PLD and RF-PLD synthesis of Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> ferroelectric thin films for electrically controlled devices

Ba_0.6Sr_0.4TiO₃ (BST) bulk ceramic synthesized by solid state reaction was used as target for thin films grown by pulsed laser deposition (PLD) and radiofrequency beam assisted PLD (RF-PLD). The X-ray diffraction patterns indicate that the films exhibit a polycrystalline cubic structure with a distorted unit cell. Scanning Electron Microscopy investigations showed a columnar microstructure with size of spherical grains up to 150 nm. The capacitance–voltage (C–V) characteristics of the BST films were performed by applying a DC voltage up to 5 V. A value of 280 for dielectric constant and 12.5% electrical tunability of the BST capacitor have been measured at room temperature.     

Electrical conduction mechanism in Fe<Subscript>70</Subscript>Pd<Subscript>30</Subscript> catalyzed multi-walled carbon nanotubes

Carbon nanotubes (CNTs) are synthesized by the catalytic decomposition of acetylene using low pressure chemical vapour deposition method (LPCVD) at 800 °C and at a chamber pressure of 10 Torr over a supported catalyst film of Fe₇₀Pd₃₀. Morphology of these CNTs is studied using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and High Resolution Transmission Electron Microscopy (HRTEM). From HRTEM image of these multi-walled carbon nanotubes (MWNTs), it is clear that these MWNTs do not possess a co-axial cylindrical structure, but are composed of imperfect and broken graphite cylinders of different sizes. The average diameter and length of the nanotubes varies between 20–70 nm and 5–60 μm respectively. Electrical transport measurements of these MWNTs are studied over a temperature range of 298–4.2 K. The results have been interpreted in terms of variable-range hopping (VRH) over the entire temperature range of 298–4.2 K. Three-dimensional variable-range hopping (VRH) is suggested for the temperature range (298–125 K), while two-dimensional VRH is observed for the temperature range (125–4.2 K).     

Effect of milling time and heat treatment on the composition of CuIn<Subscript>0.75</Subscript>Ga<Subscript>0.25</Subscript>Se<Subscript>2</Subscript> nanoparticle precursors and films

Preparation of pure phase CuIn_0.75Ga_0.25Se₂ nanoparticle powder by ball milling technique has been confirmed for the milling time of more than 45 min at 1200 rpm. Formation of shear bands responsible for breakdown of grains and generation of nanostructure during mechanical alloying, dislocation and defects induced due to milling has been studied by High-Resolution Transmission Electron Microscopy (HRTEM) analysis. Deviation in final composition of the products from those of starting materials has been discussed based on low volatilization of Se. Effect of milling time on the phase formation, particle size, and composition has been discussed in detail. Decrease in grain size from 12.44 to 7.96 nm has been observed with the increase in milling time. Mechanically induced self-propagating reaction mechanism which occurred during milling process is also discussed. Nanoparticle precursor was mixed with organic binder material for rheology of mixture to be adjusted for screen printing, and the films are subjected to heat treatment at five different temperatures in nitrogen ambient for 25 min. Average grain size calculated by Scherrer’s formula was almost the same irrespective of temperature. Reproducibility of precursor composition in the deposited films has been discussed in detail.     

Structural and optical properties of novel surfactant-coated Yb@TiO<Subscript>2</Subscript> nanoparticles

In this paper a novel hybrid approach to synthesise composite nanoparticles is presented. It is based on the laser ablation of a bulk target (Yb) immersed in a reversed micellar solution which contains nanoparticles of a different host material (TiO₂ nanoparticles) previously synthesised by chemical method. This approach thus exploits the advantages of the chemical synthesis through reversed micellar solution (size control, nanoparticle stabilisation), and of the laser ablation (“clean” synthesis, no side reactions). Central role is played by the microscopic processes controlling the deposition of the ablated Yb atoms onto the surface of TiO₂ nanoparticles which actually behave as nucleation seeds. The structural features of the resulting Yb@TiO₂ composite nanoparticles have been studied by Transmission Electron Microscopy, whereas their peculiar optical properties have been explored by UV–Vis spectroscopy and steady-state fluorescence. Results consistently show the formation of Yb and TiO₂ glued nanodomains to form nearly spherical and non-interacting nanoparticles with enhanced photophysical properties.     

Synthesis and characterization of poly(N-methylpyrrole)/TiO2 composites on steel

Poly(N-methyl pyrrole) coating was successfully electrodeposited on steel substrates in mixed electrolytes of dodecyl benzene sulphonic acid (DBSA) with oxalic acid in the absence and the presence of TiO₂ nanoparticles (NPs). The morphology and compositions were characterized by Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared Spectroscopy (FTIR), Energy-Dispersive X-ray spectroscopy (EDX). X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) were used to calculate the size of nanoparticles. Electrode/polymer/electrolyte system was studied by Electrochemical Impedance Spectroscopy (EIS). The FESEM micrographs suggest that the incorporation of TiO₂ nanoparticles affects the morphology of the film significantly and makes the TiO₂ to be loosely piled up with PMPy. The results of EIS showed that synthesized PMPy in the presence of TiO₂ NPs increases and decreases the R_po and C_c of the coating respectively. The increase of the area of synthesized PMPy in the presence of nanoparticles can increase its ability to interact with the ions liberated during the corrosion reaction of steel in NaCl solution.     

Characterization of Y<Subscript>2</Subscript>BaCuO<Subscript>5</Subscript> nanoparticles synthesized by nano-emulsion method

Nanoscale yttrium–barium–copper oxide (Y₂BaCuO₅, Y211) particles were synthesized using the emulsion method and the solution method. The basic water-in-oil (w/o) emulsion system consisted of n-octane (continuous oil phase), cetyltrimethylammonium bromide (cationic surfactant), butanol (cosurfactant) and water. The composition of the emulsion system was varied and characterized by measuring the conductivity of the solutions and droplet size. The droplet size of emulsion was determined by using the dynamic light scattering method. The water content, cosurfactant content, and surfactant/n-octane ratio affected the droplet size which was in the range of 3–8 nm, and hence the w/o emulsion system was referred to as a nano-emulsion system. A model was used to verify the droplet size. The influence of salt (Y₂(NO₃)₃) content on the droplet size was investigated and the addition of salt reduced the droplet size. The effects of reaction time and temperature on the Y211 particle sizes were also investigated. The particles were characterized using the TEM, SEM, and XRD. Nanoparticles produced by the nano-emulsion method were calcined at 850°C to form the Y211 phase as compared to solid state processing temperature of 1050°C. Based on the TEM analysis, the average diameter of the Y211 particles produced using the nano-emulsion method was in the range of 30–100 nm. The effect of adding 15% Y211 nanoparticles to the superconductor YBCO-123 as flux pinning centers, was investigated, and the transition temperature was reduced by 3 K.     

CoFe2O4 nanocrystalline powders prepared by citrate-gel methods: Synthesis, structure and magnetic properties

Nanocrystalline CoFe₂O₄ powders were prepared by decomposition of metal ion citrate precursors. Four samples were synthesized from precursor solutions having different pH values in the range <1–7.0. The powders were characterized by X-ray Diffraction, Thermogravimetry, Differential Thermal Analysis, N₂ physisorption and Transmission Electron Microscopy. Magnetic properties were explored by a SQUID magnetometer. Three out of the four samples, coming from solutions of pH 2, 4 and 7, were produced by an autocombustion reaction and are very similar as regards average size of the nanoparticles (about 20 nm), their morphology and the magnetic properties, while the fourth sample was produced by a slower thermal decomposition and is composed of smaller nanoparticles (about 10 nm).     

Immobilized TiO<Subscript>2</Subscript> nanoparticles produced by flame spray for photocatalytic water remediation

Anatase/rutile mixed-phase titanium dioxide (TiO₂) photocatalysts in the form of nanostructured powders with different primary particle size, specific surface area, and rutile content were produced from the gas-phase by flame spray pyrolysis (FSP) starting from an organic solution containing titanium (IV) isopropoxide as Ti precursor. Flame spray-produced TiO₂ powders were characterized by means of X-ray diffraction, Raman spectroscopy, and BET measurements. As-prepared powders were mainly composed of anatase crystallites with size ranging from 7 to 15 nm according to the synthesis conditions. TiO₂ powders were embedded in a multilayered fluoropolymeric matrix to immobilize the nanoparticles into freestanding photocatalytic membranes. The photocatalytic activity of the TiO₂-embedded membranes toward the abatement of hydrosoluble organic pollutants was evaluated employing the photodegradation of rhodamine B in aqueous solution as test reaction. The photoabatement rate of best performing membranes significantly overcomes that of membranes produced by the same method and incorporating commercial P25-TiO₂.     

Electrodeposition of diamond-like carbon (DLC) films on Ti

Diamond-like carbon films (DLC) were deposited on titanium substrates in acetonitrile and N,N-dimethyl formamide (DMF) liquids by the liquid-phase electrodeposition technique at ambient pressure and temperature. The applied voltage between the electrodes was high (1200 V) due to the use of resistive organic liquids. The surface morphology was examined by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Corrosion performance of the coatings was investigated by potentiodynamic polararization tests in phosphate buffer saline solution. Raman spectroscopy analysis of the films revealed two broad bands at approximately 1360 cm⁻¹ and 1580 cm⁻¹, related to D and G-band of DLC, respectively. The coated Ti was tested in a ball-on-plate type wear test machine with Al₂O₃ balls. The films presented a low friction coefficient (about 0.1), and the films deposited from DMF presented the best wear resistance.     

Hydrothermal synthesis of CeF<Subscript>3</Subscript> nanocrystals and characterization

CeF₃ nanocrystals with plate-like and perforated morphologies were successfully synthesized via a facile hydrothermal route. The nanocrystals of CeF₃@silica can dispersed in aqueous solution were also prepared. The effects of fluoride sources on the morphology and microstructure of the nanocrystals were investigated by means of transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and powder X-ray diffraction (XRD). Results indicate that the morphology of the rare earth compound nanocrystals can be well tuned by selecting proper fluoride sources. The ultraviolet (UV) absorption peak of the CeF₃ nanocrystals is slightly blue shifted along with the decrease of size. And the photoluminescence (PL) intensity of the CeF₃ nanocrystals is closely related to size and microstructure as well.     

One-step solid-state synthesis of nanosized LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode material with power properties

A simple one-step solid state reaction way of preparing nanosized LiMn₂O₄ powders with high-rate properties is investigated. Oxalic acid is used as a functional material to lose volatile gases during the process of calcining in order to control the morphology and change the particle size of materials. The results of X-ray diffraction and scanning electron microscopy show that particle size of materials decreases with the increase of the oxalic acid content. The electrochemical test results indicate that optimal LiMn₂O₄ particles (S_0.5) is synthesized when the molar ratios of oxalic acid and total Mn source are 0.5:1. It also manifests that LiMn₂O₄ sample with middle size has the optimal electrochemical performance among five samples instead of the smallest LiMn₂O₄ sample. The obtained sample S_0.5 with middle size exhibits a high initial discharge capacity of 125.8 mAh g^?1 at 0.2C and 91.4% capacity retention over 100 cycles at 0.5C, superior to any one of other samples. In addition, when cycling at the high rate of 10C, the optimal S_0.5 in this work could still reach a discharge capacity of 80.8 mAh g^?1. This observation can be addressed to the fact that the middle size particles balance the contradictory of diffusion length in solid phase and particle agglomeration, which leads to perfect contacts with the conductive additive, considerable apparent Li-ion diffusion rate, and the optimal performance of S_0.5.     

Synthesis of uniform quasi-octahedral CeO<Subscript>2</Subscript> mesocrystals via a surfactant-free route

A facile surfactant-free nonaqueous method is presented to prepare uniform quasi-octahedral ceria, CeO₂, mesocrystals, in which only Ce(NO₃)₃ and octanol were used as the reactants at a reaction temperature of 150 °C. CeO₂ sample synthesized using this technique consists of well-dispersed quasi-octahedrons and exhibits an uniform size and morphology. Based on structural characterization, it is proposed that the CeO₂ mesostructure was formed by self-assembly of primary nanocrystals based on unique 3D oriented-attachment mechanism. Optical characterization exhibited a strong quantum confinement, revealing small size of primary nanocrystals. The thermal stability and UV–Vis study reveal CeO₂ mesocrystal has various potential for high temperature applications and optical apparatus applications.     

Ultrasonication assisted and surfactant mediated synergistic approach for synthesis of calcium sulfate nano-dendrites

Calcium sulfate (CaSO₄) nano-dendrimers were fabricated successfully via ultrasonic irradiation method using calcium chloride [CaCl₂] and ammonium per sulfate [(NH₄)₂SO₄] as precursors in aqueous solution by using cetyl trimethyl ammonium bromide (CTAB) as chemical surfactants. Diffusion-induced branching growth mechanism (DIBGM), influenced with the action of head-group and hydrocarbon chain effect of cationic surfactants, was the backbone in the formation of CaSO₄ nano-dendrites. Fourier Transform Infra-red Spectroscopy (FTIR), X-Ray powder Diffraction (XRD), Atomic Emission Spectroscopy (AES), Selected Area Electron Diffraction (SAED), Field-Emission Scanning Electron Microscopy (FE-SEM), Energy-Dispersive Spectroscopy (EDS), Dynamic Light Spectroscopy (DLS) and BET surface area analyzer were used to characterize the products. Results obtained were compared with conventional stirring method that proved the superiority of sonication method to obtain well-crystalline nanostructures. Also, surfactant concentration, sonication frequency and time were noticed as the critical factors to generate such absolute morphologies at nano-crystalline size.     

Synthesis of bi-metallic Au–Ag nanoparticles loaded on functionalized MCM-41 for immobilization of alkaline protease and study of its biocatalytic activity

In this work, Au–Ag nanoparticles (Au–Ag-bi-MNPs) have been prepared on amine functionalized Si-MCM-41 (NH₂–Si-MCM-41) particles through a reduction of AgNO₃ and HAuCl₄ by NaBH₄ at ambient conditions. Au–Ag-bi-MNPs loaded on the NH2–Si-MCM-41, provide a good biocompatible surface for immobilization of the enzyme alkaline protease. This immobilization, presumably due to bonding between core shell nanoparticles and OH in serine 183 in alkaline protease seems to be of an ionic exchange nature. We found that the alkaline protease immobilized on the Au–Ag-bi-MNPs/Si-MCM-41 is an active biocatalyst, stable at different pH and temperature. The bio catalytic activity of free alkaline protease in solution was 64 U/mg (Units per milligram), whereas that of the alkaline protease immobilized on Au–Ag-bi-MNPs/Si-MCM-41 was 75 U/mg. This improvement of the biocatalytic activity may be due to a really increased activity per molecule of immobilized enzyme or to a purification of the enzyme. The alkaline protease molecules immobilized on the (Au–Ag)/ NH₂-MCM-41 surface retained as much as 80% of the catalytic activity recorded at pH=8, and showed significant catalytic activity of alkaline protease in the bioconjugate material. The biocatalytic materials were easily separated from the reaction medium by mild centrifugation and exhibits excellent reuse and stability characteristics over four successive cycles. The optimum temperature ranged from 35 ^°C–55 ^°C and pH=8 for bioactivity of the alkaline protease in the assembly system was observed to be higher than that of the free enzyme in solution. The enzyme biocatalytic activity was monitored by UV-visible spectroscopy. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and dispersive analysis of X-RAY (EDAX) were used to characterize the size and morphology of the prepared materials.     

Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> nanosquaresheets grown on Si substrate

A novel morphology of Bi₂O₃ nanomaterial (nanosquaresheets) has been successfully synthesized in large area by thermal evaporation of commercial Bi₂O₃ powder at high temperatures. The Bi₂O₃ nanosquaresheets (NSSs) are perfect regular squares and have sharp, uniform edges. The typical length of the sides is in the range of 200–600 nm. The thickness varies from 30 to 100 nm. Electron microscopy observations show that the Bi₂O₃ NSSs are single crystalline. The growth of Bi₂O₃ NSSs is probably controlled by a vapor–solid mechanism. The dominate growth directions are [2̄10] and [1̄2̄2] within the (245) planes. PACS 81.05.Hd; 81.10.Bk; 81.16.Be     

Synthesis and electrochemical performance of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C by organic solvent replacement drying method

A series of Li₃V₂(PO₄)₃/C composite cathodes have been prepared by the organic solvent replacement drying method. Five kinds of organic solvent including ethyl alcohol, butyl alcohol, 2-methoxyethanol, 1,2-propylene glycol, and ethylene glycol were used in the drying process to replace the water respectively. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge tests were employed to analyze the crystal structure, morphology, and electrochemical properties of the as-prepared materials. The results show that the organic solvent has a great influence on the secondary particle size of the as-synthesized materials. Special emphasis is placed on the sample prepared with 1,2-propylene glycol, which has the smallest average particle size and uniform distribution, thus leading to the best high rate performance and long-term cycling stability. The electrode exhibits average specific discharge capacities of 127.6, 128.3, 127.7, 126.7, 125.5, 124.4, 121.9, and 117.0 mAh g^?1 at 0.1, 0.2, 0.5, 1, 3, 5, 10, and 20C, respectively. More encouragingly, this sample delivers an outstanding cycle life with capacity retention of up to 94.68% even after 1000 cycles at 20C. Moreover, EIS results demonstrate that this sample has the minimum resistance and the largest apparent lithium ion diffusion coefficient (1.569 × 10^?7 cm² s^?1) which can facilitate to the Li⁺ diffusion during the charge/discharge process. Our results indicate that this preparation strategy can be facile and versatile for the synthesis of other high-rate and high-capacity intercalation materials.     

A novel way of modifying nano grain size by solution concentration in the growth of ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript> thin films

A novel route to the growth of thin films of ZnAl₂O₄ in nano-scale order was developed and nano-thin films of ZnAl₂O₄ are grown. The variation of grain size with solution concentration is reported. The thin film was deposited by modified liquid-phase deposition (LPD) technique using a novel acid based chemical reaction for the first time to ternary system. This modified LPD is based on a novel reaction that favours the formation of nanostructures during the treatment of a precursor (here ZnO) and a metal foil (Al) in diluted HF acid. The acid serves both as a solvent and catalyst. Usually, in wet process synthesis of binary systems, the metal foil will act as F⁻ ion scavenger. In this method, formation of a ternary compound as well as growth of thin film nanostructures of that compound was achieved by the same chemical reaction at room temperature. The role of acid concentration in the nanostructure formation is discussed. The relationship between HF concentration and grain size were also graphically enumerated. Structural, compositional and surface morphological properties of thin films were studied using Philips, Xpert-MPD: X-ray diffractometer and Philips, ESEM-TMP + EDAX, Nanoscope-III: AFM. The technique is a novel, simple and low cost route for the growth of nano-thin films of ternary oxide material.     

Synthesis of composite gold/tin-oxide nanoparticles by nano-soldering

Composite Au–SnO₂ nanoparticles (NPs) are synthesized by nano-soldering of pure Au and SnO₂ NPs. The multi-step process involves synthesis of pure Au and SnO₂ NPs separately by nanosecond pulse laser ablation of pure gold and pure tin targets in deionized water and post-ablation laser heating of mixed solution of Au colloidal and SnO₂ colloidal to form nanocomposite. Transmission Electron Microscopy (TEM) and High-Resolution Transmission Electron Microscopy (HRTEM) were used to study the effect of laser irradiation time on morphology of the composite Au–SnO₂ NPs. The spherical particles of 4 nm mean size were obtained for 5 min of post-laser heating. Increased mean size and elongated particles were observed on further laser heating. UV–vis spectra of Au–SnO₂ nanocomposites show red shift in the plasmon resonance absorption peak and line shape broadening with respect to pure Au NPs. The negative binding energy shift of Au 4f_7/2 peak observed in X-ray Photoelectron Spectra (XPS) indicates charge transfer in the nano-soldered Au–SnO₂ between gold and tin oxide and formation of soldered nanocomposite.     

Ultrasound assisted synthesis of amide functionalized metal-organic framework for nitroaromatic sensing

Nano plates of zinc(II) based metal-organic framework (MOF) were prepared via ultrasonic method without any surfactants at room temperature and atmospheric pressure. Control of particle size and morphology was enhanced in this synthesis method. Nano plates of an interpenetrated amide-functionalized metal-organic framework, [Zn₂(oba)₂(bpfb)]·(DMF)₅, TMU-23, (H₂oba = 4,4′-oxybis(benzoic acid); bpfb = N,N′-bis-(4-pyridylformamide)-1,4-benzenediamine, DMF = N,N-dimethyl formamide), was synthesized under ultrasound irradiation in different concentrations of initial precursor. The nano structure and morphology of the synthesized MOF were characterized by Field Emission Scanning Electron Microscopy (FE-SEM), powder X-ray diffraction, thermo gravimetric analysis (TGA), elemental analysis and FTIR spectroscopy. Moreover, Fluorescence emissions of nanoplates have been studied. Amide-functionalized MOF shows high selectivity for sensing of nitroaromatic compounds such as nitrophenol, nitroaniline, and nitrobenzene in acetonitrile solution. Fluorescence intensity decreased with increasing contents of nitroaromatics in acetonitrile solution due to fluorescence quenching effect.     

Photoinduced growth of Cu nanoparticles on ZnO from CuCl<Subscript>2</Subscript> in methanol

Cu nanoparticles were formed on surface of nano-ZnO by UV light induced photoreduction of CuCl₂ in methanol solution suspended with ZnO nanoparticles. By controlling the reaction conditions, the average size of the produced copper nanocrystal can be fine-tuned in the range of 10–200 nm. At constant UV irradiation, the Cu nanocrystals gradually grew up as the initial concentration of copper cation was increased, showing that the in situ formed Cu nanoparticles act as a bridge to facilitate the transferring of photoexcited electrons from ZnO surface to Cu²⁺ in solution. A Redox property was also proved for the Cu nanoparticles.