Boris G. Shulitski

Growth of few-wall carbon nanotubes with narrow diameter distribution over Fe-Mo-MgO catalyst by methane/acetylene catalytic decomposition

Few-wall carbon nanotubes were synthesized by methane/acetylene decomposition over bimetallic Fe-Mo catalyst with MgO (1:8:40) support at the temperature of 900°C. No calcinations and reduction pretreatments were applied to the catalytic powder. The transmission electron microscopy investigation showed that the synthesized carbon nanotubes [CNTs] have high purity and narrow diameter distribution. Raman spectrum showed that the ratio of G to D band line intensities of IG/ID is approximately 10, and the peaks in the low frequency range were attributed to the radial breathing mode corresponding to the nanotubes of small diameters. Thermogravimetric analysis data indicated no amorphous carbon phases. Experiments conducted at higher gas pressures showed the increase of CNT yield up to 83%. Mössbauer spectroscopy, magnetization measurements, X-ray diffraction, high-resolution transmission electron microscopy, and electron diffraction were employed to evaluate the nature of catalyst particles.

Structure, composition and magnetic properties of carbon nanotubes doped by Fe during the growth process

The results of complex investigations of the crystalline structure, composition and specific magnetization of the multi-wall carbon nanotubes (CNTs) filled by magnetic nanocomposite are performed. CNT arrays have been synthesized by the high temperature pyrolysis of fluid hydrocarbon - p-xylole [C8H10] in the presence of volatile catalyst - ferrocene [Fe(C5H5)2] at the walls of tubular-type quartz reactor of specially constructed equipment. It was revealed that the obtained CNTs constitute complex nanocomposite: C - Fe3C - Fe5C2 - Fe. The magnetic properties of such CNTs in the temperature region of 78≤T≤1060 K are conditioned by the ferric carbide (in the form Fe3C H Fe5C2) and Fe.

The effect of gas‐dynamic factors on selective carbon‐nanotube synthesis by injection CVD method for field‐emission cathodes

— Reversible selective growth of carbon-nanotube (CNT) arrays on Si/SiO2 topologies was investigated for field-emission-display applications. The method used was that of high-temperature pyrolysis of fluid hydrocarbon (p-xylene [C8H10]) in a mixture with volatile catalyst (ferrocene [Fe(C5H5)2]) using Ar as the gas carrier. The synthesized CNT arrays were analyzed by SEM, TEM, Raman, and TGA analyses. Reversible CNT growth both on Si and SiO2 surfaces was found to be sensitive to the gas-carrier flow rate and the catalyst/hydrocarbon solution injection rate into the synthesis zone. This phenomenon can be explained by inverse domination of active sites on Si and SiO2 surfaces at different flow rates of gas mixture, causing different types of catalyst precipitation followed by subsequent CNT growth. In principle, the possibility of growing CNTs using the proposed technology will allow the creation of precise geometries of field-emission cathodes excluding the step of catalyst localization.

P-120: High Efficiency Method of Selective CNT Arrays Growth on the Metal/Dielectric/Semiconductor Substrates for FEDs Application

Multi-wall carbon nanotube (CNT) arrays growth by the atmospheric pressure CVD process of thermal decomposition of fluid (o- and p-xylole C8H10) hydrocarbons in the presence of volatile catalysts (ferrocene Fe(C5H5)2) with the use of Ar as a gas-carrier on the top of different metal/dielectric/semiconductor (MDS) structures, in particular Si/SiO2, Ti/SiO2/Si, Al2O3 matrix/Ni catalyst has been investigated for the FEDs application. The obtained results are showing that the CNTs growth selectivity and density of CNTs packing can be managed under certain conditions. At the investigated types of surfaces the vertically aligned close-packed and preferably oriented low density CNT arrays have been obtained as well as single CNTs in the pores of nanoporous Al2O3 matrix with Ni catalyst.

Specific Features of the Carbon Nanotubes Nucleation and Growth in the Porous Alumina Membrane

Aligned, highly uniform multiwall carbon nanotubes (MWCNT) in a porous anodic aluminum oxide (AAO) membrane were successfully grown by chemical vapor deposition (CVD). The effectiveness of MWCNT formation was studied with various synthesis parameters. It was found that high catalyst (ferrocene) concentrations led to formation of a thick layer of MWCNT arrays on top surface of AAO membranes, which led to decrease of the pores filling with nanotubes. It was shown that the growth mechanism of the nanotubes in the AAO pores by this method was not connected with the traditionally used transition metal catalysts, no matter whether they were in a deposited (localized catalyst) or volatile (injected catalyst) state. The pre-annealing process in air atmosphere inhibited the nanotubes formation in the AAO pores. We speculate that the formation of MWCNT s in the AAO pores is governed by the pore structure reconstruction (water desorption, phase transformation) during the high-temperature (870° C) CVD process, though this phenomenon needs further investigation. KeywordsChemical Vapour Deposition; Carbon Nanotubes; Porous Aluminum Oxide; Ferrocene; Xylene

Femtosecond laser modification of an array of vertically aligned carbon nanotubes intercalated with Fe phase nanoparticles

Femtosecond lasers (FSL) are playing an increasingly important role in materials research, characterization, and modification. Due to an extremely short pulse width, interactions of FSL irradiation with solid surfaces attract special interest, and a number of unusual phenomena resulted in the formation of new materials are expected. Here, we report on a new nanostructure observed after the interaction of FSL irradiation with arrays of vertically aligned carbon nanotubes (CNTs) intercalated with iron phase catalyst nanoparticles. It was revealed that the FSL laser ablation transforms the topmost layer of CNT array into iron phase nanospheres (40 to 680 nm in diameter) located at the tip of the CNT bundles of conical shape. Besides, the smaller nanospheres (10 to 30 nm in diameter) are found to be beaded at the sides of these bundles. Some of the larger nanospheres are encapsulated into carbon shells, which sometime are found to contain CNTs. The mechanism of creation of such nanostructures is proposed.

Magnetic properties of CNT arrays synthesized by the injection CVD method at various catalyst concentrations

The arrays of multi-wall carbon nanotubes (CNTs) filled with ferromagnetic nanoparticles (MFCNTs) have been obtained by the high temperature pyrolysis of fluid hydrocarbon (o-xylene) in a mixture with the volatile source of catalyst (ferrocene) using Ar as the gas-carrier. The influence of the catalyst concentration cx (0.5%, 5%, and 10%) in the feeding solution on the composition, crystalline structure, morphology and, accordingly, magnetic properties of MFCNT arrays in a wide temperature range was investigated. The X-ray diffraction, SEM and TEM methods revealed that CNT arrays are filled by Fe3C and Fe phases and that the higher is the catalyst concentration in the feeding solution, the higher is Fe3C and Fe content in CNT arrays. Temperature dependence of the specific magnetization σ(T) shows that σ increases with the increasing of ferrocene concentration in a whole temperature range under investigation (78 ≤T < 600 K). It is shown that σ(T) follows the Bloch law in the temperature range 80-300 K with Bloch constant B=1.65.10-5 K-3/2 and the Stoner law at 300-480 K for samples with cx=10% and, correspondingly, 80-450 K with Bloch constant B=6.1.10-5 K-3/2 and 450-480 K for samples with cx=5%. The lower value of Bloch constant, which characterizes the exchange interaction, in the case of cx=10% might be attributed both to dimensional effects and the decrease of the effective magnetic momentum of Fe phases atoms. The hysteresis loops demonstrate that coercivity Hc(cx=5%) decreases, but Hc(cx=10%) is constant or even slightly increases with increasing the temperature. This phenomenon is explained by the increase both the saturation magnetization and shape anisotropy.

Self-organised hybrid nanostructures composed of the array of vertically aligned carbon nanotubes and planar graphene multi-layer

The hybrid carbon nanostructures composed of an array of vertically aligned carbon nanotubes (CNTs) and a self-organised planar graphene multi-layer (PGL) located at the top of the array (CNT-PGL nanostructures) have been obtained by the floating catalyst CVD method. The growth mechanism of CNT-PGL nanostructures is analysed. The fundamental characteristics (morphology, elemental composition and structure) of these nanostructures were characterised by Scanning and Transmission Electron Microscopy, Atomic Force Microscopy, Energy-Dispersive X-ray (EDX), Auger and Raman spectroscopy. It has been established that PGL grows by the typical epitaxial growth of multi-layer films and CNTs grow simultaneously both via root-growth mechanism (attached to the substrate) and tip-growth mechanism (attached to the planar layer). This planar layer is a layered-graphitic structure ‘graphene multi-layer’ and is connected with CNTs through the catalyst nanoparticles. It consists of disordered graphitic flakes with a size of...

Growth of few wall carbon nanotubes with narrow diameter distribution over Fe-Mo-MgO catalyst by methane/acetylene catalytic decomposition

We report of few wall carbon nanotubes (FWNT) growth by methane/acetylene decomposition over bimetallic Fe-Mo catalyst with MgO support. Our transmission electron microscopy investigation (TEM) shows high purity and narrow diameter distribution of grown nanotubes. The phase analysis of CNT product was performed by X-ray and Mossbauer techniques.

The influence of electron irradiation on the magnetic properties of carbon nanotubes filled with Fe-phases composite

The arrays of multi-wall carbon nanotubes (CNTs) filled with Fe-containing nanocomposite have been studied from the point of view of their magnetic properties stability to electron irradiation. CNTs with different content of magnetic component were synthesized by CVD method using ferrocene/xylene mixture of varied proportion. The structure, composition and magnetic properties of CNTs irradiated with a dose of 1015 cm-2 were investigated by TEM, X-ray analysis and ponderomotive method, correspondingly. It was revealed that the morphology of the magnetic particles inside CNTs were changed what, along with radiation defects, lead the deterioration the magnetic properties of CNTs.