Structure of the amorphous phase of pyrolisates of lanthanum diphthalocyanine according to X-ray scattering data

Data on X-ray diffraction in lanthanum diphthalocyanine pyrolysates synthesized at temperatures of 800–1800°С demonstrate the formation of an amorphous carbon phase with embedded lanthanum atoms. Low-temperature pyrolysis (800–900°С) creates layered carbon structures. Due to annealing at 1000°С, carbon integrates into globules whose number of atoms is m ~ 100. Such structures with gyration radii of R _g ~ 0.4–0.5 nm on the order of the precursor molecule size are synthesized in the temperature range of 1000–1800°С, and are stable in terms of size and mass. In this case, their density approaches that of graphite.     

Size-dependent transformation from Ag templates to Au–Ag nanoshells via galvanic replacement reaction in organic medium

The transformation from Ag templates to Au?CAg nanoshells via galvanic replacement reaction with HAuCl₄ was systematically studied in an organic medium in the presence of oleylamine. Decahedral (~43?nm in size) and triangular prism (~53?nm in edge length) Ag templates transformed into equiaxed and triangular prismatic Au?CAg nanoshells, respectively. The first step involved structural and morphological changes from Ag templates to Au?CAg nanoshells with an interior cavity. In the second step, the growth of the shells continued through the deposition of Au. The shell thickness increased from ~5 to ~10?nm for the equiaxed Au?CAg nanoshells (~39-nm interior cavity) and ~5 to ~8?nm for the triangular prismatic Au?CAg nanoshells (~52-nm interior edge length). Oleylamine not only served as a surfactant but also removed AgCl precipitates and reduced HAuCl₄. For the nanoshells derived from the ~20-nm Ag decahedrons, further reaction in excess HAuCl₄ collapsed the nanoshells into Au-rich solid fragments. However, the nanoshells derived from the ~43-nm Ag decahedrons, the nanoshell structure not only persisted in excess HAuCl₄, but its shell thickness also increased. The size-dependent transformation of these nanoshells is discussed.     

Surface Plasmon Resonance and Field Enhancement of Au/Ag Alloyed Hollow Nanoshells

We investigate the nanostructure, surface plasmon resonance （SPR） absorption and nonlinear enhancement of Au/Ag alloyed hollow nanoshells prepared by the replacement reaction of Ag nanoparticles in a HAuCI4 aqueous solution. As the volume of HAuCl4 increases from OmL to 0.S mL, the SPR band of the Au/Ag alloyed nanoshells is tuned from 430nm to 780nm, and the third-order nonlinear optical susceptibility is enhanced nearly by an order of magnitude, which indicates a large enhancement of local field in the Au/Ag alloyed hollow nanoshells with hole defects.     

Catalytic growth of nickel-encapsulated and hollow graphitic carbon nanoparticles during laser vaporization of cellulose char containing nickel

Nickel-encapsulated and hollow graphitic carbon nanoparticles (CNPs) with diameters of up to 200 nm were fabricated from cellulose char containing nickel, by continuous wave Nd:YAG laser vaporization. The relative yields of the Ni-encapsulated and hollow CNPs strongly depended on the laser power density and the quantity of Ni in the cellulose char. The hollow CNPs with yields of up to 90% were successfully formed with increasing laser power density. A net-like structure composed of small fragments of bending graphitic layers was also produced under an excess condition of the cellulose char. We discuss the formation mechanisms of the CNPs, in which the growth of graphitic layers around Ni particles and their separation repeatedly occur after the start of laser irradiation. PACS 81.05.Uw; 81.07.Wx; 81.16.Mk     

Effect of annealing temperature on optical and electrochemical properties of chitosan–ZnO nanostructure

Chitosan–ZnO nanostructures were prepared by chemical precipitation method using different concentration of zinc chloride and sodium hydroxide solutions. Nanorod-shaped grains with hexagonal structure for samples annealed at 300 °C and porous structure with amorphous morphology for samples annealed at 600 °C were revealed in SEM analysis. X-ray diffraction patterns confirmed the hexagonal phase ZnO with crystallite size found to be in the range of ~24.15–34.83 nm. Blue shift of UV–Vis absorption shows formation of nanocrystals/nanorods of ZnO with marginal increase in band gap. Photoluminescence spectra show that blue–green emission band at 380–580 nm. The chitosan–ZnO nanostructures used on surface of a glassy carbon electrode gives the oxidation peak potential at ~0.6 V. The electrical conductivity of chitosan–ZnO composites were observed at 2.1?×?10^?5 to 2.85?×?10^?5?S/m. The nanorods with high surface area and nontoxicity nature of chitosan–ZnO nanostructures observed in samples annealed at 300 °C were suitable as a potential material for biosensing.     

Effect of temperature on the hybrid supercapacitor based on NiO and activated carbon with alkaline polymer gel electrolyte

A hybrid supercapacitor was fabricated with NiO and activated carbon as positive and negative electrode, PVA–KOH–H₂O containing 5 M KOH as alkaline polymer gel electrolyte, respectively. Cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge measurements were applied to investigate the dependence of the hybrid supercapacitor on the temperatures from − 20 to 40 °C. The results demonstrated that the capacitive performance of the hybrid supercapacitor turned even better with the temperatures rising up from − 20 to 40 °C. The increase of temperature improved the conductivity of the alkaline polymer gel electrolyte, decreased the charge-transfer resistance and made the better contact at the interface between the electroactive materials and the alkaline gel electrolyte at higher operating temperature. The maximum of the specific capacitance and energy density of the hybrid supercapacitor were 73.4 F/g and 26.1 Wh/kg at the current density of 0.1 A/g and the operating temperature of 40 °C, respectively.     

Synthesis of nano-polycrystalline diamond from glassy carbon at pressures up to 25 GPa

ABSTRACT

Nano-polycrystalline diamond (NPD) with various grain sizes has been synthesized from glassy carbon at pressures 15–25?GPa and temperatures 1700–2300°C using multianvil apparatus. The minimum temperature for the synthesis of pure NPD, below which a small amount of compressed graphite was formed, significantly increased with pressure from ～1700°C at 15?GPa to ～1900°C at 25?GPa. The NPD having grain sizes less than ～50?nm was synthesized at temperatures below ～2000°C at 15?GPa and ～2300°C at 25?GPa, above which significant grain growth was observed. The grain size of NPD decreases with increasing pressure and decreasing temperature, and the pure NPD with grain sizes less than 10?nm is obtained in a limited temperature range around 1800–2000°C, depending on pressure. The pure NPD from glassy carbon is highly transparent and exhibits a granular nano-texture, whose grain size is tunable by selecting adequate pressure and temperature conditions.     

Effect of nickel catalyst on physicochemical properties of carbon xerogels as electrode materials for supercapacitor

Carbon xerogels and Ni-doped carbon xerogels prepared by the sol-gel polymerization were examined to reveal the effect of metallic nickel incorporated in carbon matrix on the physicochemical properties of carbon xerogels and their electrochemical performance for supercapacitor electrode in aqueous 6 M KOH solution. As shown by XRD and XPS measurements, the decomposition of nickel precursor in carbon matrix led to the creation of well-crystalline particles of metallic nickel which gave rise to the changes in the morphology, chemical and porous structure of carbon xerogels. Due to the modification of porous structure the surface area increased from 595 m²/g via 632 m²/g up to 660 m²/g for carbon xerogel, 7 wt% and 10 wt% Ni-doped composites, respectively. The enhancement of the surface area occurred along with diminishing the BJH average pore diameter. The value for nickel free xerogel amounted to 11.35 nm, whereas the value of 5.71 nm was measured for 10 wt% Ni xerogel. The changes in the porous and chemical structure created during the formation of carbon-nickel composites as well as the pseudo-capacitive effects arising from the redox reaction of nickel particles present in carbon matrix brought about a significant improvement of electrode capacitance. Electrochemical measurements showed that in comparison with capacitances measured for nickel free electrode (82.1 F/g calculated using the cyclic voltammetry and 88.8 F/g calculated using the galvanostatic charge/discharge method), the respective capacitances for 10 wt% Ni-doped carbon xerogel increased up to 103.0 F/g and 103.4 F/g. These values correspond to 25 and 16% improvement, respectively.     

Effect of annealing temperature on the structure of pyrolysates of diphthalocyanines of rare-earth elements: Neutron research

Small-angle neutron scattering is used to study the structure of carbon matrices—the pyrolysis products of diphthalocyanines with embedded metal atoms (Y, La, and Ce), synthesized at annealing temperatures of 800–1700°C. It is shown that the structure of the porous matrix on the scale of ～10⁰–10² nm is characterized by a level of small pores (3–10 nm in radius) and the next level of the structure is associated with the formation of their aggregates (above 100 nm in size). The quantity and size of the scattering objects increases sharply at annealing temperatures above 1000°C. The results are consistent with X-ray diffraction data.     

Reflectance spectroscopy of gold nanoshells: computational predictions and experimental measurements

Gold nanoshells are concentric spherical constructs that possess highly desirable optical responses in the near infrared. Gold nanoshells consist of a thin outer gold shell and a silica core and can be used for both diagnostic and therapeutic purposes by tuning the optical response through changing the core–shell ratio as well as the overall size. Although optical properties of gold nanoshells have already been well documented, the reflectance characteristics are not well understood and have not yet been elucidated by experimental measurements. Yet, in order to use gold nanoshells as an optical contrast agent for scattering-based optical methods such as reflectance spectroscopy, it is critical to characterize the reflectance behavior. With this in mind, we used a fiber-optic-based spectrometer to measure diffuse reflectance of gold nanoshell suspensions from 500 nm to 900 nm. Experimental results show that gold nanoshells cause a significant increase in the measured reflectance. Spectral features associated with scattering from large angles (~180°) were observed at low nanoshell concentrations. Monte Carlo modeling of gold nanoshells reflectance demonstrated the efficacy of using such methods to predict diffuse reflectance. Our studies suggest that gold nanoshells are an excellent candidate as optical contrast agents and that Monte Carlo methods are a useful tool for optimizing nanoshells best suited for scattering-based optical methods.     

Self-formation of GaN hollow nanocolumns by inductively coupled plasma etching

GaN hollow nanocolumns were formed by inductively coupled plasma etching. It was found that the tops of the GaN nanocolumns were hexagonal with the c axis perpendicular to the substrate surface. It was also found that the density of the GaN nanocolumns depends strongly on etching parameters, which suggests that the formation of these GaN nanocolumns was not related to the dislocation density in the original GaN epitaxial layers. With an Ar concentration of 42.86%, it was found that the diameter of the whole nanocolumns was around 80 nm and the diameter of the nanocavities inside these nanocolumns was around 40 nm, while the density of the nanocolumns was around 4.4×10⁹ cm^-2. PACS 68.65.-K; 61.70.+w; 81.10.BK     

Liquid Crystalline Dispersions of Graphene‐Oxide‐Based Hybrids: A Practical Approach towards the Next Generation of 3D Isotropic Architectures for Energy Storage Applications

We report the use of the spray pyrolysis method to design self‐assembled isotropic ternary architectures made up of reduced graphene oxide (GO), functionalized multiwalled carbon nanotubes, and nickel oxide nanoparticles for cost‐effective high‐performance supercapacitor devices. Electrodes fabricated from this novel ternary system exhibit exceptionally high capacitance (2074 Fg^?1) due to the highly conductive network, synergistic link between GO and carbon nanotubes and achieving high surface area monodispersed NiO decorated rGO/CNTs composite employing the liquid crystallinity of GO dispersions. To further assess the practicality of this material for supercapacitor manufacture, we assembled an asymmetric supercapacitor device incorporating activated carbon as the anode. The asymmetric supercapacitor device showed remarkable capacity retention (>96%), high energy density (23 Wh kg^?1), and a coulombic efficiency of 99.5%.     

Changes in the chemical state and concentration of iron in carbon nanotubes obtained by the CVD method and exposed to pulsed ion irradiation

Data on the distribution of iron in nitrogen-containing multiwall carbon nanotubes (N-MWCNTs) and changes in its chemical state and concentration under different parameters of irradiation by a pulsed ion beam are obtained by methods of transmission electron microscopy, X-ray photoelectron spectroscopy, and energy dispersion analysis. It is shown that the irradiation of N-MWCNTs with an energy density of 0.5 J/cm² lead to the formation, on their lateral surfaces, of structures with a size of 2–10 nm, consisting of metallic iron encapsulated in a carbon shell. An increase in the energy density to 1–1.5 J/cm² leads to a substantial removal of iron clusters from the tips of carbon nanotubes and a reduction in the amount of iron in the bulk of the N-MWCNT layer.

     

Hierarchically Porous NaCoPO4–Co3O4 Hollow Microspheres for Flexible Asymmetric Solid‐State Supercapacitors

A template‐free hydrothermal method is developed to prepare hierarchical hollow precursors. An inside‐out Ostwald ripening mechanism is proposed to explain the formation of the hollow structure. After the calcination in the air, hierarchically meso/macroporous NaCoPO₄–Co₃O₄ hollow microspheres can easily be obtained. When being evaluated as electrode materials for a supercapacitor, the hierarchically porous NaCoPO₄–Co₃O₄ hollow microspheres electrode shows a specific capacitance of 268 F g^?1 at 0.8 A g^?1 and offers a good cycle life. More importantly, the obtained materials are successfully applied to fabricate flexible solid‐state asymmetric supercapacitors. The device exhibits a specific capacitance of 28.6 mF cm^?2 at 0.1 mA cm^?2, a good cycling stability with only 5.5% loss of capacitance after 5000 cycles, and good mechanical flexibility under different bending angles, which confirms that the hierarchically porous NaCoPO₄–Co₃O₄ hollow microspheres are promising active materials for the flexible supercapacitor.     

Optimal design of gold nanoshells for optical imaging and photothermal therapy

Gold nanoshells are of great interest in optical imaging based on their light scattering properties and photothermal therapy due to their light absorption properties. Strong light scattering is essential for optical imaging, while effective photothermal therapy requires high light absorption. In this article, the optimal core radii and shell thicknesses of silica–gold and hollow gold nanoshells, possessing maximal light scattering and absorption at wavelengths between 700 and 1100 nm, are obtained using the Mie theory of a coated sphere. The results show that large-sized gold nanoshells of high aspect ratios (the aspect ratio is defined as the ratio of core radius to shell thickness) are the efficient contrast agents for optical imaging, while smaller gold nanoshells of high aspect ratios are the ideal therapeutic agents for photothermal therapy. From the comparison of the numerical results for silica–gold and hollow gold nanoshells, the latter are seen to offer a little superior light scattering and absorption at smaller particle size. Fitting expressions for the optimal core radii and shell thicknesses are also obtained, which can provide design guidelines for experimentalists to optimize the synthetic process of gold nanoshells.     

Synthesis,structure, and magnetic properties of iron and nickel nanoparticles encapsulated into carbon

Nanocomposites based on iron and nickel particles encapsulated into carbon (Fe@C and Ni@C), with an average size of the metal core in the range from 5 to 20 nm and a carbon shell thickness of approximately 2 nm, have been prepared by the gas-phase synthesis method in a mixture of argon and butane. It has been found using X-ray diffraction, transmission electron microscopy, and Mössbauer spectroscopy that iron nanocomposites prepared in butane, apart from the carbon shell, contain the following phases: iron carbide (cementite), α-Fe, and γ-Fe. The phase composition of the Fe@C nanocomposite correlates with the magnetization of approximately 100 emu/g at room temperature. The replacement of butane by methane as a carbon source leads to another state of nanoparticles: no carbon coating is formed, and upon subsequent contact with air, the Fe₃O₄ oxide shell is formed on the surface of nanoparticles. Nickel-based nanocomposites prepared in butane, apart from pure nickel in the metal core, contain the supersaturated metastable solid solution Ni(C) and carbon coating. The Ni(C) solid solution can decompose both during the synthesis and upon the subsequent annealing. The completeness and degree of decomposition depend on the synthesis regime and the size of nickel nanoparticles: the smaller is the size of nanoparticles, the higher is the degree of decomposition into pure nickel and carbon. The magnetization of the Ni@C nanocomposites is determined by several contributions, for example, the contribution of the magnetic solid solution Ni(C) and the contribution of the nonmagnetic carbon coating; moreover, some contribution to the magnetization can be caused by the superparamagnetic behavior of nanoparticles.     

Fabrication of microporous hollow silica spheres templated by NP-10 micelles without calcinations

We reported a novel method to fabricate hollow silica microspheres using nonionic surfactant nonyl phenol ethoxylated decylether (NP-10) micelles as template, n-octadecane as core and sodium silicate as silica precursor. The core materials were removed by ethanol during the reaction. Hollow structure formed without calcinations or chemical etching. Hierarchical silica hollow microspheres were prepared by changing the concentration of the reactants and reaction time. Size of the core materials was obtained from the temperature-dependent dynamic light scattering (DLS) measurement. Scanning election microscopy (SEM) and transmission electron microscopy (TEM) results revealed that ordered microporous hollow silica microspheres with thickness of shell about 200 nm and mean diameter 2.5 μm were prepared. Porosity and pore size were analyzed by Brunauer-Emmett-Teller (BET).     

Annealed Ni/Ti/SiC structure analysed by SIMS and GDMS

Depth profile analysis was performed using two mass spectrometry analytical techniques applying argon ion sputtering—secondary ion mass spectrometry (SIMS) and glow discharge mass spectrometry (GDMS). 150 nm Ni/20 nm Ti/4H-SiC structure was prepared by evaporation coating with titanium and nickel. The structure was analysed as prepared and annealed in 600°C in dry N₂. Obtained results allow monitoring several processes present during annealing of Ni/Ti/SiC structures. These are nickel diffusion and its reaction with SiC leading to formation of Ni₂Si, precipitation of carbon and segregation of titanium. Results are also used for comparison of the two analytical techniques used. The techniques base on different ionisation mechanisms. In SIMS, secondary ions are formed at the bombarded surface during ion sputtering process in ultra-high vacuum environment, while in GDMS, ionisation occurs in glow discharge above the eroded surface in low vacuum.     

Modification of the electronic structure of graphene by intercalation of iron and silicon atoms

The ab initio calculations of the electronic structure of low-dimensional graphene–iron–nickel and graphene–silicon–iron systems were carried out using the density functional theory. For the graphene–Fe–Ni(111) system, band structures for different spin projections and total densities of valence electrons are determined. The energy position of the Dirac cone caused by the p _z states of graphene depends weakly on the number of iron layers intercalated into the interlayer gap between nickel and graphene. For the graphene–Si–Fe(111) system, the most advantageous positions of silicon atoms on iron are determined. The intercalation of silicon under graphene leads to a sharp decrease in the interaction of carbon atoms with the substrate and largely restores the electronic properties of free graphene.

     

Spherical shape BaO-ZnO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> glass powders prepared by spray pyrolysis

Fine-sized BaO-ZnO-B₂O₃-SiO₂ (BZBS) glass powders were directly prepared by high temperature spray pyrolysis. The hollow glass powders prepared at low preparation temperature of 1000 °C had a low density of 2.65 g/cm³. However, the densities of the BZBS powders obtained at preparation temperatures of 1200 and 1400 °C were each 3.92 and 4.13 g/cm³. The mean size of the BZBS glass powders prepared by spray pyrolysis at preparation temperature of 1400 °C was 0.98 μm. The glass transition temperature (T_g) of the prepared BZBS glass powders was 518.9 °C. The dielectric layers formed from the prepared BZBS glass powders with a dense structure had a clean surface and a dense inner structure without voids at the firing temperature of 580 °C. The transparencies of the dielectric layers formed from the prepared BZBS glass powders were higher than 90% within the visible range. PACS 42.70.Ce; 85.60.Pg; 71.55.Jv