The optical constant of ZnSe/SiO2 composite thin films investigated by spectroscopic ellipsometers

In this paper, ZnSe/SiO₂ composite thin films was prepared by sol–gel process. X-ray diffraction results indicate the phase structure of ZnSe particles embedded in SiO₂ composite thin films is sphalerite (cubic ZnS). The dependence of ellipsometric angle ψ with wavelength λ of ZnSe/SiO₂ composite thin films was investigated through spectroscopic ellipsometers. The optical constant, thickness, porosity and the concentration of ZnSe/SiO₂ composite thin films were fitted according to Maxwell-Garnett effective medium theory. The thickness of ZnSe/SiO₂ composite thin films was measured through surface profile.     

Sol-gel Synthesis and Photoluminescence Characterization of Ba2SiO4:Eu2+ Green Phosphors for White-LED Application

In this paper, Ba₂SiO₄:Eu²⁺ green phosphor was synthesized by sol-gel method. TGA-DTA, XRD, SEM and PL spectra were used to characterize the as-prepared phosphors. The phosphors are composed of nanoparticles with 60 nm grain size and exhibit green light with a broad peak around 500 nm. The relationship between crystal growth, morphology and luminescent properties was studied. The structure and luminescence properties of phosphors synthesized in different conditions were also discussed.     

Preparation and physical properties of Nano-ZnSe/SiO2 mesoporous composite for assembly system

A novel synthesis route of ZnSe/gel-glass mesoporous composite was described. $ {\text{SeO}}_{4} ^{{2 - }} $ and Zn²⁺ were loaded into the porous framework of silica gel-glasses by immersion. Followed by drying and the reductive thermal treatment, the transparent, homogeneous ZnSe/SiO₂ samples with the color of light yellow were prepared. The specific surface area, grain size, structure and phase properties of nano-sized ZnSe/SiO₂ mesoporous composites were studied by powder X-ray diffraction, nitrogen sorption, SEM. The effects of pore structure properties and loading solution concentration on the optical absorption of ZnSe/SiO₂ were investigated by UV-vis absorption. It is found that the optical absorption edges of ZnSe nanoparticles in mesoporous silica shift to the red as ZnSe loading concentration increases, which is attributed to the quantum size effect. The nonlinear optical property of these samples was presented by the open aperture z-scan technique. This method has some potential advantages in comparison to the conventional methods.     

Study of PEDOT:PSS-SnO2 nanocomposite film as an anode for polymer electronics

Poly(3,4-ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate)(PEDOT:PSS) is a candidate material for applications in molecular electronics, such as organic field effect devices, organic photovoltaics, and organic light emitting devices. The properties of 3.5–4.0 nm sized SnO₂ nanoparticles doped PEDOT:PSS films were investigated for anode application. Sheet resistance was decreased and rms roughness was slightly increased with the incorporation of SnO₂ nanoparticles. However, the connectivity of conducting grains was improved by the plasticizing effect of surface –OH groups of SnO₂ nanoparticle. Using photoemission spectroscopy and near edge X-ray absorption fine structure (NEXAFS), the electronic structure of the films is studied comparatively on the C 1s NEXAFS, secondary electron emission cut off, and valence band spectra. The start of electron emission retarded and valence band maximum was increased in the PEDOT:PSS-SnO₂ nanocomposite films. These changes in the electronic structure resulted from emitted electron screening of core-hole in the PEDOT:PSS energy band and electron donation of SnO₂ nanoparticles.     

Optical Property Analysis,Contour Map and Fabrication of SiO2/Cr/SiO2/Cr Multilayer Films for High Photo-Thermal Conversion Efficiency

Abstract

It is very important for high photo-thermal conversion efficiency (HPTCE) that the optical property analysis, the contour map and optimized design of multilayer films for solar selective absorber are simulated and studied. With HPTCE of more than 96.38%, one SiO₂/Cr/SiO₂/Cr multilayer film fabricated by unbalance sputtering deposition method agrees well with the simulation result in the area of the contour maps.     

Preparation and properties of SiO2 aerogel and fabric composite based on polyurethane

ABSTRACT

The thermal insulation composite were prepared by blending aqueous polyurethane and modified SiO₂ aerogel, and then coating to the surface of fabric. The influence of the content of SiO₂ aerogel and polyurethane, crosslinking temperature and the particle size of SiO₂ aerogel on thermal insulation rate of the composite fabric were detail analysis, the heat insulation, breathable, IR, SEM surface morphology of the composite fabric were evaluated. The thermal insulation rate of the SiO₂ aerogel composite fabric is 28.97%, which is twice that of the original fabric. SiO₂ aerogel composite fabric will have a wide range of application in the thermal insulation clothing, curtains, shoe materials, industrial equipment and building insulation, etc.     

Film Thickness Dependence of Electrical Properties for Pb(Zr,Ti)O3 Thin Films Prepared on (111)Ir/TiO2/SiO2/Si and (111)Pt/TiO2/SiO2/Si Substrates by Pulsed-Metalorganic Chemical Vapor Deposition

Polycrystalline Pb(Zr,Ti)O₃ (PZT) films with various film thicknesses were deposited on (111)Ir/TiO₂/SiO₂/Si and (111)Pt/TiO₂/SiO₂/Si substrates at 540°C by source-gas-pulsed metalorganic chemical vapor deposition (pulsed-MOCVD). PZT films deposited on (111)Ir/TiO₂/SiO₂/Si substrates showed good surface flatness and lower leakage current density. The rate of the decrease of remanent polarization (P _r ) and the rate of increase of coercive field (E _c ) for the films with decreasing the film thickness smaller on (111)Ir/TiO₂/SiO₂/Si substrates than those of (111)Pt/TiO₂/SiO₂/Si substrates. In addition, P _r and E _c values saturated at low voltage when the film thickness was the same. As a result, good ferroelectricity with P _r and E _c values of 40 μC/cm² and 140 kV/cm were obtained for 35 nm-thick films prepared on (111)Ir/TiO₂/SiO₂/Si substrates by pulsed-MOCVD.     

Polymer modified hematite nanoparticles for electrophoretic display

Hematite nanoparticles (Fe₂O₃) as a red inorganic pigment were encapsulated with poly (methyl methacrylate-co-acrylamide) (PMMA-co-AAM) for application in the electronic paper display. Since the Fe₂O₃ nanoparticle has relatively high density (ρ?=?5.07 g/cm³), it usually causes severe sedimentation problem in the suspending medium. In order to reduce density mismatch between inorganic pigment and dielectric medium, the Fe₂O₃ nanoparticles were modified by dispersion polymerization method. Zeta potential and electrophoretic property of the inorganic pigment coated with copolymers in a low dielectric medium were investigated by using electrophoretic light scattering. The surface morphology and molecular structure of the fabricated particles were measured via SEM and FT-IR, respectively. The amount of polymeric coating was also examined by using TGA.     

Ferroelectric properties of SrBi2Ta2O9 thin films on Si (100) with a LaZrO x buffer layer

To obtain a metal–ferroelectric–insulator–semiconductor (MFIS) structure, we fabricated ferroelectric SrBi₂Ta₂O₉ (SBT) film on a p-type Si (100) wafer with a LaZrO _x (LZO) buffer layer by means of a sol–gel technique. The sol–gel deposited LZO film according to the different annealing temperatures had a good surface morphology even though the crystalline phase was not an amorphous phase. In particular, the root-mean-squared (RMS) surface roughness of the 750-°C-annealed LZO film was about 0.365 nm and its leakage current density was about 8.2?×?10^?7 A/cm² at 10 V. A Au/SBT/LZO/Si structure with different SBT film was fabricated. The C–V characteristics of the Au/SBT/LZO/Si structure showed a clockwise hysteresis loop. The memory window width increased as the SBT film thickness increased. The 600-nm-thick SBT film was crystallized in a polycrystalline phase with a highly preferred (115) orientation. The memory window width of the 600-nm-thick SBT film was about 1.94 V at the bias sweep voltage ±9 V and the leakage current density was about 6.48?×?10^?8 A/cm² at 10 V.     

Catalytic activity of carbon-sphere/Co3O4/RuO2 nanocomposite for Li-air batteries

A carbon-sphere/Co₃O₄/RuO₂ nanocomposite was fabricated as part of a new approach to develop advanced Li–air batteries. The nanocomposite showed homogeneously dispersed Co₃O₄ and RuO₂ nanoparticles on the surface of carbon spheres, whose shape was effective in increasing the catalytic surface area and enhancing the stability of carbon and the catalyst. A high discharge capacity, relatively stable reversibility, and low overpotential were observed in electrochemical tests of an electrode containing this carbon-sphere/Co₃O₄/RuO₂ nanocomposite. The results showed that the nanocomposite can be introduced as a promising catalyst in Li–air cells.     

Application of fluorinated SiO2 interlayer dielectrics for ferroelectric memory

Abstract

Fluorine-doped silicon oxide (SiOF) as interlayer dielectric (ILD) was deposited over PZT capacitors by electron cyclotron resonance (ECR) chemical vapor deposition using SiF₄ and N₂O gases. In the conventional deposition of SiO₂ ILD layer using hydrogen-contained source gases, the properties of ferroelectric capacitors are known to be degraded during the formation of SiO₂ layer. In this study, we examined the degradation of electrical properties of SiOF-deposited PZT capacitors. The remnant polarization and leakage currents were not degraded after the deposition of SiOF. We observed that the fluorine atoms were not diffused into the metal electrode in both cases of the SiOF deposited PZT capacitors and post-deposition annealed capacitors. The SiOF films deposited in the high CF₄ flow rate exhibited rough columnar structure on the metal electrodes. We can successfully deposit SiOF in a smooth morphology by introducing TiO₂buffer layer or using the novel deposition method of changing the SiF₄ flow rate, namely two-layer-deposition method.     

Characterization of Ba(Zr0.05 Ti0.95)O3 thin film prepared by sol-gel process

Ba(Zr_0.05Ti_0.95)O₃ (BZT) thin film (∼330 nm) was grown on Pt/Ti/SiO₂/Si(100) substrate by a simple sol-gel process. The microstructure and the surface morphology of BZT thin film were studied by X-ray diffraction and atomic force microscopy. The optical properties of BZT thin film were obtained by spectroscopic ellipsometry. The optical bandgap was found to be 3.74 eV of direct-transition type. Ferroelectric and dielectric properties of BZT thin film were also discussed. The electrical measurements were conducted on BZT films in metal-ferroelectric-metal (MFM) capacitor configuration. The results showed the film exhibited good ferroelectrity with remanent polarization and coercive electric field of 3.54 μC/cm² and 95.5 kV/cm, respectively. At 10 kHz, the dielectric constant and dielectric loss of the film are 201 and 0.029, respectively.     

Evaluation of microscopic structural randomness in SiO2 by analysis of photoluminescence decay profiles

Microscopic structural randomness in SiO₂, a typical electrical insulating material, was evaluated by observing the decay profile of the photoluminescence due to oxygen vacancies (≡Si-Si≡). As samples with different degrees of randomness, an ion-implanted thermal SiO₂ film, SiO₂ films formed by plasma-enhanced chemical vapor deposition of tetraethoxysilane with and without doped fluorine, a buried oxide film prepared by SIMOX (separation by ion-implanted oxygen), and a bulk silica glass prepared by the soot-remelting method were tested. By analyzing the decay profile with a stretched exponential function, it was found that the deviation of the decay profile from a single exponential function is larger in the samples whose infrared absorption properties and HF etch rate suggest greater structural randomness. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 119 (3): 1–6, 1997     

Ferroelectric properties of Ba1−x Sr x TiO3 thin films synthesized by using novel sol–gel technique through carbonates

Ba_1?x Sr _x TiO₃ (BST) thin films were prepared on the substrate of Pt/Ti/SiO₂/Si by using novel sol–gel process through carbonates. The surface morphology and domain contrast of the films were investigated by atomic force microscopy (AFM), and the domain structures of the BST film were observed when AFM were operated in piezoelectric force microscopic (PFM) analysis and in the friction mode (FFM). The ferroelectric properties of the films were also investigated. It is shown that BST films obtained by the new sol–gel process through carbonates exhibit good properties.     

Neodymium substituted Bi4Ti3O12 nanostructures through self-assembly

For the sake of fabricating the ultrahigh density ultralarge scale integration (ULSI) memory chips, the ferroelectric nanostructures fabricated through self-assembly are studied. In this paper, we synthesized the neodymium substituted Bi₄Ti₃O₁₂ nanostructures on Pt/Ti/SiO₂/Si substrates. The method we used here was spin coating precursors with a series of different concentrations on the substrates and then annealing at 750 °C in the oxygen atmosphere to get the self-patterning nanoparticles. In order to avoid the influence of the Pt/Ti/SiO₂/Si substrates to the largest extent, the substrates were annealed first for different time in oxygen atmosphere to select appropriate conditions. Scanning probe microscope, and X-ray diffraction were used to detect the morphology and the crystalline structure of the nanoparticles respectively. The well-separated Bi_3.15Nd_0.85Ti₃O₁₂ particles have a typical lateral size about 100–150 nm and height about 20–25 nm. XRD reveals pyrochlore phase in the low concentration samples. The lower the precursor’s concentration, the higher the excess of Bi element is needed to form the pure perovskite nanoparticles.     

Electrophoretic TiO2 nanoparticle modified with poly (methyl methacrylate)

Although TiO₂ nanoparticle displays good electrophoretic mobility, its relatively high density causes severe sedimentation problems when suspended in media. Thereby, in order to improve the density mismatch in the suspension, surface of the TiO₂ nanoparticles with hydrophilic surface characteristics was coated with poly(methyl methacrylate) (PMMA) via a dispersion polymerization technique as a core-shell structure. A charge control agent (CCA) was also added to the suspending fluid in order to enhance surface charge of the nanoparticles and stabilize them suspended in low dielectric media. Chemical structure, particle size distribution and surface morphology, and particle shape of PMMA coated TiO₂ nanoparticles were examined via FT-IR, electrophoretic light scattering spectrophotometer and scanning electron microscope (SEM), respectively. Mobility of PMMA coated TiO₂ nanoparticles was also measured for different CCA concentrations.     

Effect of Aluminum Doping on the Performance and Microstructure of Methyl-Modified SiO2 Sol

Abstract

With methyltriethoxysilane as hydrophobic precursors and aluminum isopropoxide as the aluminum source, the Al₂O₃/SiO₂ sols and their gel materials were prepared. The effects of aluminum content (n_Al) on the viscosity (η), density (ρ), reaction rate constant (k), Gibbs energies of activation for viscous flow (ΔG*), particle size of Al₂O₃/SiO₂ sols were studied. And the high temperature calcined materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). The results show that, with the increase of n_Al, the η, n and ΔG* values of the Al₂O₃/SiO₂ sols decrease while the k and ρ values and average particle sizes increase. There is strong intermolecular interaction between the Al₂O₃ and SiO₂ sol molecules. The Al-O-Si bond exists in the Al₂O₃/SiO₂ materials before and after calcination at 350?°C. Calcination at 350?°C in N₂ atmosphere can change the phase structure of Al₂O₃/SiO₂ sample greatly, which can make the γ-AlOOH in the Al₂O₃/SiO₂ gel material convert to γ-Al₂O₃ through dehydration.     

Influence of Au particles on the photocurrent of TiO2 films

Au/TiO₂ composite films were employed in an attempt to improve the photon-electron conversion efficiency of TiO₂ film in the visible region, using the surface plasma resonance (SPR) of Au nanoparticles. For investigating the relationship between SPR of Au particle and photocurrent of TiO₂ film, a series of Au/TiO₂ films with different Au concentrations were synthesized by sol-gel method. Results of studies on the influence of Au particle size on crystallization of TiO₂ film, UV-vis absorption and photocurrents generated are discussed. It was shown that SPR performance of the Au nanoparticles was not only related to their size, but also to their distribution in the TiO₂ matrix. Even in TiO₂ films with large Au particle sizes (100 nm), SPR in visible region was still observed. However, this SPR performance did not contribute to the photon-electron conversion of TiO₂ film in the visible region. Contrarily, embedded Au nanoparticles depressed the photocurrent generated by the TiO₂ film in UV region. The reason for this decrease is thought to be partly due to the Au simply blocking some of the light and partly because the extent of crystallization of TiO₂ decreased with high Au levels.     

Synthesis and Luminescence Properties of Eu3+ Doped Sr2SiO4 Phosphor

Abstract

The europium doped Sr₂SiO₄ phosphors were prepared by the combustion synthesis technique. The prepared samples of europium doped Sr₂SiO₄ phosphors were characterized by the X-Ray Diffraction (XRD), Ultraviolet Visible spectroscopy (UV), Fourier Transform Infrared Spectroscopy (FT-IR), Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectra (EDS) and Photoluminescence Technique (PL). The orthorhombic crystal structure of the prepared sample was confirmed by using XRD. The formation of fiber like nano structured nature was confirmed by the images captured using the FE-SEM technique. The band gap energies were calculated using the UV-Visible spectra of the samples and these band gap energies were observed as 4.5826?eV for Sr₂SiO₄ and 4.1748?eV for Eu (5?m%) doped Sr₂SiO₄. The two different PL emission peaks were observed for two different excitation wavelengths. One peak was observed at the 590?nm under 393?nm excitation and another peak was observed at the 615?nm under 408?nm excitation. The CIE color coordinates of the Eu³⁺ doped Sr₂SiO₄ phosphors are x?≈?0.6615, y?≈?0.3382 (red color) observed for 408?nm excitation and x?≈?0.5636, y?≈?0.4356 (orange) observed for 393?nm excitation calculated using the color calculator program radiant imaging.     

Structural, dielectric and electrical studies of MgAl2−2xY2xO4 (x = 0.00–0.05) cubic spinel nano aluminate

Investigations were carried out on a series of MgAl_2-2xY_2xO₄ (x?=?0.00–0.05) nanoparticles prepared in steps of 0.01 by chemical co-precipitation method to study the effect of yttrium substitution at aluminum site on the structural, dielectirc and electrical properties. The single phase cubic spinel structure of all the samples was confirmed by X-ray diffraction (XRD). The Fourier transform infrared spectroscopy (FTIR) study shows two strong absorption bands in the frequency range 400–800 cm^?1, on the tetrahedral and octahedral sites respectively. Elemental analysis by Energy dispersive X-ray fluorescence (EDXRF) shows that samples are stoichiometric. The scanning electron microscopy (SEM) study reveals surface morphology of nanoparticles. Transmission electron microscopy (TEM) study shows the individual nanoparticles size and validates the nanocrystalline nature of the samples. The variation of dielectric permittivity at room temperature as a function of frequency (1 KHz to 1 MHz) suggests the dielectric dispersion due to Maxwell-Wagner Interfacial Polarization. AC conductivity study reveals that the conduction is due to small polaron hopping. The electrical modulus analysis shows that nanocrystalline MgAl_2?2xY_2xO₄ system exhibits non Debye type relaxation. The dc resistivity was found to increase with increase in yttrium content.