was shown to lead to a considerable increase in the emission current and a decrease in the work function φ of studied emitters with multiwalled nanotubes. The work function was established to decrease to φ ~ 3.1 eV at an optimal thickness of coating with cesium atoms and to φ ~ 2.9 eV in the case of doping with potassium atoms. Cesium and potassium deposition conditions optimal for the attainment of a maximum emission current were found.

     

碳纳米管的变温场发射

考察了温度变化对沉积在钨丝针尖上的碳纳米管场发射的影响，发现碳纳米管场发射电流随温度升高而增大，场发射电流的稳定性基本没有变化. 多根碳纳米管的场发射特性随温度变化出现偏离Fowler-Nordheim理论的现象，这种现象可能来自碳纳米管的不均匀性.     

多壁碳纳米管束储氢机理的X射线吸收谱研究

采用X射线吸收精细结构光谱探索性地研究了多壁碳纳米管束.在多壁碳纳米管束不同入射角的X射线吸收精细结构光谱中，观察到C—H σ^*共振峰强度随入射角的变化而发生变化.在常温常压下出现C—H键可能与多壁碳纳米管束中存在缺陷有关，缺陷数量越大C—H σ^*共振峰的强度越大.光谱中C—C π^*和C—C σ^*共振峰强度的变化趋势都不同于C—H σ^*共振峰，这有力地证明了在常温常压条件下氢原子是吸附在多壁碳纳米 关键词： X射线吸收精细结构光谱 碳纳米管 储氢 化学吸附     

Characterization of fluorinated multiwalled carbon nanotubes by x-ray absorption spectroscopy

The C 1s and F 1s x-ray absorption spectra of fluorinated multiwalled carbon nanotubes with different fluorine contents and reference compounds (highly oriented pyrolytic graphite crystals and “white” graphite fluoride) were measured using the equipment of the Russian-German beamline at the BESSY II storage ring with a high energy resolution. The spectra obtained were analyzed with the aim of characterizing multiwalled carbon nanotubes and their products formed upon treatment of the nanotubes with fluorine at a temperature of 420°C. It was established that, within the probing depth (～15 nm) of carbon nanotubes, the process of fluorination occurs uniformly and does not depend on the fluorine concentration. The interaction of fluorine atoms with multiwalled carbon nanotubes in this case proceeds through the covalent attachment of fluorine atoms to graphene layers of the graphite skeleton and is accompanied by a change in the hybridization of the 2s and 2p valence electron states of the carbon atom from the trigonal (sp ²) to tetrahedral (sp ³) hybridization.     

Effect of annealing on the microwave characteristics of carbon nanotubes and the nanocomposite materials based on them

Transmission and reflection spectra of electromagnetic microwave radiation are used to determine the complex permittivity of the composite materials consisting of a dielectric matrix and multiwalled carbon nanotubes subjected to high-temperature annealing in an inert atmosphere. The dependence of the electrical conductivity of multiwalled carbon nanotubes on the annealing temperature in an inert atmosphere is shown to be nonmonotonic.     

Characterization of fluorinated multiwalled carbon nanotubes with X-ray absorption,photoelectron and emission spectroscopies

The combined investigation of the chemical bond formation in fluorinated multiwalled carbon nanotubes with 15 wt.% fluorine concentrations (MWCNTs + F 15 wt.%) using X-ray absorption, emission and photoelectron spectroscopy at C 1s and F 1s thresholds is presented. All measurements were performed at BESSY II. The analysis of the soft X-ray and photoelectron spectra point to the formation of covalent chemical bonding between fluorine and carbon atoms in the fluorinated nanotubes. Based on results of this combined study the depth dependent effects are discussed.     

Comparative X-ray absorption investigation of fluorinated single-walled carbon nanotubes

The C 1s and F 1s X-ray absorption spectra of pristine and fluorinated single-walled carbon nanotubes with different fluorine contents and nanodiamond as a reference compound have been measured with the aim of characterizing single-walled carbon nanotubes and their products formed upon treatment of the nanotubes with molecular fluorine at a temperature of 190°C. The spectra obtained have been analyzed by thoroughly comparing with the previously measured spectra of highly oriented pyrolytic graphite and fluorinated multiwalled carbon nanotubes and the spectrum of nanodiamond. It has been established that the fluorination of single-walled and multiwalled carbon nanotubes leads to similar results and is characterized by the attachment of fluorine atoms to carbon atoms on the lateral surface of the nanotube with the formation of the σ(C-F) bonds due to the covalent mixing of F 2p and C 2p _z π valence electron states.     

Specific features of the electronic structure of fluorinated multiwalled carbon nanotubes in the near-surface region

The C 1s and F 1s X-ray photoelectron spectra of fluorinated multiwalled carbon nanotubes with different fluorine contents have been measured using the equipment of the Russian-German beamline at the BESSY storage ring by varying the energy of exciting photons. It has been established that two fluorocarbon phases in which the chemical bonding is characterized by a different electron transfer from carbon atoms to fluorine atoms are formed in the near-surface region of nanotubes with fluorine concentrations of 10–39 wt %. The content of the dominant first phase with a large electron transfer in nanotubes remains unchanged with an increase in the probing depth. This phase is identified as a bulk phase formed as a result of the covalent attachment of fluorine atoms to graphene layers of the graphite skeleton without its destruction. The second phase with a small electron transfer is a near-surface phase, because it is predominantly located within two or three upper graphene monolayers and its contribution considerably decreases with an increase in the probing depth of fluorinated multiwalled carbon nanotubes.     

Photoluminescence of multiwalled carbon nanotubes excited at different wavelengths

In this paper the multiwalled carbon nanotubes (MWNTs) were synthesized by a chemical vapour deposition and the SEM graph shows that the sample has good construction. The micro-Raman spectrum shows the characteristic line of the MWNTs and an additional line produced by the defects on the outer surface of MWNTs. The photoluminescence (PL) spectra observed experimentally are variable under different excitation wavelengths and the strong excitation wavelength dependence of luminescence indicates a distribution of emitters which include electron $\pi$ in excited states and the Van Hove singularities. The absorption spectra confirm the transition channels which are consistent with the PL emission.     

On ballistic transport in carbon nanotubes

We investigate theoretically the ballistic regime exhibited by conduction electrons in multiwalled carbon nanotubes in relation to the conductance quantization in these tubes. Starting from the fact that electron drift mobility is quantized in multiwall tubes, essential aspects related to both ballistic and diffusive regimes are discussed.     

A Simple and Facile Approach to Synthesize Water-Soluble Multiwalled Carbon Nanotubes Wrapped by Poly(4-Vinylpyridine)

By simple grinding, water-soluble linear polymers poly(4-vinylpyridine) (PVP) wrapped around multiwalled carbon nanotubes (MWCNTs) and thus rendered them reversibly soluble in water, ethanol, and DMF. The structure and properties of the resulting nanocomposite, CNTs wrapped by PVP, were evaluated by SEM, AFM, TGA, and FTIR spectroscopy. Individual tubes are clearly observed after PVP-wrapped nanotubes were spin-coated onto a silicon wafer as determined by SEM and AFM. Subsequently, a novel and facile approach to attach high-density and uniform size gold nanoparticles on individual multiwalled carbon nanotubes was achieved by in situ reduction of HAuCl₄ in the homogeneous aqueous solution of MWCNTs–PVP.     

多壁碳纳米管对p型Ba0.3FeCo3Sb12化合物热电性能的影响

用两步固相反应法合成了P型Ba填充方钴矿化合物Ba0.3FeCo3Sb12，并采用放电等离子烧结法(SPS)制备了Ba0.3FeCo3Sb12／多壁碳纳米管复合材料．研究了Ba0.3FeCo3Sb12／多壁碳纳米管复合材料的结构及多壁碳纳米管对其热电性能的影响规律：SEM分析表明多壁碳纳米管比较均匀地分布在Ba0.3FeCo3Sb12基体中；随着碳纳米管添加量的增加，Ba0.3FeCo3Sb12／多壁碳纳米管复合材料的电导率下降、塞贝克系数略微下降、晶格热导率大幅度降低，当碳纳米管含量为5％时其晶格热导率最小；当碳纳米管的含量为3％时，本研究得到的Ba0.3FeCo3Sb12／碳纳米管复合材料的最大ZT值达0．78．     

基于碳纳米管场效应管构建的纳电子逻辑电路

展示了由碳纳米管场效应管构成的三种逻辑电路，分别为单个p型碳纳米管场效应管的开关电路、由集成在同一片硅片上的单个p型碳纳米管场效应管和单个n型掺氮碳纳米管场效应管构成的互补型反相器，以及两个独立的p型碳纳米管场效应管构成的或非门. 其中p型碳纳米管场效应管以单壁碳纳米管作为沟道，而n型碳纳米管场效应管则以掺氮的多壁碳纳米管作为沟道，器件的源漏电极均为铂电极. 关键词： 碳纳米管 场效应管 逻辑电路     

Disordered multiwalled carbon nanotube mat for light spot position detecting

Photovoltaic effects in a disordered multiwalled carbon nanotube mat/nickel heterostructure have been investigated. It is found that the photovoltage in the whole mat between two nickel electrodes under the irradiation of a 532-nm laser shows a single-valued function dependence on the light spot position, while it shows an almost linear dependence on light intensity. Based on the ‘position effect’, the prototype of the light spot position detector has been constructed for the applications of the disordered multiwalled carbon nanotubes in precision measurement. PACS 85.60.-q; 72.40.+w; 73.63.-b; 81.07.De; 78.67.-n     

Light emission from carbon nanofilaments/nanotubes at field electron emission

The spatial distribution of light emission has been studied in planar field electron emitters with long and sparse carbon nanofilaments/nanotubes. The photographic recording of light emission of the emitting nanofilaments/nanotubes is shown to be efficient to determine the position of individual nanofilaments/ nanotubes in different emitter surface areas, as well as to highlight the nanofilaments/nanotube agglomerate distribution over the emitter surface, which mainly contributes to its emission.     

Thermal and Tensile Properties of Epoxy Nanocomposites Reinforced by Silane-functionalized Multiwalled Carbon Nanotubes

Epoxy nanocomposites with unmodified multiwalled carbon nanotubes (u-MWCNTs) and silanized multiwalled carbon nanotubes (si-MWCNTs) were prepared by a cast molding method. The effects of 3-aminopropyltriethoxysilane functionalization of MWCNTs on thermal, tensile, and morphological properties of the nanocomposites were examined. The nanocomposites were characterized by thermogravimetric analysis, dynamic mechanical thermal analysis, and tensile testing. The results showed that epoxy composites based on si-MWCNTs showed better thermal stability, glass transition temperature, and tensile properties than the composites based on u-MWCNTs. These results prove the effect of silane functionalization on the interfacial adhesion between epoxy and MWCNTs. This was further confirmed by morphology study of fractured surfaces of nanocomposites by field emission scanning electron microscopy.