Effect of deposition temperature on structural, surface, optical and magnetic properties of pulsed laser deposited Al-doped CdO thin films

The objective of this work is to study the influence of deposition temperature on structural, surface, optical and magnetic properties of the Al doped CdO thin films prepared by pulsed laser deposition (PLD) technique. KrF excimer laser (λ = 248 nm, τ_l = 20 ns, ν = 10 Hz, ?_l = 2.5 J/cm²) was employed for the deposition of thin films. It is observed by XRD results that films grown at room temperature and 100 °C show preferential growth along (1 1 1) and (2 0 0) directions while high temperatures (200-400 °C) lead to preferential growth along the (2 0 0) direction only. The optical constants (n, k, α, and optical band gap energy) of films measured by spectroscopic ellipsometry show strong dependence upon deposition temperature. M-H loop of films, measured by vibrating sample magnetometer, deposited at 25 °C and 100 °C show paramagnetic nature while films deposited at temperatures (200-400 °C) exhibit ferromagnetic character. Scanning electron micrographs show degraded elongated grains at lower deposition temperatures, while smooth and compact surface is observed for films deposited at higher deposition temperatures.     

High-quality vertically aligned ZnO nanorods synthesized by microwave-assisted CBD with ZnO-PVA complex seed layer on Si substrates

We successfully synthesized vertically aligned zinc oxide (ZnO) nanorods on seeded silicon substrates using chemical bath deposition assisted by microwave heating. ZnO nanorods were grown on seed layers of ZnO-polyvinyl alcohol (PVA) nanocomposites spin-coated on p-type Si (1 1 1). The nanorod's diameter was found to be dependent on the annealing temperature of the ZnO-PVA seed layer. We produced ZnO nanorods with diameters in the range of 50-300 nm from five groups of seed layers annealed at 250 °C, 350 °C, 380 °C, 450 °C, and 550 °C. The nanorods were examined with X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy, which revealed hexagonal wurtzite structures perpendicular to the substrate along the z-axis in the direction of (0 0 2). Photoluminescence measurements revealed high UV emission at a high I_UV/I_vis ratio of 175. We also conducted Raman scattering studies on the ZnO nanorods to estimate the lattice vibration modes.     

High-repetition rate pulsed laser deposition of ZrC thin films

ZrC thin films were grown on (100) Si substrates by the pulsed laser deposition (PLD) technique using a high-repetition rate excimer laser working at 40 Hz. The substrate temperature during depositions was set at 300 °C and the cooling rate was 5 °C/min. X-ray diffraction investigations showed that the films were crystalline. Films deposited under residual vacuum or 2 × 10^− 3 Pa of CH₄ atmosphere exhibited a (200)-axis texture, while those deposited under 2 × 10^− 2 Pa of CH₄ atmosphere were found to be equiaxed. The surface elemental composition of as-deposited films, analyzed by Auger electron spectroscopy (AES), showed the usual high oxygen contamination of carbides. Once the topmost − 3-5 nm region was removed, the oxygen concentration rapidly decreased, being around 3-4% only in bulk. Scanning electron microscopy (SEM) investigations showed a smooth, featureless surface morphology, corroborating the roughness values below 1 nm (rms) obtained from simulations of the X-ray reflectivity (XRR) curves. From the same simulations we also estimated films mass density values of around 6.32-6.57 g/cm³ and thicknesses that correspond to a deposition rate of around 8.25 nm/min. Nanoindentation results showed a hardness of 27.6 GPa and a reduced modulus of 228 GPa for the best quality ZrC films deposited under an atmosphere of 2 × 10^− 3 Pa CH₄.     

Vacuum sintering of WC-8 wt.% Co hardmetals from WC powders with different dispersity

The effect of sintering temperature and particle size of tungsten carbide WC on phase composition, density and microstructure of hardmetals WC-8 wt.% Co has been studied using X-ray diffraction, scanning electron microscopy and density measurements. The sintering temperature has been varied in the range from 800 to 1600 °C. The coarse-grained WC powder with an average particle size of 6 μm, submicrocrystalline WC powder with an average particle size of 150 nm and two nanocrystalline WC powders with average sizes of particles 60 and 20 nm produced by a plasma-chemical synthesis and high-energy ball milling, respectively, have been used for synthesis of hardmetals. It is established that ternary Co₆W₆C carbide phase is the first to form as a result of sintering of the starting powder mixture. At sintering temperature of 1100-1300 °C, this phase reacts with carbon to form Co₃W₃C phase. A cubic solid solution of tungsten carbide in cobalt, β-Co(WC), is formed along with ternary carbide phases at sintering temperature above 1000 °C. Dependences of density and microhardness of sintering hardmetals on sintering temperature are found. The use of nanocrystalline WC powders is shown to reduce the optimal sintering temperature of the WC-Co hardmetals by about 100 °C.     

Perpendicular magnetic anisotropy in 70 nm CoFe2O4 thin films fabricated on SiO2/Si(1 0 0) by the sol-gel method

Cobalt ferrite CoFe₂O₄ films were fabricated on SiO₂/Si(1 0 0) by the sol-gel method. Films crystallized at/above 600 °C are stoichiometric as expected. With increase of the annealing temperature from 600 °C to 750 °C, the columnar grain size of CoFe₂O₄ film increases from 13 nm to 50 nm, resulting in surface roughness increasing from 0.46 nm to 2.55 nm. Magnetic hysteresis loops in both in-plane and out-of-plane directions, at different annealing temperatures, indicate that the films annealed at 750 °C exhibit obvious perpendicular magnetic anisotropy. Simultaneously, with the annealing temperature increasing from 600 °C to 750 °C, the out of plane coercivity increases from 1 kOe to 2.4 kOe and the corresponding saturation magnetization increases from 200 emu/cm³ to 283 emu/cm³. In addition, all crystallized films exhibit cluster-like structured magnetic domains.     

Effects of growth temperature on structure and electrical properties of dielectric (Ba,Sr)TiO3 capacitors with transparent conducting oxide electrodes

200 nm-thick BST thin films were grown on Zr-doped In₂O₃/SrTiO₃ (1 0 0) substrates at 550-750 °C. X-ray diffraction results show that the as-deposited BST films were polycrystalline with random crystallographic orientations. X-ray diffraction patterns reveal that the BST film grown at 650 °C had the best crystalline quality of all the deposition temperatures. Atomic force microscopy and secondary ion mass spectrometry showed that the surface and interface structures of the BST films became rough as the growth temperature increased. The BST film grown at 650 °C showed the best electrical properties, with a dielectric constant of 420 at 1 MHz, dielectric tunability of 32.1%, dielectric loss of 0.015 at 300 kV/cm, and a mean optical transmittance in visible wavelength of 71.3%.     

Formation of epitaxial 3C-SiC layers by microwave plasma-assisted carbonization

Epitaxial 3C-SiC (β-SiC) thin layers are grown on Si (001) substrates by carbonization in moderate-pressure microwave plasmas, typically used for diamond film deposition. The substrate temperature and the CH₄ gas concentration diluted in H₂ gas are varied from 1000 to 1200 °C and from 2 to 8 vol.%, respectively. The grown layers are characterized by scanning electron microscopy, Raman spectroscopy, x-ray diffraction, Fourier transform infrared spectroscopy, reflection high energy electron diffraction, and energy-dispersive x-ray spectroscopy. For 2% CH₄, epitaxial 3C-SiC about 10 nm thick is grown only when the temperature is increased to 1200 °C, while polycrystalline 3C-SiC is grown for temperatures less than 1200 °C. For 8% CH₄, epitaxial 3C-SiC is grown even for temperatures less than 1200 °C, but the thickness of the SiC layer is reduced. Some amounts of amorphous carbon and diamond phases are found to grow on the SiC layers.     

The Al-rich region of the Al-Mn-Ni alloy system. Part I: Ternary phases at 750-950 °C

Ternary phases in the Al-rich region of the Al-Mn-Ni alloy system were studied at 950, 850 and 750 °C. Two new ternary intermetallic compounds were revealed: the φ-phase (Al₅Co₂-type, hP26, P6₃/mmc: a = 0.76632(16) and c = 0.78296(15) nm) and the κ-phase (κ-Al_14.4Cr_3.4Ni_l.1-type, hP227, P6₃/m: a = 1.7625(10) and c = 1.2516(10) nm). The formation of the O-phase (Pmmn; oP650; O-Al₇₇Cr₁₄Pd₉-type; a = 2.3316(16), b = 1.2424(15) and c = 3.2648(14) nm) was confirmed and its chemical composition as well as thermodynamic stability was specified.     

Ferroelectric relaxor behavior and dielectric spectroscopic study of 0.99(Bi0.5Na0.5TiO3)-0.01(SrNb2O6) solid solution

0.99(Bi_0.5Na_0.5TiO₃)-0.01(SrNb₂O₆) was prepared by simple solid state reaction route. Material stabilized in rhombohedral perovskite phase with lattice constants a = 3.9060 Å, α = 89.86° and a_h = 5.4852 Å, c_h = 6.7335 Å for hexagonal unit cells. Density of material was found 5.52 g_m/cm³ (92.9% of theoretical one) in the sample sintered at 950 °C. The temperature dependent dielectric constant exhibits a broad peak at 538 K (?_m = 2270) at 1 kHz that shows frequency dependent shifts toward higher temperature - typical relaxor behavior. Modified Curie-Weiss law was used to fit the dielectric data that exhibits almost complete diffuse phase transition characteristics. The dielectric relaxation obeys the Vogel-Fulcher relationship with the freezing temperature 412.4 K. Significant dielectric dispersion is observed in low frequency regime in both components of dielectric response and a small dielectric relaxation peak is observed. Cole-Cole plots indicate polydispersive nature of the dielectric relaxation; the relaxation distribution increases with increase in temperature.     

A study of the Al-rich region of the Al-Cu-Mo alloy system

Partial isothermal sections at 810, 700 and 585 °C are presented for a high-Al compositional range of Al-Cu-Mo. The maximal solubility of Cu in the Al₅Mo phase(s) was found to be ∼3 at.%. The previously reported Al₃Ti-type phase was found to be formed around the Al_68.5Cu_6.5Mo₂₅ composition. The other ternary phase forming in a small compositional range around Al₇Cu₂Mo has a hexagonal structure with a = 0.86796(8) and c = 1.51948(12) nm.     

Constitution, microstructure, and battery performance of magnetron sputtered Li-Co-O thin film cathodes for lithium-ion batteries as a function of the working gas pressure

Li-Co-O thin film cathodes have been deposited onto Si and stainless steel substrates by RF magnetron sputtering from a ceramic LiCoO₂ target at various working gas pressures from 0.15 to 25 Pa. Composition, crystal structure and thin film morphology were examined and properties such as intrinsic stress, conductivity and film density were determined. As-deposited films at 0.15 Pa as well as in the range between 5 Pa and 10 Pa working gas pressure showed a nanocrystalline metastable rocksalt structure with disordered cation arrangement and were nearly stoichiometric. To induce a cation ordering the films were annealed in a furnace at temperatures between 100 and 600 °C for 3 h in argon/oxygen atmosphere (Ar:O₂ = 4.5:5) of 10 Pa. This cation ordering process was observed by XRD and Raman spectroscopy. For the films deposited at 10 Pa gas pressure an annealing temperature of 600 °C leads to the formation of the high temperature phase HT-LiCoO₂ with a layered structure. The Raman spectrum of the films deposited at 0.15 Pa and annealed at 400 °C indicates the formation of the low temperature phase LT-LiCoO₂ with a cubic spinel-related structure, which is assumed to be stabilized due to high compressive stress in the film. The electrochemical characterisation of annealed thin film cathodes revealed that the discharge capacity strongly depends on the crystal structure. Thin Li-Co-O films with a perfect layered HT-LiCoO₂ structure showed the highest discharge capacities.     

The Al-rich region of the Al-Mn-Ni alloy system. Part II. Phase equilibria at 620-1000 °C

Phase equilibria in the Al-rich region of the Al-Mn-Ni alloy system were studied at 1000, 950, 850, 750, 700, 645 and 620 °C. Three ternary thermodynamically stable intermetallics, the φ-phase (Al₅Co₂-type, hP26, P6₃/mmc; a = 0.76632(16), c = 0.78296(15) nm), the κ-phase (κ-Al_14.4Cr_3.4Ni_l.1-type, hP227, P6₃/m; a = 1.7625(10), c = 1.2516(10) nm), and the O-phase (O-Al₇₇Cr₁₄Pd₉-type, Pmmn, oP650,: a = 2.3316(16), b = 1.2424(15), c = 3.2648(14) nm), as well as three ternary metastable phases, the decagonal D₃-phase with periodicity about 1.25 nm, the Al₉(Mn,Ni)₂-phase (Al₉Co₂-type, P112₁/a, mP22; a = 0.8585(16), b = 0.6269(9), c = 0.6205(11) nm, β = 95.34(10)°) and the O₁-phase (base-centered orthorhombic, a ≈ 23.8, b ≈ 12.4, c ≈ 32.2 nm) were revealed. Their physicochemical behaviour in the Al-Mn-Ni alloy system was studied.     

Electrical and thermal characterization of Sm doped ceria electrolytes synthesized by combustion technique

Nanocrystalline samarium doped ceria electrolyte [Ce_0.9Sm_0.1O_1.95] was synthesized by citrate gel combustion technique involving mixtures of cerium nitrate oxidizer (O) and citric acid fuel (F) taken in the ratio of O/F = 1. The as-combusted precursors were calcined at 700 °C/2 h to obtain fully crystalline ceria nano particles. It was further made into cylindrical pellets by compaction and sintered at 1200 °C with different soaking periods of 2, 4 and 6 h. The sintered ceria was characterized for the microstructures, electrical conductivity, thermal conductivity and thermal diffusivity properties. In addition, the combustion derived ceria powder was also analysed for the crystallinity, BET surface area, particle size and powder morphology. Sintered ceria samples attained nearly 98% of the theoretical density at 1200 °C/6 h. The sintered microstructures exhibit dense ceria grains of size less than 500 nm. The electrical conductivity measurements showed the conductivity value of the order of 10⁻² S cm⁻¹ at 600 °C with activation energy of 0.84 eV between the temperatures 100 and 650 °C for ceria samples sintered at 1200 °C for 6 h. The room temperature thermal diffusivity and thermal conductivity values were determined as 0.5 × 10⁻⁶ m² s⁻¹ and 1.2 W m⁻¹ K⁻¹, respectively.     

Structural, morphological and electrical properties of spray deposited nano-crystalline CeO2 thin films

Nanocrystalline, uniform, dense, and adherent cerium oxide (CeO₂) thin films have been successfully deposited by a simple and cost effective spray pyrolysis technique. CeO₂ films were deposited at low substrate and annealing temperatures of 350 °C and 500 °C, respectively. Films were characterized by differential thermal analysis, X-ray diffraction, scanning electron microscopy, atomic force microscopy; two probe resistivity method and impedance spectroscopy. X-ray diffraction analysis revealed the formation of single phase, well crystalline thin films with cubic fluorite structure. Crystallite size was found to be in the range of 10-15 nm. AFM showed formation of smooth films with morphological grain size 27 nm. Films were found to be highly resistive with room temperature resistivity of the order of 10⁷ Ω cm. Activation energy was calculated and found to be 0.78 eV. The deposited film showed high oxygen ion conductivity of 5.94 × 10⁻³ S cm⁻¹ at 350 °C. Thus, the deposited material shows a potential application in intermediate temperature solid oxide fuel cells (IT-SOFC) and might be useful for μ-SOFC and industrial catalyst applications.     

Growth and characterization of perovskite LaGaO3 crystals doped with Sr and Mn

Single crystals of LaGaO₃ doped with Sr and Mn (LSGMn) were grown by the Czochralski method from the melt with compositions: La_1−xSr_xGa_1−yMn_yO₃, x = y = 0.02; 0.05 and x = 0.05, y = 0.06. Single crystals with 20 mm diameter with convex crystal-melt interface were grown on LaGaO₃ oriented seed with pulling rate of 2 mm/h. Single crystals were dark and have strong tendency to spiral growth. This tendency was decreased with increasing the Mn content in comparison with Sr. Effective segregation coefficients for Sr and Mn in LaGaO₃ are lower than 1. Room-temperature structural measurements by X-ray powder diffraction showed perovskite structure with Pbnm space group for all measured samples. Orthorhombic b and c lattice parameters decrease, whereas a slightly increases with decreasing orthorhombic unit cell volume that is related to increased amount of Mn and Sr in the melt. Thermal analysis and Raman investigations showed that the temperature of the first order phase transitions temperature form orthorhombic to rhombohedral structure observed in pure LaGaO₃ at about 150 °C decreases to about 49 °C at the bottom part of crystal with x = y = 0.05 composition.     

A new temperature stable microwave dielectric ceramics: ZnTiNb2O8 sintered at low temperatures

The phases, microstructure and microwave dielectric properties of ZnTiNb₂O₈-xTiO₂ composite ceramics with different weight percentages of BaCu(B₂O₅) additive prepared by solid-state reaction method have been investigated using the X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The results showed that the microwave dielectric properties were strongly dependent on densification, grain sizes and crystalline phases. The sintering temperature of ZnTiNb₂O₈ ceramics was reduced from 1250 °C to 950 °C by doping BaCu(B₂O₅) additive and the temperature coefficient of resonant frequency (τ_f) was adjusted from negative value of −52 ppm/°C to 0 ppm/°C by incorporating TiO₂. Addition of 2 wt% BaCu(B₂O₅) in ZnTiNb₂O₈-xTiO₂ (x = 0.8) ceramics sintered at 950 °C showed excellent dielectric properties of ?_r = 38.89, Q × f = 14,500 GHz (f = 4.715 GHz) and τ_f = 0 ppm/°C, which represented very promising candidates as LTCC dielectrics for LTCC applications.     

Ba(Ti1 − xSnx)O3 (x = 0.13) nanomaterials produced by low-temperature aqueous synthesis

BaTi_0.87Sn_0.13O₃ (BTS₁₃) nanopowder was prepared by low-temperature aqueous synthesis (LTAS) method. The evolution of the structure and microstructure of the precursor precipitate, heated at temperatures up to 1000 °C was studied by TGA, FT-IR, SEM and XRD techniques. The dried precipitate showed a microstructure consisting of nano-sized grains (∼40 nm) with great tendency to agglomeration. BaTi_0.87Sn_0.13O₃ single phase was obtained at 800 °C. The ceramics prepared from as-obtained BTS₁₃ powders (60-70 nm) show good dielectric and ferroelectric characteristics. The dielectric constant was about 4800 and the dielectric loss (tan δ) was 0.229 at 1 kHz and at the Curie temperature (31 °C). The remanent polarization (P_r) and the coercive field (E_C) of Ba_0.97Ho_0.03TiO₃ ceramics, at 1 kHz, were P_r = 13 μC/cm² and E_C = 0.89 kV/cm. The ferroelectric parameters E_C and P_r decrease with increasing frequency in the domain 100 Hz to 10 kHz.     

Post annealing effect on transport properties of La0.67Ca0.33MnO3 films grown on vicinal cut substrates

La_0.67Ca_0.33MnO₃ thin films have been grown on 10°, 15°, and 20° vicinal cut SrTiO₃ (1 0 0) substrates by pulse laser deposition. The single phase and the least textured growth have been studied by X-ray diffraction analysis. The post annealing effect with high temperature and high oxygen pressure on the transport properties of films has been investigated by resistance versus temperature measurements. Films with post annealing show large enhancement of metal-insulator transition temperature T_p about 20-30 K towards higher temperature and obvious decrease of resistance, which is attributed to the refilling of oxygen, the change of Mn-O-Mn angle and the improvement of crystallinity by the post annealing effect. Specially, film on 20° vicinal cut substrate exhibits the biggest range gap of peak resistance drop, which may originate from more defects caused by steps at this tilt angle and many of these defects are removed after post annealing.     

Microwave dielectric properties and its compatibility with silver electrode of Li2MgTi3O8 ceramics

The effects of BaCu(B₂O₅) (BCB) additions on the sintering temperature and microwave dielectric properties of Li₂MgTi₃O₈ ceramic have been investigated. The pure Li₂MgTi₃O₈ ceramic shows a relative high sintering temperature (∼1000 °C) and good microwave dielectric properties as Q × f of 40,000 GHz, ?_r of 27.2, τ_f of 2.6 ppm/°C. It was found that the addition of a small amount of BCB can effectively lower the sintering temperature of Li₂MgTi₃O₈ ceramics from 1025 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 0.5 wt% BCB added Li₂MgTi₃O₈ ceramic sintered at 900 °C for 2 h exhibited good microwave dielectric properties of Q × f = 36,200 GHz (f = 7.31 GHz), ?_r = 26 and τ_f = −2 ppm/°C. Compatibility with Ag electrode indicates this material can be applied to low temperature-cofired ceramics (LTCC) devices.