rf reactive co-sputtered Au-Ag alloy nanoparticles in SiO2 thin films

We have studied formation of Au-Ag alloy nanoparticles in sputtered SiO₂ thin films. Silica thin films containing Au-Ag nanoparticles were deposited on quartz substrates using rf reactive magnetron co-sputtering technique. The films heat-treated in reducing Ar + H₂ atmosphere at different temperatures. They were analyzed by using UV-vis spectrophotometry, atomic force microscopy and X-ray photoelectron spectroscopy (XPS) methods for their optical, surface morphological as well as structural and chemical properties. The optical absorption of the Au-Ag alloy nanoparticles illustrated one plasmon resonance absorption peak located at 450 nm between the absorption bands of pure Au and Ag nanoparticles at 400 and 520 nm, respectively, for the thin films annealed at 800 °C. XPS results showed that the alloys were in metallic state, and they had a greater tendency to lose electrons as compared to their corresponding monometallic state. Using lateral force microscopy analysis, we have found that the alloy particles were uniformly distributed on the surface with grain size of about 20 nm.     

ZnS/PVA nanocomposites for nonlinear optical applications

We have found a correlation between ZnS nanocomposite nonlinear optical features and technological processing using electrolytic method. In the earlier researches this factor was neglected. However, it may open a new stage for operation by photovoltaic features of the well known semiconductors within a wide range of magnitudes. The titled nanostructured zinc sulfide (ZnS) was synthesized by electrolytic method. The obtained ZnS nano-crystallites possessed nano-particles sizes varying within 1.6 nm…1.8 nm. The titled samples were analyzed by XRD, HR-TEM, STEM, and nonlinear optical methods such as photo-induced two-photon absorption (TPA) and second harmonic generation (SHG). For this reason the nano-powders were embedded into the photopolymer poly(vinyl) alcohol (PVA) matrices. Role of aggregation in the mentioned properties is discussed. Possible origin of the such correlations are discussed.     

Determination and analysis of dispersive optical constants of CuIn3S5 thin films

CuIn₃S₅ thin films were prepared from powder by thermal evaporation under vacuum (10⁻⁶ mbar) onto glass substrates. The glass substrates were heated from 30 to 200 °C. The films were characterized for their optical properties using optical measurement techniques (transmittance and reflectance). We have determined the energy and nature of the optical transitions of films. The optical constants of the deposited films were determined in the spectral range 300-1800 nm from the analysis of transmission and reflection data. The Swanepoel envelope method was employed on the interference fringes of transmittance patterns for the determination of variation of refractive index with wavelength. Wemple-Di Domenico single oscillator model was applied to determine the optical constants such as oscillator energy E₀ and dispersion energy E_d of the films deposited at different substrate temperatures. The electric free carrier susceptibility and the ratio of the carrier concentration to the effective mass were estimated according to the model of Spitzer and Fan.     

Derivation of the optical constants of spin coated CeO2-TiO2-ZrO2 thin films prepared by sol-gel route

Ternary thin films of cerium titanium zirconium mixed oxide were prepared by the sol-gel process and deposited by a spin coating technique at different spin speeds (1000-4000 rpm). Ceric ammonium nitrate, Ce(NO₃)₆(NH₄)₂, titanium butoxide, Ti[O(CH₂)₃CH₃]₄, and zirconium propoxide, Zr(OCH₂CH₂CH₃)₄, were used as starting materials. Differential calorimetric analysis (DSC) and thermogravimetric analysis (TGA) were carried out on the CeO₂-TiO₂-ZrO₂ gel to study the decomposition and phase transition of the gel. For molecular, structural, elemental, and morphological characterization of the films, Fourier Transform Infrared (FTIR) spectral analysis, X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), cross-sectional scanning electron microscopy (SEM), and atomic force microscopy (AFM) were carried out. All the ternary oxide thin films were amorphous. The optical constants (refractive index, extinction coefficient, band gap) and thickness of the films were determined in the 350-1000 nm wavelength range by using an nkd spectrophotometer. The refractive index, extinction coefficient, and thickness of the films were changed by varying the spin speed. The oscillator and dispersion energies were obtained using the Wemple-DiDomenico dispersion relationship. The optical band gap is independent of the spin speed and has a value of about E_g≈2.82±0.04 eV for indirect transition.     

化学溶液法制备的Pb(Mg1/3Nb2/3)O3-PbTiO3薄膜的光学性能

用化学溶液方法在宝石衬底及有LaNiO₃缓冲层的Pt/TiO₂/SiO₂/Si衬底上制备了92%Pb(Mg_1/3Nb_2/3)O₃-8%PbTiO₃(PMNT)薄膜，X射线衍射测试结果表明：在有LaNiO₃缓冲层的Pt/TiO₂/SiO₂/Si衬底上制备的PMNT薄膜几乎是纯钙钛矿相，且薄膜 关键词： PMNT薄膜 光学性能 化学溶液法     

Electrical and optical properties of thermally-evaporated thin films from A2[TiO(C2O4)2] (A = K, PPh4) and 1,8-dihydroxyanthraquinone

In this work, the synthesis of molecular materials formed from A₂[TiO(C₂O₄)₂] (A = K, PPh4) and 1,8 dihydroxyanthraquinone is reported. The synthesized materials were characterized by atomic force microscopy (AFM), infrared (IR) and ultraviolet-visible (UV-vis) spectroscopy. IR spectroscopy showed that the molecular-material thin-films, deposited by vacuum thermal evaporation, exhibit the same intra-molecular vibration modes as the starting powders, which suggests that the thermal evaporation process does not alter the initial chemical structures. Electrical transport properties were studied by dc conductivity measurements. The electrical activation energies of the complexes, which were in the range of 0.003-1.16 eV, were calculated from Arrhenius plots. Optical absorption studies in the wavelength range of 190-1090 nm at room temperature showed that the optical band gaps of the thin films were around 1.9-2.3 eV for direct transitions Eg_d. The cubic NLO effects were substantially enhanced for materials synthesized from K₂[TiO(C₂O₄)₂], where χ⁽³⁾ (−3ω; ω, ω, ω) values in the promising range of 10⁻¹² esu have been evaluated.     

Photo-induced anisotropy in ZnO/PVA nanocomposites prepared by modified electrochemical method in PMA matrix

Substantial photo-induced optical anisotropy was discovered in ZnO/PVA nanocomposites under the influence of external bicolor laser illumination. Zinc oxide nanoparticles were synthesized by electrolysis of a sodium chloride aqueous medium including poly-methacrylic acid (PMA) in a cell system having a soluble zinc anode. The structural analysis of the ZnO powder samples has been carried out by X-Ray Diffractometry (XRD) and Scanning Electron Microscopy (SEM). The polyvinyl alcohol (PVA) embedded ZnO films obtained from the powder samples possess larger grain sizes than those in powder form. The films were prepared from the same polymer matrix but elaborated with two different PVA contents which are respectively 15% and 30%. The photoinduced anisotropy was identified by using two bicolor Er: glass laser beams incident at different angles. Substantial influence of the technological processes on the embedded nanoparticle sizes and related birefringence was explored. The process of laser induced anisotropy shows an occurrence of birefringence saturation.     

Synthesis and crystal structures and luminescent properties of divalent europium-doped Ba2ZnSi2O7 and BaZn2Si2O7

The monoclinic Ba₂ZnSi₂O₇:Eu²⁺ blue-green-emitting phosphor and the orthorhombic BaZn₂Si₂O₇:Eu²⁺ green-emitting phosphor were prepared by combustion-assisted synthesis method as the fluorescent materials for ultraviolet-light-emitting diodes (UV-LEDs) performed as a light source. The crystallinity and luminescence were investigated using X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. Pure monoclinic Ba₂ZnSi₂O₇ and orthorhombic BaZn₂Si₂O₇ crystallize completely at 1100 °C. The doped Eu²⁺ ions did not cause any significant change in the host structure. The emission spectra presented an emission position red shift of up to 16 nm from Ba₂ZnSi₂O₇:Eu²⁺ to BaZn₂Si₂O₇:Eu²⁺. The excitation spectra of Ba₂ZnSi₂O₇:Eu²⁺ and BaZn₂Si₂O₇:Eu²⁺ were broad-banding, extending from 260 to 465 nm, which match the emission of UV-LEDs.     

Preparation of Cu2ZnSnS4 thin films by hybrid sputtering

In order to fabricate Cu₂ZnSnS₄ thin films, hybrid sputtering system with two sputter sources and two effusion cells is used. The Cu₂ZnSnS₄ films are fabricated by the sequential deposition of metal elements and annealing in S flux, varying the substrate temperature. The Cu₂ZnSnS₄ films with stoichiometric composition are obtained at the substrate temperature up to 400 °C, whereas the film composition becomes quite Zn-pool at the substrate temperature above 450 °C. The Cu₂ZnSnS₄ film shows p-type conductivity, and the optical absorption coefficient and the band gap of the Cu₂ZnSnS₄ film prepared in this experiment are suitable for fabricating a thin film solar cell.     

Synthesis and characterization of thermotropic liquid crystalline polyester/multi-walled carbon nanotube nanocomposites

Thermotropic liquid crystalline polyester (TLCP) was synthesized via low-temperature solution polycondensation from 1,4-Bis(4-Hydroxybenzoyloxy)butane and terephthaloyl dichloride. Polymer nanocomposites based on a small quantity of multi-walled carbon nanotubes (MWNTs) were prepared by in situ polymerization method. The wide-angle X-ray diffraction (WAXD) results suggested that the addition of MWNTs to TLCP matrix did not significantly change the crystal structure of TLCP. The interactions between the molecules of the TLCP host phase and the carbon nanotubes were investigated through Raman spectroscopy investigations. We detected a distinct wave number shift of the radial breathing modes, confirming the carbon nanotubes interacted with the surrounding liquid crystal molecules, most likely through aromatic interactions (π-stacking). The interactions between liquid crystal host and nanotube guests were also evident from a polarizing microscopy (POM) study of the liquid crystal-isotropic phase transition in the proximity of nanotubes. The thermal properties and the morphological properties of the TLCP/MWNTs nanocomposites were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). TGA data demonstrated the addition of a small amount of MWNTs into TLCP matrix could improve the thermal stability of TLCP matrix. DSC results revealed that melt transition temperatures and isotropic transition temperatures of the hybrids were enhanced.     

Thin films of molecular materials synthesized from C32H20N10M (M = Co, Pb, Fe): Film formation, electrical and optical properties

In this work, the synthesis of molecular materials formed from metallic phthalocyanines and 1,4-phenylenediamine is reported. The powder and thin film (∼80-115 nm thickness) samples of the synthesized materials, deposited by vacuum thermal evaporation, show the same intra-molecular bonds in the IR spectroscopy studies, which suggests that the thermal evaporation process does not alter these bonds. The morphology of the deposited films was studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM) and their optical and electrical properties were studied as well. The optical parameters have been investigated using spectrophotometric measurements of transmittance in the wavelength range 200-1200 nm. The absorption spectra recorded in the UV-vis region for the deposited samples showed two bands, namely the Q and Soret bands. The optical activation energy was calculated and found to be 3.41 eV for the material with cobalt, 3.34 eV for the material including lead and 3.5 eV for the material with iron. The effect of temperature on conductivity was measured for the thin films and the corresponding conduction processes are discussed in this work.     

Synthesis and magnetic properties of carbon-coated Ni/SiO_2 core/shell nanocomposites

A simple method for the synthesis of carbon-coated Ni/SiO2 core/shell nanocomposites is reported. The Ni nanoparticles were coated with silica layers via a combined procedure of sol-gel fabrication and hydrogen reduction prior to carbon coating via acetylene decomposition at an appropriate temperature. It was found that the anti-acid ability of the Ni/SiO2 composites was greatly enhanced after carbon coating. The results of magnetization measurement show that the real part (μ′) of complex permeability of the as-obtained sample is almost independent of frequency, and the imaginary part (μ″) stays small up to a frequency of 1 GHz. The encapsulation of Ni particles with SiO2 results in the rise of Ni nanoparticles resistivity. The outcome is the reduction in effect of eddy current at high frequency, making the real part μ′ almost constant and the imaginary part μ″ very small. Thus, this simple method may be effective for preparing composites of soft magnetic properties, especially in the high-frequency range.     

椭偏光散射分析类金刚石薄膜的散射特性

 基于光学薄膜反射椭偏法的测量原理,对光学薄膜散射椭偏特性进行了研究。给出了光学薄膜散射逆问题的解决方法,并对不同脉冲频率下采用脉冲真空电弧离子镀技术沉积的类金刚石薄膜的散射特性进行了研究。分析了光学薄膜界面的相关特性以及膜层中局部缺陷对散射光椭偏特性的影响。结果表明:随着脉冲频率的增加,所沉积的类金刚石薄膜的相关性变差,且薄膜中的局部缺陷引起的体散射越明显。     

Synthesis and magnetic properties of carbon-coated Ni/SiO2 core/shell nanocomposites

A simple method for the synthesis of carbon-coated Ni/SiO₂ core/shell nanocomposites is reported. The Ni nanoparticles were coated with silica layers via a combined procedure of sol-gel fabrication and hydrogen reduction prior to carbon coating via acetylene decomposition at an appropriate temperature. It was found that the anti-acid ability of the Ni/SiO₂ composites was greatly enhanced after carbon coating. The results of magnetization measurement show that the real part (μ′) of complex permeability of the as-obtained sample is almost independent of frequency, and the imaginary part (μ″) stays small up to a frequency of 1 GHz. The encapsulation of Ni particles with SiO₂ results in the rise of Ni nanoparticles resistivity. The outcome is the reduction in effect of eddy current at high frequency, making the real part μ′ almost constant and the imaginary part μ″ very small. Thus, this simple method may be effective for preparing composites of soft magnetic properties, especially in the high-frequency range. Supported by the Jiangsu Postdoctoral Foundation of Jiangsu Province and the Major Project of National Basic Research Program of China (Grant No. 2005CB623605)     

Improvement of the mechanical and rheological properties of HDPE/PET/MWCNT nanocomposites

High density polyethylene (HDPE)/poly (ethylene terephthalate) (PET) (90/10 wt.%) blends and HDPE/PET/multi-walled carbon nanotubes (MWCNTs) nanocomposites were prepared by melt mixing process, and the influence of MWCNTs on the mechanical and rheological properties of the nanocomposites was investigated. MWCNTs were added up to 5 wt.% in the HDPE/PET matrix. Transmission electron microscopy images reveal that the MWCNTs were homogeneously dispersed in the HDPE/PET matrix. Improvement of mechanical properties was observed by the addition of MWCNTs compared with HDPE/PET blends. Prominent increases in the complex viscosity and storage modulus of the nanocomposites were found with increasing MWCNT content.     

Giant photoinduced optical bleaching at room and liquid helium temperatures in Sb/As2S3 multilayered films

We report the observation of giant photo induced optical bleaching in Sb/As₂S₃ multilayered film at room and liquid He temperatures, when irradiated with 532 nm laser at moderate intensities. The experimental results show a dramatic increase in transmittance near the band gap regime at both the temperatures; however the rates at which transmission change occurs are rather slow at low temperature. The huge change in transmission is due to the photo induced intermixing of As₂S₃ layer with Sb. Our XPS measurements show that photo induced intermixing occurs through the wrong homopolar bonds, which under actinic light illumination are converted into energetically favored hetropolar bonds.     

Low cost fabrication of SiO2 optical waveguides by laser direct writing on Ti-doped Sol-Gel films

A commercial direct laser writing (DLW) system operating at 1070 nm was used to fabricate SiO₂ optical waveguides on silicon wafers. A Ti-doped SiO₂ Sol-Gel film was deposited on the SiO₂/Si substrate by the dip-coating technique, based on which SiO₂ optical waveguides were patterned by DLW using a Ytterbium fiber laser and followed by chemical etching. The effects of laser parameters and the preheated temperature of Sol-Gel films on the dimensions of optical waveguides were studied systematically. The differences of etching rate between laser irradiated and non-irradiated areas in Sol-Gel films preheated at various temperatures are characterized by measuring the thickness of the films. Results demonstrate that the available laser power density range for laser densification and the width of the patterned optical waveguides are influenced strongly by the preheated temperature of the Sol-Gel films. The width of the optimized optical waveguide in this work is 25 μm. The minimum propagation loss of the fabricated optical waveguides is 1.7 dB cm⁻¹ at the wavelength of 1550 nm.     

Morphological and optical properties of sol-gel derived 6SrO·6BaO·7Al2O3 thin films

A novel 6SrO·6BaO·7Al₂O₃ (S6B6A7) thin film deposited onto soda lime float glass via sol-gel dip coating technique is reported. The morphological and compositional properties of the S6B6A7 thin films have been investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) revealing that the films were composed of S6B6A7 nanoparticles. The optical properties of the S6B6A7 films are affected by sol concentration, film thickness and annealing temperature as revealed by UV-vis transmittance. The transparency of S6B6A7 films improved on increasing annealing temperature up to 450 °C in air. The S6B6A7 films prepared using 2, 5, and 8 (wt.%) sols and annealed at 450 °C exhibit an average transmittance of over ∼91% in wide visible range.     

Magnetic properties of mechanochemically prepared iron-wüstite (Fe-FeyO) nanocomposites

In this work, iron-wüstite (Fe-Fe_yO) nanocomposites have been prepared via high-energy ball milling (HEBM), using high-purity hematite (α-Fe₂O₃) and iron (Fe) powders as the raw materials with different Fe/Fe₂O₃ mole ratios (MR)=0.6, 0.9, 1.0, 2.3, 4.9 and 13.6. X-ray diffraction studies of the as-milled powders show that a single-phase wüstite was formed for the lowest mole ratio (MR=0.6) and mixtures with MRs higher than 0.6 result in iron-wüstite nanocomposites, except for MR=13.6 that is dominantly a pure iron phase. The mean crystallite sizes of the iron and wüstite in the nanocomposites have been calculated by Scherrer's formula, which were 9±1 and 7±1 nm, respectively. Using the formula a=3.856+0.478y, for Fe_yO, where “a” is the lattice parameter of wüstite, it is possible to estimate the value of “y” for different nanocomposites and a composition of Fe_0.93O was estimated for the wüstite single phase (MR=0.6). In addition, a gradual decrease in “y” from 0.87 to 0.83 was obtained by increasing MR values from 0.9 to 4.9, respectively. The room-temperature Mössbauer spectrum of the single-phase wüstite shows considerable asymmetry due to two overlapping quadrupole doublets. For higher MRs, room-temperature Mössbauer spectra exhibit sextets, which confirm the existence of iron in the samples. The Mössbauer spectrum of the sample with the highest mole ratio (MR=13.6) shows only a sextet related to α-Fe without any detection of wüstite, which is in agreement with the XRD results. The nanosized prepared wüstite shows ferrimagnetic like behavior, which was interpreted according to spinel-like defect clusters. The M_s values obtained from VSM measurements and those calculated based on the Mössbauer data and chemical reaction are in good agreement. By increasing MR from 0.6 to 2.3, the coercivity (H_c) increases sharply to its maximum value at about MR=2.3, for which the value of Fe content is 45% and then drops off. This behavior is discussed based on α-Fe contents in the nanocomposites and percolation threshold.     

Sol-gel derived 6SrO·6BaO·7Al2O3 thin films using metal alkoxides

A novel 6SrO·6BaO·7Al₂O₃ (S6B6A7) thin film has been deposited onto soda lime float glass via sol-gel dip coating technique. The optical and electrical properties of S6B6A7 films annealed in air and H₂ atmosphere have been investigated. The structural and compositional properties of the S6B6A7 thin films have been investigated using Fourier transferred infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The S6B6A7 films prepared using 5 (wt.%) sol and annealed at 450 °C in air and H₂ atmosphere exhibit an average transmittance of over ∼91% in wide visible range. The electrical properties of the S6B6A7 films affect film thickness as revealed by sheet resistance measurements. The sheet resistance of the 150 nm S6B6A7 films was 67.85 and 6.06 kilo ohms per square for air and H₂ annealed, respectively.