Bunyod Allabergenov

Enhanced blue photoluminescence realized by copper diffusion doping of ZnO thin films

ZnO thin films with blue photoluminescence (PL) have been fabricated through Cu diffusion doping. A CuOx-ZnO mixture, and Cu/ZnO double layer, films were prepared on amorphous SiOx/Si substrates by pulsed laser deposition (PLD), and electron beam (e-beam) deposition, respectively. After sequential oxygen annealing, CuOx-ZnO mixture films exhibited green emission centered at 523 nm. However, Cu/ZnO double layer films differed in producing a blue emission centered at 480 nm. Detailed analysis identified that this blue shift in the emission center resulted from increased blue emissions attributed to Cu dopants in the film by e-beam deposition. Luminescence intensity was increased to 6 cd/m2 for a sample annealed at 700 °C. Color points were close to the locus of points following the line of a black-body-radiator on the CIE 1931 XY chromaticity diagram. The present results show that Cu-doped ZnO has strong potential as a cost effective phosphor for use in down converting LEDs.

Enhancement of frequency modulation response time for polymer-dispersed liquid crystal

ABSTRACT Through the ferroelectric nanoparticles of BaTiO3 (BTO) doping, the response time for the frequency modulation of the polymer-dispersed liquid crystal (PDLC) was improved. The BTO-doped PDLC cells were prepared by polymerisation induced phase separation (PIPS) process using UV light. The capacitance of the PDLC composites was measured with an impedance analyzer in the frequency range of 100 Hz–1 MHz at 1 V. The dynamic signal for the response time of the PDLC devices was monitored through a digital oscilloscope. The electro-optical properties of the PDLC were found to strongly depend on the doped BTO concentration. The BTO doping caused a large increase in the capacitance. The dielectric constants were drastically decreased in the samples with rather low BTO doping ratio at a high frequency. No outstanding difference in the rising time of the LC was observed in the BTO-doped PDLC device, but the falling time was significantly decreased from 0.334 to 0.094 s. The present results imply that the nanoparticle-doping technology could improve the electro-optical performance of the PDLC requiring fast response and frequency modulation, such as optical modulators and PDLC-hybrid electroluminescence device for flexible electronic devices. GRAPHICAL ABSTRACT

Optical and photoelectric properties of Mn-doped ZnS thin film on a flexible indium-tin-oxide/polyethylene terephthalate substrate prepared by pulsed laser deposition

Optical and photoelectric properties of Mn-doped ZnS thin films on indium–tin–oxide (ITO)/polyethylene terephthalate (PET) substrates by pulsed laser deposition (PLD) were investigated. The XRD patterns revealed that the thin film deposited at room temperature (RT) had a wurtzite phase, which changed to a sphalerite phase at a substrate temperature of approximately 100 °C. The transmittance of the films was approximately 87% in the visible range. The optical bandgap of the film deposited at RT was 3.29 eV, which increased to 3.361 eV with increasing substrate temperature to 200 °C. The photoluminescence (PL) intensity at 468 nm and the photocurrent by UV irradiation increased in proportion to the substrate temperature. The present results imply that Mn-doped ZnS films deposited on flexible PET substrates are useful for fabricating flexible optoelectronic devices such as flexible UV detectors.

Red photoluminescence and blue-shift caused by phase transformation in multilayer films of titanium dioxide and zinc sulfide

The most versatile methods for altering the properties and behavior of materials involve a phase transformation in the solid state. In this article, we report multilayered films of ZnS/TiO2/ZnS on amorphous SiOx/Si substrates by pulsed laser deposition (PLD). After sequential vacuum annealing at various temperatures, we investigated the effects of TiO2 on the phase transformation of ZnS films and the consequential changes in photoluminescence (PL) property. PL spectra of the film revealed red emission centered at 686 nm after annealing at 600 °C, however, this emission disappears, and the color shifts to blue after annealing at 700 °C. Detailed analysis identified that TiO2 acts as a catalytic agent for the phase transformation of ZnS at this temperature, and that the color shift to blue resulted from decreased red emissions attributed to oxygen in the film. The present results show that catalytic agent-mediated phase transformation has strong potential for the modification of material properties.

The Evaluation of Photocatalytic Properties of Iron Doped Titania Photocatalyst by Degradation of Methylene Blue Using Fluorescent Light Source

Transition metal ion-doped titanium dioxide (TiO2) powders were prepared by mechanochemical milling. Photocatalytic properties of the prepared semiconductor were evaluated using photodegradation of methylene blue under UV and visible light. Dye bleaching was observed spectrophotometrically. Color removal was reached after 120 min. The effect of varying concentration of organic dye, amount of TiO2 photocatalyst, particle size, pH, and stirring rate was observed on the efficiency of reaction. The maximum photocatalytic decomposition of methylene blue solution was achieved with 25nm particle size TiO2, which was ascribed to the enlarged surface area. All obtained results were discussed.

Emission control of multilayered thin films of ZnO/CuO prepared by pulsed laser deposition (Conference Presentation)

In this report, we present on a research result of the microstructural and optical properties of ZnO/CuO multilayered films. Three types of multilayer ZnO/CuO stacks were prepared by pulsed laser deposition (PLD) on amorphous SiO2/Si substrates, and then annealed at 500oC for 30 min to improve crystallinity. TEM and XRD analysis of the thin films revealed the formation of multiple crystallographic defects and modification of the dominant growth plane. Consequently, near-band-edge emission in ZnO can be controlled through the number of CuO layers. The detailed microstructure and electro optical properties of multilayered ZnO/CuO thin films will be discussed.

Effective control over near band-edge emission in ZnO/CuO multilayered films

We report on a study of the microstructural and photoluminescent properties of ZnO/CuO multilayered films. Multilayered ZnO/CuO thin films were deposited on amorphous SiO2/Si substrates by a pulsed laser technique and their microstructural and optical properties were characterized by transmission electron microscopy (TEM) and photoluminescence spectroscopy. TEM and XRD analyses of annealed ZnO/CuO films reveal the formation of multiple crystallographic defects and modification of the dominant growth plane, indicating effective doping of Cu atoms into the ZnO lattice. Consequently, near-band-edge emission in ZnO can be controlled through the number of CuO layers. Redshift of the near-band-edge emission peak from 385 nm up to 422 nm is achieved by increasing the number of CuO layers up to a certain number, above which a downward shift is observed. The results demonstrate that the emission properties of ZnO can be modified and precisely controlled by incorporation of CuO thin layers as a Cu-doping source.

Mechanical properties of stainless steel composites with titanium carbonitride consolidated by spark plasma sintering

In this paper, stainless steel–titanium carbonitride-based composites were fabricated and analyzed to utilize for bipolar plate in fuel cells. In order to study the size effect of titanium carbonitride on the mechanical and corrosion resistance properties of the composites, micro and nanosize titanium carbonitride powders were used. Stainless steel–carbonitride composites were prepared by spark plasma sintering and subsequently annealed at different temperatures up to 1100℃ to improve the morphological and mechanical properties. Various properties of the obtained samples were compared before and after annealing. It was shown that after heat treatment, the mechanical properties of the stainless steel–carbonitride composites improved due to the diffusion of titanium carbonitride particles into stainless steel. Addition of microsized titanium carbonitride powders was found to be effective to improve the mechanical properties, such as microhardness and compressive strength, of the composite. However, addition of nanosized titanium carbonitride powders led to an increase of corrosion resistivity of the composite. Physical properties, such as thermal and chemical stability of the obtained composite samples were investigated by microhardness tester, potentiostat, field emission-scanning electron microscope, EDX and X-ray diffraction.

Fabrication and Characterization of Amine Compounds Synthesized from Carbon Dioxide and Ammonia Water Using Transition Metal Doped TiO2

Capture and reforming fume gases from atmosphere became an ultimate task recently. Photocatalytic reduction to useful compounds is a key to the future. Photoinduced reduction of carbon dioxide and ammonia aqueous solution into amine compounds at room temperature and atmospheric pressure using transition metal doped titanium dioxide is reported in this paper. UV-visible spectra showed a high absorbance at 200 nm wavelength which is a characteristic of urea. High Performance Liquid Chromatography revealed presence of amine compounds and urea was found a main product of photocatalytic reaction.

Synthesis, Characterization and Functionalization of the Coated Iron Oxide Nanostructures

The iron oxides nanoparticles and iron oxide with other compounds are of importance in fields including biomedicine, clinical and bio-sensing applications, corrosion resistance, and magnetic properties of materials, catalyst, and geochemical processes etc. In this work we describe the preparation and investigation of the properties of coated magnetic nanoparticles consisting of the iron oxide core and organic modification of the residue. These fine iron oxide nanoparticles were prepared in air environment by the co-precipitation method using of Fe 2+ : Fe 3+ where chemical pre- cipitation was achieved by adding ammonia aqueous solution with vigorous stirring. During the synthesis of nanoparti- cles with a narrow size distribution, the techniques of separation and powdering of nanoparticles into rather monodisperse fractions are observed. This is done using controlled precipitation of particles from surfactant stabilized solutions in the form organic components. It is desirable to maintain the particle size within pH range, temperature, solution ratio wherein the particle growth is held at a minimum. The iron oxide nanoparticles can be well dispersed in an aqueous solution were prepared by the mentioned co-precipitation method. Besides the iron oxide nanowires were prepared by using similar method. These iron oxide nanoparticles and nanowires have controlled average size and the obtained products were investigated by X-ray diffraction, FESEM and other methods.