Structural and electrochemical studies of Co oxide films formed by the sol-gel technique

Two different types of Co oxide films, each having a distinct electrochemical signature correlated with the film drying temperature, were formed using the sol-gel (SG) technique. Two different states of gelation of the film precursor were also explored. Cyclic voltammograms, collected in alkaline solutions for the low temperature films, displayed two pairs of peaks corresponding to the Co(II) to Co(III) and Co(III) to Co(IV) transitions, centered at 1.2 and 1.4 V, respectively, while the high temperature films underwent only the Co(III) to Co(IV) redox process at 1.4 V. The charge densities obtained for the lower temperature films (particle sizes 2–10 nm in diameter) ranged between 40 and 70 mC/cm²; charge densities for the higher temperature films (particle sizes of 5–40 nm), otherwise formed identically, were between 10 and 20 mC/cm². The more viscous Co oxide gels led to significantly higher charge densities than less viscous gels, as well as greater film stability during electrochemical cycling. Using a wide range of film characterization techniques, it was shown that Co oxide films formed at > 180∘C are composed mainly of Co³O⁴ spinel, while films formed at < 180∘C consist predominantly of CoO.     

Structural, compositional, thermoelectrical and photoelectrochemical properties of CdSe thin films

Cadmium selenide thin films have been deposited on non-conducting glass and stainless steel substrates. Films were characterized by X-ray diffraction, atomic absorption spectroscopy. The electrical and thermoelectrical properties also studied. The X-ray diffraction analysis shows that the film samples are in cubic crystal structure. Film was found to be cadmium deficient. The efficiency of photoelectrode was found to be 1.15 % using sulphide-polysulphide electrolyte.     

Fabrication and properties of Fe/Fe oxide and Co/Co oxide films

Evaporation of Fe and Co at a residual O2pressure of 10^-5to 10^-4Torr yielded magnetic films of high coercivities up to 500 Oe and magnetizations of about 1000 EMU/cm³. While the Co films were continuously deposited in the O2atmosphere, a sandwich structure of Fe and Fe2O3was formed by intermittently altering the evaporation conditions. Both kinds of films were produced in the same geometrical arrangement. The Fe/Fe2O3films showed shape anisotropy caused by the oblique incidence deposition, while no uniaxial anisotropy was observed on the Co films. For both, Co films and Fe/Fe2O3sandwich films, it was possible to adjust the magnetic properties within a certain range. In both cases the coercivity increased considerably by annealing at 200°C.     

Structural, optoelectronic and electrochemical properties of nickel oxide films

Thin nickel oxide (NiO) films were deposited by the electron beam evaporation technique. The films were post annealed in air at 450–500 °C for 5 h and the effect of annealing on the structural, microstructural, electrical and optical properties were studied. X-ray diffraction studies indicated the polycrystalline nature of the films. The microstructural parameters were evaluated. The band gap of the films was found to be about 3.60 eV. Electrical resistivity of the films was 4.5 × 10⁻⁴ Ω cm. FTIR studies indicated a broad spectrum centered at 461.6 cm⁻¹. Cyclic voltammetry studies in 1 M KOH solution revealed good electronic electrochromic behaviour.     

Structural properties of non-stoichiometric zinc oxide films

We report a study of the crystal structure and microstructure of sputtered non-stoichiometric ZnO _x thin films for which 0.7 < x < 1. A substrate r.f. discharge was used to control film stoichiometry during deposition. All films had a columnar microstructure, and the film surface progressed from rough to smooth with increased oxidation. X-ray diffraction analysis detected no presence of crystalline zinc in any film. The crystallite size, strain and orientation of ZnO, detected in all films, was dependent on film composition and substrate r.f. discharge power. A model of film structure incorporating the competing effects of ion bombardment (causing amorphization) and increased oxygen content (creating improved crystallinity and orientation) is used to explain the observed variation of ZnO _x crystal structure.     

Optical and structural properties of NiMgO thin films formed by sol-gel spin coating

Ni_1−xMg_xO thin films across the full compositional range were formed by a low-cost sol-gel spin coating method. Optical transmission of the resultant films in the ultraviolet-visible spectral region increased to as high as 90% upon sintering, and X-ray diffraction verified an increase in crystallinity for sintering temperatures up to 1000 °C, with root mean square roughness below 1 nm when sintered between 600 and 800 °C. The lattice parameter of the rock salt Ni_1−xMg_xO films showed a linear shift with increased magnesium concentration, consistent with a Vegard's Law relationship between the two binaries. Optical energy gaps from 3.6 to > 6.5 eV were realized by adjusting the composition of the Ni_1−xMg_xO films, demonstrating the suitability of the ternary for optical devices in the UV-C spectral region.     

Structural and magnetotransport properties in Co/nonmagnetic films

Four types of thin films were prepared by sequentially depositing ultrathin Co layers and nonmagnetic layers, including an insulator Al₂O₃, a semiconductor ZnO, a semimetal C, and a normal metal Cu on glass substrates. The zero-field-cooled and field-cooled measurements and transmission electron microscopy studies confirmed that the films consist of Co particles dispersed in the matrix. All films show negative magnetoresistance at room temperature except those with C. The films with the ZnO spacer exhibit the largest magnetoresistance, which makes the system a candidate for useful spintronic devices. The magnetic circular dichroism data show that ZnO electrons are partially spin-polarized, which may account for the large magnetoresistance of granular films.     

Structural evolution, dielectric and electro-optic properties of sol-gel derived potassium titanyl phosphate thin films

Transparent potassium titanyl phosphate (KTiOPO₄) thin films were prepared by a sol-gel coating technique. The structural evolution of the KTP thin films was examined by means of DTA/TGA, FT-IR, XRD and SEM. The effect of UV irradiation on the crystallization behavior was investigated and it was found that the UV irradiation decreases the crystallization temperature of the KTP thin films and dried gels. The dielectric and electro-optic properties were evaluated. The dielectric measurement results show that the KTP thin films have a low dielectric constant of 12 in the temperature range of 25–100 °C and frequency range of 1–1000 kHz. The electro-optic results indicate that the KTP thin films exhibit a quadratic electro-optic effect and may have potential applications for electro-optic devices.     

溶胶-凝胶法制备氧化铝绝缘薄膜及其电性能研究

以乙二醇乙醚为溶剂,异丙醇铝为前驱物,乙酰丙酮为螯合剂,采用溶胶-凝胶法和旋转涂覆工艺,在不同衬底上制备了氧化铝薄膜.通过X射线衍射仪(XRD)、场发射扫描电子显微镜(FESEM)和金相显微镜等手段对薄膜的微观结构和表面形貌进行了表征。结果表明,溶胶-凝胶法制得的薄膜为无定形结构,表面均匀、致密、无裂纹。通过对薄膜电流密度与电场和时间(J-E和J-t)曲线的测量,对薄膜的电学性能进行了研究。薄膜击穿场强约为2.0～3.0MV/cm,在电场强度为0.5MV/cm时,漏电流密度约为9.0×10-6 A/cm2。     

The photocatalytic properties of bismuth oxide films prepared through the sol-gel method

In this research, thin bismuth oxide films were prepared through the sol-gel method. In order to study the influence of bismuth oxide crystal phases on the photocatalytic properties of bismuth oxide films, these films were annealed at different temperatures and then applied to decompose a typical textile industry pollutant (Rhodamine B). Scanning electron microscopy, X-ray diffraction and profilometry were applied to characterize these films. It has been found that different annealing temperatures cause the transformation of different bismuth oxide crystal phases, which leads to the different removals of Rhodamine B photolyzed using bismuth oxide films as photocatalyst.     

Structural, dielectric and ferroelectric properties of multilayer lithium tantalate thin films prepared by sol-gel technique

Multilayer lithium tantalate thin films were deposited on Pt-Si [Si(111)/SiO₂/TiO₂/Pt(111)] substrates by sol-gel process. The films were annealed at different annealing temperatures (300, 450 and 650 °C) for 15 min. The films are polycrystalline at 650 °C and at other annealing conditions below 650 °C the films are in amorphous state. The films were characterized using X-ray diffraction, atomic force microscopy (AFM) and Raman spectroscopy. The AFM of images show the formation of nanograins of uniform size (50 nm) at 650 °C. These polycrystalline films exhibit spontaneous polarization of 1.5 μC/cm² at an application of 100 kV/cm. The dielectric constant of multilayer film is very small (6.4 at 10 kHz) as compared to that of single crystal.     

Physical properties of natively textured yttrium doped zinc oxide films by sol-gel

Sol-gel derived yttrium doped ZnO films of various thicknesses have been deposited by the dip coating technique. The investigations of microstructural, electrical and optical properties of post heat-treated films in air as a function of thickness have been made. It is found that high quality films are obtained at an annealing temperature of 550 ^∘C. The (002) preferential growth of both the doped and undoped ZnO films changes to (101) as the thickness of the films were increased. The full width at half maximum of (002) X-ray peak decreases with annealing temperature and the lattice constant is found to approach the value of bulk ZnO. Natively textured films have been obtained for film having thickness greater than 0.8 μm. The thinner films are found to be non-textured with high resistivity. The formation of the textured surface of the film is linked to the suppression of c-axis (002) orientation and the columnar growth in the thick film.     

Structural and electrical properties of sputtered indium-zinc oxide thin films

In this study, indium-zinc oxide (IZO) thin films have been prepared at a room temperature, 200 and 300 °C by radio frequency magnetron sputtering from a In₂O₃-12 wt.% ZnO sintered ceramic target, and their dependence of electrical and structural properties on the oxygen content in sputter gas, the substrate temperature and the post-heat treatment was investigated. X-ray diffraction measurements showed that amorphous IZO films were formed at room temperature (RT) regardless of oxygen content in sputter gas, and micro-crystalline and In₂O₃-oriented crystalline films were obtained at 200 and 300 °C, respectively. From the analysis on the electrical and the structural properties of annealed IZO films under Ar atmosphere at 200, 300, 400 and 500 °C, it was shown that oxygen content in sputter gas is a critical parameter that determines the local structure of amorphous IZO film, stability of amorphous phase as well as its eventual crystalline structure, which again decide the electrical properties of the IZO films. As-prepared amorphous IZO film deposited at RT gave specific resistivity as low as 4.48 × 10^− 4 Ω cm, and the highest mobility value amounting to 47 cm²/V s was obtained from amorphous IZO film which was deposited in 0.5% oxygen content in sputter gas and subsequently annealed at 400 °C in Ar atmosphere.     

Structural and electrical properties of annealed CdSe films on Ni substrate

Preparation and characterization of CdSe thin film semiconductors, prepared by cathodic electrodeposition from an acid sulphate solution (CdSO₄-SeO₂) before and after thermal treatment in nitrogen atmosphere, were investigated. The effect of the bath temperature and how it affects the cadmium selenide (CdSe) deposits were studied. The formation of compact barrier layers of zinc blende CdSe was attained. Scanning electron microscopy and X-ray diffraction patterns present a remarkably intense cubic structure, even after thermal treatment. The Ni/CdSe/Au structure may exhibit rectifying properties depending on the temperature during the electrodeposition. Thermal annealing in nitrogen gas increases the conductivity of CdSe and intensifies the rectification properties of the Ni/CdSe/Au structure.     

Ni,Co, Cu,Ni-Co,and Ni-Cu nanoparticles in opal matrices and mesoporous silica gels

NiCo solid solutions and Ni-Cu bimetallic particles have been prepared in opal-matrix nanocomposites by reacting Ni, Co, and Cu double salts and oxides with supercritical (SC) isopropanol. According to X-ray diffraction and transmission electron microscopy data, the nanocomposites have an X-ray amorphous opal matrix and contain crystalline nanoparticles of individual metals, solid solutions, or bimetallic materials of various morphologies in the opal pores. Mesoporous silica gel matrix composites remain X-ray amorphous after treatment in SC alcohols because of the small particle size of the metallic phase, or form solid solutions between Ni and Co silicates. The phase composition of the composites can be controlled by varying experimental conditions.     

Structural properties of electrophoretically deposited europium oxide nanocrystalline thin films

The structural properties of nanocrystalline europium oxide (Eu₂O₃) thin films, produced via electrophoretic deposition (EPD), were investigated. We found that EPD from our Eu₂O₃ nanocrystal solutions yielded both translucent films, with uniform size and distribution of the microstructure, and opaque films, with marked anisotropy to the size and distribution of the constituents of the microstructure. The disparity in the film morphology arose from the initial temperature conditions of the nanocrystal solution. The translucent films, produced from pre-chilled (−25 °C) EPD solutions, were bimodal films, comprised of homogeneous, tightly packed, glassy nanocrystalline films interspersed with micron-sized nanocrystal aggregates. In contrast, the opaque films, produced from room temperature solutions, consisted of an irregularly distributed and shaped microstructure. The evolution of the microstructure was monitored for the chilled samples as a function of film thickness (deposition time) and juxtaposed with the resultant structure of the room temperature film. Optical microscopy and scanning electron microscopy were employed to characterize the films.     

Structural and magnetic properties of Co and Co71Ni29 nanowire arrays prepared by template electrodeposition

A comparative study on the structural and magnetic properties of Co and Co₇₁Ni₂₉ nanowire arrays prepared by AC electrodeposition in alumina templates has been presented. The Co and Co₇₁Ni₂₉ nanowires observed by SEM and TEM have a 45 nm diameter and exhibit high aspect ratio. Also, the nanowires of both Co and Co₇₁Ni₂₉, determined by XRD, have an identical crystallographic structure. The Co₇₁Ni₂₉ nanowires exist in a cobalt solid solution. Both the as-obtained Co and Co₇₁Ni₂₉ nanowire arrays measured by VSM show obvious magnetic anisotropy, dominated by shape anisotropy. Compared to the Co nanowire arrays, Co₇₁Ni₂₉ nanowire array shows an enhanced coercivity Hc (⊥) and approximate square ratio Mr/Ms(⊥).     

Structural and optical properties of TiO2 thin films grown by sol-gel dip coating process

The mono and bi-layer TiO₂ thin films have been prepared by sol-gel method on glass. X-Ray diffraction, Raman spectroscopy, atomic force microscopy, spectroscopic ellipsometry and m-lines spectroscopy techniques have been used to characterize the TiO₂ films. The mono-layer film is found to be amorphous, while the bi-layer film shows the presence of anatase phase. The bi-layer film exhibits more homogeneous surface with less roughness. The thickness effect on the refractive index, extinction ceofficient, packing density and optical band gap is analysed. The waveguiding measurements of the bi-layer film exhibit single-guided TE₀ and TM₀ polarized modes from which we can measure the refractive index and the film thickness.     

Cadmium oxide, indium oxide and cadmium indate thin films obtained by the sol-gel technique

Thin films of the mixed CdO-In₂O₃ system were deposited on glass substrates by the sol-gel technique. The precursor solution was obtained starting from the mixture of two precursor solutions of CdO and In₂O₃ prepared separately at room temperature. The In atomic concentration percentages (X) in the precursor solution with respect to Cd (1 − X), were: 0, 16, 33, 50, 67, 84 and 100. The films were sintered at two different sintering temperatures (Ts) 450 and 550 °C, and after that, annealed in a 96:4 N₂/H₂ gas mixture at 350 °C. X-ray diffraction patterns showed three types of films, excluding those constituted only of CdO and In₂O₃ crystals: i) For X ≤ 50 at.%, the films were constituted of CdO + CdIn₂O₄ crystals, ii) For X = 67 at.%, the films were only formed of CdIn₂O₄ crystals and iii) For X = 84 at.% the films were constituted of In₂O₃ + CdIn₂O₄ crystals. In all films in the 0 < X < 100 range, the formation CdIn₂O₄ crystals of this material was prioritized with respect to the formation of CdO and In₂O₃ materials. All films showed high optical transmission and an increase of the direct band gap value from 2.4 (for CdO) to 3.6 eV (for In₂O₃), as the X value increases. The resistivity values obtained were in the interval of 8 × 10^− 4 Ω cm to 10⁶ Ω cm. The CdIn₂O₄ films had a resistivity value of 8 × 10^− 3 Ω cm and a band gap value of 3.3 eV.