Glass Formation in the GeS2–EuS System

Crystalline and glassy alloys in one of the highest temperature glass-forming systems GeS₂–EuS are studied by differential thermal analysis, x-ray diffraction, chemical analysis, and IR spectroscopy. The glass-transition, crystallization, and melting temperatures of the alloys are determined with a high accuracy. The results indicate that, with increasing EuS content, the glass-transition temperature decreases from 492 to 448°C. The most homogeneous glasses can be prepared at EuS contents below 15 mol %. To obtain homogeneous glasses in the range 25–30 mol % EuS, an increased cooling rate is needed: 20–30°C/s.     

Large magnetocaloric effect in sintered ferromagnetic EuS

We present magnetocaloric effect measurements of the ferromagnetic semiconductor EuS in the vicinity of its ordering temperature. Single phase EuS powder was synthesized by CS₂ gas sulfurization of Eu₂O₃. A sintered compact with relative density over 95% was prepared by pulsed electric current sintering of the powder. Temperature and magnetic field dependence of the magnetization and specific heat were characteristic of a paramagnetic to ferromagnetic second order phase transition. The entropy change induced by an external magnetic field and the specific heat were both close to those of a single crystal. We obtained an entropy-temperature (S–T) diagram of the EuS sintered compact. Carnot cycle liquefaction of hydrogen using EuS was compared with several other materials, with results indicating that sintered EuS is an excellent magnetic refrigerant for hydrogen liquefaction.     

Search for Spin Filtering by Electron Tunneling Through Ferromagnetic EuS Barriers in PbS

Perpendicular transport through single- and double-barrier eterostructures made up of ferromagnetic EuS layers embedded into a PbS matrix was investigated. Both resonant tunneling and probably spin filtering through EuS barrier were observed.     

Diffraction from carbon nanotubes

Full symmetry based analysis enables direct insight into various features of the diffraction patterns of carbon nanotubes. In particular, determination of the chiral indices of nanotubes may be performed.     

Fabrication, structural characterization and formation mechanism of multiferroic BiFeO3 nanotubes

Multiferroic BiFeO3 (BFO) nanotubes have been successfully fabricated by the modified sol-gel method within the nanochannels of porous anodic aluminum oxide (AAO) templates. The morphology, structure and composition of the nanotubes were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), selected-area electron diffraction (SAED), high resolution TEM, (HRTEM) and energy-dispersive X-ray spectroscopy (EDX). Postannealed (650 degrees C for 1 h), BFO nanotubes were polycrystalline and X-ray diffraction study revealed that they are of the rhomohedrally distorted perovskite crystal structure. The results of SEM and TEM revealed that BFO nanotubes possessed a uniform length (up to 60 microm) and diameter (about 200 nm), which were controlled by the thickness and the pore diameter of the applied AAO template, respectively and the thickness of the wall of the BFO nanotube was about 15 nm. Y-junctions in the BFO nanotubes were observed. EDX analysis demonstrated that stoichiometric BiFeO3 was formed. HRTEM analysis confirmed that the obtained BFO nanotubes made up of nanoparticles (3-6 nm). The possible formation mechanism of BFO nanotubes was discussed.     

Facile attachment of magnetic nanoparticles to carbon nanotubes via robust linkages and its fabrication of magnetic nanocomposites

Magnetic nanoparticles were facilely attached to multi-walled carbon nanotubes (MWCNTs) by high-temperature reaction of ferric triacetylacetonate in 1-methyl-2-pyrrolidone in the presence of carboxylated MWCNTs. X-ray diffraction, transmission electron morphology and thermogravimetric analysis were used to demonstrate the successful attachment of iron oxide nanoparticles to MWCNTs. It was found that the attached nanoparticles were mainly magnetite. Investigations using Fourier transform infrared spectroscopy proved that the tight attachment was due to the robust linkages: metal-carbonyl coordination. Modified carbon nanotubes were introduced into epoxy resins to fabricate magnetic nanocomposites. Magnetic properties were analyzed by vibrating sample magnetometer.     

Sonochemical preparation of nickel alumina nanotubes templated by anionic surfactant assemblies

Nickel alumina nanotubes templated by dodecylsulfate assemblies have been successfully synthesized for the first time using a sonochemical process. These nanotubes were characterized by scanning electron microscope (SEM), a transmission electron microscope (TEM), X-ray diffraction (XRD). The formation mechanism of these nanotubes is also discussed. They were also calcined to study the change of the nanostructure morphology with the temperature. It was found that the nanotubes transformed from short nanotubes into dendritic structures of aggregations of nanoparticles into monodisperse nanoparticles, and these nanostructures hold high specific surface area.     

An electrokinetic route to rapid synthesis of nickel hydroxide and nickel oxide nanotubes

An electrokinetic route was developed for the synthesis of Ni(OH)2 nanotubes in the nanochannel of anodic alumina oxide (AAO) template. The nanotubes in the template were then converted to NiO nanotubes by calcination in air at 300 degrees. Uniform ordered nanotubes were obtained after selecting proper experimental conditions, such as the ionic concentration, the reaction time and the kind of nickel salts. X-ray diffraction (XRD) analysis indicated that the as-prepared Ni(OH)2 nanotubes were crystalline. Thermogravimetric analysis (TGA) was employed to determine the correlation between temperature and weight lose of the nanotubes. The transmission electron microscope (TEM) and scanning electron microscope (SEM) were used to characterize the morphology and structure of the nanotubes.     

A facile method to crystallize amorphous anodized TiO₂ nanotubes at low temperature

Anodic growth of TiO(2) nanotubes has attracted intensive interests recently. However, the as-prepared TiO(2) nanotubes are usually amorphous and they generally need to be crystallized by sintering above 450 °C. Here, we report on a facile method to crystallize amorphous anodized TiO(2) nanotubes at a low temperature. We find that, simply by immersing them into hot water, the anodized TiO(2) nanotubes can be transformed from amorphous to crystalline state at a temperature as low as 92 °C. Results indicate that the hot water treatment might be a versatile strategy to crystallize amorphous anodized TiO(2) nanotubes at low temperature. Field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, UV-vis spectroscopy, and Brunauer-Emmett-Teller (BET) analysis via N(2) adsorption are used to characterize the resulting samples. In addition, the TiO(2) nanotubes in powder form are taken as photocatalysts to explore their potential applications. Results indicate that the sample after 35 h of hot water treatment shows the highest photoactivity, which is as efficient as the commercial photocatalyst Degussa P25. The photocatalytic testing results demonstrate that the hot water treatment reported in this study can be an alternative approach to the conventional methods.     

碳纳米管的催化裂解聚苯乙烯法的制备及其表征研究

利用流动催化裂解法以聚苯乙烯为碳源,二茂铁为催化剂前躯体制备出了碳纳米管.用扫描电子显微镜,透射电子显微镜,拉曼光谱和X射线衍射对碳纳米管的结构进行了表征.再者,通过导入噻吩,合成了一种有很多细碳纳米管分支的碳纳米管.该制备过程工艺简单,碳源价格低廉.利用这个方法,通过控制条件,可得到不同结构的碳纳米管.     

Synthesis of ordered ZnS nanotubes by MOCVD-template method

Semiconductor ZnS nanotubes arrays were synthesized in the pores of the porous anodic alumina (PAA) membranes by using metal organic chemical vapor deposition (MOCVD) template methods. The morphology and structure of the ZnS nanotubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and X-ray diffraction (XRD). It is found that the ZnS nanotubes with diameters in range of 140–250 nm and the length up to tens of microns are polycrystalline. Energy-dispersion spectroscopy (EDS) and X-ray photoelectron spectroscopy analysis (XPS) indicate that the stoichiometric ZnS was formed. A green-blue emission band centered at 510 nm was observed in the photoluminescence spectrum of the ZnS nanotubes.     

Growth of carbon nanostructures on carbonized electrospun nanofibers with palladium nanoparticles

This paper studies the mechanism of the formation of carbon nanostructures on carbon nanofibers with Pd nanoparticles by using different carbon sources. The carbon nanofibers with Pd nanoparticles were produced by carbonizing electrospun polyacrylonitrile (PAN) nanofibers including Pd(Ac)(2). Such PAN-based carbon nanofibers were then used as substrates to grow hierarchical carbon nanostructures. Toluene, pyridine and chlorobenzine were employed as carbon sources for the carbon nanostructures. With the Pd nanoparticles embedded in the carbonized PAN nanofibers acting as catalysts, molecules of toluene, pyridine or chlorobenzine were decomposed into carbon species which were dissolved into the Pd nanoparticles and consequently grew into straight carbon nanotubes, Y-shaped carbon nanotubes or carbon nano-ribbons on the carbon nanofiber substrates. X-ray diffraction analysis and transmission electron microscopy (TEM) were utilized to capture the mechanism of formation of Pd nanoparticles, regular carbon nanotubes, Y-shaped carbon nanotubes and carbon nano-ribbons. It was observed that the Y-shaped carbon nanotubes and carbon nano-ribbons were formed on carbonized PAN nanofibers containing Pd-nanoparticle catalyst, and the carbon sources played a crucial role in the formation of different hierarchical carbon nanostructures.     

Sol-gel electrophoretic deposition of PZT nanotubes

Sol-gel electrophoretic deposition was utilized to grow lead zirconate titanate (PZT) nanotubes through a template-based process, using porous anodic alumina templates and an acetic acid-based PZT sol. The templates were prepared employing various anodizing voltages and times to achieve different pore diameters and lengths. The PZT sol was deposited into the template channels under the influence of a DC electric field. A single-firing process was developed to transform the dried precursor gels into the perovskite PZT phase. Scanning and transmission electron microscopy show the applicability of electrophoresis technique for the deposition of tubular PZT arrays. Electron diffraction patterns also indicate the amorphous nature of the template and polycrystalline structure of the tubes. X-ray diffraction studies indicate the perovskite structure of the grown PZT nanotubes.     

The effect of acidic treatment on the lithium storage capacity of multi-walled carbon nanotubes

In this research, multi-walled carbon nanotubes (MWCNTs) were modified by nitric acidic treatment to improve their electrochemical performance. The electrochemical performance of MWCNTs was evaluated by charge and discharge cycles. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectrum analysis techniques were used to characterize the samples. The closed tip or cap structures of pristine MWCNT were opened and the nanotubes were chopped after acidic treatment, which is beneficial to improve the lithium ion insertion/extraction into/from MWCNTs and lithium storage capacity. The graphite crystallinity of acid treated MWCNTs reduced slightly and disordered carbon structures were introduced at the surface of MWCNTs, which led to the large initial irreversible capacity.     

Hydrothermal synthesis of vanadium oxide nanotubes from oxide precursors

Vanadium oxide nanotubes were synthesized as the main product by a direct hydrothermal treatment of oxide precursors and long chain amines as structure-directing templates. The morphology and structure of nanotubes was characterized by powder X-ray diffraction, electron microscopy, and thermal analysis. Nanotubes of high aspect ratio with layered structures were found to grow together in the form of bundles. The paper also discusses the chemistry issues involved in synthesizing nanostructured vanadium oxides.     

Lithium insertion into multi-walled raw carbon nanotubes pre-doped with lithium

Raw carbon nanotubes are synthesized by the electric arc method and pre-doped with lithium. Electrochemical intercalation of lithium into the raw carbon nanotubes pre-doped with lithium is investigated. The results show that the irreversible and reversible capacity of the sample is about 500 and 200 mAh g⁻¹, respectively. The reversible capacity is higher than that of the raw carbon nanotubes and the open carbon nanotubes. The main reason is that LiNO₃ absorbed by the carbon nanotubes is decomposed into LiNO₂ at high temperature, and the lithium nitrite can form a film before the electrode contacts the electrolyte. The Li-containing compound film on the electrode surface can prevent the solvent to decompose into other products, so little charge is consumed in the electrolyte decomposition process. Complementary characterization techniques (elemental analysis, X-ray diffraction, scanning electron microscopy, constant-current charge–discharge tests) are used for a full structural characterization of the carbon nanotubes pre-doped with lithium and the electrochemical intercalation of lithium.     

Adsorption of streptavidin onto single-walled carbon nanotubes: application in fluorescent supramolecular nanoassemblies

We report the solubilization of full-length single-walled carbon nanotubes into a physiological buffer by sonication in presence of streptavidin. Transmission electron microscopy showed that the resultant dispersion was enriched of individual/small ropes of nanotubes. By the analysis of the crystal structure of tetrameric streptavidin and of the tryptophan emission of adsorbed proteins we hypothesized that proteins adsorbed onto SWNT sidewalls through their amine functionalities. Our results suggested using streptavidin as an interlinker between carbon nanotubes and semiconducting nanocrystals. We fabricated a supramolecular luminescent nanoassembly composed of individual or small ropes of full-length single-walled carbon nanotubes decorated with streptavidin-conjugated quantum dots. The luminescent nanoassembly was stably dispersed under physiological conditions and was readily visible by optical fluorescent microscopies.     

Ferromagnetic domains in EuS investigated by low-temperature Lorentz microscopy

Thin films of EuS, prepared by electron beam evaporation, were investigated by Lorentz microscopy in a special low-temperature object stage. In the thermally demagnetized state of an isotropic film, a multidomain configuration is observed with the smallest detectable domain size being about 200 nm. In the ac-demagnetized state, the domain configuration is similar to the configuration during a magnetization reversal. The magnetization reversal in an isotropic film starts by nucleation of small domains at inhomogeneities in the film, mostly at the edges, and by the growth of the nuclei. The domain configuration is strongly influenced by mechanical stress. The mechanical stress has an effect on the magnetization reversal of EuS similar to a field-induced anisotropy in NiFe films. The walls in EuS films down to a film thickness of 7 nm are Bloch walls.     

Synthesis of ZnO nanotube arrays and heterostructures of Cu-ZnO coaxial nanotubes by electrodeposition-oxidation method

Semiconductor ZnO nanotube arrays and heterostructures of Cu-ZnO coaxial nanotubes have been synthesized by electrodeposition into porous anodic alumina membranes and subsequent oxidation. Scanning electron microscopy and transmission electron microscopy indicate that the ZnO nanotubular arrays and Cu-ZnO coaxial nanotubular arrays are of large-area and highly ordered. X-ray diffraction patterns show that the nanotubes are polycrystalline. Photoluminescence spectra of the Cu-ZnO nanotubes show that a violet peak, a blue peak and a green peak are centered at 422 nm, 480 nm and 537 nm, respectively. The ordered ZnO nanotube arrays and heterostructures of Cu-ZnO coaxial nanotubes may have promising potential applications in nanodevices.     

Controlled fabrication of noble metal nanoparticles loaded on the surfaces of cyclotriphosphazene-containing polymer nanotubes

We report on the fabrication of noble metal nanoparticles loaded on the surfaces of cross-linked poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) nanotubes of high stability. PZS nanotubes were first synthesized by precipitation polymerization between hexachlorocyclotriphosphazene and 4,4′-sulfonyldiphenol based on in situ template mechanism. Then the PZS nanotubes were directly used as scafford to load metal Au, Ag, and Pd nanoparticles, respectively, through cation complexation followed by gentle reduction. The structure and morphology of the metal/PZS nanocomposites were determined by means of Fourier transform infrared spectra, energy dispersive X-ray spectroscopy, elemental analysis, X-ray diffraction, scanning electron microscope, transmission electron microscope, and thermogravimetric analysis (TGA). Results showed that the metal/PZS nanocomposites possessed 460 °C of initial thermal decomposition temperature under air atmosphere and the loading amount of metal nanoparticles on the PZS nanotube surfaces could be controlled easily. As-fabricated metal/PZS nanocomposites are expected to have potential applications in catalysis.