Journal of Nano Structures
Volume:4 Issue: 4, Autumn 2014

Lithium disilicate nano-powders were synthesized via a mild condition hydrothermal reaction at 180 ºC for 48 and 72 h with a non stoichiometric1:2 Li:Si molar ratio in NaOH aqueous solution using Li2CO3 and SiO2.H2O as raw materials. The synthesized materials were characterized by powder X-ray diffraction (PXRD) technique and Fourier transform infrared (FTIR) spectroscopy. The XRD data showed that the obtained materials crystallized in a monoclinic crystal structure with a space group of Ccc2. The morphologies of the synthesized nanomaterials were studied by field emission scanning electron microscope (FESEM). Ultraviolet–visible spectra showed that the nanostructured lithium disilicate powders had good light absorption properties in the ultraviolet light region. Photo luminescence spectra of the obtained materials were investigated in an excitation wavelength of 281 nm. Cell parameter refinement data of the obtained materials showed that with increasing the reaction time, parameters a and b were increased. So there is an expansion in the unit cell.

Iron oxide (Fe2O3) is widely used as a catalyst, pigment and gas sensitive material. In this article, α-Fe2O3 nano-rods were first synthesized via a simple chemical method using iron(III) nitrate 9- hydrate (Fe(NO3)3.9H2O) as precursor. XRD pattern showed that the iron oxide nanoparticles exhibited alpha-Fe2O3 (hematite) structure in nanocrystals. The single-phase α- Fe2O3 nano-rods were prepared when the samples calcined at 500 °C. The smallest particle size was found to be 18 nm in diameter. The SEM studies depicted rod-like shaped particles with formation of clusters by increasing annealing temperature. The sharp peaks in FTIR spectrum determined the purity of Fe2O3 nanoparticles and absorbance peak of UV-Vis spectrum showed the small bandgap energy of 2.77 ev. The VSM result showed a coercive field and saturation magnetism around 90 G and 9.95 emu/g, respectively.

In this paper metal-assisted chemical etching has been applied to pattern porous silicon regions and silicon nanohole arrays in submicron period simply by using positive photoresist as a mask layer. In order to define silicon nanostructures, Metal-assisted chemical etching (MaCE) was carried out with silver catalyst. Provided solution (or materiel) in combination with laser interference lithography (LIL) fabricated different reproducible pillars, holes and rhomboidal structures. As a result, Submicron patterning of porous areas and nanohole arrays on Si substrate with a minimum feature size of 600nm was achieved. Measured reflection spectra of the samples present different optical characteristics which is dependent on the shape, thickness of metal catalyst and periodicity of the structure. These structures can be designed to reach a photonic bandgap in special range or antireflection layer in energy harvesting applications. The resulted reflection spectra of applied method are comparable to conventional expensive and complicated dry etching techniques.

Thermoluminecsence (TL) characteristics of pure CaSO4 nanoparticles produced by co-precipitation method are presented. The formation of the nanoparticles was confirmed by X-ray diffraction (XRD) and scanning electron microscope (SEM). TL glow curve of this phosphor, exposed to gamma radiation exhibits five overlapping glow peaks in the complex glow curve at 463, 470, 483, 498 and521(K) respectively, using a computerized glow curve deconvolution procedure. A photoluminescence (PL) emission band at 393 nm was observed for the synthesized nanoparticles. Different synthesis conditions were examined in order to achieve highest TL sensitivity. The produced nanoparticles exhibit superior thermoluminescent sensitivity compared to that of its bulk equivalent.

Structural properties and chemical composition change the photocatalytic activity in TiO2-SiO2 nanopowder composite. The SiO2-TiO2 nanostructure is synthesized based on sol–gel method. The nanoparticles are characterized by x-ray fluorescents (XRF), xray diffraction (XRD), tunneling electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), UV-vis. Spectrophotometer and furrier transmission create infrared absorption (FTIR) techniques. The rate constant k for the degradation of methylen blue in its aqueous solution under UV irradiation is determined as a measure of photocatalytic activity. Dependence between photocatalytic activity and SiO2 content in the composite is determined. Rate constant k is found dependent on the content of SiO2 in the composite that calcined at 900 oC. The addition of low composition SiO2 to the TiO2 matrix (lower than 45%) enhances the photocatalytic activity due to thermal stability and increasing in the surface area. The effects of chemical compositions on the surface topography and the crystallization of phases are studied.

Alumina nanomaterials were synthesized via a solution combustion technique using tris-(acetylacetonato) aluminum(III) complex (1) and tris-(2-formylphenolate) aluminum(III) complex (2) at 600, and 1000 °C for 3h. The obtained data showed that the procedure without using fuel resulted in a better phase and morphology. To investigate the phase formation, powder X-ray diffraction technique was used. Also, FESEM micrographs were used to investigate the morphology of the obtained materials. It showed that the morphology of the obtained materials was in the form of different types of porous and particle materials. The optical properties of the obtained materials were studied by FTIR spectra. According to the data, it was found that with annealing at 600 °C, the phase formation of the obtained materials showed cubic crystal structures with cell parameter a = 3.14 Å for gamma phase. With increasing the annealing temperature to 1000 °C, the obtained material was found to be in a mixture of orthorhombic and hexagonal crystal structures.

Fe49Co33Ni18 nanowire arrays (175 nm in diameter and lengths ranging from 5 to 32μm) were fabricated into nanopores of hard-anodized aluminum oxide templates using pulsed ac electrodeposition technique. Hysteresis loop measurements indicated that increasing the length decreases coercivity and squareness values (from 274 Oe and 0.58 to200 Oe and 0.105, respectively), indicating the increase in magnetostatic interactions between the nanowires (NWs).On the other hand, first-order reversal curve measurements showed a linear correlation between the magnetostatic interactions and length of NWs. It was also found that with increasing length, the domain structure of NWs changed from single-domain to pseudo single-domain state. A multidomain-like behavior is also seen for the longest NWs length.Increasing the length of NWs resulted in an increase inthe interaction and decrease in the array coercive field(H Array/c) as beingsmaller than that of individual NWs (H FORC/c).The observed CFD component in the FORC diagrams of FeCoNi NWs with shorter lengths was a consequence ofnon-uniform length distributions.

Tellurium (Te) nanostructures have been successfully synthesized via a simple hydrothermal methodfrom the reaction of a TeCl4 aqueous solution with thioglycolic acid (TGA) as a reductant. TGA can be easily oxidized to the corresponding disulfide [SCH2CO2H]2, which in turn can reduce TeCl4 to Te. The obtained Te was characterized by XRD, SEM, EDS, and DRS. The effect of reducing agent on morphology and size of the products were also studied. Additionally, Te thin film was deposited on the FTO-TiO2 by Drblading then employed to solar cell application and measured open circuit voltage (Voc), short circuit current (Isc), and fill factor (FF) were determined as well. The studies showed that particle morphology and sizes play crucial role on solar cell efficiencies.

In this work firstly Fe3O4 nanoparticles were synthesized via a sono-chemical method. At the second step magnesium hydroxide shell was synthesized on the magnetite-core under ultrasonic waves. For preparation Fe3O4-MgO the product was calcinated at 400 ºC for 2h. Properties of the product were examined by X-ray diffraction pattern (XRD), scanning electron microscope (SEM) and Fourier transform infrared (FT-IR) spectroscopy. Vibrating sample magnetometer (VSM) shows nanoparticles exhibit superparamagnetic behavior. The photo-catalytic behavior of Fe3O4- Mg(OH)2 nanocomposite was evaluated using the degradation of a methyl orange (MeO) aqueous solution under ultraviolet (UV) light irradiation. The results show that Fe3O4-Mg(OH)2 nanocomposites have applicable magnetic and photo-catalytic performance.