Onion-like fullerenes synthesis from coal

Onion-like fullerenes (OLFs) were synthesized in high yields from coal by radio frequency plasma. The morphologies and structures of the products were characterized by high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) technique. Results reveal that OLFs can be prepared from coal with high purity. The particles display a clear polyhedral or quasi-spherical morphology with hollow center, having an average diameter ranging from 10 nm to 35 nm and high degree of graphitization.     

Template free synthesis of highly ordered mullite nanowhiskers with exceptional photoluminescence

An efficient method to produce highly ordered mullite nanowhiskers using B₂O₃-doped molten salt synthesis was reported in this work. The morphology and optical properties of the obtained nanowhiskers were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) spectroscopy. The results show that highly ordered mullite nanowhiskers with uniform morphology in large scale are obtained at 1000 °C for 3 h in air. The structure of mullite is Al-rich and single crystalline. The diameter is in the range of 90–110 nm and length up to 20–30 μm. The reaction mechanism of the highly ordered mullite nanowhiskers is attributed to local concentration gradient. Due to the Al-rich structure, mullite nanowhiskers demonstrate strong photoluminescence (PL) emission at 399 nm, 452 nm and 468 nm, implying mullite nanowhiskers can be applied as a promising candidate in optical and electronic fields.     

Low-temperature synthesis of CdWO4 nanorods via a hydrothermal method

Cadmium tungstate (CdWO₄) nanorods were successfully synthesized via a hydrothermal process and characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and photoluminescent spectra techniques (PL). A pure monoclinic phase of well-crystallized CdWO₄ nanorods, with lengths of 250–400 nm and widths of 30–60 nm, could be readily synthesized at as low temperature as 70 °C.The CdWO₄ nanorods showed a PL emissions peak at 435 nm.     

Core–shell BaMoO4@SiO2 nanospheres: Preparation,characterization, and optical properties

Core–shell BaMoO₄@SiO₂ nanospheres were prepared in reverse microemulsions and exhibited enhanced photoluminescence (PL) intensity as compared to that of the uncoated BaMoO₄. Characterization was performed using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX), and X-ray powder diffraction (XRD). It was found that the silica shell could increase the PL intensity, but the shell is not the thicker the better. The PL emission can be decomposed into three individual Gaussian components: two UV emissions at 308 nm and 369 nm and a visible emission at 448 nm. Such short emission wavelengths can be attributed to quantum size effect of the small BaMoO₄ cores (～16 nm).     

Growth mechanism of β-SiC nanowires in SiC reticulated porous ceramics

Polycarbosilane (PCS) was used as a precursor to prepare SiC reticulated porous ceramics (RPCs) with in situ growth of β-SiC nanowires at 1000–1300 °C. The nanowires in diameters of ∼50 nm exist on the surface of the strut and in the fracture surface of strut in SiC RPCs. High resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) indicate that the nanowire consists of a twinned β-SiC, which grows along the 〈1 1 1〉 direction. Field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS) reveal that β-SiC nanowire grows by the vapor–liquid–solid (VLS) process at low temperature. The morphologies of the nanowire formed at different temperatures testify the process. As the heat-treated temperature increased, the growth mechanism of the nanowire changes from VLS to vapor–solid (VS).     

Effect of substrate temperature on microstructure and optical properties of nanocrystalline alumina thin films

Aluminum oxide (Al₂O₃) thin films were deposited on silicon (100) and quartz substrates by pulsed laser deposition (PLD) at an optimized oxygen partial pressure of 3.0×10^?3 mbar in the substrate temperatures range 300–973 K. The films were characterized by X-ray diffraction, transmission electron microscopy, atomic force microscopy, spectroscopic ellipsometry, UV–visible spectroscopy and nanoindentation. The X-ray diffraction studies showed that the films deposited at low substrate temperatures (300–673 K) were amorphous Al₂O₃, whereas those deposited at higher temperatures (≥773 K) were polycrystalline cubic γ-Al₂O₃. The transmission electron microscopy studies of the film prepared at 673 K, showed diffuse ring pattern indicating the amorphous nature of Al₂O₃. The surface morphology of the films was examined by atomic force microscopy showing dense and uniform nanostructures with increased surface roughness from 0.3 to 2.3 nm with increasing substrate temperature. The optical studies were carried out by ellipsometry in the energy range 1.5–5.5 eV and revealed that the refractive index increased from 1.69 to 1.75 (λ=632.8 nm) with increasing substrate temperature. The UV–visible spectroscopy analysis indicated higher transmittance (>80%) for all the films. Nanoindentation studies revealed the hardness values of 20.8 and 24.7 GPa for the films prepared at 300 K and 973 K respectively.     

Effect of plating parameters on the properties of pulse electrodeposited Ni–TiN thin films

The influence of pulse plating parameters on the microstructure, microhardness, and properties of the Ni–TiN thin films was investigated by transmission electron microscopy (TEM), atomic force microscopy (AFM), X–ray diffraction (XRD), scanning electron microscopy (SEM), and corrosion and wear tests. The results indicated the Ni–TiN thin films prepared via electrodeposition at 4 A/dm² current density to show an optimum microhardness and TiN content values of 984.7 HV and 8.69 wt%, respectively. The average grain sizes of Ni and TiN in the films obtained at 200 Hz were 127.8 and 48.5 nm, respectively. Numerous large pores can be noticed in the films prepared at pulse frequencies of 200 Hz and 500 Hz, whereas only a few small pits are visible on the surface of the Ni–TiN thin films deposited at 800 Hz. The films prepared at 20% duty cycle experienced the least weight loss.     

Preparation of carbon microfibers from coal liquefaction residue

Carbon microfibers (CMFs) were synthesized directly from coal liquefaction residue (CLR) by arc-jet plasma method at atmospheric pressure, and were examined using scanning electron microscopy and EDX spectroscopy. It has been found that the as-synthesized CMFs are smooth in surface and quite uniform in diameter that is smaller than 1 μm and centers at 700 nm. The possible mechanism involved in the formation process of CMFs is proposed and discussed in terms of the special chemical composition of CLR and the process parameters. This work may open a new way for direct and effective utilization of the CLR.     

Fabrication of cadmium titanate nanofibers via electrospinning technique

Here we present an electrospinning technique for the fabrication of cadmium titanate/polyvinyl-pyrrolidone composite nanofibers. The composite nanofibers are then annealed at 600 °C to obtain ilmenite rhombohedral phase cadmium titanate nanofibers. The structure, composition, thermal stability and optical properties of as synthesized and annealed cadmium titanate nanofibers are characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy and ultraviolet–visible spectroscopy. The average diameter and length of the nanofibers are found to be ～150–200 nm and ～100 μm, respectively.     

Onion-like carbon nanoparticles generated by multiple laser irradiations on laser-ablated particles

A one-step process to synthesize onion-like carbon nanoparticles at room temperature under atmospheric pressure was developed. Periodic pulsed laser irradiation of carbon nanoparticles confined in the cavity of a carbon target rod induces drastic changes to their structure, changing them from amorphous to ordered concentric graphitic shells. The size distribution of gas-borne nanoparticles measured by a scanning mobility particle sizer showed the mean mobility diameter decreased from 83 nm to 18 nm as a result of restructuring of carbon agglomerates. Polyhedral and unagglomerated nanoparticles with shell structures composed of multiple graphene sheets were observed by a transmission electron microscopy.     

Grazing-incidence small-angle X-ray scattering study on ultrananocrystalline diamond films

In this work, an ultrananocrystalline diamond film was studied with grazing-incidence small-angle X-ray scattering (GISAXS) to determine the diamond grain size and average distance of the grains with a non-destructive method and with excellent sampling statistics. The measured 2D GISAXS patterns were modelled with the assumption of monodisperse spheres. The best fits were obtained with the "buried layer" model where the spheres are correlated within the film plane. This correlation was approximated with a two-dimensional Percus–Yevick structure factor. The average diamond grain size of D = 8.0–8.5 nm and a centre-to-centre distance of the grains with 10.4–11.9 nm agrees well with transmission electron microscopy results of comparable samples.     

Electrochemical durability of single-wall carbon nanotube electrode against anodic oxidation in water

The electrochemical capability of single-wall carbon nanotube (SWCNT) electrodes is investigated to establish their reliability in practical applications. Direct current (DC) voltage of +10 V is applied across the SWCNT anode and Pt cathode in water, and the electrochemical fracturing behavior of SWCNTs is analyzed using transmission electron microscopy and atomic force microscopy. A considerable number of short SWCNTs, with lengths of less than 200 nm, are observed to be electrochemically generated. This result suggests that the anodic corrosion of SWCNTs occurs even in water, a non-electrolyte liquid. Raman spectroscopy and a comparison study of the anodization behavior of SWCNTs with narrow (0.9 nm) and wide (1.8 nm) diameters indicate that the durability of narrow SWCNTs is lower than that of the wide SWCNTs.     

Preparation and characterization of CuS hollow spheres

CuS hollow spheres have been successfully prepared using styrene–acrylic acid copolymer (PSA) latex particles as template. The process involved the deposition of inorganic coatings on the surface of PSA latex particles and subsequent removal of the latex particles by dispersing in toluene. The synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) and UV–vis absorption spectroscopy. The results showed the wall thickness of CuS shell to be about 20 nm and the pore diameter to be about 150 nm. The possible formation mechanism of CuS hollow spheres has been proposed.     

Formation of anatase TiO2 nanoparticles by simple polymer gel technique and their properties

Pure anatase nano-TiO₂ powders were successfully prepared by a simple polymer gel technique using poly-(vinylpyrrolidone) (PVP) as the polymer. The products were systematically characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), UV–visible spectroscopy and photoluminescence studies. The XRD and XPS results indicate that the prepared powder had a pure anatase nano-TiO₂ structure with lattice parameters a and c of 0.378 and 0.951 nm, respectively. The particle size analysed by TEM ranged between 7 and 12 nm. The maximum UV absorption for the TiO₂ nanoparticles was below 400 nm with an estimated direct band gap (Eg) of 3.55 eV. The photoluminescence peaks of the nanopowder were observed at 391 and 468 nm. The nanosized materials were produced using a simple and cost effective polymer gel technique.     

Heterogeneous diamond phases in compressed graphite studied by electron energy-loss spectroscopy

Chemical mapping imaged by electron energy-loss spectroscopy based on scanning transmission electron microscopy was conducted on a compressed graphite specimen containing different carbon allotropes (hexagonal diamond, cubic diamond, and graphite phases). This imaging process allows visualization of the complex spatial distribution of different diamond phases, and their coexistence was confirmed using dark field (DF) imaging. The chemical mapping images showed spatial distribution of local bonding state for hexagonal and cubic diamond phases in the whole specimen, while the DF images showed only a part of crystalline segments with long-range order. Thus, the chemical mapping method has an advantage for the purpose of observing locally the existence of individual carbon allotropes in the whole specimen. The size distribution of the hexagonal diamond phase is approximately 10–100 nm. These findings indicate that the compressing method can potentially synthesize ~ 100 nm large diamond phases.     

YAG:Ce3+ nanostructured particles obtained via spray pyrolysis of polymeric precursor solution

Cerium-doped yttrium aluminum garnet (YAG:Ce³⁺) powder phosphor is synthesized via spray pyrolysis of polymeric precursor solution obtained by dissolving the corresponding nitrates in ethylenediaminetetraacetic acid (EDTA). Ultrasonically generated aerosol droplets are decomposed at 600 °C in argon atmosphere. Following the initial attempt in providing pure YAG:Ce³⁺ phase generation the particles were additionally thermally treated for 3 h in air at 1000 and 1100 °C. The powder morphology is followed with scanning electron microscopy (SEM), while inner particle structure is analysed by analytical and high-resolution transmission electron microscopy (TEM). Phase identification is performed by X-ray powder diffraction (XRPD) based on which a structural refinement through Rietveld method was done. The spherical submicronic particles have grained sub-structure comprising clustered garnet monocrystals sized below 100 nm. The YAG:Ce³⁺ emission shows wide peak in the range 470–600 nm with the maximum near 520 nm.     

Growth and physical properties of individual single-walled carbon nanotubes

We have developed a versatile catalyst-assisted chemical vapor deposition (CVD) technique for the synthesis of single-walled carbon nanotubes (SWNTs) from discrete nickel nanoparticles (average diameter of 4.7 ± 1.4 nm). Atomic force microscopy (AFM), transmission electron microscopy (TEM) and micro-Raman spectroscopy are used to characterize these as-grown nanotubes. Using a conventional set-up, we are able to produce isolated SWNTs with a narrow diameter distribution (1.5 ± 0.5 nm). The advantages of such a versatile CVD method for the study of physical properties at the single nanotube level are illustrated by means of two prospective studies on vibrational and electrostatic properties of SWNTs.     

Investigation on mechanochemical combustion behavior of Mg–V2O5–Co3O4-C reactive system to synthesize VC–Co nanocomposite powder

VC–Co nanocomposite powders were obtained by mechanochemical combustion synthesis from a mixture of V₂O₅, Co₃O₄, C and Mg powders. The synthesized powders were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). VC–Co nanocomposite was directly produced after 10 min milling through a mechanically induced self-sustaining reaction without further heat treatment. TEM analysis showed that a nanostructured powder with a mean particle size of 100 nm was procured in the sample milled for 10 min.     

Fabrication of manganese oxide/three-dimensional reduced graphene oxide composites as the supercapacitors by a reverse microemulsion method

Manganese oxide (MnO₂)/three-dimensional (3D) reduced graphene oxide (RGO) composites were prepared by a reverse microemulsion (water/oil) method. MnO₂ nanoparticles (3–20 nm in diameter) with different morphologies were produced and dispersed homogeneously on the macropore surfaces of the 3D RGO. Scanning electron microscopy and transmission electron microscopy were applied to characterize the microstructure of the composites. The MnO₂/3D RGO composites, which were annealed at 150 °C, displayed a significantly high specific capacitance of 709.8 F g⁻¹ at 0.2 A g⁻¹. After 1000 cycles, the capacitance retention was measured to be 97.6%, which indicates an excellent long-term stability of the MnO₂/3D RGO composites.     

Carbon tubules containing nanocrystalline SiC produced by the graphitization of sugar cane bagasse

Sugarcane bagasse was milled using a high-pressure (100 MPaG) homogenizer and then graphitized in the temperature range 1800–2400 °C. The samples obtained were examined by transmission electron microscopy. Carbon tubules containing nanocrystalline SiC were discovered. Their diameter and length were ca. 50–200 nm and 2–30 μm, respectively.