Microwave absorbing properties of Ag-coated Ni-Zn ferrite microspheres prepared by electroless plating

This investigation presents an electromagnetic radiation absorptive composition comprising Ag-coated ferrite microspheres dispersed in a silicone rubber matrix for use as a thin microwave absorber in GHz frequencies. Ni-Zn ferrite microspheres with an average diameter of 50 μm were prepared by spray-drying and sintering at 1130 °C. A conductive Ag layer was coated on the ferrite spheres by electroless plating. Uniform Ag coating can be obtained using the plating solution with a high AgNO₃ concentration. For particle compacts of the conductive Ni-Zn ferrite spheres, electrical resistance is reduced to as low as 10⁻² Ω. Rubber composites containing the Ag-plated ferrite spheres exhibit a high value of both real and imaginary parts of complex permittivity, while the complex permeability spectrum is not significantly changed with Ag plating. Due to the conductive and magnetic property of the microspheres, matching thickness can be reduced to as low as 2 mm at the frequency of 7.6 GHz, which is much thinner than non-coated ferrite absorbers.     

Preparation and characterization of ZnO/Cu/ZnO transparent conductive films

ZnO/Cu/ZnO transparent conductive thin films were prepared by RF sputtering deposition of ZnO target and DC sputtering deposition of Cu target on n-type (001) Si and glass substrates at room temperature. The morphology, structure, optical, and electrical properties of the multilayer films were characterized by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), UV/Vis spectrophotometer, and Hall effect measurement system. The influence of Cu layer thickness and the oxygen pressure in sputtering atmosphere on the film properties were studied. ZnO/Cu/ZnO transparent conductive film fabricated in pure Ar atmosphere with 10 nm Cu layer thickness has the best performance: resistivity of 2.3×10-4 Ω·cm, carrier concentration of 6.44×1016cm-2 , mobility of 4.51cm2·(V·s)-1 , and acceptable average transmittance of 80 % in the visible range. The transmittance and conductivity of the films fabricated with oxygen are lower than those of the films fabricated without oxygen, which indicates that oxygen atmosphere does not improve the optical and electrical properties of ZnO/Cu/ ZnO films.     

Effect of manganese substitution on the magnetic properties of nickel-zinc ferrite

The effect of manganese (Mn)-ion substitution on the structural, magnetic, and electrical properties of nickel-zinc (Ni-Zn) ferrite of chemical formula Ni_0.6−t Mn _t Zn_0.4Fe₂O₄ (t=0.0, 0.1, 0.2, 0.3, 0.4, 0.45, 0.5, 0.55, 0.6) has been studied. It was found that Mn ion substitution increases the average grain diameter and improves the magnetization as well as the initial permeability. At the same time, the direct current (dc) resistivity at room temperature was found to increase with Mn ion substitution. The increase of both magnetization and dc resistivity due to the Mn substitution in a Ni-Zn ferrite is a promising result for applications in high-frequency fields.     

Fabrication and structure characterization of ITO transparent conducting film by sol-gel technique

Using In（NO3）3·5H2O and acetylacetone as raw materials and anhydrous SnCl4 as dopant, the transparent conducting indium tin oxide（ITO） films were prepared by sol-gel and dip-coating technique. The phase transformation, structure properties and physical properties （sheet resistance and transmittance） of the films were investigated by DTA-TG, XRD, SEM, four-probe method and UV-Vis spectrometry. The results indicate that it is feasible to fabricate 1TO films on the quartz substrates by sol-gel technique, and the ITO films are formed by accumulating of particles with the size of several decades of nanometers. The prepared ITO film has cubic bixbyite structure, and （111） is its preferred plane. After five-times dip-coating, the 1TO film has a thickness less than 150 nm, a sheet resistance of 110Ω/□, a resistivity of 1.65×10^-3Ω· cm and a transparency of 90% .     

Physicochemical Properties of Spray-Deposited CoFe2O4 Thin Films

Cobalt ferrite thin films are deposited onto quartz glass substrates by chemical spray pyrolysis technique at different substrate temperatures using ferric nitrate and cobalt nitrate as precursors. Thermogravimetric analysis (TGA) study indicates the formation of CoFe₂O₄ by decomposition of cobalt and ferric nitrates after 800 °C. X-ray diffraction studies reveal that annealed films are polycrystalline in nature and exhibit spinel cubic crystal structure. Crystallite size varies from 39 to 44 nm with the substrate temperatures. Direct optical band gap energy of CoFe₂O₄ thin films is found to be 2.57 eV. The AFM images show that roughness and grain size of the CoFe₂O₄ thin film are about 9 and 138 nm, respectively. The measured DC resistivity of the deposited thin films indicates that as temperature increases the resistivity decreases indicating the semiconductor nature of the films. Decrease in dielectric constant (ε′) and loss tangent (tanδ) has been observed with frequency and attains the constant value at higher frequencies. The AC conductivity of cobalt ferrite thin films increases with increase in frequency. Thus, the prepared films show normal dielectric performance of the spinel ferrite thin film. Room-temperature complex impedance spectra show the incomplete semicircles as films exhibit high resistance values at lower frequencies.     

Characteristics of TiN thin films grown by ALD using TiCl4 and NH3

Titanium nitride thin film was deposited on a silicon wafer by the Atomic Layer Deposition (ALD) method using TiCl₄ and NH₃ as source chemicals. Nitrogen gas was used for carrying the TiCl₄ and purging the reactants. The gases were introduced into the reaction chamber in the sequence of TiCl₄?N₂?NH₃?N₂ for the saturated surface reaction on the wafer. TiN film was grown with [100] preferred orientation at 350°C, while with [111] preferred orientation at 450°C and higher temperatures. The deposition rate was constant as 0.17 Å/cycle irrespective of deposition temperature, which demonstrates TiN film was grown by the ALD growth mechanism. TiN thin films grown at a temperature higher than 450°C with thickness of 320 Å showed electrical resistivity as low as 72×10^?6 Ωcm.     

Effect of substrate rotation speed on structure and properties of Al-doped ZnO thin films prepared by rf-sputtering

Al-doped ZnO (AZO) thin films were deposited on glass substrates by rf-sputtering at room temperature. The effects of substrate rotation speed (ω_S) on the morphological, structural, optical and electrical properties were investigated. SEM transversal images show that the substrate rotation produces dense columnar structures which were found to be better defined under substrate rotation. AFM images show that the surface particles of the samples formed under substrate rotation are smaller and denser than those of a stationary one, leading to smaller grain sizes. XRD results show that all films have hexagonal wurtzite structure and preferred c-axis orientation with a tensile stress along the c-axis. The average optical transmittance was above 90% in UV-Vis region. The lowest resistivity value (8.5×10^?3 Ω·cm) was achieved at ω_S=0 r/min, with a carrier concentration of 1.8×10²⁰ cm^?3, and a Hall mobility of 4.19 cm²/(V·s). For all other samples, the substrate rotation induced changes in the carrier concentration and Hall mobility which resulted in the increasing of electrical resistivity. These results indicate that the morphology, structure, optical and electrical properties of the AZO thin films are strongly affected by the substrate rotation speed.     

Effects of oxygen partial pressure on film growth and electrical properties of undoped ZnO films with thickness below 100 nm

The dependences of electrical and structural properties on film thickness below 100 nm have been studied on polycrystalline undoped zinc oxide (ZnO) thin films on glass substrates at 200 °C prepared by plasma-assisted electron-beam deposition. From Hall effect measurements, we find that resistivity decreases from 0.47 to 0.02 Ω cm with increasing film thickness, whereas carrier concentration remains almost constant, 1.65-2.0 × 10¹⁹ cm^− 3, Hall mobility increases from 1.7 to 16.7 cm²/Vs with increasing film thickness. From both high-resolution out-of-plane and in-plane X-ray diffraction (XRD) data, we find substantial changes in the lattice parameters with increasing film thickness below 40 nm; a reduction in the lattice parameter of the a-axis and an increase in the lattice parameter of the c-axis. Williamson-Hall analysis reveals an increase in in-plane grain size with increasing film thickness. This indicates that the dominant scattering mechanism that determines electrical properties is a boundary scattering mechanism.     

Effect of chromium substitution on structural,electrical and magnetic properties of NiZn ferrites

Ni_0.5Zn_0.5Fe_2−xCr_xO₄ (0≤x≤0.5) ferrites were successfully prepared by conventional solid state reaction method to investigate the effect of chromium substitution on the structural, electrical and magnetic properties. X-ray powder diffraction results demonstrate that all the prepared samples are well crystallized single-phase spinel structures without secondary phase. As chromium concentration increases, the lattice parameter and crystallite size gradually decrease. The magnetic measurement indicates that saturation magnetization is substantially suppressed by Cr³⁺ doping, changing from 73.5 A·m²/kg at x=0 to 46.3 A·m²/kg at x=0.5. While the room-temperature electrical resistivity is more than four orders of magnitude enhanced by Cr³⁺ substitution, reaching up to 1.1×10⁸ Ω·cm at x=0.5. The dielectric constant monotonously decreases with rising frequency for these ferrites, showing a normal dielectric dispersion behavior. The compositional dependence of dielectric constant is inverse with that of electrical resistivity, which originates from the reduced Fe²⁺/Fe³⁺ electric dipole number by doping, indicating inherent correlation between polarization and conduction mechanism in ferrite.     

碳纤维含量对导电涂层雷达波反射特性的影响研究

目的获得不同碳纤维含量导电涂层对雷达波反射特性的影响规律,实现假目标雷达波反射特性控制。方法选择碳纤维粉为导电功能填料,丙烯酸聚氨酯树脂为粘结剂,制得碳纤维质量分数为0%~20%的导电涂料。研究碳纤维含量对涂层试板雷达波反射特性、涂层表面电阻率的影响,并在聚氨酯泡沫圆锥体构件模型上进行了试验验证。结果碳纤维质量分数从0%增加4%时,涂层表面电阻率从2.40×10~(11)?迅速降低至1.80×10~3?,雷达散射截面积(RCS)从-3.07 dBsm急剧增大至10.54 dBsm;增大到10%时,涂层表面电阻率呈波动缓慢下降的趋势,RCS缓慢增大至11.05 dBsm;继续增至20%时,涂层表面电阻率和RCS均变化很小。构件模型雷达波反射特性测试表明,碳纤维质量分数达10%时,聚氨酯泡沫圆锥体模型的表面电阻率为6.29×10~2?,0°~360°RCS达-7.12 dBsm,与贴铝膜诱饵的RCS(-6.48 dBsm)接近。结论碳纤维含量对涂层表面电阻率和雷达波反射特性的影响显著,在4%~10%为宜,在此范围内,涂层表面电阻率明显降低,呈现明显的金属化特征,雷达波反射特性与金属材料接近。     

Synthesis and characterization of nanocrystalline ZrNxOy thin films on Si by ion plating

Based on the optimum deposition conditions of ZrN thin film from our previous study, by varying oxygen flow rate ranging from 0 to 8 sccm, nanocrystalline ZrN_xO_y thin films were deposited on p-type (100) Si substrates using hollow cathode discharge ion-plating (HCD-IP) system. The objective of this study was to investigate the effect of oxygen content on the composition, structure and properties of the ZrN_xO_y thin films. The oxygen content of the thin film, determined using X-ray photoelectron spectroscopy (XPS), increased with increasing oxygen flow rate. As the oxygen content increased, the color of the ZrN_xO_y thin film changed from golden yellow to blue and then slate blue, and the microstructure observed by scanning electron microscopy (SEM) varied from columnar structure to finer grains and finally flat and featureless structure. Phase separation of ZrN_xO_y to ZrN and monoclinic ZrO₂ was found from X-ray diffraction (XRD) patterns when the oxygen content was higher than 9.7 at.%. The hardness of the film slightly increased as the oxygen content was less than 9.7% and then decreased to 15.7 GPa, a typical hardness of ZrO₂ phase, as the oxygen content further increased. The total residual stress of the film was measured using an optical method, and the residual stresses of ZrN and ZrO₂ phases were determined separately using modified XRD sin²ψ method. The total stress was close to the stress in ZrN phase as the ZrO₂ fraction was less than 30%, and was close to that in ZrO₂ phase as the ZrO₂ fraction was over 30%. The electrical resistivity of the film increased significantly with the increase of oxygen content. The film properties showed consistent trend with phase separation. As the fraction of ZrO₂ phase was small, the apparent properties of the films were more close to those in ZrN. When ZrO₂ fraction was over 30%, the films mainly exhibited the properties of ZrO₂.     

Characterization of rapid thermally processed LiMn204 thin films derived from solution deposition

Cathode material LiMn₂O₄ thin films were prepared through solution deposition followed by rapid thermal annealing. The phase identification and surface morphology were studied by X-ray diffraction and scanning electron microscopy. Electrical and electrochemical properties were examined by four-probe method, cyclic voltammetry and galvanostatic charge-discharge experiments. The results show that the film prepared by this method is homogeneous, dense and crack-free. As the annealing temperature and annealing time increase, the electronic resistivity decreases, while the capacity of the films increases generally. For the thin films annealed at different temperatures for 2 min, the thin film annealed at 800 °C has the best cycling behavior with the capacity loss of 0.021% per cycle. While for the thin films annealed at 750 °C for different times, the film annealed for 4 min possesses the best cycling performance with a capacity loss of 0.025% per cycle. For the lithium diffusion coefficient in LiMn₂O₄ thin film, its magnitude order is 10⁻¹¹ cm²·s⁻¹.     

Effects of Mg substitution on the structural, optical, and electrical properties of CuAlO2 thin films

Mg-doped CuAlO₂ thin films are prepared by the chemical solution method. The XRD results show that the solid solubility of Mg species on Al sites in CuAlO₂ lattice is lower than 2 at.%. When less than 2 at.% of Mg is added to the CuAlO₂ film, the surface roughness of the films was reduced with Mg substitution. Moreover, the c-axis orientation of the films improves because the in-plane fusion between CuAlO₂ crystallites is hindered. Optical and electrical measurements show that substituting Al³⁺ in the films with Mg²⁺ increases both their transmittance in the visible region and their optical band gaps. As well, their electrical conductivity is enhanced. At 300 K, the conductivity of the 1 at.% Mg-doped sample is up to 5.2 × 10⁻³ S/cm. Thus, Mg-doped CuAlO₂ films may have potential applications as transparent conductive oxides.     

溅射气压对ZnO透明导电薄膜光电性能的影响

采用射频磁控溅射方法,在普通玻璃上制备了具有高度c轴取向的ZnO薄膜,研究了溅射气压(0.2～1.5 Pa)对ZnO薄膜的微观结构和光电性能的影响.AFM、XRD、UV-Vis分光光度计及四探针法研究表明:随着溅射气压的增大,ZnO薄膜沿c轴方向的结晶质量提高,晶粒细化,薄膜表面更加致密,晶粒大小更加均匀;ZnO薄膜在400～900nm范围内的平均透过率均高于85%,其中在0.5～1.5 Pa范围内其透过率高于90%;样品在高纯氮气气氛中经350 ℃,300 s退火后,电阻率最低达到10-2 Ω-cm量级.     

Electrical and optical properties dependence on evolution of roughness and thickness of Ga:ZnO films on rough quartz substrates

The paper studies GZO films deposited on quartz substrates by a laser deposition system. The XRD and AFM results as well as the calculation of height-height correlation function H (r, t) and its parameters w(t) and ξ(t) reveal that the film growth can be divided into two stages, and that the turning point of these two stages is the time when the film exhibits fractal characteristics. The influence of thickness and morphology roughness evolution on the electrical resistivity and optical transmittance in these two stages are described. It is found that the electrical resistivity mainly depends on the film thickness in the first stage, while in the following stage, the film possess self-affine fractal characteristics. The morphology roughness evolution plays an important role in the resistivity. The transmittance is found to decrease with the increase of film thickness in the two stages and it is also found to be sensitive to the evolution of surface roughness. The lowest resistivity obtained is 4.85 × 10^− 4 Ω cm with an average optical transmittance of 85% in the 200 nm thick film deposited for 10 min.     

溅射功率对射频磁控溅射Al掺杂ZnO（ZAO）薄膜性能的影响

用射频磁控溅射技术,在纯氩气氛中不同溅射功率（120 W~210 W）下于玻璃衬底上制备了Al掺杂ZnO（ZAO）薄膜。利用X射线衍射仪（XRD）、扫描电子显微镜（SEM）、光谱仪和四探针测试仪等对所制备的薄膜进行了晶体结构、光学和电学性能分析。结果表明,纯氩气氛中不同溅射功率下玻璃衬底上原位沉积的ZAO薄膜具有明显的c轴择优取向性,它没有改变ZnO的六角纤锌矿结构;ZAO薄膜的可见光区平均透光率不强烈依赖于溅射功率,为75%左右;原位沉积ZAO薄膜的电阻率达到102Ω.cm数量级范围,随溅射功率由120 W增大到210 W时,薄膜电阻率从132.67Ω.cm降低到21.08Ω.cm。     

Fabrication and characterization of ITO thin films on heat-resistant transparent flexible clay films

Transparent conductive indium tin oxide (ITO) thin films were deposited on transparent flexible clay films with heat resistant and high gas barrier properties by rf magnetron sputtering. The electrical, structural, and optical properties of these films were examined as a function of deposition temperature. A lowest resistivity of 4.2 × 10^− 4 Ωcm and an average transmittance more than 90% in the visible region were obtained for the ITO thin films fabricated at deposition temperatures more than 300 °C. It was found that ITO thin films with low resistivity and high transparency can be achieved on transparent flexible clay film using conventional rf magnetron sputtering at high temperature, those characteristics are comparable to those of ITO thin films deposited on a glass substrate.     

Misfit strain–film thickness phase diagrams and related electromechanical properties of epitaxial ultra-thin lead zirconate titanate films

The phase stability of ultra-thin (0 0 1) oriented ferroelectric PbZr_1–xTi_xO₃ (PZT) epitaxial thin films as a function of the film composition, film thickness, and the misfit strain is analyzed using a non-linear Landau–Ginzburg–Devonshire thermodynamic model taking into account the electrical and mechanical boundary conditions. The theoretical formalism incorporates the role of the depolarization field as well as the possibility of the relaxation of in-plane strains via the formation of microstructural features such as misfit dislocations at the growth temperature and ferroelastic polydomain patterns below the paraelectric–ferroelectric phase transformation temperature. Film thickness–misfit strain phase diagrams are developed for PZT films with four different compositions (x = 1, 0.9, 0.8 and 0.7) as a function of the film thickness. The results show that the so-called rotational r-phase appears in a very narrow range of misfit strain and thickness of the film. Furthermore, the in-plane and out-of-plane dielectric permittivities ε₁₁ and ε₃₃, as well as the out-of-plane piezoelectric coefficients d₃₃ for the PZT thin films, are computed as a function of misfit strain, taking into account substrate-induced clamping. The model reveals that previously predicted ultrahigh piezoelectric coefficients due to misfit-strain-induced phase transitions are practically achievable only in an extremely narrow range of film thickness, composition and misfit strain parameter space. We also show that the dielectric and piezoelectric properties of epitaxial ferroelectric films can be tailored through strain engineering and microstructural optimization.     

Influence of indium doping on the properties of spray deposited CdS0.2Se0.8 thin films

Polycrystalline indium doped CdS_0.2Se_0.8 thin films with varying concentrations of indium have been prepared by spray pyrolysis at 300 °C. The as deposited films have been characterized by XRD, AFM, EDAX, optical and electrical resistivity measurement techniques. The XRD patterns show that the films are polycrystalline with hexagonal crystal structure irrespective of indium doping concentration. AFM studies reveal that the RMS surface roughness of film decreases from 34.68 to 17.76 with increase in indium doping concentration up to 0.15 mol% in CdS_0.2Se_0.8 thin films and further it increases for higher indium doping concentrations. Traces of indium in CdS_0.2Se_0.8 thin films have been observed from EDAX studies. The optical band gap energy of CdS_0.2Se_0.8 thin film is found to decrease from 1.91 eV to 1.67 eV with indium doping up to 0.15 mol% and increase after 0.15 mol%. The electrical resistivity measurement shows that the films are semiconducting with minimum resistivity of 3.71 × 10⁴ Ω cm observed at 0.15 mol% indium doping. Thermoelectric power measurements show that films exhibit n-type conductivity.     

Electrically Conductive Flame Sprayed Aluminum Coatings on Textile Substrates

In this study, electrically conductive and flexible aluminum coatings using powder and wire flame spraying were successfully deposited onto diverse textiles. The influences of various process parameters and fabric materials on the electrical conductivity and microstructure of the metal-fabric composites were investigated. Preliminary results show that to obtain excellent coating surface conductivity values a specific coating quantity of higher than 20 mg/cm² is required. After further optimization of the spraying parameters, very good specific surface conductivities (～500 S_A) could be obtained even with reduced coating quantities. Through an adequate parameter optimization a reduction in the specific coating quantity was also achieved while high conductivity values were retained. In addition, when the coating quantity was reduced, the flexibility of the fabric substrates was better conserved. This investigation illustrates that optimized electrically conductive composites with flexible fabric substrates can be produced without any preliminary thermal or chemical fabric specifications.