Improvement of high-frequency characteristics of FeCoHfO/AlOx multilayered films

High-permeability magnetic films can enhance the inductance of thin-film inductors in dc-dc converters. The FeCoHfO/AlO_x multilayered films were fabricated by dc reactive magnetron co-sputtering. Inserting the AlO_x layers can decrease the anisotropic field of the FeCoHfO magnetic films, which was beneficial to raise the permeability of the FeCoHfO/AlO_x multilayered films. With this optimum configuration of a nine-layer structure [FeCoHfO (133 nm)/AlO_x (10 nm)]₉, low anisotropic field (H_K = 65 Oe) and high permeability (permeability over 170 at 30-50 MHz) were obtained. The permeability increased nearly six times from 30 (M1) to 175 (M9). The permeability was evidently improved by the employment multilayered coating.     

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.     

多晶TaN1-δ薄膜的电输运性质研究

利用射频溅射法在石英玻璃基底上制备了一系列面心立方结构的多晶TaN_1-δ薄膜, 并对其晶体结构和2–350 K温度范围的电子输运性质进行了系统研究. 薄膜呈多晶结构, 并且平均晶粒尺寸随着基底温度的升高逐渐增大. 电输运测量结果表明, TaN_1-δ薄膜在5 K以下表现出类似超导体-绝缘体颗粒膜的电输运性质; 随着温度的升高, 薄膜在10–30 K表现出类似金属-绝缘体颗粒膜的性质; 在70 K以上, 热涨落诱导的遂穿导电机理主导着电阻率的温度行为. 我们的结果表明: TaN_1-δ多晶薄膜的类颗粒膜属性使其具有较高的电阻率和负的电阻温度系数.     

Optical properties of Si-rich SiO2 films in relation with embedded Si mesoscopic particles

Optical properties of Si-rich SiO₂ films prepared by an RF cosputtering method are discussed. From the infrared and Raman spectroscopy together with the electron microscopy, it is shown that Si mesoscopic particles embedded in solid matrices with the sizes ranging from ˜ 10 nm (nanocrystals) to less than ˜1 nm (clusters) can be obtained by the cosputtering and post-annealing. The absorption and photoluminescence spectra are presented. For our samples, a red luminescence peak analogous to that of porous Si is observed for films containing Si clusters rather than nanocrystals. Raman spectra which evidence the success in the heavy doping of B atoms into Si nanocrystals are also discussed.     

Study of optical and magneto-optical properties of CoFe–HfO2 granular magnetic films

Granular films of composition (CoFe)_x(HfO₂)_1−x with continuous variation of the Co_0.5Fe_0.5 volume fraction in the range 0.1<x<0.9 have been prepared by e-beam co-evaporation. The optical properties of the thin granular composite films have been determined from transmission and reflection spectra in the 300–1100 nm region. The optical characteristics of the granular films as a function of x were also determined by the ellipsometrical method at λ=632.8 nm. We find that the transmission and reflection spectra and the dielectrical function have anomalies near the percolation threshold at x_p≈0.45. The Faraday rotation in the films was determined at λ=632.8 nm. The spectral dispersion of Faraday effects have peak in the region of the plasmon frequency. The Faraday effect is greatly enhanced near x_p. The calculated optical and magneto-optical parameters, described in the framework of the effective medium approximation, are in qualitative agreement with experimental data.     

Structure-related infrared optical properties of BaTiO3 thin films grown on Pt/Ti/SiO2/Si substrates

BaTiO₃ thin films with different thickness have been grown on Pt/Ti/SiO₂/Si substrates by a modified sol-gel method. X-ray diffraction analyses show that the BaTiO₃ thin films are polycrystalline. The crystalline quality of the films is improved with increasing thickness. The infrared optical properties of the BaTiO₃ thin films have been investigated using an infrared spectroscopic ellipsometry in the wave number range of 800-4000 cm⁻¹ (2.5-12.5 μm). By fitting the measured pseudodielectric functions with a three-phase model (Air/BaTiO₃/Pt), and a derived classical dispersion relation for the thin films, the optical constants and thicknesses of the thin films have been simultaneously obtained. The refractive index of the BaTiO₃ thin films increases and on the other hand, the extinction coefficient does not change with increasing thickness in the entirely measured wave number range. The dependence of the refractive index on the film thickness has been discussed in detail and was mainly due to both the crystalline quality of the films and packing density. Finally, the absorption coefficient was calculated in the infrared region for applications in the pyroelectric IR detectors.     

Magnetoelectric properties of Mn-substituted BiFeO3 thin films with a TiO2 barrier

Multiferroic thin films with the general formula TiO₂/BiFe_1−xMn_xO₃ (x=0.00, 0.05, 0.10 and 0.15) (TiO₂/BFMO) were synthesized on Au/Ti/SiO₂/Si substrates using a chemical solution deposition (CSD) method assisted with magnetron sputtering. X-ray diffraction analysis shows the thin films contained perovskite structures with random orientations. Compared with BFMO films, the leakage current density of the TiO₂/BFMO thin films was found to be lower by nearly two orders of magnitude, and the remnant polarizations were increased by nearly ten times. The enhanced ferroelectric properties may be attributed to the lower leakage current caused by the introduction of the TiO₂ layer. The J-E characteristics indicated that the main conduction mechanism for the TiO₂/BFMO thin film was trap-free Ohmic conduction over a wide range of electric fields (0-500 kV/cm). In addition, ferromagnetism was observed in the Mn doped BFO thin films at room temperature. The origin of ferromagnetism is related to the competition between distortion of structure and decrease of grain size and decreasing net magnetic moment in films due to Mn doping.     

Enhanced optical nonlinear absorption of graded Au--TiO2 composite films

This paper reports that single-layer and graded Au-TiO2 granular composite films with Au atom content 15%- 66% were prepared by using reactive co-sputtering technique. The third-order optical nonlinearity of single-layer and graded composite films was investigated by using s- and p-polarized Z-scans in femtosecond time scale. The nonlinear absorption coefficient βeff of single-layer Au-TiO2 films is measured to be -2.3×10^3-0.76×10^3 cm/GW with Au atom content 15%-66%. The βeff value of the 10-layer Au-TiO2 graded film is enhanced to be -2.1×10^4cm/GW calculated from p-polarized Z-scans, which is about ten times the maximum βeff of single-layer films. Broadened response in the wavelength region 730-860 nm of the enhanced optical nonlinearity of graded Au-TiO2 composite films was also investigated.     

Raman properties embeddedof GaSb nanoparticlesin SiO2 films

The Raman shifts of nanocrystalline GaSb excited by an Ar^ ion laser at wavelengths 514.5, 496.5, 488.0, 476.5,and 457.9nm are studied by an SPEX-1403 laser Raman spectrometer respectively, and they are explained by phonon confinement, tensile stress, resonant Raman scattering and quantum size effects. The Stokes and anti-Stokes Raman spectra of GaSb nanocrystals strongly support the Raman feature of GaSb nanocrystals. The calculated optical spectra compare well with experimental data on Raman scattering GaSb nanocrystals.     

异质界面对Ca(Mg1/3Nb2/3)O3/CaTiO3叠层薄膜结构和介电性能的影响

采用异质叠层方式制备出一定厚度的Ca(Mg_1/3Nb_2/3)O₃/CaTiO₃(CMN/CT)叠层薄膜,研究了异质界面对薄膜结构、微观形貌及介电性能的影响及其规律.根据实验测试结果,提出CMN/CT叠层薄膜的模拟等效电路,建立介电常数和介电损耗的理论计算公式.结果表明:CMN/CT异质叠层薄膜具有完全正交钙钛矿结构,结构致密,厚度均匀,薄膜中存在独立的CMN和CT相.异质界面处存在过渡层,随着薄膜中异质界面个数增加,介电常数增大,介电损耗减小.减小界面过渡层的厚度,有利于提高CMN/CT叠层薄膜的介电性能.     

Structural and magnetic studies of Fe2O3/SiO2 granular nanocomposites

Fe₂O₃/SiO₂ nanocomposites were synthesized by mechanical alloying, using Fe and SiO₂ powders as precursors. After 340 h milling, the sample essentially consists of hematite and amorphous silica. TEM images show hematite particles embedded in and surrounded by an amorphous silica matrix. A broad size distribution—5–50 nm—of hematite particles is found, and other group of very small—2–3 nm—unidentified particles are observed. Room temperature Mössbauer spectra show a paramagnetic doublet, which may correspond to a non-crystalline phase in the sample (probably the small unidentified particles), and a sextet corresponding to hematite. Magnetic properties were investigated by measuring hysteresis curves at different temperatures (5–300 K) and by zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves (10 mT). The hysteresis loops were well fitted by a ferromagnetic contribution. No evidence of Morin transition is found down to 5 K.     

ZnSe/SiO2复合薄膜光学常数与荧光光谱的研究

采用溶胶-凝胶工艺与原位生长技术，制备了ZnSe/SiO₂复合薄膜.X射线衍射分 析表明薄膜中ZnSe晶体呈立方闪锌矿结构.X射线荧光分析结果显示薄膜中Zn与Se摩尔比为1 ∶1.01—1∶1.19.利用场发射扫描电子显微镜观察了复合薄膜的表面形貌，结果表明复合薄 膜表面既存在尺寸约为400nm的ZnSe晶粒，也存在尺寸小于100nm的ZnSe晶粒.利用椭偏仪测 量了薄膜椭偏角Ψ，Δ与波长λ的关系，采用Maxwell-Garnett有效介质理论对薄膜的光学 常数、厚度、气孔率、ZnS 关键词： 2复合薄膜')" href="#">ZnSe/SiO₂复合薄膜 光学性质 椭偏光度法 荧光光谱     

Study of interactions in Co–SiO2 granular films by means of MFM and magnetization measurements

A study of Co[SiO₂] granular films using magnetic force microscopy (MFM), transmission electron microscopy and DC magnetization is presented. MFM shows large strip magnetic domains in the percolated system and allows a more direct investigation of the magnetic interaction among grains in the film with the lowest metal volume fraction.     

Interfaces analysis of the HfO2/SiO2/Si structure

The physical and chemical properties of the HfO₂/SiO₂/Si stack have been analyzed using cross-section HR TEM, XPS, IR-spectroscopy and ellipsometry. HfO₂ films were deposited by the MO CVD method using as precursors the tetrakis 2,2,6,6 tetramethyl-3,5 heptanedionate hafnium—Hf(dpm)₄ and dicyclopentadienil-hafnium-bis-diethylamide—Сp₂Hf(N(C₂H₅)₂)₂.The amorphous interface layer (IL) between HfO₂ and silicon native oxide has been observed by the HRTEM method. The interface layer comprises hafnium silicate with a smooth varying of chemical composition through the IL thickness. The interface layer formation occurs both during HfO₂ synthesis, and at the annealing of the HfO₂/SiO₂/Si stack. It was concluded from the XPS, and the IR-spectroscopy that the hafnium silicate formation occurs via a solid-state reaction at the HfO₂/SiO₂ interface, and its chemical structure depends on the thickness of the SiO₂ underlayer.     

Microstructural and electromagnetic properties of MnO2 coated nickel particles with submicron size

Nickel particles with submicron size are prepared by using the solvothermal method. These spheres are then coated with a layer of MnO2 using the soft chemical method. The microstructure is characterized by x-ray diffraction, transmission electron microscopy, and scanning electron microscopy. Energy x-ray dispersive spectrometry and high-resolution images show that the granular composites have a classical core/shell structure with an MnO2 superficial layer,no more than 10 nm in thickness. The hysteresis measurements indicate that these submicron-size Ni composite powders have small remanence and moderate coercivity. The electromagnetic properties of the powders measured by a vector network analyzer in a frequency range of 2-18 GHz are also reported in detail.     

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.     

辐照激光能量对SiO2薄膜特性及结构的影响

 为了认识SiO2薄膜在激光辐照下的变化,本文以K9玻璃为基底,采用电子束热蒸发方法制备了SiO2薄膜,并将此组在相同实验条件下制备的薄膜加以不同能量的激光辐照,研究在激光辐照前后样片的透射率、折射率、消光系数、膜厚、表面形貌及激光损伤阈值（LIDT）的变化。结果表明,样片膜厚随激光能量的增加而减小,辐照激光能改善薄膜表面形貌,并使样片LIDT值提高,最终能使样片的LIDT值从16.96 J/cm2提高至18.8 J/cm2。     

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.     

Optical and magneto-optical properties of Co/Pt multilayered films

Both experimental and computer-simulated magneto-optical (MO) and optical spectroscopies of Co/Pt multilayered films (MLF) with a nearly constant Pt sublayer thickness and variable Co sublayer thickness, as well as pure Co and Pt, and Co_0.51Pt_0.49 alloy films, have been performed in the energy range 1.1–4.7 eV. The simulations were achieved by solving the multireflection task for various models of the MLF. The comparison between experimental and computer-simulated optical properties of the Co/Pt MLF allowed us to evaluate the thickness of the interfacial regions with the alloyed components. The diagonal and off-diagonal components of the optical conductivity tensor were calculated not only for the pure Co and Co_0.51Pt_0.49 alloy films, and the whole Co/Pt MLF, but also for the spin-polarized Pt layers in the Co/Pt MLF.     

Enhanced dielectric and ferroelectric properties of Pb1−3x/2Lax(Zr0.5Ti0.5)O3 thin films with low lanthanum substitution

Effects of lanthanum (La) substitution (0.003 ≤ x ≤ 0.015) on the dielectric and ferroelectric properties of Pb(Zr_0.5Ti_0.5)O₃ thin films have been investigated. The films were synthesized on the Pt (1 1 1)/Ti/SiO₂/Si (1 0 0) substrates by a sol-gel method. Large dielectric constants of the films are obtained within range of 800-1600 which are almost comparable to those observed in bulk ceramics. The films also show improved remnant polarization values and reduced coercive field values with the increasing addition of La substitution. Our results suggest that low La substitution contributes to enhance film electric properties due to the improvement of non-180° domain wall mobility as well as the stabilization of tetragonal phase.