Characteristics of ZnGa2O4 phosphors synthesized by solution combustion method

ZnGa₂O₄ phosphors were synthesized by both SCM (solution combustion method) and SSRM (solid state reaction method). The characteristics of the both ZnGa₂O₄ phosphors were investigated by TGA (Thermogravimetric analysis), SEM (scanning electron microscope), BET (Brunauer Emmett Teller), PL (photoluminescence) and XRD (X-ray diffraction). The particle size of SCM phosphor was about one-hundredth of SSRM phosphor. The PL intensity of SCM phosphor was about 1.5 fold higher than that of SSRM phosphor. The SCM phosphor was also tried to be doped with Mn⁺² ions. The highest PL peak was observed with Mn⁺² ions of 0.003 mole fraction. The peak was shifted from blue (470 nm) to green (513 nm) color. These results might be very useful for high efficiency phosphors for displays such as field emission displays and plasma display panels.     

ZnGa2O4 thin films fabricated by Sol-gel spinning coating process

ZnGa₂O₄ thin film phosphors have been synthesized on ITO coated glass and soda-lime glass at a firing temperature of 500^∘C and an annealing temperature of 500^∘C and 600^∘C via a chemical solution method using Zinc acetate dihydrate, Gallium nitrate hydrate and 2-methoxiethanol as a solution. XRD patterns of the film phosphors synthesized showed the peaks of ZnGa₂O₄ crystalline phases. AFM surface morphologies of the ZnGa₂O₄ thin film phosphors revealed marked differences according to an annealing temperature of 500^∘C and 600^∘C under an annealing atmosphere (3% H₂/Ar). On the other hand, the sheet resistance of ZnGa₂O₄ thin film phosphors, which were measured by four-point probe instrument, was approximately 5.76 Ω /square and 7.86 Ω /square with annealing temperature, respectively. The ZnGa₂O₄ thin film phosphors exhibited blue emission spectra with peak wavelength of 434 nm and 436 nm by ultra-violet excitation around 230 nm.     

Photoluminescence properties of Y2O3co-doped with Eu and Bi compounds as red-emitting phosphor for white LED

Bismuth doped Y₂O₃: Eu was used as a red phosphor with a very high efficiency and an appropriate emission wavelength of around 310–400 nm. This red phosphor was synthesized by the solid state reaction which is normally used in the field of white LEDs. In this study, we synthesized Y₂O₃: Eu, Bi phosphors using a solid state reaction. We investigated the effect of the Eu^{3 +} and Bi^{3 +} concentrations and additive fluxes on the emission characteristics. The fabricated phosphors were investigated by analyzing their particle size and crystal structure with scanning electron microscopy and X-ray diffraction (XRD). Their photoluminescence (PL) spectra were also measured at room temperature.     

Microwave dielectric properties of B2O3-added Li2MgTiO4 ceramics for LTCC applications

Li₂MgTiO₄ (LMT) ceramics which are synthesized using a conventional solid-state reaction route. The LMT ceramic sintered at 1250°C for 4 h had good microwave dielectric properties. However, this sintering temperature is too high to meet the requirement of low-temperature co-fired ceramics (LTCC). In this study, the effects of B₂O₃ additives and sintering temperature on the microstructure and microwave dielectric properties of LMT ceramics were investigated. The B₂O₃ additive forms a liquid phase during sintering, which decreases the sintering temperature from 1250°C to 925°C. The LMT ceramic with 8 wt% B₂O₃ sintered at 925°C for 4 h was found to exhibit optimum microwave dielectric properties: dielectric constant 15.16, quality factor 64,164 GHz, and temperature coefficient of resonant frequency -28.07 ppm/°C. Moreover, co-firing of the LMT ceramic with 8 wt% B₂O₃ and 20 wt% Ag powder demonstrated good chemical compatibility. Therefore, the LMT ceramics with 8 wt% B₂O₃ sintered at 925°C for 4 h is suitable for LTCC applications.     

Effect of synthetic conditions on particle size and photo-luminescence properties of Y2O3:Eu3+ nanophosphor

In this paper, effect of synthetic conditions on the particle size, crystal structure, and the photoluminescence properties of the Y₂O₃:Eu³⁺ nanophosphor was investigated. Solvent and dispersing agent were determined as the synthetic parameters. The nanophosphor synthesized from methanol solvent showed the smaller particle size of 4 nm. The XRD analysis indicates that the crystal structure of the Y₂O₃:Eu³⁺ nanophosphor is mainly cubic crystal with orientation of (222), (440), (400), and small peak of (511) indicating monoclinic crystal. The Y₂O₃:Eu³⁺ nanophosphor synthesized by using methanol solvent and 0.1 wt.% hydroxypropyl cellulose (HPC) as a dispersing agent showed higher degree of crystallization of 10.5 of I ₍₂₂₂₎/I ₍₅₁₁₎ ratio than that without HPC. Also, the photoluminescence properties of the nanophosphor showed red color that excitation and emission wavelengths of the nanophosphor were 250 and 611 nm, respectively. Using the 250 nm UV source, the highly intensive photoluminescence peak could be achieved at 611 nm under the synthetic condition of methanol solvent adding 0.1 wt.% HPC.     

High temperature electrical characterization of nano-crystalline BaTiO3 synthesized using Ba(NO3)2 and TiO2

The reaction of Ba(NO₃)₂ with TiO₂ was studied by thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques up to 1000°C and in nitrogen atmosphere. It was found that the formation of BaTiO₃ takes place above 600°C. BaTiO₃ powder was prepared by calcination of Ba(NO₃)₂ and TiO₂ precursor mixture at 800°C for 8 h. X-ray diffraction analysis of the synthesized BaTiO₃ confirmed the formation of tetragonal phase. Average crystallite size was found to be 44 nm, For the electrical and morphological characterization pellets of the obtained powder were sintered at 1000 °C for 12 h. Scanning electron micrograph (SEM) exhibits spherical and rod shaped grains. The dielectric constant, dissipation factor, complex plane impedance and ac conductivity of the sintered pellet has been measured in the temperature range of 40–600°C and frequency range of 100 Hz–2 MHz. DC conductivity of the sample was obtained from the impedance data. The conductivities (both ac and dc) and relaxation time (τ) exhibit two regions of temperature dependence, namely region I, which represents (280–450°C) and region II, which governs (450-600°C). Conduction and relaxation in both the temperature regions are explained in terms of hopping of electrons and doubly ionized oxygen vacancies (V_O^??).     

CHARACTERISTICS OF METAL-FERROELECTRIC-INSULATOR-SILICON DEVICES USING HFSION BUFFER LAYERS

ABSTRACT

In this work, metal-ferroelectric-insulator-silicon (MFIS) devices were fabricated using HfSiON as buffer layers and their electrical properties were studied. Ultra-thin HfSiON films were fabricated by electron-beam evaporation at room temperature and post-annealed using different parameters such as temperature, time in O₂. By annealing a 2 nm-thick HfSiON film at 800°C for 60s in O₂, a negligible hysteresis loop and small equivalent oxide thickness of 2.3 nm were obtained with a corresponding leakage current density of 6.8 × 10^{? 5} A/cm² at a voltage shifted from the flat band voltage by 1 V. In the fabrication of MFIS diodes, Sr_0.8Bi_2.2Ta₂O₉ (SBT) films with 400 nm thickness were formed by chemical solution deposition. For Pt/SBT (400 nm)/HfSiON(2 nm)/Si diodes, a memory window of 0.8 V in width was observed during double capacitance-voltage sweep between +5 and –5 V. At the same time, excellent data retention properties were observed. The high and low capacitances in the hysteresis loop were well distinguishable even after 24 h had elapsed.     

Thermoelectricity of p-Fe2O3-SO3-SiO2-others and n-Fe2O3-SiO2-CuO-others

Thermoelectric minerals have been found at Loei Province, in the northeastern part of Thailand. Local mineral specimens were prepared in the powders and bulk solids form by crushing, calcination and annealing, pressure and sintering, cutting and polishing. Mineral samples were used to analyze the composition and phase, determine the thermoelectric property and efficiency, design and construct a thermoelectric generator. Chemical composition and phase identification of powder samples were analyzed by the x-ray fluorescence (XRF) and x-ray diffraction (XRD), respectively. XRF and XRD results indicated that the mineral samples comprised the SO₃-CaO-SiO₂-others, Fe₂O₃-SO₃-SiO₂-others, Fe₂O₃-SiO₂-others and Fe₂O₃-SiO₂-CuO-others. From the thermoelectric property and efficiency determinations, the p-SO₃-CaO-SiO₂-others, p-Fe₂O₃-SO₃-SiO₂-others, n-Fe₂O₃-SiO₂-others and n-Fe₂O₃-SiO₂-CuO-others bulks were found to exhibit the thermoelectric figure of merit in orders of 10^?14, 10^?11, 10^?14 and 10^?13 K^?1, respectively. A fabricated thermoelectric generator made from ten pairs of p-Fe₂O₃-SO₃-SiO₂-others and n-Fe₂O₃-SiO₂-CuO-others legs that can be provided the open circuit voltage and short circuit current up to 48.30 mV and 0.14 μA for a temperature difference of 39.80 K at room temperature, respectively. While the internal resistance decreased and reached a value of 665 kΩ.     

Characterization of the CeO2 thin films for insulation layer and Pt/SrBi2Ta2O9/CeO2/Si MFISFET structure

Abstract

CeO₂ and SrBi₂Ta₂O₉ (SBT) thin films for MFISFET (metal-fcrroelectrics-insulator-semiconductor field effect transistor) were deposited by rf sputtering and pulsed laser deposition method, respectively. The effects of oxygen partial pressure during deposition for CeO₂ films were investigated. The oxygen partial pressure significantly affected the preferred orientation, grain size and electrical properties of CeO₂ films. The CeO₂ thin films with a (200) preferred orientation were deposited on Si(100) substrates at 600°C. The films deposited under the oxygen partial pressure of 50 % showed the best C-V characteristics among those under various conditions. The leakage current density of films showed order of the 10^?7～10^?8 A/cm² at 100 kV/cm. The SBT thin films on CeO₂/Si substrate showed dense microstructure of polycrystalline phase. From the C-V characteristics of MFIS structure composed of the SBT film annealed at 800°C, the memory window width was 0.9 V at ±5 V. The leakage current density of Pt/SBT/CeO₂/Si structure annealed at 800°C was 4×10^?7 A/cm² at 5 V.     

Photocatalytic property of SiO2/TiO2 nanoparticles prepared by sol-hydrothermal process

Silica-embedded nanocrystalline TiO₂ powders were synthesized by sol-hydrothermal process. The influence of the composition of the solvent and the embedded silica content on the phase transition, grain growth and subsequently, on the photoactivity of TiO₂ were investigated. The volume ratio of ethanol to water for the solvent composition was varied from 0.125 to 8 and the mole fraction of silica content was changed from 0 to 0.4, while the condition for hydrothermal reaction was fixed at 250^∘C for 2 hour. With an increase in ethanol content in solvent composition, the crystallite sizes of pure TiO₂ particles decreased from 15 nm to 6 nm and crystal phase changed from rutile/anatase mixed phase to pure anatase phase. Addition of silica to TiO₂ brought about an increase in the photocatalytic activity by suppressing the phase transition from anatase to rutile. Judging from the result of the decomposition of 1, 4-dichlorobenzene, the most efficient catalyst was found to be 0.2 mole fraction SiO₂ embedded TiO₂ prepared with ethanol-rich solvent (the volume ratio of ethanol to water is 4).     

Preparation and performance of PMMA/R-TiO2 and PMMA/A-TiO2 electrospun fibrous films

ABSTRACT

In this paper, the PMMA/R-TiO₂ and PMMA/A-TiO₂ nanofiber membranes were prepared by electrospinning and its photocatalytic performance was studied. Accordinly, the obtained composites nanofibers were characterized by SEM, Porosity and TG in order to characterize morphologically the nanostructures and their distribution in the polymeric matrix, thermal properties. The R-TiO₂ and A-TiO₂ content of 5%, the minimum average fiber diameters of 436 nm and 409 nm, the fibers appear smooth and continuous, and the two kinds of composite fibers have higher porosities. The TG curve showed that PMMA/R-TiO₂ nanofibers residual amount was higher than PMMA/A-TiO₂, which indicated that R-TiO₂ could improve thermal stability of the composites. It evaluated their photocatalytic activity by degradation of some dyes and methyl orange in an aqueous medium. The results showed that with the increase of TiO₂ content, the composite nanofibers degradation rate of methyl orange improved. At the same conditions, when the TiO₂ content was 10%, the photocatalytic degradation rate of PMMA/R-TiO₂ and PMMA/A-TiO₂ composite nanofibers were 21.8% and 51.3% respectively.     

Thermal Conductivity of Nano ZnO Doped CaFe2O4

The research objective of this study was to examine whether Zn was an effective doping element for thermal conductivity. Ca_1-xZn_xFe₂O₄ (x = 0.0–0.5) were synthesized by solid state reaction method. The XRD results showed that all samples were mixed phase of CaFe₂O₄ and ZnFe₂O₄. The structure of Ca_1-xZn_xFe₂O₄ (x = 0.0–0.5) belonged to a group of an orthorhombic system (space group: Pbnm). It was observed that all the samples of Ca_1-xZn_xFe₂O₄ (x = 0.0–0.5) had positive Seebeck coefficient as shown on p-type semiconductor behavior. Thus thermal conductivity tended to decrease with increasing x value. The Ca_0.6Zn_0.4Fe₂O₄ showed lowest thermal conductivity of 6.52 W m^?1 K^?1 at 473 K, which was lower than 50.81% of CaFe₂O₄. These results suggested that Zn was an effective doping element for improving the thermal conductivity of Ca_1-xZn_xFe₂O₄.     

Enhancement in the physical properties of K0.5Na0.5NbO3 ceramics by the addition of 0.5 Li2O – 0.5K2O – 2B2O3 glass

The addition of powdered 0.5 Li₂O–0.5K₂O–2B₂O₃ (LKBO) glass (0.5 to 2 wt%) to potassium sodium niobate, K_0.5Na_0.5NbO₃ (KNN) powder facilitated higher densification which resulted in improved physical properties that include dielectric, piezoelectric and ferroelectric. The required polycrystalline powders of KNN were synthesized through solid-state reaction route, while LKBO glass was obtained via the conventional melt-quenching technique. Pulverized glass was added to KNN powders in different wt% and compacted at room temperature and these were sintered around 1100°C. Indeed the addition of optimum amount (1 wt %) of LKBO glass to KNN ceramics facilitated lowering of sintering temperature accompanied by larger grains (8 µm) with improved density. The dielectric constant (?_r) measured at room temperature was 475 (at 10 kHz), whereas it was only 199 for the LKBO glass free KNN. The piezoelectric coefficient (d₃₃) was found to be 130 pC/N for 1 wt% LKBO added glass, which was much higher than that of pure KNN ceramics (85 pC/N). Indeed, the LKBO glass added samples did exhibit well saturated P versus E hysteresis loops at room temperature. Though there was no particular trend observed in the variation of P_r with the increase in glass content, the P_r values were higher than that obtained for KNN ceramics. The improved physical properties of KNN ceramics encountered in these studies were primarily attributed to enhancement in density and grain size.     

TiO2 Ultraviolet Detectors with Sandwich Structure

In this letter, sandwich structure TiO₂ ultraviolet detectors with Pt electrodes have been fabricated. TiO₂ thin films were prepared by sol-gel method, and Pt film was deposited by radio frequency magnetron sputtering directly on the semiconductor films. At 5 V bias, the dark current and photocurrent of the detectors were 6 nA and 69.2 μA, respectively. Under irradiation of 310 nm UV light, the detector with sandwich structure achieved a higher photoresponse of 197.4 A/W. The rise time of the device was 426.6 ms and the fall time was 509.2 ms, respectively.     

Structural and Multiferroic Properties of Bi3.4La0.6Ti3O12/CoFe2O4 Composite Thin Films

Bi_3.4La_0.6Ti₃O₁₂ and CoFe₂O₄ were synthesized by chemical solution route, and Bi_3.4La_0.6Ti₃O₁₂/CoFe₂O₄ multilayers were deposited by spin coating on Pt substrate. X-ray diffraction of multilayer structures reveals composite-like polycrystalline film. Leakage current is less than 10^?5 A at electric field < 90 KV/cm and follows the Ohmic behavior. Dielectric response shows relaxation and the loss (tan δ) is below 3% at 10⁶ Hz. Room temperature ferrroelectric polarization (P_r) = 20.2 μC/cm² and ferromagnetic memory (M_r) = 46.5 emu/cm³ has been obtained. Co-existence of FE and FM response can be attributed to stress and different permeability and permittivity involved in multilayer structures.     

Electrical properties of ultrathin HfO2 gate dielectrics on partially strain compensated SiGeC/Si heterostructures

Ultrathin HfO₂ gate dielectrics have been deposited on strained Si_0.69Ge_0.3C_0.01 layers by rf magnetron sputtering. The polycrystalline HfO₂ film with a physical thickness of ∼6.5 nm and an amorphous interfacial layer with a physical thickness of ∼2.5 nm have been observed by high resolution transmission electron microscopy (HRTEM). The electrical properties have been studied using metal-oxide-semiconductor (MOS) structures. The fabricated MOS capacitors on Si_0.69 Ge_0.3C_0.01 show an equivalent oxide thickness (EOT) of 2.9 nm, with a low leakage current density of ∼4.5 × 10 ^{− 7} A/cm² at a gate voltage of –1.0 V. The fixed oxide charge and interface state densities are calculated to be 1.9 × 10¹² cm^{− 2} and 3.3 × 10 ¹¹ cm^{− 2}eV⁻¹, respectively. The temperature dependent gate leakage characteristics has been studied to establish the current transport mechanism in high-k HfO₂ gate dielectric to be Poole–Frenkel one. An improvement in electrical properties of HfO₂ gate dielectrics has been observed after post deposition annealing in O₂ and N₂ environments.     

Facile synthesis of superparamagnetic Fe3O4 nanoparticles just using ferric citrate and water

Fe₃O₄ nanoparticles were synthesized by a facile one-pot hydrothermal process just using ferric citrate and water without any additional reagent and post-treatment. The temperature of hydrothermal reaction had important influence on the crystallinity and magnetic property of Fe₃O₄ samples. Fe₃O₄ sample synthesized at 200 °C for 24 h showed a narrow size distribution (4 to 8 nm in diameter), and exhibited apparent superparamagnetism with saturated magnetization of 55.1 emu/g. The narrow size distribution and superparamagnetism were the interesting features of these Fe₃O₄ nanoparticles.     

Synthesis and Characterization of Zn-Doped TiO2 Nanoparticles via Sonochemical Method

Zn-doped TiO₂ nanoparticles were successfully fabricated using sonochemical method accompanying post calcination process. Titanium isopropoxide (Ti[OC₃H₇]₄) and Zinc chloride (ZnCl₂) were used as starting precursors for Ti and Zn sources, respectively. The homogeneous mixing solution of different Zn (0–1 mol%) and Ti ratio were irradiated in high intensity ultrasound sonometer (750 W 20 kHz) for 30 min at room temperature to obtain as-synthesized Zn-doped TiO₂ nanoparticles followed by calcination at 400–700°C. To evaluate the structure and phase identification of prepared powders, the X-ray diffraction (XRD) and Raman spectroscopy were employed. The results reveal that the as-synthesized Zn-doped TiO₂ nanoparticles are in anatase phase and their crystallinity increases with increasing calcined temperature. The morphology of as-synthesized powders was investigated by transmission electron microscope (TEM). The effect of Zn content and calcinations temperature on TiO₂ properties was also discussed.     

Photoluminescence and photocurrent characteristics of Eu2 + activated MAl2O4 (M = Ba, Ca, Sr) phosphors

Photoluminescence and photocurrent characteristics of Eu^{2 +} activated MAl₂O₄ (M = Ba, Ca, Sr) phosphors during and after Ultraviolet ray and visible light irradiation have been investigated. The photoluminescence (PL) and the photocurrent (PC) of the phosphors, in order to elucidate the relationship between the PL and the PC, were measured simultaneously on the same samples within a specially designed measuring box. Composition effects, such as a presence of Dy^{3 +} as a co-activator and Al-rich composition on the PL and PC characteristics have been investigated. Also, sensing characteristics on UV and visual light have been tested. The simultaneous measurement of PL and PC on the same sample clearly indicated that the presence of co-activator and vacant site, namely Al-rich composition, acted as a hole trap; the introduction of co-activator and vacant site decreased the PC and increased the PL during and after UV and visible light irradiation, whose PC was much lower than that of MAl₂O₄ with only Eu^{2 +} as an activator. The electrical intensity affected on the PL characteristics after UV and visual light irradiation(afterglow); with increasing in the electrical intensity, the afterglow lasted more longer and intensively. The PC of MAl₂O₄ showed a good proportional relationship to UV and visible light intensity. Especially, SrAl₂O₄ showed an excellent linearity within 1–5 mW/cm², but showed somewhat delayed response and hysterisis as seen in CdS photoelectric cell.