The effect of repeated annealing temperature on the structural,optical, and electrical properties of TiO<Subscript>2</Subscript> thin films prepared by dip-coating sol–gel method

In this study, we have studied the effect of repeated annealing temperatures on TiO₂ thin films prepared by dip-coating sol–gel method onto the glasses and silicon substrates. The TiO₂ thin films coated samples were repeatedly annealed in the air at temperatures 100, 200, and 300 °C for 5 min period. The dipping processes were repeated 5 to 10 times in order to increase the thickness of the films and then the TiO₂ thin films were annealed at a fixed temperature of 500 °C for 1 h period. The effect of repeated annealing temperature on the TiO₂ thin films prepared on glass substrate were investigated by means of UV–VIS spectroscopy, X-ray diffraction (XRD), and atomic force microscopy (AFM). It was observed that the thickness, average crystallite size, and average grain size of TiO₂ samples decreased with increasing pre-heating temperature. On the other hand, thickness, average crystallite size, and average grain size of TiO₂ films were increased with increasing number of the layer. Al/TiO₂/p-Si metal–insulator–semiconductor (MIS) structures were obtained from the films prepared on p-type single silicon wafer substrate. Capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements of the prepared MIS structures were conducted at room temperature. Series resistance (R _s) and oxide capacitance (C _ox) of each structures were determined by means of the C–V curves.     

Effect of high-temperature annealing on the microstructural formation of Sn–3.7Ag–0.9Zn–xAl lead-free solder

The effect of high-temperature annealing on the microstructural formation of Sn–3.7Ag–0.9Zn–xAl (with x = 0, 0.5 and 1.0 wt.%) lead-free solder is investigated. The addition of minor Al in the Sn–3.7Ag–0.9Zn solder promotes the formation of Ag₂Al intermetallic compounds (IMCs), and depresses the separation of AgZn and Ag₃Sn IMCs. With prolonging the high-temperature annealing time, the formed Ag₂Al IMCs, distributed in the β-Sn phase matrix phase, grew and finally became ∼10 μm particles.     

Structure and electrochemical hydrogen storage properties of Pd/Mg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/Pd thin films prepared by pulsed laser deposition

Three-layered Pd/Mg_1−x Al _x /Pd (x = 0, 0.13, 0.21, 0.39) thin films were prepared by means of pulsed laser deposition. In the present Al concentration range, X-ray diffraction analyses showed that the Mg_1−x Al _x layer was constituted of a single phase Mg(Al) solid solution. The Mg(Al) grains are preferentially orientated along the c-axis and their size decreased (from 18.5 to 10.5 nm) as the Al content increased. Scanning electron microscopy and atomic force microscopy observations indicated that all the films exhibited a globular surface structure. However, the surface roughness of the films decreased as the Al concentration increased. Rutherford backscattering spectroscopy revealed that the Mg–Al layer density (porosity) was strongly dependent on the Al content. Successive hydriding charge/discharge cycles were performed on the different Pd/Mg_1−x Al_x/Pd films in alkaline media. The highest discharge capacity was obtained with the Pd/Mg_0.79Al_0.21/Pd film, namely ~85 μAh cm⁻² μm⁻¹ or 320 mAh g⁻¹, which corresponds to a H/M atomic ratio of ~0.48 in the Mg–Al layer.     

Direct bonding of Cu to oxidized silicon nitride by wetting of molten Cu and Cu(O)

When pressureless sintered silicon nitride with the main additives Y₂O₃ and Al₂O₃, having a thermal conductivity K = 20 W/m K, was oxidized at 1240–1360 °C in still air, the resulting surface oxide layer easily bonded to a copper plate in the temperature region between 1065 and 1083 °C, and in the oxygen concentration range of 0.008–0.39 wt%, as shown in a Cu–O phase diagram. The oxide on the silicon nitride was characterized as Y₂O₃·2SiO₂ and mixed silicate glass with additives and impurities that diffused through the grain boundary. The bonding strength of Cu/Si₃N₄ depends on the amount or layer thickness of silicate glass and reaches as high as 100 MPa by shear at room temperature. Detailed analysis of the oxidation layer and the peeled-off surfaces of directly bonded Si₃N₄/Cu reveal that the main mechanism of bonding is wetting to glassy silicate phase by mixtures of molten Cu and α-solid solution Cu(O), which solidify to α + Cu₂O below 1065 °C by a eutectic reaction. The direct reactive wetting of molten Cu, supplied from the grain boundary of a Cu plate, on the glassy phase enables very tight chemical bonding via oxygen atoms.     

Effect of aluminum doping on electrical and dielectric aging behavior against current impulse of ZPCCY-based varistors

The electrical and dielectric aging behavior against current impulse (5–1,200 A) in the Zn-Pr-Co-Cr-Y-based varistors was investigated with aluminum doping level (0–0.01 mol%). The varistors doped with 0–0.001 mol% Al were destroyed at higher current impulse beyond 900 A and the varistors doped with 0.005–0.01 mol% Al exhibited high stability against current impulse. The clamp ratio (K) at given current impulse ranges decreased with increasing Al doping level. The varistor doped with 0.01 mol% Al exhibited the lowest K value, with 1.65 at a current impulse of 10 A and 2.38 at a current impulse of 1,200 A. The best electrical and dielectric stability against current impulse of 1,200 A was obtained at 0.01 mol% Al, where %\Updelta E_{1  \textmA/cm²} = -3.4%\%\Updelta E_{1\;\text{mA/cm}^2} = -3.4\%, %Δα = 0%, %ΔJ _L = −26.3%, %Δε′_APP = +3.4%, and %Δtanδ = −7.7%. Conclusively, Al doping level was optimized at 0.01 mol% in terms of the surge withstand capability (SWC).     

Investigation of mechanical,electrical, and thermal properties of a Zn–1.26 wt% Al alloy

Zn–1.26 wt% Al alloy was directionally solidified upward with a constant growth rate (V = 16.6 μm/s) in a wide range of temperature gradients (1.94–5.15 K/mm) and with a constant temperature gradient (G = 5.15 K/mm) in a wide range of growth rates (8.3–500 μm/s) with a Bridgman-type directional solidification furnace. The microhardness (HV) and tensile strength (σ) of alloy were measured from directionally solidified samples. The dependency of the microhardness, tensile strength for directionally solidified Zn–1.26 wt% Al alloy on the solidification parameters (G, V) and microstructure parameters (λ₁, λ₂) were investigated and the relationships between them were experimentally obtained using regression analysis. According to present results, the microhardness and tensile strength of directionally solidified Zn–1.26 wt% Al alloy increase with increasing solidification processing parameters and decrease with the microstructure parameters. Variations of electrical resistivity (ρ) with the temperature in the range of 300–650 K were also measured using a standard dc four-point probe technique for cast samples. The enthalpy of fusion and specific heat for same alloy was also determined by means of differential scanning calorimeter (DSC) from heating trace during the transformation from solid to liquid.     

Vacuum arc deposition of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> coatings: arc behavior and coating characteristics

Al₂O₃–ZrO₂ coatings were deposited using a vacuum arc deposition system equipped with two co-planar cathodes. The plasma was injected into a cylindrical magnetic duct through annular anode apertures toward a substrate or an electrostatic ion current probe positioned on the duct axis, in vacuum and in a low-pressure oxygen or argon + oxygen background. Ion current and arc voltage measurements and visual observation of the cathode spots were used to find stable arcing conditions, using a straight plasma duct configuration. The cathode spot operation and transport of the plasma beam in the duct were studied as a function of arc current (I _arc = 25–200 A) and oxygen or oxygen + argon pressures (P = 0.1–1.5 Pa). Coatings were fabricated by exposing Si or WC–Co substrates simultaneously to Al and Zr plasmas using a 1/8 torus filter configuration in O₂ + Ar pressures. The coating composition, structure, microhardness, adhesion, and wear behavior were studied as functions of the deposition parameters. Favorable conditions for stable arcing were obtained with I _arc = 75 and 100 A for Al and Zr plasmas, respectively. The ion current decreased, and the arc voltage increased with the oxygen pressure. Behavior of the ion current and arc voltage suggested that cathode poisoning started at P = 0.5 Pa. Deposition rates were 0.3-0.6 μm/min, depending on the substrate position. All coatings were “Zr rich”, i.e., the Zr:Al ratio was in the range of 1.2–5.6 depending on the substrate position and deposition conditions. The coatings with higher ZrO₂ concentration were harder and had better resistance to wear. The coating’s hardness reached a maximum of ~22–24 GPa at a deposition temperature of 500 °C or a negative bias voltage of 75–100 V.     

Aqueous co-precipitation of Pd-doped cerium oxide nanoparticles: chemistry, structure, and particle growth

Nanoparticles of palladium-doped cerium oxide (Pd–CeO₂) have been prepared by aqueous co-precipitation resulting in a single phase cubic structure after calcination according to X-ray diffraction (XRD). Inhomogeneous strain, calculated using the Williamson–Hall method, was found to increase with palladium content, and the lattice contracts slightly, relative to nano-cerium oxide, as palladium content is increased. Moreover, high resolution transmission electron microscopy reveals some instances of defective microstructure. These factors combined imply that palladium is in solid solution with CeO₂ in these nanoparticles, but palladium (II) oxide (PdO) peaks in the Raman spectra indicate that solid solution formation is partial and that highly dispersed PdO is present as well as the solid solution. Nevertheless, the addition of palladium to the CeO₂ lattice inhibits the growth of the 6% Pd–CeO₂ particles compared to pure CeO₂ between 600 and 850 °C. Activation energies for grain growth of 54 ± 7 and 79 ± 8 kJ/mol were determined for 6% Pd–CeO₂ and pure CeO₂, respectively, along with pre-exponential Arrhenius factors of 10 for the doped sample and 600 for pure cerium oxide.     

Wetting of grain boundaries in Al by the solid Al<Subscript>3</Subscript>Mg<Subscript>2</Subscript> phase

The microstructure of binary Al_100−x –Mg _x (x = 10, 15, 18 and 25 wt%) alloys after long anneals (600–4000 h) was studied between 210 and 440 °C. The transition from incomplete to complete wetting of Al/Al grain boundaries (GBs) by the second solid phase Al₃Mg₂ has been observed. The portion of completely wetted GBs increases with increasing temperature beginning from T _wsmin = 220 °C. Above T _wsmax = 410 °C all Al/Al GBs are completely wetted by the Al₃Mg₂ phase.     

Photoluminescence of II–IV–V2 and I–III–VI2 crystals passivated in a sulfide solution

An investigation was made to determine how chemical treatment of the surface of II–IV–V₂ and I–III–VI₂ semiconductor crystals (such as CdSiAs₂, ZnSnP₂, CuGaSe₂, and r-AgInS₂) using a solution of ammonium sulfide in tert-butyl alcohol influences their photoluminescence properties. It is shown that the photoluminescence intensity is enhanced substantially after treatment with the spectral profile and energy position of the band peaks remaining unchanged. Pis’ma Zh. Tekh. Fiz. 24, 17–22 (November 26, 1998)     

Synthesis and properties of LaNi<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3−δ</Subscript> as cathode materials in SOFC

The synthesis of LaNi_{1− x} Fe _x O_3−δ (LNF) perovskites with x = 0.0–1.0, for use as cathode materials for an IT-SOFC, was investigated using four combustion methods, Water Citrate (WC), Modified Water Citrate (MWC), Nitric Citrate (NC), and Modified Nitric Citrate (MNC). The structures and homogeneities of the synthesized powders were examined using an XRD, and the particle sizes were examined using an SEM and a particle size analyzer. All four combustion methods gave the single phase perovskites with the same structure. The main difference was shown in a particle size that the smallest to the largest sizes were obtained from MNC, MWC, NC, and WC, respectively. In this LNF series, as x is 0–0.5, the crystal structure is cubic and rhombohedral at the calcination temperature of 700 and 900 °C, respectively. Further investigation indicated that the cubic structure changed to rhombohedral structure at 900 °C, and was stable up to 1200 °C. As x is 0.6–1.0, the crystal structure is in orthorhombic phase when calcined between 700 and 1000 °C. This orthorhombic phase decomposed above 1100 °C. From the XRD and SEM–EDX results, LaNi_0.6Fe_0.4O_3−δ (LNF64) has a good chemical compatibility with 8YSZ from room temperature up to 900 °C. In addition, its thermal expansion coefficient is 13.2 × 10⁻⁶ K⁻¹ close to that of 8 mol% Y₂O₃ (8YSZ). Therefore, LNF64 also has a good physical compatibility with 8YSZ.     

Single step synthesis of nanosized CeO2–MxOy mixed oxides (MxOy?=?SiO2, TiO2, ZrO2, and Al2O3) by microwave induced solution combustion synthesis: characterization and CO oxidation

Various CeO₂ –M _x O _y (M _x O _y  = SiO₂, TiO₂, ZrO₂, and Al₂O₃) mixed oxides were prepared by microwave induced solution combustion method and analyzed by different complimentary techniques, namely, X-ray diffraction (XRD), Raman spectroscopic (RS), UV–Vis diffuse reflectance spectroscopy (UV-DRS), X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG-DTA), and BET surface area. XRD analyses revealed that CeO₂ –SiO₂ and CeO₂ –TiO₂ mixed oxides are in slightly amorphous form and exhibit only broad diffraction lines due to cubic fluorite structure of ceria. XRD lines due to the formation of cubic Ce_0.5Zr_0.5O₂ were observed in the case of CeO₂ –ZrO₂ sample. RS results suggested defective structure of the mixed oxides resulting in the formation of oxygen vacancies. The UV-DRS measurements provided valid information about Ce⁴⁺ ← O²⁻ and Ce³⁺ ← O²⁻ charge transfer transitions. XPS studies revealed the presence of cerium in both Ce³⁺ and Ce⁴⁺ oxidation states. The ceria–zirconia combination exhibited better oxygen storage capacity (OSC) and CO oxidation activity when compared to other samples. The significance of present synthesis method lays mostly on its simplicity, flexibility, and the easy control of different experimental factors.     

Formation of interfacial structure of Sn–3.7Ag–0.9Zn eutectic solder with different Al additions

The structural evolution of interfaces between the Sn–3.5Ag–0.9Zn–xAl (x = 0.5 and 1.0) solders and Cu substrate has been investigated by microstructural observations. The results suggest that the addition of Al in the Sn–3.5Ag–0.9Zn restrains the formation of Cu₅Zn₈ intermetallic compounds (IMCs) at the soldered interface. Moreover, the formation of Al₂Cu and Cu₉Al₄ IMCs leads to a crack failure near the interface of the Sn–3.7Ag–0.9Zn–1Al and Cu pad. It is suggested that the increase of Al content (e.g. 1 wt%) in the Sn–Ag–Zn eutectic solder would do harm to the reliability of the solder joint.     

Specific contact resistance and metallurgical process of the silver-based paste for making ohmic contact structure on the porous silicon/p-Si surface of the silicon solar cell

Porous silicon has been considered as a promising optoelectronic material for developing a variety of optoelectronic devices and sensors. In the present study, the electrical properties and metallurgical process of the screen-printed Ag metallization formed on the porous silicon surface of the silicon solar cell have been investigated. The contact structure consists of thick-film Ag metal contact patterned on the top of the porous silicon surface. The sintering process consists of a rapid firing step at 750–825 °C in air ambient. It results in the formation of a nearly perfect contact structure between the Ag metal and porous silicon/p-Si structure that forms the top metalization for the screen-printed silicon solar cells. The SEM picture shows that Ag metal firmly coalesces with the silicon surface with a relatively smooth interfacial morphology. This implies that high temperature fire-through step has not introduced any signs of adverse effect of junction puncture or excessive Ag indiffusion, etc. The three-point probe (TPP) method was applied to estimate the specific contact resistance, ρ _c (Ω-cm²) of the contact structure. The TPP measurement shows that contact structure has excellent ohmic properties with ρ _c = 1.2 × 10⁻⁶ Ω-cm² when the metal contact sintered at 825 °C. This value of the specific contact resistance is almost three orders of magnitude lower than the corresponding value of the ρ _c = 7.35 × 10⁻³ Ω-cm² obtained for the contact structure sintered at 750 °C. This improvement in the specific contact resistance indicates that with increase in the sintering temperature, the barrier properties of the contact structure at the interface of the Ag metal and porous silicon structure improved which in turn results a lower specific contact resistance of the contact structure.     

Inversed solid-phase grain boundary wetting in the Al–Zn system

The microstructure of binary Al–10 at% Zn and Al–15 at% Zn alloys after long anneals (800–4000 h) was studied between 190 and 258 °C. The contact angles between (Zn) particles and (Al)/(Al) grain boundaries (GBs) were measured. They decrease with decreasing temperature. First (Al)/(Al) GBs completely wetted by the second solid phase (Zn) appear below T _wsAl0% = 205 ± 5 °C. Above T _wsAl0% = 205 ± 5 °C all (Al)/(Al) GBs are incompletely wetted by (Zn) solid phase. The extrapolation of the maximal contact angle θ to zero permits to obtain the T _wsAl100% = 125 ± 10 °C. Below this line all (Al)/(Al) GBs has to be completely wetted by (Zn) solid phase.     

Effect of the frequency and temperature on the complex impedance spectroscopy (C–V and G–V) of p-ZnGa2Se4/n-Si nanostructure heterojunction diode

X-ray diffraction pattern and AFM results confirm the nanostructure of p-ZnGa₂Se₄/n-Si. The unit cell lattice parameters, the crystallite size L, the dislocation density δ, and the main internal strain ε were calculated. The temperature and frequency-dependent electrical characteristics of the Al/p-ZnGa₂Se₄/n-Si/Al heterojunction diode (HJD) have been investigated to determine the interface states which are responsible for the non-ideal behavior of the characteristics of the diode. The capacitance–voltage (C–V), conductance–voltage (G–V), and series resistance–voltage (R _s–V) characteristics of the diode have been analyzed in the frequency range of 5 kHz–1 MHz and temperature range of 303–423 K. The interfaces states of the diode were determined using conductance–voltage technique. The interface state density profile for the diode was obtained as a function of temperature and frequency. The values of the built-in potential V _bi, the doping concentration N _d and the barrier height φ _b(C–V) of the diode were calculated at different temperatures and frequencies. Our experimental results revealed that both the series resistance and interface state density values must be taken into account in studying the impedance spectroscopy of HJD to stand up their performance for electronic applications characteristics.     

Effect of Al doping and deposition runs on structural and optical properties of In<Subscript>2</Subscript>S<Subscript>3</Subscript> thin films grown by CBD

β-In_2−x Al _x S₃ thin films have been grown on glass substrate by chemical bath deposition for different value of Al concentration y = (([Al])/([In]))_sol (0 ≤ y ≤ 5 at.%). Samples have been characterized using X-ray diffraction, atomic force microscopy and by spectrophotometric measurements. The influence of the increase of y ratio in the structural and optical properties are described and discussed in terms of crystallinity improvement. In order to increase film thickness of β-In_2−x Al _x S₃, we have been realized multi-deposition system. The structural, the surface morphology as well as the optical properties seem to be improved as the film thickness is of about 1200 nm.     

Growth behavior of compounds due to solid-state reactive diffusion between Cu and Al

To examine experimentally the kinetics of the reactive diffusion between solid-Cu and solid-Al, sandwich Al/Cu/Al diffusion couples were prepared by a diffusion-bonding technique and then isothermally annealed in the temperature range of T = 693–753 K for various times up to 336 h. Owing to annealing, compound layers of the γ ₁, δ, ζ ₂, η ₂, and θ phases are formed between the Cu and Al specimens. The γ ₁, δ, ζ ₂, η ₂, and θ phases are the only stable compounds at T = 693–753 K in the binary Cu–Al system. At each annealing time, the thickness of the θ phase is much greater than those of the δ, ζ ₂, and η ₂ phases but smaller than that of the γ ₁ phase. Hence, the overall growth of the compound layers is governed by the γ ₁ and θ phases. The mean thickness of each compound layer is proportional to a power function of the annealing time. For the γ ₁ phase, the exponent m of the power function is 0.5 at T = 753 K. Such a relationship is called a parabolic relationship. As the annealing temperature T decreases, however, m gradually increases and then reaches to 0.66 at T = 693 K. On the other hand, for the θ phase, m is close to 0.5 at T = 723–753 K and becomes 0.42 at T = 693 K. In the γ ₁ and θ phases, grain growth occurs at T = 693–753 K. Thus, the layer growth of the θ phase is controlled by volume diffusion at T = 723–753 K but partially by boundary diffusion at T = 693 K. On the other hand, for the γ ₁ phase, volume diffusion is the rate-controlling process of the layer growth at T = 753 K, but interface reaction contributes to the rate-controlling process at T = 693–723 K. Consequently, the rate-controlling process varies depending on the annealing temperature in a different manner for each compound.     

Functional properties of silicon/non-native-oxide heterostructures

It is shown possible to use Al/SnO₂/Si and Al/WO₃/Si metal-oxide-semiconductor structures as photodiodes with a large-area heterojunction. For structures with a film of amorphous tungsten trioxide (a-WO₃) they show promise for applications associated with the development of varicaps and photovaricaps and also chemical sensors of the capacitance type. Pis’ma Zh. Tekh. Fiz. 23, 7–13 (June 26, 1997)     

The synthesis of mesoporous Ce1?xZrxO2 by modified evaporation-induced self-assembly method

Mesoporous Ce_1−x Zr _x O₂ with high surface area was synthesized using a modified evaporation-induced self-assembly method that combined citric acid as complexing agent and cetyltrimethyl ammonium bromide as surfactant. The samples with different Ce/Zr molar ratio were characterized by thermogravimetry and differential thermal analysis, X-ray diffraction, transmission electron microscopy, selected area electron diffraction, Brunauer–Emmett–Teller (BET), and Barrett–Joyner–Halenda methods. It was found that when the Zr molar fraction was larger than 0.3, a mixture of cubic phase and tetragonal phase was formed. Ce_0.7Zr_0.3O₂ solid solution had the largest BET surface area (217 m² g⁻¹) and mesoporous structure. The catalytic performances of mesoporous Ce_1−x Zr _x O₂ for CO oxidation were examined. Mesoporous Ce_0.7Zr_0.3O₂ solid solution demonstrated the best catalytic activity due to the high surface area and an enhanced redox property caused by appropriate Zr⁴⁺ incorporation.