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An appropriate dispersion of carbon nanotubes (CNTs) is a prerequisite for their use in improving the mechanical properties of cement-based composites. In this study two types of carbon nanotubes (CNTs) having different morphologies were investigated. To obtain a uniform distribution of CNTs in the cement matrix, the effect of sonication on the deagglomeration of CNTs in combination with anionic and nonionic surfactants in varying concentrations was quantitatively investigated when preparing aqueous dispersions of CNTs for the subsequent use in cement paste. The relationships between the quality of CNT-dispersion on the one hand and the sonication time and surfactant concentration on the other were determined using UV–vis spectroscopy. After dispersion, nitrogen-doped CNTs were found mostly as individual, broken CNTs. In contrast, after the treatment of the mixture of single-, double-, and multi-walled CNTs, a net-like distribution was observed where destruction of the CNTs due to sonication could not be distinguished. Modification of the cement pastes with dispersions of CNTs led to a pronounced increase, up to 40%, in compressive strength and, in some cases, to a moderate increase in tensile strength under high strain-rate loading. However, no significant improvement in strength was observed for quasi-static loading. Microscopic examination revealed that the bridging of the C–S–H phases differed depending on the type of CNT. This explained, at least partly, the observed effects of CNT-addition on the mechanical properties of hardened cement pastes.

Multi-walled carbon nanotubes were chemically functionalized with methacrylic acid and methacrylated bovine serum albumin by free radical grafting reaction to obtain novel nanocomposites. The nanotubes were synthesized by aerosol-assisted chemical vapor deposition, and then the monomers were directly grafted by the action of hydrogen peroxide/ascorbic acid redox pair which allows operating in water-compatible and eco-friendly environment without the generation of any toxic reaction by-product. A multi-technique approach was used to evaluate the effectiveness of the grafting process employing Fourier transform infrared, Raman, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analyses. Considering the high importance of methacrylate polymers and bovine serum albumin, the proposed nanocomposites could be of great applicability in biomedical and pharmaceutical fields.

We report the encapsulation of the antiferromagnetic and magnetoelectric oxide Cr2O3 inside both multi - and single-walled carbon nanotubes. This is achieved by a two step post-synthesis filling process which involves the filling of nanotubes with CrO3 either from aqueous solution or from the molten phase, followed by appropriate annealing sequences. TEM imaging confirms significant filling rates for both multi- and single-walled carbon nanotubes. Analytical transmission electron microscopy implies that after secondary annealing Cr2O3 is formed inside the nanotubes.

Using carbon nanotubes filled with α-Fe, we have shown that aggregated ferronematic colloids demonstrate reliable and very effective response to a weak (

Objectives To prove the possibility of covalently functionalizing multi-walled carbon nanotubes (CNTs) by free radical grafting of gallic acid on their surface with the subsequent synthesis of materials with improved biological properties evaluated by specific in-vitro assays. Methods Antioxidant CNTs were synthesized by radical grafting of gallic acid onto pristine CNTs. The synthesis of carbon nanotubes was carried out in a fixed-bed reactor and, after the removal of the amorphous carbon, the grafting process was performed. The obtained materials were characterized by fluorescence and Fourier transform infrared spectroscopy (FT-IR) analyses. After assessment of the biocompatibility and determination of the disposable phenolic group content, the antioxidant properties were evaluated in terms of total antioxidant activity and scavenger ability against 2,2′-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl and peroxyl radicals. Finally the inhibition activity on acetylcholinesterase was evaluated. Key findings The covalent fuctionalization of CNTs with gallic acid was confirmed and the amount of gallic acid bound per g of CNTs was found to be 2.1 ± 0.2 mg. Good antioxidant and scavenging properties were recorded in the functionalized CNTs, which were found to be able to inhibit the acetylcholinesterase with potential improved activity for biomedical and pharmaceutical applications. Conclusions For the first time, a free radical grafting procedure was proposed as a synthetic approach for the covalent functionalization of CNTs with an antioxidant polyphenol.

The electrical percolation behaviour of five different kinds of carbon nanotubes (CNTs) synthesised by two CVD techniques was investigated on melt mixed composites based on an insulating polyamide 6.6 matrix. The electrical percolation behaviour was found to be strongly dependent on the properties of CNTs which varied with the synthesis conditions. The lowest electrical percolation threshold (0.04 wt.%) was determined for as grown multi-walled carbon nanotubes without any purification or chemical treatment. Such carbon nanotubes were synthesised by the aerosol method using acetonitrile as ferrocene containing solvent and show relatively low oxygen content near the surface, high aspect ratio, and good dispersability. Similar properties could be found for nanotubes produced by the aerosol method using cyclohexane, whereas CNTs produced by the fixed bed method using different iron contents in the catalyst material showed much higher electrical percolation thresholds between 0.35 and 1.02 wt.%.

We present a detailed magnetic study of iron containing carbon nanotubes (Fe-CNT), which highlights their potential for contactless magnetic heating in hyperthermia cancer treatment. Magnetic field dependent AC inductive heating experiments on Fe-CNT dispersions show a substantial temperature increase of Fe-CNT dispersions in applied AC magnetic fields. DC and AC magnetization studies have been done in order to elucidate the heating mechanism. We observe a different magnetic response of Fe-CNT powder compared to Fe-CNT dispersed in aqueous solution, e.g., ferromagnetic Fe-CNT in powder do not show any hysteresis when being dispersed in liquid. Our data indicate the motion of Fe-CNT in liquid in applied magnetic fields.

Due to their particular magnetic properties, nanoparticles of metallic iron are promising candidates for magnetic fluid hyperthermia when compared to the commonly used iron oxides. However, the difficulty of handling these structures in ambient conditions without oxidation hinders its practical application. In this work, iron filled carbon nanotubes non-covalently functionalized by human serum albumin are studied as potential agents for hyperthermia. Here the iron is encapsulated inside of the carbon shells and protected from reactions with its environment. Besides protecting the iron and biological environment against each other, the carbon shells can also work as an interface for conjugation with other biological molecules of interest. In order to assess if such structures could induce any toxic effect in human cell cultures, we have probed its biocompatibility on a dosage and time dependent manner by measuring metabolic activity, cell proliferation, cell cycle distribution and apoptosis. Our results have shown that those nanotubes strongly associate with cells within a short incubation period and do not pose any significant toxic effect. The magnetic properties of iron filled carbon nanotubes in biological environment, i.e., associated to cells, have been studied and a possible rotation as a function of the applied magnetic field is discussed. Our initial findings encourage the further study of these structures as potential hyperthermia agents.

Aims: A carbon-wrapped nanoscaled thermometer for a contactless temperature control in biological systems on the cellular level is presented. Materials & methods: The thermometer is based on multiwalled carbon nanotubes (MWCNTs) filled with materials with strongly temperature-dependent nuclear magnetic resonance (NMR) parameters. The NMR frequency shift and relaxation time were measured in cuprous-iodide-filled CNTs at different temperatures. Results: The experimental data indicate a pronounced temperature dependence of the NMR parameters, thereby realizing the nanoscaled thermometer. Conclusion: This study is a proof-of-concept that the functionalized CNTs can be used as a contactless thermometer in biomedical applications.

Aim: In this paper, carbon nanotubes (CNTs) are presented as feasible carriers for carboplatin, a therapeutic agent for cancer treatment. The drug was introduced into CNTs to demonstrate that they are suited as nanocontainers and nanocarriers and can release the drug to initialize its medical virtue. Method: The filling was accomplished by a wet-chemical approach after the CNTs were opened. The effect on cell proliferation and cytotoxicity of the carboplatin-filled CNT was investigated by using a viability assays. Results: Using different analysis methods such as electron energy loss spectroscopy and x-ray photoelectron spectroscopy the structure of carboplatin incorporated into the CNTs was found to be retained. In vitro studies showed that carboplatin-filled CNTs inhibited growth of bladder cancer cells whereas unfilled, opened CNTs barely affected cancer cell growth. Conclusion: A reversible filling–emptying process could be performed successfully within this work. This highlights the potential of CNTs for applications in the field of drug delivery.

We report on a systematic approach to exploit the potential of filled carbon nanotubes (CNT) to act as sensors that might provide non-invasive temperature control in biological systems on a cellular level. In this case the temperature is detected by measuring NMR parameters on the filling materials. The beneficial feature of a carbon nanotube is to provide protection of both (i) a human body against toxic adverse effects from the filling material and (ii) a filling material against chemical and biochemical exposure. The feasibility of this concept has been demonstrated on the example of the temperature-dependent NMR frequency and relaxation time measured on the CNT filled with the appropriate sensor materials.

Using a modified “fixed-bed” chemical vapor deposition method, diamagnetic single-, double-, and multiwalled carbon nanotubes were synthesized. For the first time, we show that rhenium is a suitable catalyst for the synthesis of such diamagnetic nanotubes with uniform diameter and a defined numbers of shells. Scanning and transmission electron microscopy investigations, Raman spectroscopy, and magnetic measurements show the tubular structure, the high crystallinity, and the diamagnetic character of the grown nanotubes. We compare the growth mechanism of the Re-catalyzed nanotubes with the growth behavior supported by the conventional catalyst metals ferromagnetic iron, cobalt, and nickel.

Arrays of vertically aligned Fe‐filled multi‐wall carbon nanotubes (MWNTs) on oxidized silicon substrates were prepared by pyrolysis of ferrocene in a dual furnace system and characterized by electron microscopy and magnetometry measurement. The effect of the growth temperature on both the filled nanotube morphology and their magnetic behavior was studied. Increasing the growth temperature in the range of 845–1035°C the nanotube alignment becomes worse and the diameter of the encapsulated Fe nanowires increases from 10 to 40 nm. Both the coercivity and the remanence ratio of the arrays of Fe‐filled MWNTs decrease with the increase of the growth temperature. Factors causing the observed magnetic behavior are discussed.

Fe‐filled multi‐wall carbon nanotubes (MWNTs) were produced by pyrolysis of ferrocene in a dual furnace system. They grew vertically aligned on oxidized silicon substrates placed inside the reaction zone of a chemical vapor deposition reactor. A variation of the growth parameters has been performed in order to evaluate the possibility to control the Fe‐filled nanotube growth process and thereby the nanotube‐ and the filling length, diameter and yield, and also the nanotube alignment. Electron microscopy studies show nanotubes with quite different morphologies. The relation between the aligned Fe‐filled MWNTs growth and the most important growth parameters is discussed.

The thermal decomposition of ferrocene combined with a catalyst-assisted structuring of a Si-substrate surface is a favourable way to produce Fe-filled carbon nanotubes in good quality and in high yields. In this work we have studied the growth of such aligned filled nanotubes on iron and cobalt pre-coated Si-substrates and their dependence on the deposition time. The nanotube diameter depends on the used catalyst metal on the substrate surface. Magnetization measurements were carried out perpendicular (along tube axis) and parallel to the substrate and show excellent coercivities, a strong uniaxial anisotropy (ratios of H c,per / H c,par up to 6) and high saturation magnetization moments per substrate square. The magnetic behavior has been also interpreted as a function of deposition time and of the catalyst metal on the substrate. These investigations were complemented by X-ray diffraction, which revealed a majority fraction of α-Fe and a small amount of Fe 3 C.

The properties of multi‐walled carbon nanotubes filled with iron, which is assembled in nanowires inside the nanotubes, were studied with electron spin resonance and conductivity methods. The low‐temperature decrease of magnetization in zero‐field cooled samples was found depending on the relative orientation of magnetization and the nanotube axes. The azimuthal variation of magnetization can be ascribed to inhomogeneous arrangement of Fe inside the nanotubes, that can be also concluded from the conductivity and spectroscopy measurements.

This paper presents melt mixed composites where two ways of introducing nanotubes in polymer matrices were used. In the first case, commercially available masterbatches of nanotube/polymer composites are used as the starting materials that are diluted by the pure polymer in a subsequent melt mixing process (masterbatch dilution method) while in the other case nanotubes are directly incorporated into the polymer matrix. As an example of the masterbatch dilution method, composites of polycarbonate with MWNT are presented which are produced using a Brabender PL‐19 single screw extruder. In this system, electrical percolation was found at about 0.5 wt% MWNT. The nanotube dispersion as observed by TEM investigations is quite homogeneous. The direct incorporation method is discussed in composites of polycarbonate with MWNT and SWNT. For commercial MWNT percolation was found between 1.0 and 3.0 wt% depending on the aspect ratio and purity of the materials. For HiPCO‐SWNT from CNI percolation occurred be...

Aligned Fe–Co alloy–filled multi-walled carbon nanotubes (MWNTs) were synthesized on silicon substrates via the pyrolysis of a ferrocene/cobaltocene mixture. The nanotubes are aligned normal to the substrate surface. The encapsulated metal nanowires have diameters of 10–20 nm and a length of up to a few micrometers. They consist of single crystals with BCC structure. Alternating gradient magnetometry investigations show that the magnetic wires exhibit a clear ferromagnetic behavior at room temperature. An enhanced coercivity of about 126 mT and uniaxial magnetic anisotropy with the easy axis of magnetization along the wire axis were observed.

We report on a method for the selective growth of aligned cobalt (Co)‐filled multi‐walled carbon nanotubes (MWNTs) using the pyrolysis of cobaltocene. The nanotubes grow preferentially on Fe structures patterned onto SiO2/Si substrates by a lift‐off process. The filling is discontinuous and forms a sequence of nanowire segments located along the tube. The nanowires consist of single crystalline grains with fcc structure. They have diameters of 10–20 nm and their length reaches several hundred nanometers. Our method allows the building of a system of oriented MWNTs filled with ferromagnets. It may be applied for fabricating nanotube‐based microelectronic devices.

Carpet-like flakes (area < 9 mm 2 ; thickness < 50 μm) of well-aligned Co-filled multi-walled carbon nanotubes were grown by decomposition of cobaltocene. The nanotubes have outer diameters of 50-90 nm and a metal core of 15-30 nm diameter. They are discontinuously filled with f.c.c.-Co nanowires of up to a few micrometers in length. Magnetometry studies show a weak uniaxial magnetic anisotropy with the easy axis along the nanowires and a high coercivity of about 59 mT. Electron holography provides information about the magnetic characteristics of individual nanowires.

Single- and multi-walled carbon nanotubes are very interesting nanoscaled materials with many possible applications in nanoelectronics. Especially, nanotubes filled with ferromagnetic materials (Fe, Co, Ni) may have significant potential in data storage. Such structures may help to exceed the best available storage densities (>65 Gb/inch2) and show in the case of Fe-filled nanotubes higher coercivities compared to bulk Fe. In addition, metal-filled carbon nanotubes are promising nanowires with excellent oxidation protection. In this paper we describe the synthesis of Fe-, Ni- and Co-filled carbon nanotubes by using the chemical vapor deposition method. Varying the deposition conditions we have obtained filled nanotubes with relatively uniform core diameters and different thicknesses of the carbon walls. The core diameters vary between 15 and 30 nm and the thickness of the carbon shells between 2 and 60 nm. The length of the tubes amounts up to 30 μm. The filled carbon nanotubes are characterised by scanning and transmission electron microscopy and energy dispersive X-ray analysis. The magnetic behaviour of the aligned Fe-filled tubes is investigated using alternating gradient magnetometry measurements and electron holography. The hysteresis loops indicate a magnetic anisotropy. The coercivity depends on the direction of the applied magnetic field. The observed enhanced coercivities are significantly higher than in bulk Fe.

We report on the magnetic properties of Fe-filled multiwalled carbon nanotubes (MWNTs) grown by chemical vapor deposition (CVD) on Si substrates with ferrocene as precursor. The MWNTs are aligned perpendicularly to the substrate plane. X-ray diffraction analyses indicate the presence of both bcc and fcc iron with a relatively strong texture. Magnetometry measurements show a pronounced magnetic anisotropy with the easy axis perpendicular to the substrate plane and parallel to the axis of the aligned MWNTs, respectively. The low-temperature behavior suggests a negligible coupling between the two iron phases. We accessed the magnetic properties of individual Fe-filled MWNTs by electron holography using a transmission electron microscope (TEM).

We describe the preparation and the properties of Fe-filled multi-walled carbon nanotubes on Co-coated oxidized silicon substrates. The material was grown by pyrolysis of ferrocene, using a chemical vapor deposition process. Scanning and transmission electron microscopy studies indicate that the material consists of filled and aligned MWNTs. They have outer diameters of 40–100 nm and diameters of the metal core of 20–40 nm. Energy dispersive X-ray analysis of individual tubes reveals that their filling consists of pure Fe. Alternating gradient magnetometry investigations demonstrate the ferromagnetic behavior of the filled tubes. We observe unique magnetic properties differing from those of bulk Fe.

Molecular imprinting is a recent new and rapidly evolving technique which allows the creation of synthetic receptors (MIPs) consisting of highly cross-linked porous-rich polymers with recognition properties comparable to the biological systems related to the presence of specific recognition sites complementary in shape, size and functional groups to a target molecule. It is a facile concept, which involves the construction of sites of specific recognition, commonly within synthetic polymers. The template of choice is entrapped within a pre-polymerization complex, consisting of functional monomers with good functionality, which chemically interacts with the template. Polymerization in the presence of crosslinker serves to freeze these template-monomer interactions and subsequent removal of the template results in the formation of a molecularly imprinted polymer matrix. Due to the advantages of MIPs such as low cost, stability, and easy preparation compared with natural molecular recognition products (e.g. antibody), Molecular imprinting is a welldeveloped tool in the analytical field, mainly for separating and quantifying very different substances, including drugs and bio-active molecules contained in relatively complex matrices. Despite the application of MIPs as sensor matrices or separation materials, they suffer from basic limitations associated with the limited concentration of imprinted sites, and the bulk volume of the polymer matrices that requires long diffusion paths of the imprinted host molecules. These limitations lead to inefficient sensing or separation processes. MIP nanomaterials are proposed as a pain reliever for headache by improving the accessibility and the homogeneity of the binding sites. In particular, with high strength, the extremely large surface area and unique chemical properties, Carbon nanotubes (CNTs) could serve as the reinforcing element or core in fabricating core–shell structural MIPs.

Thanks to their capillary-like structure CNTs provide a well-characterized container material for hosting miscellaneous fillings. Here we present basic studies on the use of CNTs for drug delivery. By introducing carboplatin, an anticancer drug, into the CNTs via a wet chemical approach, drug-filled nanotubes have been produced. The maintenance of the structure of carboplatin was proven using electron energy loss spectroscopy and X-ray photoelectron spectroscopy. It was shown that the drug is released into cell culture medium leading to cell death. Cell viability assays performed with bladder cancer cells EJ28 demonstrated the cytotoxicity of CNTs filled with carboplatin. For comparison a reference of unfilled, open ended CNTs did not affect the cell viability. These results point out the general capabilities of CNTs as nanocarriers for drug delivery.

Due to their particular magnetic properties, nanoparticles of metallic iron are promising candidates for magnetic fluid hyperthermia when compared to the commonly used iron oxides. However, the difficulty of handling these structures in ambient conditions without oxidation hinders its practical application. In this work, iron filled carbon nanotubes non-covalently functionalized by human serum albumin are studied as potential agents for hyperthermia. Here the iron is encapsulated inside of the carbon shells and protected from reactions with its environment. Besides protecting the iron and biological environment against each other, the carbon shells can also work as an interface for conjugation with other biological molecules of interest. In order to assess if such structures could induce any toxic effect in human cell cultures, we have probed its biocompatibility on a dosage and time dependent manner by measuring metabolic activity, cell proliferation, cell cycle distribution and apoptosis. Our results have shown that those nanotubes strongly associate with cells within a short incubation period and do not pose any significant toxic effect. The magnetic properties of iron filled carbon nanotubes in biological environment, i.e., associated to cells, have been studied and a possible rotation as a function of the applied magnetic field is discussed. Our initial findings encourage the further study of these structures as potential hyperthermia agents.

Ferromagnetic-filled carbon nanotubes are new nanostructured materials with many possible applications. They can be synthesized using the thermal decomposition of metallocenes of the iron triad. Two different methods (solid and liquid source CVD) are suitable for producing, at very high filling rates, filled nanotubes on precoated Si substrates. The diameters of deposited filled nanotubes are particularly dependent on the size of catalyst particles on the substrate, while the lengths depend more on the sublimation and decomposition rate of metallocene. The growth mechanism of filled carbon nanotubes is based on the root growth mode. Multiwalled carbon nanotubes, filled with body-centered cubic Fe, show unusual magnetic properties. Aligned-growth nanotube ensembles can reach coercivities up to 130 mT (bulk iron 0.09 mT). Ferromagnetic-filled carbon nanotubes can be successfully used both as cantilever tips in magnetic force microscopy and as a nanocontainer for new therapies in medicine.

This paper presents melt mixed composites where two ways of introducing nanotubes in polymer matrices were used. In the first case, commercially available masterbatches of nanotube/polymer composites are used as the starting material which are diluted by the pure polymer in a subsequent melt mixing process (masterbatch dilution method) while in the other case nanotubes are directly incorporated into the polymer matrix. As an example of the masterbatch dilution method, composites of polycarbonate with MWNT are presented which are produced using different melt mixing equipments. The lowest percolation threshold was found at about 0.5 wt% MWNT using a Brabender PL‐19 single screw extruder. The nanotube dispersion as observed by TEM investigations is quite homogeneous. The direct incorporation method is discussed in composites of polycarbonate with MWNT and SWNT. The nanotube addition significantly changes the stress‐strain behavior of the composites: modulus and stress are increased; however, elongation is reduced especially above the percolation concentration.

Fe-57 transmission Mossbauer spectroscopy (TMS) and back scattered conversion electron Mossbauer spectroscopy (CEMS) measurements were carried out on Fe-filled multiwalled carbon nanotubes (Fe-MWCNTs) grown by chemical vapor deposition with ferrocene as precursor. Samples of Fe-MWCNTs material deposited on the inner wall of the quartz tube reactor and samples of aligned Fe-MWCNTs grown perpendicularly to the oxidized Si substrate were characterised by the TMS method. The data show that Fe phases encapsulated within the carbon nanotubes comprise alpha-Fe, gamma-Fe, and Fe3C in different percentage ratio depending on the sample preparation. These results are in a good accordance with the previously measured magnetic characteristics and with the structural data found by x-ray diffraction as well by selected area electron diffraction methods and allow a new complementary characterization of the Fe(Fe-alloy)-MWCNT systems. The CEMS method applied for the characterization of metal containing MWCNTs reveals that close to the top surface of the aligned Fe-MWCNTs samples only the gamma-Fe phase is found. This technique shows an additional potential for further investigation of the spatial distribution of the crystalline phases in the depth of aligned Fe-MWCNT samples. (C) 2004 American Institute of Physics.

TG measurements of the univariant reactions in the Y-Ba-Cu-O system at 0.21×10 5 Pa O 2 pressure indicate that independently of temperature and coexisting solid phases the melt composition corresponds to a YO 1.5 -BaO-CuO 0.68 section. This behaviour is quite similar to the binary Cu-O system. Consequences for techniques of YBa 2 Cu 3 O 7-δ synthesis involving melts are discussed

The catalytic chemical vapor deposition (CCVD) is a very promising process with respect to large scale production of different kinds of carbon nanostructures. By modifying the deposition temperature, the catalyst material and the hydrocarbon nanofibers with herringbone structure, multi-walled nanotubes with tubular structure and single-walled nanotubes were deposited. Furthermore, layers of aligned multi-walled nanotubes could be obtained on oxidized silicon substrates coated with thin sputtered metal layers (Co, permalloy) as well as onto WC-Co hardmetals by using the microwave assisted plasma CVD process (MWCVD). The obtained carbon modifications were characterized by scanning (SEM) and transmission (TEM) electron microscopy. The hydrogen storage capability of the nanofibers and nanotubes and the electron field emission of the nanotube layers was investigated.

In this paper we report on the magnetic properties of single- and multiwalled carbon nanotubes synthesized using different chemical vapour deposition methods and with variety of catalyst materials (ferromagnetic Fe, FeCo and diamagnetic Re). Different methods yield carbon nanotubes with different morphologies and different quantity of residual catalyst material. Catalyst particles are usually encapsulated in the nanotubes and influence the magnetic respond of the samples. Varying ferromagnetic properties depending on the shape, size and type of catalyst are discussed in detail. The data are compared with M(H) characteristics of carbon nanotubes without catalysts and with nonmagnetic rhenium, as a reference.

We have synthesized by chemical vapor deposition (CVD) single-, double-, and multiwalled carbon nanotubes without magnetic impurities. In particular, we have applied a rhenium-based CVD technique yielding nonmagnetic carbon nanotubes with diamagnetic Re particles. In addition, carbon nanotubes prepared with iron as catalyst particles are annealed at very high temperatures in which the catalyst material is completely vaporized, while the carbon nanotubes are structurally preserved. Detailed magnetic studies show for both approaches a clear diamagnetic behavior typical for pure carbon nanotubes but no indication of ferromagnetic or paramagnetic material.

We have performed morphological analysis of samples of Fe nanowires encapsulated into aligned multiwalled carbon nanotubes (Fe-MWCNTs) via Fe57 Mossbauer spectroscopy. The aligned Fe-MWCNTs were obtained by pyrolysis of ferrocene onto an oxidized Si substrate. Transmission Mossbauer spectroscopy (TMS) and backscattered conversion electron Mossbauer spectroscopy (CEMS) were applied in order to distinguish different Fe phases and their spatial distribution within the whole sample and along the tubes’ height. A characterization (on a large spatial scale) of the aligned CNT samples was performed by obtaining TMS spectra for selected spots positioned at different locations of the sample. While the total Fe content changes considerably from one location to another, the γ-Fe∕α-Fe phase ratio is constant onto a relatively large area. Using TMS and CEMS for all aligned Fe-MWCNT samples it is also shown that along the CNT axes, going to the top of the nanotube the relative content of the γ-Fe phase increases. Going...

By optimization of the synthesis of ferromagnetic-filled carbon nanotube ensembles on Si substrates (catalytic decomposition of ferrocene) and following annealing at 645°C, marked hysteresis loops can be measured by the alternating-gradient method. Unusually high coercivities and strong anisotropies with an easy magnetic axis parallel to the alignment of the nanotubes are observed from the as-grown samples, whereas an enhanced magnetic saturation moment (up to a factor of 2) and a decreased anisotropy are realized after annealing at 645°C. The increase of the magnetic saturation moment of the Fe-filled carbon nanotube ensembles is caused by the entire transformation within the tubes of the γ-Fe and Fe3C phases to ferromagnetic α-Fe and graphite. X-ray diffraction with different glancing incidence shows that the γ-Fe is predominantly at the tips of the nanotubes, while the iron carbide resides closer to the substrate. However, after the annealing process only α-Fe is found. At an annealing temperature of 6...

Phase equilibrium investigations along the sections Y 2 BaCuO 5 CuO x and YBa 2 Cu 3 O 7−δ CuO x have been carried out in air. Furthermore, a pseudobinary phase diagram in dependence on p(O 2 ), T and x is discussed.