BaTiO3基Au纳米颗粒复合薄膜的制备及其光学性质研究

采用溶胶-凝胶(sol-gel)方法,成功的将高体积百分比的Au纳米颗粒复合到BaTiO₃的非晶薄膜中,并对其光学性质进行了研究.用XRD、TEM、椭偏仪、吸收光谱、光克尔效应0KE(Optical Kerr Effect)方法对薄膜进行了表征和测试.从吸收光谱观察到表面等离子体共振SPR(Surface Plasma Resonance)峰随热处理温度升高而红移的现象.光学非线性测试表明薄膜具有高的三阶非线性极化率x⁽³⁾和超快的响应时间.     

Optical bistability in BaTiO3

In this paper experimental results concerning the optical bistability of a ferroelectric monocrystal of BaTiO₃ are presented. Two laser beams were used to interact with the monocrystal which resulted in the bistability of the intensity of the transmitted wave. This was achieved without the application of any optical resonator. The feedback was provided by the electronic system through a mechanism typical to all photorefractive materials.     

Optical nonlinearities of Fe2O3 nanoparticles investigated by Z-scan technique

The single beam Z-scan technique has been used to measure the third-order nonlinear refractive index, γ, the two-photon absorption coefficient, ß, and the variation of refractive index per unit photoexcited carrier density σ_r, and the free carrier absorption cross section σ_ab for quantum-confined Fe₂O₃ nanoparticles coated by a layer of organic molecular in toluene and bare particles in hydrosol. For coated Fe₂O₃ nanoparticles, the ratio γ/ß is enhanced by a factor of five compared to the bare sample. Their figures of merit related to linear and two-photon absorption for ultrafast all-optical devices application were determined.     

Optical nonlinearities of Au nanocluster composite fabricated by 250 keV ion implantation

Metal nanocluster composite glass prepared by 250 keV Au ions into silica with dose of 1 × 10¹⁷ ions/cm² has been studied. The microstructural properties of the nanoclusters are characterized by optical absorption spectra and transmission electron microscopy (TEM). Third-order optical properties of the nanoclusters are studied by the Z-scan technique under 1064 nm and 532 nm excitations. The nonlinear refraction index, nonlinear absorption coefficient, and the real and imaginary parts of the third-order nonlinear susceptibility are deduced. The results of the investigation of nonlinear refraction using the off-axis Z-scan configuration are presented and the mechanisms responsible for the nonlinear response are discussed. The third-order nonlinear susceptibility χ⁽³⁾ of this kind of sample was determined to be 1.6 × 10⁻⁷ esu at 532 nm and 1.3 × 10⁻⁷ esu at 1064 nm.     

Dissolution properties of BaTiO3 nanoparticles in aqueous suspensions

Dissolution of barium ion from aqueous suspensions of commercial nano-sized barium titanate powders (BaTiO₃) has been studied at various pH values, solids loading, different time intervals and different electrolyte concentrations. Zeta potential measurements at various pH values and Fourier transform infrared spectroscopy study were also carried out to know the surface behaviour. Dissolution of Ba²⁺ depends on the suspension pH and stirring time period. The iso-electric points were found at 3.4 and 12.2 for as-received BaTiO₃ powder and 2.3 for the leached BaTiO₃. The Ba²⁺-leached BaTiO₃ suspension retards further leaching of Ba²⁺ ions at different pH values, which favours the achievement of stable suspension.     

Preparation of BaTiO3 nanoparticles by combustion spray pyrolysis

BaTiO₃ nanoparticles were synthesized by combustion spray pyrolysis using a 1:1 molar ratio of oxidizer and fuel. To prepare solution precursor, Ba(NO₃)₂, TiO(NO₃)₂, CH₆N₄O, and NH₄NO₃ with the molar ratio of 1:1:4:2.75 were mixed in distilled water with 10% ethyl alcohol. A 0.01 M solution was ultrasonically sprayed into a quartz tube heated at 800 °C. The number concentration of droplets was decreased and large particles were removed by passing the droplets through a metal screen filter. The synthesized particles were well crystallized tetragonal BaTiO₃. The median diameter of BaTiO₃ was 60 nm.     

Optical nonlinearities of gallium nitride

Luminescence, induced absorption and degenerate four wave mixing experiments are performed on GaN epilayers grown on a sapphire substrate by MOCVD. We measure the nonlinear behaviour of the luminescence spectra near the excitonic resonance, by using an excitation at 4.026 eV from an excimer laser. At low intensities of excitation, spectra show a saturation of the I₂ line due to the finite donor density in the sample. Higher intensities of excitation induce collision process between photo-created particles. Using a dye laser as a pump beam, we measure the induced variation of absorption of a probe beam as a function of the intensity and of the wavelength of the excitation. With increasing intensities of the pump beam, curves show a red-shift of the absorption edge and of the excitonic resonance. Pulsed degenerate four-wave mixing experiments were performed using the third harmonics of a picosecond Nd-YAG laser at 3.492 eV. A characteristic time of 16 ps has been measured, which is independent of the temperature, of the fringe spacing and of the intensity of the pump beams.     

Effect of the dispersibility of BaTiO3 nanoparticles in BaTiO3/polyimide composites on the dielectric properties

We have investigated the effect of coupling agents with different organic moiety on the dielectric properties of polyimide/BaTiO₃ (70 nm) composite films. INAAT (isopropyl tris(N-amino-ethyl aminoethyl)titanate, KR 44) and APTS (3-amino-propyl-triethoxysilane) were used as coupling agents, respectively, for homogeneous dispersion of BaTiO₃ particles into a polyimide matrix. The composite films were prepared by pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA)-based polyimide. Enhanced dispersion of BaTiO₃ particles was obtained by the use of INAAT with more organic moiety compared to that afforded by APTS. The polyimide composite with BaTiO₃ particles (BaTiO₃ content at 50 vol.%) treated by INAAT showed an increased dielectric constant of 19.03 while retaining an appropriate dielectric loss of 0.0109, as compared to the dielectric constant (14.64) of polyimide/APTS-treated BaTiO₃ composite. The results of this work demonstrate the potential use of an INAAT coupling agent with more organo functional groups for obtaining enhanced dielectric properties in a polyimide/BaTiO₃ composite for application in an embedded capacitor.     

Optical nonlinearities of Au/TiO2 films excited by high-repetition-rate femtosecond laser

The Au/TiO₂ composite films have been fabricated using the pulsed laser deposition technique. The optical transmission spectra of the films were investigated in the range from 300 to 900 nm and the surface plasmon resonance peaks were observed varying from 550 nm to 650 nm. The optical nonlinearities of the as-deposited and annealed samples were investigated by the Z-scan method using a high-repetition-rate femtosecond laser. It was found that, for the as-deposited samples, the sign of nonlinear absorption coefficients (β) changed from negative to positive with increasing Au concentration. However, for all the annealed samples, the sign of β was found to be negative. The nonlinear responses induced by the cumulative thermal effects were suggested to contribute to this phenomenon.     

Nonlinear refraction and saturable absorption in Au:BaTiO3 composite films

Composite thin films Au:BaTiO3, comprising nanometer-sized gold particles embedded in barium titanate matrices, were synthesized on MgO (100) substrates with the pulsed laser deposition technique. The nanostructure of the films and the size distributions of the Au particles were analyzed by high-resolution transmission electron microscopy. Crystal lattice fringes from the Au nanocrystals and the BaTiO3 matrices were observed. The nonlinear optical properties of the Au:BaTiO3 films were measured with the z-scan method at a wavelength of 532 nm, which was closed to the surface plasmon resonance of nanoscale Au particles. The features of the closed-aperture z-scan transmittance curves were affected by the ratio, which increased greatly at a high metal concentration, of the imaginary part to the real part of the third-order nonlinear susceptibility chi(3).     

Shape-Tunable BaTiO3 Crystals Presenting Facet-Dependent Optical and Piezoelectric Properties

BaTiO₃ octahedra, edge-, and corner-truncated cubes, and cubes with four tunable sizes from 132 to 438 nm are synthesized by a solvothermal growth approach. Acetic acid treatment can cleanly remove BaCO₃ impurity. Rietveld refinement of X-ray diffraction patterns and Raman spectra help to confirm the particles have a tetragonal crystal structure. The crystals also exhibit size- and facet-dependent bandgap shifts. BaTiO₃ octahedra show larger piezoelectric, ferroelectric, and pyroelectric effects than truncated cubes and cubes. The measured dielectric constant differences should be associated with their various facet-dependent behaviors. Piezoelectric nanogenerators fabricated from BaTiO₃ octahedra consistently show the best performance than those containing truncated cubes and cubes. In particular, a nanogenerator with 30 wt.%-incorporated octahedra displays an open-circuit voltage of 23 V and short-circuit current of 324 nA. The device performance is also highly stable. The maximum output power reaches 3.9 µW at 60 MΩ. The fabricated nanogenerator can provide sufficient electricity to power light-emitting diodes. This work further demonstrates that various physical properties of semiconductor crystals show surface dependence.     

常压液相法制备纳米钛酸钡粉体

以TiCl4、BaCl2·2H2O和NaOH为主要原料，采用常压液相法制备了BaTiO3纳米晶。研究了物料配比、反应物浓度、反应时间等条件对产物组成、产率和粒径大小的影响。采用XRD、TEM等分析手段对样品物相、形貌进行了分析，结果表明，所得BaTiO3粉体的形貌为球形，属立方晶系，钙钛矿结构。其平均颗粒尺寸约为60nm，颗粒尺寸分布均匀，实验证实，当反应温度为70℃、反应时间2h和NaOH：TiCl4=10：1时，所得样品最佳。     

The role of epoxy matrix occlusions within BaTiO3 nanoparticles on the dielectric properties of functionalized BaTiO3/epoxy nanocomposites

In this work, the effects of controlled nanoparticles aggregations of barium titanate (BaTiO₃) on the dielectric properties of epoxy nanocomposites are investigated in detail with respect to different experimental parameters like frequency, ceramic content and temperature. Dispersing silanized BaTiO₃ nanopowder under ultrasonic and stir, nanocomposites of epoxy-amine matrix with different morphologies are obtained. The nanoparticles silane functionalization containing amine end groups effectively improve the compatibility of the nano-BaTiO₃ and the epoxy matrix. Storage modulus, glass transition temperature, tensile and flexural properties of nanocomposites and dielectric properties are increased until 10% by weight of nano-BaTiO₃ loading, well dispersed in the matrix. Above 10 wt.% of nano-BaTiO₃, scanning electronic microscopy and thermal analysis showed that agglomeration of nanoparticles occurs. Rheological and mechanical nanocomposites properties were evaluated and matrix occlusion behaviors were identified. In light of the specific behavior of the occluded polymer, the dielectric properties, especially dielectric loss are discussed.     

Optical symmetry filtering by use of anisotropic self-diffraction in BaTiO3 crystals

We propose what we believe to be a novel and simple method for optical symmetry filtering, using anisotropic self-diffraction in BaTiO(3) crystals. This method allows us to distinguish a centrosymmetric pattern from a noncentrosymmetric pattern easily with scale invariance. It is self-referential; no extra reference element is required. Both the theory and the experiment are demonstrated.     

亲油性金纳米粒子的合成

利用相转移法成功地合成了粒径在2～7nm的硫醇表面修饰Au纳米粒子.采用透射电子显微镜、纳米粒度分布仪、红外光谱分析仪等现代测试技术对所合成的Au纳米粒子进行了表征.结果表明,表面为硫醇所修饰的Au纳米粒子,在有机溶剂中具有很好的分散性,表面修饰层的存在不仅有效地阻止Au纳米粒子的团聚,而且使得纳米粒子粒径分布窄,粒径可控.     

Photorefractive Incoherent-to-Coherent Optical Converter Based on Anisotropic Self-Diffraction in BaTiO(3)

A photorefractive incoherent-to-coherent optical converter (PICOC) is demonstrated; conversion is accomplished by anisotropic self-diffraction in BaTiO(3). The setup of the PICOC is easy, and only two writing beams are required. The diffraction efficiency reaches 50%, and the resolution is 22 line pairs (lp)/mm in a typical-size crystal. Further, the resolution reaches 40 lp/mm when a BaTiO(3):Rh crystal of thickness 1.2 mm is used, and the diffraction efficiency is as high as 51%. The resolution of the PICOC can be increased effectively by reduction of the crystal thickness with no penalty for low diffraction efficiency.     

Highly concentrated solvothermal synthesis of sub-10-nm BaTiO3 nanoparticles for optical applications

Single-crystalline barium titanate: BaTiO₃ (BT) nanoparticles (NPs) with sub-10-nm size have been successfully obtained by a highly concentrated solvothermal synthesis using a high concentration of Ba(OH)₂ and a titanium complex. To obtain sub-10-nm NPs, we focused on the gradual increase in the OH^– ion concentration and the decrease in the dielectric constant of solvents, and BT NPs were produced in 1 h even at a low temperature of 200 °C. High-resolution transmission electron microscopy (HR-TEM) observation revealed that the resulting BT NPs were single-nanometer size, consisting of a single-crystalline structure. ¹H-nuclear magnetic resonance (NMR) relaxation time (T₂) and zeta potential measurements demonstrated that our BT NPs had high dispersibility and dispersion stability under acidic conditions. The yellowness index measurements revealed that the BT NPs dispersions exhibited colorless property. The resulting single nanometer-sized BT NPs are promising as high refractive index materials for optical applications due to being dispersed in optical resins.     

室温研磨-微波加热合成钛酸钡纳米粒子

以氢氧化钡和钛酯丁酯为原料,采用室温研磨-微波加热合成了BaTiO3纳米粒子.用XRD、TEM、ED、IR和ICP对产品进行了表征.结果表明,微波加热10～20min可获得平均粒径为10～30nm的纳米粒子,该粒子大小分布均匀,晶相结构为立方相,钡钛物质的量之比约为1.0.氢氧化钡中的结晶水对粒子的大小、晶化程度有重要的影响.     

超小型Fe3O4/Au纳米复合微粒的制备与表征

用反向微乳液法成功制备了超小型Fe3O4/Au磁性纳米复合微粒,并利用3-巯基丙酸将复合微粒直接从微乳液分离到有机溶剂中.用UV-Vis、VSM和TEM对产物进行了鉴定与表征,结果表明复合微粒分散良好,平均粒径为6.7nm,饱和磁化强度为9.7A·m2/kg.     

Nonhomogeneous surface premelting of Au nanoparticles

A reversible nonhomogeneous surface premelting of Au nanoparticles is demonstrated through molecular dynamics simulations. With increasing temperature, liquid-like atoms first appear at some vertices and edges of surface facets, then small liquid regions grow and, at temperatures close to the particle melting temperature, most of the remaining solid-like surface atoms reside on {111} planes which are the most stable against surface premelting. The appearance of a contiguous liquid layer (complete surface premelting) is size dependent and is not observed in very small nanoparticles.