Effects of Al doping on properties of xAl–3%In–TiO2 photocatalyst prepared by a sol–gel method

A sol–gel method was used to prepare Al–In co-doped TiO₂ photocatalyst. The materials were characterized by XRD, FT–IR, XPS, and N₂ adsorption–desorption measurements. Photocatalytic degradation of methyl orange on the materials was investigated. The diffraction peaks of all the samples are in accordance to the diffraction peaks of anatase phase TiO₂. The addition of Al and In can lead to crystallite size shrinking of anatase TiO₂ in xAl–3%In–TiO₂. The incorporation of Al³⁺ ions into TiO₂ crystal are in the way of substituting Ti⁴⁺ ions in anatase lattice. 0.5%Al–3%In–TiO₂ has the maximum specific surface area of 108.9 m²/g and the smallest average pore size of 7.0 nm. The aluminum doped xAl–3%In–TiO₂ materials have larger adsorption capacity than that of 3%In–TiO₂. Total decoloration efficiency increases gradually with increasing Al content up to 0.5%, while 0.5%Al–3%In–TiO₂ has the maximal decoloration efficiency. 0.5%Al–3%In–TiO₂ also shows much improved activity as compared to 3%In–TiO₂ in each reuse cycle.     

Photocatalytic and magnetic properties of Zn1−xCrxO nanocomposites prepared by a co-precipitation method

Polyvinyl pyrrolidone (PVP) capped Zn_1−xCr_xO (0.000001≤x≤0.1) nanocomposites were successfully synthesized using a simple chemical co-precipitation technique. The synthesized nanostructures were characterized by X-ray powder diffraction (XRD), transmission electron microscope (TEM), energy dispersive X-ray fluorescence (EDXRF), Fourier-transform infrared spectroscopy (FTIR), UV–visible spectroscopy, photoluminescence (PL) and vibrating sample magnetometer (VSM) measurements. The structural characterization by XRD, TEM, FTIR and EDXRF confirmed the formation of wurtzite structure and incorporation of Cr in the ZnO lattice. The photocatalytic activities of as prepared nanocomposites were evaluated by degradation of methylene blue (MB) dye in aqueous solution under UV/sunlight light irradiation. The results demonstrated that Zn_1−xCr_xO (x=0.0001) nanocomposite effectively bleached out MB, showing as impressive photocatalytic enhancement over pure ZnO and ZnS nanoparticles. This enhanced photocatalytic activity at optimum concentration was attributed to increased absorption ability of light and high separation rate of photoinduced charge carriers on the nanocomposite photocatalyst surface. The VSM measurements showed significant ferromagnetism in Cr-doped ZnO nanostructures and the value of saturated magnetism was found to decrease with increase in Cr content.     

Cu–Al intermetallic compound investigation using ex-situ post annealing and in-situ annealing

In Cu wire technology, it is observed that the Cu–Al IMC formation increases from a very thin layer of a few nm to a few μm after subjected to annealing process. The identified IMC phases are mainly CuAl₂, CuAl and Cu₉Al₄, whereas the other three phases which are less reported are Cu₄Al₃, Cu₃Al₂ and Cu₃Al. The reliability risk of Cu–Al IMC is commonly known, with the degradation of voids or crack propagation from ball periphery to internal ball bond direction after long duration of annealing. However, the cause of the degradation is not well established. This paper will focus on the study of the degradation of Cu–Al IMC layers with and without the presence of a mold compound by using ex-situ post annealing and in-situ annealing method on the same assembled sample. The ex-situ post annealing sample is studied using focus ion beam (FIB) after the molded sample had underwent a standard High Temperature Storage (HTS) at 150 °C for 1000 h. The in-situ annealing sample is studied using a transmission electron microscope (TEM) on a lamella with Cu–Al interface but without the presence of a mold compound. The result shows that the IMC formed are identified as CuAl₂, CuAl and Cu₉Al₄ via Energy Dispersive Spectrometer (EDX). These IMC are seen to grow increasingly with the duration of annealing process for both methods. The native Al oxide lines are seen for both methods and were embedded in between the IMC. The degradation starts at the ball periphery with cracks and voids at IMC are seen for the ex-situ postannealing sample but it is not observed under in-situ annealing sample. It is found that the degradation of the IMC is not caused by propagation of microcrack; instead it is assumed to be the influence of additive within the mold compound itself.     

Characterization of ZrTiO4 thin films prepared by sol–gel method

The electrical properties, memory switching behavior, and microstructures of ZrTiO₄ thin films prepared by sol–gel method at different annealing temperatures were investigated. All films exhibited ZrTiO₄ (111) and (101) orientations perpendicular to the substrate surface, and the grain size increased with increasing annealing temperature. A low leakage current density of 1.47×10^?6 A/cm² was obtained for the prepared films. The I–V characteristics of ZrTiO₄ capacitors can be explained in terms of ohmic conduction in the low electric field region and Schottky emission in the high electric field region. An on/off ratio of 10² was measured in our glass/ITO/ZrTiO₄/Pt structure with an annealing temperature of 600 °C. Considering the primary memory switching behavior of ZrTiO₄, ReRAM based on ZrTiO₄ shows promise for future nonvolatile memory applications.     

Influences of laser energy density and annealing on structure properties of AlN films prepared by pulsed laser deposition

Aluminum nitride (AlN) films with h<100> crystalline orientation are fabricated on p-Si (100) substrates at room tempera- ture by pulsed laser deposition. The effects of laser energy density and annealing on the quality of the films are studied by x-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. The crystalline quality of AlN films is improved considerably by increasing the laser energy density while there is increased number of farraginous particles on the surface. The annealing treatment at 600oC produces a recrystallization process in the film, characterized by the improvement of the original crystallinity, the appearance of new crystalline orientations, and the increase of the crystallites. The surface becomes rougher due to the increase of the grain size during annealing.     

High thermal annealing effect on structural and optical properties of ZnO–SiO2 nanocomposite

The effect of annealing temperature on photoluminescence (PL) of ZnO–SiO₂ nanocomposite was investigated. The ZnO–SiO₂ nanocomposite was annealed at different temperatures from 600 °C to 1000 °C with a step of 100 °C. High Resolution Transmission Electron Microscope (HR-TEM) pictures showed ZnO nanoparticles of 5 nm are capped with amorphous SiO₂ matrix. Field Emission Scanning Electron Microscope (FE-SEM) pictures showed that samples exhibit spherical morphology up to 800 °C and dumbbell morphology above 800 °C. The absorption spectrum of ZnO–SiO₂ nanocomposite suffers a blue-shift from 369 nm to 365 nm with increase of temperature from 800 °C to 1000 °C. The PL spectrum of ZnO–SiO₂ nanocomposite exhibited an UV emission positioned at 396 nm. The UV emission intensity increased as the temperature increased from 600 °C to 700 °C and then decreased for samples annealed at and above 800^°C. The XRD results showed that formation of willemite phase starts at 800 °C and pure willemite phase formed at 1000 °C. The decrease of the intensity of 396 nm emission peak at 900 °C and 1000 °C is due to the collapse of the ZnO hexagonal structure. This is due to the dominant diffusion of Zn into SiO₂ at these temperatures. At 1000 °C, an emission peak at 388 nm is observed in addition to UV emission of ZnO at 396 nm and is believed to be originated from the willemite.     

Evaluation of the corrosion performance of Cu–Al intermetallic compounds and the effect of Pd addition

Copper wire has become a mainstream bonding material in fine-pitch applications due to the rising cost of gold wire. In recent years, palladium-coated copper (Pd–Cu) wire is being increasingly used to overcome some constraints posed by pure Cu wire. During wire bonding with aluminum bond pads, different intermetallic compound (IMC) phases that have been identified at the bond interface are typically CuAl₂, CuAl and Cu₉Al₄. However, the corrosion susceptibility of these IMCs has not been investigated. This paper compares the electrical impedance and corrosion performance of the three types of Cu–Al IMCs in an acidic chloride medium by employing electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The analysis of the potentiodynamic polarization results was performed using Tafel extrapolation. A comparison was made with pure Cu and Al. The effect of Pd alloy on the IMC corrosion performance has also been studied. Among the three Cu–Al IMCs, Cu₉Al₄ was observed to have the largest corrosion rate followed by CuAl₂ and CuAl. For the metals, Cu was observed to have the lowest corrosion rate and Al is the most easily corroded. The addition of Pd of up to 10 wt.% replacement of the Cu in the alloys slightly improves the corrosion resistance of the metals and IMCs.     

Bimodal and monomodal diamond particle effect on the thermal properties of diamond-particle-dispersed Al–matrix composite fabricated by SPS

Diamond-particle-dispersed aluminum (Al) matrix composites consisting of monomodal and bimodal diamond particles were fabricated in spark plasma sintering process, where the mixture of diamond, pure Al and Al–5 mass% Si alloy powders were consolidated in liquid and solid co-existent state. Microstructures and thermal properties of the composites fabricated in such a way were investigated and the monomodal and bimodal diamond particle effect was evaluated on the thermal properties of the composites. The composites can be well consolidated in a temperature range between 773 K and 878 K and scanning electron microscopy detects no reaction product at the interface between the diamond particle and the Al matrix. Relative packing density of the composite containing monomodal diamond particles decreased from 99.1% to 87.4% with increasing volume fraction of diamond between 50% and 60%, whereas that of the composite containing bimodal diamond particles was higher than 99% in a volume fraction of diamond up to 65%. The thermal conductivity of the composite containing bimodal diamond particles was higher than that of the composite containing monomodal diamond particles in a volume fraction of diamond higher than 60%. The coefficients of thermal expansion (CTEs) of the diamond-particle-dispersed Al–matrix composites fall in the upper line of Kerner model, indicating good bonding between the diamond particle and the Al matrix in the composite. The thermal conductivity of the composite containing 70 vol.% bimodal diamond particles was 578 W/m K and its CTE was 6.72 × 10⁻⁶ at R.T.     

Effect of multi-cycle annealing on the C49–C54 phase transformation in TiSi2 thin film

In this paper, the multi-cycle rapid thermal annealing process was proposed as an alternative method to the conventional annealing process for TiSi₂ formation for the first time. Our experimental results and analysis showed that by using this method, some physical defects that act as the nucleus sites for the C49 phase formation can be induced into the Ti/Si interface due to the thermal mismatch between Ti and Si. As a result, the number of the C49 grains increased and the C49 grain size became smaller. With the shrinking of the C49 grain size, more triple junction sites for the C54 phase to nucleate will be contained in the C49 grain boundaries and an easy C49–C54 phase transformation can be expected. The enhancement of the low-resistivity C54 phase formation finally makes the reduction in sheet resistance (R_s) possible. These results are beneficial because the reduction of R_s can be achieved without increasing the annealing temperature or extending the holding time.     

Effect of Cu–Al substitution on the structural and magnetic properties of Co ferrites

In this work copper aluminum substituted cobalt nanocrystalline spinel ferrites having general formula Co_1−xCu_xFe_2−x Al_xO₄, with 0.0≤x≤0.8 have been synthesized by using a co-precipitation method. The Cu–Al substituted samples were annealed at 600 °C and characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM). XRD analysis confirmed a single phase spinel structure and the crystalline size calculated using Scherrer׳s formula found to be in the range of 14−24 nm. This crystalline size is small enough to achieve the suitable signal to noise ratio in the high density recording media. The FTIR spectra reveal two prominent frequency bands in the wave number range 350–600 cm⁻¹, which confirm the cubic spinel structure and completion of chemical reaction. Magnetic studies reveal that the coercivity (H_c) attains a maximum value of 1142 Oe at 14 nm. The increasing trend of magnetic parameters (coercivity and retentivity) is consistent with crystallinity. The role played by the Cu–Al ions in improving the structural and magnetic properties are analyzed and understood. The optimized magnetic parameters suggest that the material with composition Co_0.6Cu_0.4Fe_1.6Al_0.4O₄ may have a potential application for high density recording media. Our simple, economic and environmental friendly preparation method may contribute towards the controlled growth of high quality ferrite nanopowder, potential candidates for recording.     

Formation of Cu6Sn5 phase by cold homogenization in nanocrystalline Cu–Sn bilayers at room temperature

Solid state reaction between nanocrystalline Cu and Sn films was investigated at room temperature by depth profiling with secondary neutral mass spectrometry and by X-ray diffraction. A rapid diffusion intermixing was observed leading to the formation of homogeneous Cu₆Sn₅ layer. There is no indication of the appearance of the Cu₃Sn phase. This offers a way for solid phase soldering at low temperatures, i.e. to produce homogeneous Cu₆Sn₅ intermediate layer of several tens of nanometers during reasonable time (in the order of hours or less). From the detailed analysis of the growth of the planar reaction layer, formed at the initial interface in Sn(100 nm)/Cu(50 nm) system, the value of the parabolic growth rate coefficient at room temperature is 2.3 × 10^− 15 cm²/s. In addition, the overall increase of the composition near to the substrate inside the Cu film was interpreted by grain boundary diffusion induced solid state reaction: the new phase formed along the grain boundaries and grew perpendicular to the boundary planes. From the initial slope of the composition versus time function, the interface velocity during this reaction was estimated to be about 0.5 nm/h.     

The effect of the film thickness and doping content of SnO2:F thin films prepared by the ultrasonic spray method

This paper reports on the effects of film thickness and doping content on the optical and electrical properties of fluorine-doped tin oxide. Tin(II) chloride dehydrate, ammonium fluoride dehydrate, ethanol and HCl were used as the starting materials, dopant source, solvent and stabilizer, respectively. The doped films were deposited on a glass substrate at different concentrations varying between 0 and 5 wt% using an ultrasonic spray technique. The SnO2 :F thin films were deposited at a 350 C pending time(5, 15, 60 and 90 s). The average transmission was about 80%, and the films were thus transparent in the visible region. The optical energy gap of the doped films with 2.5 wt% F was found to increase from 3.47 to 3.89 eV with increasing film thickness, and increased after doping at 5 wt%. The decrease in the Urbach energy of the SnO2:F thin films indicated a decrease in the defects. The increase in the electrical conductivity of the films reached maximum values of 278.9 and 281.9( cm)1for 2.5 and 5 wt% F, respectively, indicating that the films exhibited an n-type semiconducting nature. A systematic study on the influence of film thickness and doping content on the properties of SnO2:F thin films deposited by ultrasonic spray was reported.     

Temperature dependence of current–voltage characteristics of MoS2/Si devices prepared by the chemical vapor deposition method

Layers of MoS₂ are directly deposited on the n-type Si (n-Si) substrate by chemical vapor deposition for fabricating a MoS₂/n-Si heterojunction device. The rectification current–voltage (I–V) characteristics of MoS₂/n-Si devices were measured in the temperature range from 80 to 300 K in steps of 20 K. The temperature-dependent forward-bias I–V characteristics can be explained on the basis of the thermionic emission theory by considering the presence of the interfacial inhomogeneous barriers at the MoS₂/n-Si interfaces. The dominance of the induced carrier capture/recombination by states at the MoS₂/n-Si interface that lead to the formation of the inhomogeneous barriers serves to influence the photo-response at room temperature. The fabricated MoS₂/n-Si devices exhibit reversible switching between high and low current densities, when the simulated sunlight is turned on and off. The sensitivity of the I–V characteristics to temperature provides an opportunity to realize stable and reliable rectification behaviors in the MoS₂/n-Si devices. It is found that the electron mobility in the n-Si layer reduces as temperature increases, which leads to the noticeably increased value of the series resistance of MoS₂/n-Si devices.     

Properties of fluorine-doped SnO2 thin films by a green sol–gel method

Fluorine doped tin oxide (FTO) films were fabricated on a glass substrate by a green sol–gel dip-coating process. Non-toxic SnF₂ was used as fluorine source to replace toxic HF or NH₄F. Effect of SnF₂ content, 0–10 mol%, on structure, electrical resistivity, and optical transmittance of the films were investigated using X-ray diffraction, Hall effect measurements, and UV–vis spectra. Structural analysis revealed that the films are polycrystalline with a tetragonal crystal structure. Grain size varies from 43 to 21 nm with increasing fluorine concentration, which in fact critically impacts resultant electrical and optical properties. The 500 °C-annealed FTO film containing 6 mol% SnF₂ shows the lowest electrical resistivity 7.0×10⁻⁴ Ω cm, carrier concentration 1.1×10²¹ cm⁻³, Hall mobility 8.1 cm²V⁻¹ s⁻¹, optical transmittance 90.1% and optical band-gap 3.91 eV. The 6 mol% SnF₂ added film has the highest figure of merit 2.43×10⁻² Ω⁻¹ which is four times higher than that of un-doped FTO films. Because of the promising electrical and optical properties, F-doped thin films prepared by this green process are well-suited for use in all aspects of transparent conducting oxide.     

Structural and dielectric properties of ZrO2–TiO2–V2O5 nanocomposite prepared by CO-precipitation calcination method

Nanocrystalline ZrO₂–V₂O₅–TiO₂ composite was synthesized by co-precipitation method and calcined at 500 and 700 °C. The formation of the composite material has been confirmed by X-ray diffraction analysis. The surface morphology was determined by SEM and HRTEM and it was seen that increase in calcination temperature increases the grain size. EDX analysis confirms the presence of zirconium, titanium and vanadium in the lattice. Optical absorption studies reveal a very low absorption in the visible region for both the samples. The dielectric constant, loss and ac conductivity of the pelletized samples have been examined at different temperatures as functions of frequency and the activation energies were calculated. The results indicated that the dielectric constant increases with calcination temperature. It was seen that the dielectric constant increases on the addition of Vanadia to zirconia–titania composite making it ideal for use as a gate dielectric material.     

Investigations about the effect of annealing temperatures in the presence of oxygen flow on optical and electronic properties of titanium nano-layers by using Kramers–Kronig and DFT methods

Nano-layers of titanium were deposited on glass substrates by resistive evaporation at room temperature. Thickness of the layers was measured 66.8 nm, by a quartz crystal method. Deposition conditions such as deposition rate, vacuum pressure, incidence of angle and substrate temperature were the same for all layers. After producing pure Ti layers a post-annealing method was used in the presence of a uniform oxygen flow of 6 cm³/s and different 100 °C, 200 °C and 300 °C annealing temperatures. Optical reflectance and transmittance of the layers were measured in the wave length of 200–4100 nm by a spectrophotometer. Kramers–Kronig relations were used to calculate the optical constants. The influence of annealing temperature and oxygen flow on optical properties is investigated. Also to make the obtained optical results clearer, a full-potential linearized augmented plane wave (FP-LAPW) method within the generalized gradient approximation (GGA) has been used. Comparison results confirm that in higher annealing temperatures the obtained structure is more similar to anatase crystalline one. According to AFM images, by increasing annealing temperature in the presence of oxygen flow, configuration of layers change and due to high annealing temperature and surface diffusion effect, void fraction increases. With increase in annealing temperature to 300 °C, anatase phase structure (A(004)) gets clearer and sharper also other phase structures are about to grow.     

The structural composite effect of Au–WO3–Al interconnecting electrode on performance of each unit in stacked OLEDs

In this article, we report the effects of the thickness of metal and oxide layers of the Al/WO₃/Au interconnecting structure on the electrical and optical characteristics of the upper and bottom units of the two-unit stacked organic-light-emitting-devices (OLEDs). It is found that light emission performance of the upper unit is sensitive to the transmittance of semitransparent Al/WO₃/Au structure, which can be improved by changing the thickness of each layer of the Al/WO₃/Au structure. It is important to note that the introduction of WO₃ between Al and Au significantly enhances the current efficiency of both the upper and bottom units with respect to that of the corresponding Al/Au structure without WO₃. In addition, the emission spectra of both the upper and bottom units are narrower than that of the control device due to microcavity effect. Our results indicate that the Al/WO₃/Au interconnecting structure is a good candidate for fabricating independently controllable high efficiency stacked OLEDs.     

A method for the amplitude–phase synthesis of antenna array based on control of the set of nonidentical partial beams

An iterative method for the amplitude–phase synthesis of antenna arrays based on control of the set of partial beams is proposed. In this method, two additional partial beams are added to the radiation pattern at each step. The shape of each beam is optimized with consideration for the difference between the synthesized and specified radiation patterns. Parameters specifying the shape of additional partial beams are chosen with the help of the genetic algorithm. The results of numerical studies allowing comparison of the proposed synthesis method to the least-squares method and the method based on control of the set of identical partial beams are presented.     

Geometry effect on mechanical performance and fracture behavior of micro-scale ball grid array structure Cu/Sn–3.0Ag–0.5Cu/Cu solder joints

Solder joint integrity has long been recognized as a key issue affecting the reliability of integrated circuit packages. In this study, both experimental and finite element simulation methods were used to characterize the mechanical performance and fracture behavior of micro-scale ball grid array (BGA) structure Cu/Sn–3.0Ag–0.5Cu/Cu solder joints with different standoff heights (h, varying from 500 to 100 μm) and constant pad diameter (d, d = 480 μm) and contact angle under shear loading. With decreasing h (or the ratio of h/d), results show that the stiffness of BGA solder joints clearly increases with decreasing coefficient of stress state and torque. The stress triaxiality reflects the mechanical constraint effect on the mechanical strength of the solder joints and it is dependent on the loading mode and increases dramatically with decreasing h under tensile loading, while the change of h has very limited influence on the stress triaxiality under shear loading. Moreover, when h is decreased, the concentration of stress and plastic strain energy along the interface of solder and pad decreases, and the fracture location of BGA solder joints changes from near the interface to the middle of the solder. Both geometry and microstructure greatly affect the shear behavior of joints, the average shear strength shows a parabolic trend with decreasing standoff height. Furthermore, the brittle fracture of BGA solder joints after long-time isothermal aging was investigated. Results obtained show that, under the same shear force, the stress intensity factors, K_I and K_II, and the strain energy release rate, G_I, at the Sn–3.0Ag–0.5Cu/Cu₆Sn₅ interface and in the Cu₆Sn₅ layer obviously decrease with decreasing h, hence brittle fracture is more prone to occur in the joint with a large standoff height.