Formation of V2O3 nanocrystals by thermal reduction of V2O5 thin films

We report the formation of homogeneous and stable V₂O₃ nanocrystals, directly from V₂O₅ thin films, at 600 °C, as observed by using in situ electron microscopy experiments. Thermally-induced reduction of V₂O₅ thin films in vacuum is remarkably different when compared to reduction of V₂O₅ single crystals and results in the formation of nanophase V₂O₃. Thermally grown V₂O₃ nanocrystals exhibit hexagon or square shape and are stable at higher temperature as well as room temperature. The formation of stable nanocrystals through the reduction process in a non-chemical environment (vacuum) could provide a basis for understanding the complex processes of vanadium oxide phase transitions and for controlling the chemical processes to produce oxide nanocrystals.     

Structure and surface characterization of ZrO2-Y2O3-Cr2O3 system

3-mol% Y₂O₃ and 0.3 to 3-mol % Cr₂O₃ co-doped ZrO₂ nanopowders were synthesized using co-precipitation technique and investigated by terms of X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Structural analysis shows no significant impact of chromium on powders structure except of presence of small amount of m-phase. Surface analysis reveals segregation of yttrium and chromium atoms to the surface along with surface enrichment by oxygen that can be attributed to residual water. Chromium surface atoms present in three oxidation states with catalytically active Cr²⁺ sites possibly controlling m-phase appearance through lattice distortion.     

Synthesis of LECBD grown cluster assembled SeO2 thin films

Cluster assembled selenium oxide (SeO₂) thin films, as a function of oxygen flow pressure (OFP) have been synthesized by a low energy cluster beam deposition (LECBD) technique. The OFP dependent surface morphology leading to well separated nanoclusters (size ranging from 50 to 200 nm) and fractal features are confirmed from transmission electron microscopic (TEM) measurements. A diffusion limited aggregation (DLA) mediated fractal growth with dimension as 1.71 ± 0.01 has been observed for high OFP (60 mbar). Structural analysis by glancing angle X-ray diffraction (GXRD) and selected area diffraction (SAD) studies identify the presence of tetragonal phase SeO₂ in the deposit. Micro-Raman studies indicate the shifts in bending and stretching vibrational phonon modes in cluster assembled SeO₂ as compared to their bulk counter part due to the phonon confinement effect.     

Electrostatic assembly of Cu2O nanoparticles on DNA templates

In this paper, a method for highly ordered assembly of cuprous oxide (Cu₂O) nanoparticles (NPs) by DNA templates was reported. Cetyltrimethylammonium bromide (CTAB)-capped Cu₂O NPs were adsorbed onto well-aligned λ-DNA chains to form necklace-like one-dimensional (1D) nanostructures. UV-vis, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the nanostructure. The Cu₂O nanostructures fabricated with the method are both highly ordered and quite straight.     

Structural studies of annealed neodymia-silica composite synthesized by solgel technique

Nd₂O₃-SiO₂ binary oxide was prepared by solgel technique using tetra-ethoxysilane and neodymium nitrate as precursor materials and HCl as a catalyst. The prepared samples were subjected to heat treatment in the temperature range from 600 to 1100 °C for different time duration. Characterization of heat treated samples was carried out by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The effect of sintering temperature and time on structural changes of Nd-doped silica has been discussed. The sample sintered at 1100 °C for 12 h shows the formation of monoclinic Nd₂O₃ nanocrystallites in silica matrix with average grain size ∼18 nm.     

Formation of gold nanoparticles in heat-treated reactive co-sputtered Au-SiO2 thin films

In this work, formation of gold nanoparticles in radio frequency (RF) reactive magnetron co-sputtered Au-SiO₂ thin films post annealed at different temperatures in Ar + H₂ atmosphere has been investigated. Optical, surface topography, chemical state and crystalline properties of the prepared films were analyzed by using UV-visible spectrophotometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and X-ray diffractometry (XRD) techniques, respectively. Optical absorption spectrum of the Au-SiO₂ thin films annealed at 800 °C showed one surface plasmon resonance (SPR) absorption peak located at 520 nm relating to gold nanoparticles. According to XPS analysis, it was found that the gold nanoparticles had a tendency to accumulate on surface of the heat-treated films in the metallic state. AFM images showed that the nanoparticles were uniformly distributed on the film surface with grain size of about 30 nm. Using XRD analysis average crystalline size of the Au particles was estimated to about 20 nm.     

Synthesis and characterization of novel red emitting nanocrystal Gd6WO12:Eu phosphors

Novel nanosized Gd₆WO₁₂:Eu³⁺ phosphors were synthesized via a co-precipitation reaction. The crystal structure and morphology of the phosphors were characterized by using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). It was found that the resultant powders show a regular and sphere-like shape with average particle size of 60 nm. Intrinsic red emission originating from Eu³⁺ was observed while excited at the W⁶⁺→O²⁻ and Eu³⁺→O²⁻ charge transfer bands or f-f absorption bands. The color coordinates of the phosphors were calculated to be x=0.625, y=0.375. The concentration dependence of the luminescence was studied, and optimum doping concentration for obtaining maximum emitting intensity was confirmed to be around 12 mol%. It was also found that the electric dipole-dipole interaction plays an important role for quenching luminescence of Eu³⁺.     

Magnetic properties of chalcogenide spinel CuCr2Se4 nanocrystals

The magnetic properties of chalcogenide spinel CuCr₂Se₄ nanocrystals have been studied as a function of crystallite size (15-30 nm). A solution-based method is used for the facile synthesis of the nanocrystals with good size control. They have close to cubic morphology with a narrow size distribution and exhibit superparamagnetic behavior at room temperature. The Curie temperature and saturation magnetization of the nanocrystals are lower as compared with the bulk and decrease with decreasing nanocrystal size. A similar trend is observed in the paramagnetic state for the Curie-Weiss temperature and effective magnetic moment. The low temperature magnetization behavior can be qualitatively explained by spin glass dynamics.     

Magnetic nanocomposite thin films of BaFe12O19 and TiO2 prepared by sol-gel method

The composite films with different weight ratio of barium ferrite to titanium dioxide are successfully prepared using sol-gel method for the first time. The morphology, crystal structure and magnetic properties of composite films are investigated with atomic force microscopy, X-ray diffraction and vibrating sample magnetometry. The results show that the composite films are uniform with no microcracks. The grain diameters are less than 100 nm. With the increase of barium ferrite, the grain diameter decreases. The composite films are composed of M-type hexagonal barium ferrite and rutile titanium dioxide. The composite films possess the excellent magnetic properties. The specific saturation magnetization and coercivity reach 18.3 emu/g and 3350 Oe, respectively. The application of composite films in magnetic recording and electromagnetic absorption fields is promising.     

Structural and Optical Properties of Nanocrystal In2O3 Films by Thermal Oxidation of In2S3 Films

In₂S₃ nanocrystalline films are prepared on glass substrates by the spray pyrolysis technique using indium chloride and thiourea as precursors. The deposition is carried out at 350°C on glass substrates. The films are then annealed for two hour at 200, 400, 600, and 800°C in O₂ flow. This process allows the transformation of nanocrystal In₂O₃ films from In₂S₃ films and the reaction completes at 600°C. These results indicate that the In₂O₃ film prepared by this simple thermal oxidation method is a promising candidate for electro-optical and photovoltaic devices.     

Preparation of the SrFe12O19-based magnetic composites via boron oxide glass devitrification

Magnetic composites were obtained in the system SrO–Fe₂O₃–B₂O₃ by oxide glass heat treatment at 600–950 °C. Samples of the composites were investigated using XRD analysis, magnetic measurements, electron microcopy, and thermal analysis. It was shown that chemical composition of the precursor oxide glass and thermal treatment conditions influenced on the SrFe₁₂O₁₉ particles morphology and magnetic properties. The composites and powders were obtained containing hexaferrite as single domain platelet crystals or polycrystalline aggregates with a coercive force up to 6300 Oe in the former case and 4200 Oe in the latter case.     

EPR and magnetic properties of MgO-CaO-SiO2-P2O5-CaF2-Fe2O3 glass-ceramics

Glass-ceramics have been derived from 4.5MgO(45−x)CaO34SiO₂16P₂O₅0.5CaF₂xFe₂O₃ (x=5, 10, 15, 20 wt%) glasses by heat treatment. Room temperature electron paramagnetic resonance (EPR) spectra and temperature-dependent magnetic susceptibility (χ) of the glass-ceramics have been obtained. The EPR absorption line centered at g≈4.3 disappeared at higher concentrations of iron oxide. The intensity and line width of the EPR absorption line centered at g≈2.1 increased as the iron oxide concentration was increased. Temperature-dependent magnetization of samples with low iron oxide content revealed ferrimagnetic as well as paramagnetic contributions. Information about the structural changes involving iron ions, their valence state and the type of magnetic interactions between the Fe ions as a function of composition was obtained using EPR and χ studies.     

Effects of precursor types of Fe and Ni components on the properties of NiFe2O4 powders prepared by spray pyrolysis

The effects of the precursor types of Ni and Fe components on the morphology, mean size, and magnetic property of NiFe₂O₄ powders prepared by spray pyrolysis from the spray solution, with citric acid were studied. The precursor powders with hollow and thin wall structure turned to the nano-sized NiFe₂O₄ powders after post-treatment at a temperature of 800 °C. The nickel ferrite powders obtained from the spray solution with ferric chloride had nanometer sizes and narrow size distributions irrespective of the types of nickel precursor. The nickel ferrite powders obtained from the spray solution with ferric nitrate and nickel chloride also had nanometer size and narrow size distribution. The saturation magnetizations of the NiFe₂O₄ powders changed from 37 to 42 emu/g according to the types of the Fe and Ni precursors. The saturation magnetizations of the NiFe₂O₄ powders increased with increasing the Brunauer-Emmett-Teller (BET) surface areas of the powders.     

Rapid exothermic synthesis of chalcopyrite-type CuInSe2

Chalcopyrite-type CuInSe₂ (CIS) was synthesized from Cu, In and Se powders by a mechanochemical process (MCP) without any additional heating. When the transparent reactor bottle was strongly shaken, the elemental powders underwent an explosive reaction. The reaction generated a large amount of heat accompanied by simultaneous strong light emission. The product was confirmed to be chalcopyrite-type CIS by X-ray powder diffraction analysis. From the results, we categorized that preparation of CIS by MCP is a form of ‘self-propagating high-temperature synthesis’ (SHS) or ‘gasless combustion synthesis’. In ordinary SHS, a reaction is initiated from a sample surface by a heat flux such as a heated wire, electric spark, or laser beam. On the other hand, in the present reaction system (Cu+In+2Se), was naturally ignited only by mechanical stimulation. Following initiation by an external stimulus, the reaction was self continuing via the exothermic heat generated. The reaction mechanism of the preparation of CIS by the MCP is discussed on the basis of present reaction observations and thermochemical data.     

Solution-combustion synthesis of Tb-doped Y3Al5O12 nanoparticles

Nano-sized YAG:Tb powder phosphors were prepared by a solution-combustion method, using the general inorganic salts as starting materials. The X-ray diffraction (XRD) measurements showed that the precursor can be well-crystallized at 900 °C. As-prepared particles have sizes mostly in the range between 30 and 100 nm as obtained by scanning electron microscope (SEM) and transition electron microscope (TEM). Selected area electron diffraction (SAED) patterns proved that the larger particles are monocrystalline. The effects of annealing temperature and Tb-doping concentration on the luminescence intensity were studied.     

Room temperature synthesis of Cu2O nanocubes and nanoboxes

Monodisperse Cu₂O nanocubes are synthesized by reducing freshly prepared Cu(OH)₂ with N₂H₄·H₂O in water at room temperature. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations show that most of these nanocubes are uniform in size, with the average edge length of ∼500 nm. Selected area electron diffraction (SAED) investigation reveals that these nanocubes are single crystalline. Further, Cu₂O nanoboxes are obtained by etching Cu₂O nanocubes with acetic acid solution at room temperature. The nanoboxes retain the size and external morphology of the nanocubes.     

Preparation and characterization of C54 TiSi2 nanoislands on Si (1 1 1) by laser deposition of TiO2

We present the preparation of C54 TiSi₂ nanoislands on Si (1 1 1) with a method of the pulsed laser deposition of titanium oxide thin films. The TiO₂ thin films with nominal thicknesses of 1 nm on Si (1 1 1) were annealed at 850 °C for about 4 h in situ. The X-ray diffraction patterns and the X-ray photoelectron spectra indicate that the nanoislands are in C54 TiSi₂ phase. The characterization using a scanning tunneling microscope shows that the nanoislands with triangular, polygonal and rod-like shapes on Si (1 1 1) exhibit the Volmer-Weber growth mode. The sizes of the polygonal islands distribute in two separated ranges. For the small islands, they have a narrow lateral size distribution centered at 4 nm and a height range in 0.6-3.6 nm, while for the large islands, their lateral sizes are in the range of 12-40 nm and the heights in the range of 4-9 nm. The sizes of the well-shaped triangular islands are intermediate with the lateral sizes in range of 5-20 nm and the heights of 2-3.5 nm. The rod-like islands are about 50-200 nm in length, 5 nm in height and about 15-20 nm in width. The origination of the various shapes of the nanoislands is attributed to the symmetry of Si (1 1 1) substrate and the lattice mismatch between the C54 TiSi₂ and the Si (1 1 1) surface.     

Melting Transition of Small Aluminium Clusters Al11-20

Heat capacities of small aluminium clusters A111-20 are investigated using MD simulation with empirical many- body Gupta potential. The heat capacities of some clusters A111, A112, A113 and A119 show well-defined peaks while the heat capacities of Alls-ls indicate a gradual melting transition. The spectra of isomers obtained by quenches along the MD trajectory give good interpretation for those results.     

The effect of 3-aminopropyltrimethoxysilane on the formation of NiFe2O4/SiO2 nanocomposites

NiFe₂O₄/SiO₂ nanocomposites were prepared using a sol–gel method with the addition of 3-aminopropyltrimethoxysilane (APS). Different phases and morphologies of NiFe₂O₄/SiO₂ nanocomposites were obtained when different amounts of APS were used. The structural properties of the products were examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Sheet-like morphology was observed at higher molar ratio of APS to NiFe₂O₄, while spherical NiFe₂O₄/SiO₂ nanoparticles separated from each other were formed at lower molar ratio of APS to NiFe₂O₄. The magnetic properties of the nanocomposites were also investigated, indicating that the interparticle interactions exhibit strong dependence on the molar ratio of APS to NiFe₂O₄.     

Study of the microstructure influence on the transport properties of Bi86.5Sb13.5 polycrystalline alloy

This study is focused on the investigation of the transport properties of Bi_86.5Sb_13.5 polycrystalline alloys. Bulk materials were prepared by cold pressing ultrafine powders of alloy and by annealing the resulting pellets. Special care was taken to avoid contamination of the powders. Starting with powders of average grain size of 0.06 μm bulk semi-conducting sample with mean grain size respectively of 0.1, 0.8, 2.5 and 200 μm were obtained. The influence of the grain size on both electrical resistivity, thermal conductivity, thermoelectric power, thermoelectric figure of merit is presented within the range 80-330 K. The thermoelectric properties are discussed and compared with those of single crystals presented in previous studies.