Mo<Subscript>6</Subscript>Cl<Subscript>12</Subscript>-Incorporated Sol-Gel for Oxygen Sensing Applications

Excitation of hexanuclear molybdenum complexes such as Mo₆Cl₁₂ and its derivatives in the ultraviolet results in a strongly red-shifted luminescence centered at 750nm. Since oxygen efficiently quenches the luminescence, these thermally stable inorganic complexes are candidate lumophores for real-time, high temperature optical fiber based sensing of oxygen. Sol-gel films containing the acetonitrile complex of Mo₆Cl₁₂ were deposited on quartz substrates by dip coating. After drying, the films were heated at 200^∘C for 1 h. The luminescence lineshapes of films before and after heating were unchanged, indicating that heating did not adversely affect the cluster photophysics. Compared to solutions of the acetonitrile complex, quenching by oxygen was smaller in the as-prepared films, but heating at 200^∘C for 1 h increased the quenching, apparently due to increased oxygen permeability resulting from the loss of water or other small molecules from the matrix. These results confirm the potential of hexanuclear molybdenum complexes such as Mo₆Cl₁₂⋅2CH₃CN as the lumophores in fiber optic oxygen sensors that can operate up to 200^∘C.     

Inkjet printing of Ce<Subscript>0.8</Subscript>Gd<Subscript>0.2</Subscript>O<Subscript>2</Subscript> thin films on Ni-5%W flexible substrates

The successful inkjet printing of a cerium gadolinium oxide (Ce_0.8Gd_0.2O₂) precursor solution on highly textured Ni-5%W is reported. A stable ink was synthesised from metal acetates and propionic acid with rheological properties suitable for inkjet printing and also the development of solid–liquid interface comparable with thin film formation by dip coating. Two different drop-on-demand print heads were used for deposition: a 16-nozzle piezoelectric cartridge and a single electromagnetic nozzle. Two different rastering patterns with different droplet sizes and spacing were compared. Thermogravimetry and X-ray diffractometry were used to study the thermal decomposition of the metal oxide precursors and to determine the shortest possible heat treatment of the deposited layers, potentially suitable for continuous large scale production. The results from X-ray diffraction show that the single phase Ce_0.8Gd_0.2O₂ was obtained in all cases, but only piezoelectric inkjet printing with optimised drop overlapping produces a highly textured buffer layer. Optical micrographs and atomic force microscopy also indicate the good quality of deposited films after heat treatment.     

Electrochemical deposition of Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> for thermoelectric microdevices

The electrolyses of solutions of bismuth oxide and tellurium oxide in nitric acid with molar ratios of Bi:Te=3:3–4:3 lead to cathodic deposits of films of bismuth telluride (Bi₂Te₃), an n-type semiconductor. Current densities of 2–5 mA/cm² were applied. Voltammetric investigations showed that Bi₂Te₃ deposition occurred at potentials more negative than −0.125 V (Ag/AgCl, 3 M KCl). The deposit was identified as bismuth telluride (γ-phase) by X-ray analysis. Hall-effect measurements verified the n-type semiconducting behaviour. The films can be deposited in microstructures for thermoelectric microdevices like thermoelectric batteries or thermoelectric sensors.     

Structure and properties of films based on HfO<Subscript>2</Subscript>-Sc<Subscript>2</Subscript>O<Subscript>3</Subscript> double oxide

The results of the investigation of the chemical constitution and structure of (HfO₂) _x (Sc₂O₃)_1−x thin films are reported. The films are obtained by chemical vapor deposition (CVD) from hafnium 2,2,6,6-tetramethyl-3,5-heptandionate (Hf(thd)₄) and scandium 2,2,6,6-tetramethyl-3,5-heptandionate (Sc(thd)₃) coordination compounds. It is demonstrated by powder X-ray diffraction and infrared spectroscopy that depending on the scandium content in the films the structure is changed from monoclinic to cubic. Voltage-capacity dependences of test Al/(HfO₂) _x (Sc₂O₃)_1−x /Si structures are used to calculate the dielectric constant of the films. For the films with the cubic structure it is found that k = 21, while for the films with the monoclinic structure k = 9.     

Synthesis specifics of Mg(Fe<Subscript>0.8</Subscript>Ga<Subscript>0.2</Subscript>)<Subscript>2</Subscript>O<Subscript>4</Subscript> films on GaN

Mg(Fe_0.8Ga_0.2)₂O₄ films 340 nm thick were prepared by ion-beam sputtering on aluminasmoothed GaN substrates. Reactions that can occur between the components of heterostructure during its crystallization in the range 298.15–1273 K are analyzed. In order for Mg(Fe_0.8Ga_0.2)₂O₄ films to be continuous, their crystallization temperature should be lowered and alumina deposition—sputtering on GaN should be repeated several times.     

Electrodeposition of thin Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> films

The electrochemical behavior of copper(II), zinc(II), and thiosulfate (S₂O₃ ^2-) ions on the molybdenum electrode in individual 0.2 М sodium sulfate solutions (рН 6.7) and with addition of either 0.1 М tartaric acid (рН 4.6) or 0.1 М citric acid (рН 4.7) is studied. A one-step electrochemical method is developed for the deposition of thin Cu₂ZnSnS₄ films, which is carried out on the molybdenum electrode at a constant potential in sodium sulfate solutions containing tartaric acid. The effect of the concentration of electrolyte components on the chemical composition of Cu₂ZnSnS₄ films is determined. The phase composition is confirmed by the Raman spectroscopy data. The surface morphology of synthesized films is studied by means of scanning-electron and atomic-force microscopes. The photoelectrochemical characteristics of Cu₂ZnSnS₄ films are determined. Samples of these coatings on the Mo electrode are found to be highly photosensitive.     

Gas-sensitivity properties of nanoscale Au-In<Subscript>2</Subscript>O<Subscript>3</Subscript> materials

A possibility was demonstrated of producing the chemical sensors based on Au-In₂O₃ obtained using a sol-gel technology. The sensors exhibit high sensitivity and selectivity toward CO. The differences in gas-sensitivity properties of In₂O₃ sensor with respect to CO and CH₄ at different ways of doping with Au(III) was examined. The effect of the gold nanoparticles size and the state of the indium oxide surface on the characteristics of Au-In₂O₃ and Au/In₂O₃ sensors at the detection of CO and CH₄ was examined.     

Advanced Bi<Subscript>2</Subscript>O<Subscript>2.7</Subscript>/Bi<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> composite film with enhanced visible-light-driven activity for the degradation of organic dyes

Bi₂O_2.7/Bi₂Ti₂O₇ composite photocatalyst films are synthesized by sol–gel dip-coating. The ratio of adding Bi and Ti precursors can be controlled during the preparation process. The phase structure is confirmed by X-ray diffraction. The UV–visible diffuse reflectance spectrum shows that the composite catalysts present light absorption in the visible region. The obtained Bi₂O_2.7/Bi₂Ti₂O₇ composite films possess superior photocatalytic degradation of rhodamine B, owing to the visible light response of Bi₂O_2.7 and the separation of photogenerated electrons and holes between the two components. As a result, the Bi₂O_2.7/Bi₂Ti₂O₇ (Bi/Ti = 1:1) displays the highest photocatalytic activity under visible light or UV light irradiation for the degradation of different organic dyes, including methyl blue, methyl orange and acid orange 7.     

Sensors based on SnO<Subscript>2</Subscript> + In<Subscript>2</Subscript>O<Subscript>3</Subscript> composite films for detecting CO in air

The sensor properties of nanostructured films of SnO₂, In₂O₃, and their combinations for detecting CO in air in the temperature range of 330–520°C were investigated. It was found that SnO₂ films show the least sensitivity to CO. Sensitivity grows as the concentration of In₂O₃ in SnO₂ increases, and it reaches its maximum value in pure In₂O₃. At the same time, the maximum of sensitivity to CO in air shifts towards low temperatures. Sensor response time was found to be about 1 s for the studied SnO₂ and In₂O₃ films, and about 0.5 s for the composite film. The mechanism of sensor sensitivity for the studied metal oxide films in detecting CO in air is discussed.     

Microstructure and electrical properties of lead zirconate titanate thin films deposited by sol-gel method on La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript>/Si substrate

(La_0.7Sr_0.3)MnO₃ thin films were deposited on SiO₂/Si substrates by a metal-organic decomposition (MOD) method, and then Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films were grown on (La_0.7Sr_0.3)MnO₃-coated SiO₂/Si substrates by a sol-gel method. The effects of annealing temperature on the crystalline phases, microstructures and electrical properties of the PZT films were investigated. X-ray diffraction analysis results indicated that the PZT films with a perovskite single phase could be obtained by annealing at 650°C. The dielectric constant and the remnant polarization of the PZT films increased with increasing annealing temperature. The remnant polarization and the coercive field of the films annealed at 650°C were 18.3 μC/cm² and 35.5 kV/cm, respectively, whereas the dielectric constant and loss value measured at 1 kHz were approximately 1100 and 0.81, respectively.     

Conductivity of SnO<Subscript>2</Subscript>-In<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocrystalline composite films

The conductivity of films consisting of a mixture of SnO₂ and In₂O₃ nanocrystals at 200–500°C was studied. Based on the experimental data, it was assumed that in films containing less than 20 wt % In₂O₃, the current flows along SnO₂ nanocrystals. A model of conductivity in these films is presented; it includes an electron transfer from In₂O₃ to SnO₂, which forms positively charged In₂O₃ nanocrystals that contact the negatively charged SnO₂ nanocrystals. In the presence of In₂O₃ nanocrystals, the activation energy of the electron transfer between SnO₂ nanocrystals decreased substantially because of a decrease in the barrier of electron transfer between SnO₂ crystals under the action of the negative charge. As a result, a percolation cluster of charged SnO₂ crystals formed. At high contents of In₂O₃ (over 20 wt %), the conductivity increased dramatically. The curve of the temperature dependence of conductivity changed because of the appearance of a percolation cluster of In₂O₃ nanocrystals, in which the current passed. The conductivity of a mixed film of this kind differed from that of the nanocrystalline film of pure In₂O₃.     

Dielectric and tunable properties of highly (110)-oriented (Ba<Subscript>0.65</Subscript>Sr<Subscript>0.35</Subscript>)TiO<Subscript>3</Subscript> thin films deposited on Pt/LaNiO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript>/Si substrates

Highly (110)-oriented Ba_0.65Sr_0.35TiO₃ films were deposited on Pt/LaNiO₃/SiO₂/Si substrates by a sol–gel method. It was found that the (110)-preferred Pt film was very effective for growing (110)-oriented ferroelectric films with perovskite structure. The as-grown Ba_0.65Sr_0.35TiO₃ films showed good dielectric properties with dielectric constant and loss tangent tan δ = 0.026. Excellent dielectric tunability was also achieved in the (110)-oriented films. With applying an electric field of 230 kV/cm at 100 kHz, the dielectric tunability and the figure of merit can reach up to 63.4% and 16, respectively. These results indicate that the highly (110)-oriented Ba_0.65Sr_0.35TiO₃ film is a promising candidate for the applications in microwave tunable devices.     

The microstructure and magnetic properties of Ni<Subscript>0.4</Subscript>Zn<Subscript>0.6</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> films prepared by spin-coating method

Nickel zinc ferrite (Ni_0.4Zn_0.6Fe₂O₄) films on Si (100) substrate were synthesized using a spin-coating method. The crystallinity of the Ni_0.4Zn_0.6Fe₂O₄ films with the thickness of about 386 nm became better as the annealing temperature increased. The films have smooth surface, relatively good packing density and uniform thickness. The volatilization of Zn is serious at 900 °C. With the increase of annealing temperature, the saturation magnetization M _s increases in the temperature ranging from 400 to 700 °C, however, decreases above 700 °C, and the coercivity H _c increases in the temperature range 400–800 °C, decreases above 800 °C. After annealed at 700 °C for 2 h in air with the heating rate 2 °C/min, the film shows a maximum saturation magnetization M _s of 349 emu/cc and low coercivity H _c of 66 Oe. The M _s is higher than others which prepared by this method, however, the H _c is lower. The M _s of Ni_0.4Zn_0.6Fe₂O₄ films annealed at 700 °C increases with increasing annealing time and the H _c changes slightly.     

Characteristics of Ag/Bi<Subscript>3.25</Subscript>La<Subscript>0.75</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript>/p-Si heterostructure prepared by sol-gel processing

The metal-ferroelectric-semiconductor (MFS) heterostructure has been fabricated using Bi_3.25La_0.75Ti₃O₁₂ (BLT) as a ferroelectric layer by sol-gel processing. The effect of annealing temperature on phase formation and electrical characteristics of Ag/BLT/p-Si heterostructure were investigated. The BLT thin films annealed at from 500°C to 650°C are polycrystalline, with no pyrochlore or other second phases. The C-V curves of Ag/BLT/p-Si heterostructure annealed at 600°C show a clockwise C-V ferroelectric hysteresis loops and obtain good electrical properties with low current density of below 2×10⁻⁸ A/cm² within ±4 V, a memory window of over 0.7 V for a thickness of 400 nm BLT films. The memory window enlarges and the current density reduces with the increase of annealing temperature, but a annealing temperature over 600°C is disadvantageous for good electrical properties.     

Yttria stabilized zirconia solid electrolyte surface modification with ZrO<Subscript>2</Subscript>, Y<Subscript>2</Subscript>O<Subscript>3</Subscript>, and ZrO<Subscript>2</Subscript> + 9 mol % Y<Subscript>2</Subscript>O<Subscript>3</Subscript> films

The surface of ceramic electrolyte ZrO₂ + 9 mol % Y₂O₃, hereinafter referred to as YSZ (abbreviated yttria stabilized zirconia), was modified with 0.1 to 0.2 μm oxide films of ZrO₂, Y₂O₃, and YSZ (same composition as substrate) by dip coating in alcohol solutions of the relevant salts and further annealing. The results of scanning electronic microscopy and X-ray diffraction evidence epitaxial film growth. By means of impedance spectroscopy at the temperatures of 500 to 600°C, the effect of YZS electrolyte surface modification with ZrO₂, Y₂O₃, and YSZ films to the polarization resistance of silver electrode was studied.     

Electrochemical Synthesis of Co-intercalation Compounds in the Graphite-H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-H<Subscript>3</Subscript>PO<Subscript>4</Subscript>System

Anodic oxidation of highly oriented pyrolytic graphite in an electrolyte containing concentrated sulfuric and anhydrous phosphoric acids is studied for the first time. The synthesis was carried out under galvanostatic conditions at a current I = 0.5 mA and an elevated temperature (t = 80°C). Intercalation compounds of graphite (ICG) are shown to form at all concentration ratios of H₂SO₄ and H³PO⁴ acids. The intercalation compound of step I forms in solutions containing more than 80 wt % H₂SO₄, a mixture of compounds of intercalation steps I and II forms in 60% H²SO⁴, intercalation step II is realized in the sulfuric acid concentration range from 10 to 40%, and a mixture of compounds of intercalation steps III and II is formed in 5% H₂SO₄ solutions. The threshold concentration of H₂SO₄ intercalation is ∼2%. With the decrease in active intercalate (H₂SO₄) concentration, the charging curves are gradually smoothed, the intercalation step number increases, and the potentials of ICG formation also increase. As the sulfuric acid concentration in the electrolyte changes from 96 to 40 wt %, the filled-layer thickness d _i in ICG monotonously increases from 0.803 to 0.820 nm, which apparently is associated with the greater size of phosphoric acid molecules. With further increase in H₃PO₄ concentration in solution, d _i remains unchanged. According to the results of chemical analysis, both acids are simultaneously incorporated into the graphite interplanar spacing and their ratio in ICG is determined by the electrolyte composition.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 651–655.Original Russian Text Copyright © 2005 by Leshin, Sorokina, Avdeev.     

Photoelectrochemical study of electrodeposited TiO<Subscript>2</Subscript> thin films onto F:SnO<Subscript>2</Subscript> substrates

TiO₂ thin films have been effectively fused onto F:SnO₂ (FTO) substrates via the electrodeposition method. The influence of deposition temperature on the synthesis of F:SnO₂ substrates and relative information of as-deposited and annealed TiO₂ thin films have been studied. Novel TiO₂ microspheres are detected on F:SnO₂ substrates at an optimized electrodeposition potential. Raman bands approve the creation of single-anatase-phase TiO₂. The optimized deposition surroundings show a decrease in the band gap of F:SnO₂ substrates and TiO₂ thin films. The determined photoelectrochemical properties of annealed TiO₂ thin films indicate a fill factor of 51% and power conversion efficiency of 0.15% for application in solar cells.     

Permeation studies on transparent multiple hybrid SiO<Subscript>2</Subscript>-PMMA coatings-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> barriers on PEN substrates

In this work we report the performance of permeation barriers based on organic/inorganic multilayer stacks. We have used PMMA-SiO₂ (poly methyl methacrylate-silica) hybrid films synthesized through a sol–gel route as organic–inorganic components, whereas Al₂O₃ thin films were used as the inorganic component. The hybrid layers were deposited by dip coating and the Al₂O₃ by atomic layer deposition (ALD), films were prepared on polyethylene naphthalene (PEN) substrates. The permeability of the films and stacks is evaluated using helium as the diffusion gas in a custom made ultra-high vacuum system. The results show that permeability for PEN is reduced from 5 × 10⁻³ g/m²-day to about 9 × 10⁻⁵ g/m²-day for the best multiple barrier evaluated. Increased barrier properties are due to the increasing in the path and hence the lag-time of the permeating gas. In particular, we report the surface roughness of the different layers and its impact on the barrier performance. The hybrid layers reduced notably the roughness of the bare PEN substrate improving the quality of the Al₂O₃ layer in the barrier. The optical transmittance of the barriers in the visible region is higher than 80% in all the studied cases.     

Tin trifluoroacetylacetonate [Sn(C<Subscript>5</Subscript>H<Subscript>4</Subscript>O<Subscript>2</Subscript>F<Subscript>3</Subscript>)<Subscript>2</Subscript>] as a precursor of tin dioxide in APCVD process

A new method of synthesis of volatile complex, tin trifluoroacetylacetonate [Sn(C₅H₄O₂F₃)₂], was proposed. The prepared compound was identified by IR spectroscopy, CH analysis, X-ray powder diffraction, and DTA/TGA, the composition was confirmed by MALDI-TOF mass spectrometry, crystal structure was established. Thin films of tin dioxide on silicon were obtained by atmospheric pressure chemical vapor deposition using [Sn(C₅H₄O₂F₃)₂] as a precursor. The morphology and composition of the films were studied by scanning electron microscopy, EDX elemental analysis, and X-ray powder diffraction. Surface resistance and light transmission in visible and near IR region were studied.     

Site engineering in chemical-solution-deposited Bi<Subscript>3.25</Subscript>La<Subscript>0.75</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films using Ce,Zr, Mn and Si atoms

Ferroelectric Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films were fabricated by depositing sol-gel solutions on Pt(111)/Ti/SiO₂/Si (100) substrates. Crystallographic orientations of the BLT films were random, but the preferred orientations along (00l) and (117) axes were found. All films showed a single-phase bismuth-layered structure but the orientation in the films could be engineered by optimizing the growth condition, as well as by introducing dopant atoms such as Ce and Zr in the films, which in turn influenced the ferroelectric properties of the films significantly. The shape of c-axis-oriented grains was more plate-like, while that of (117)-oriented grains was rod-like. Small % substitution of Ce, Mn, and Zr atoms at Ti site enhanced the remanent polarization by approximately 20%, while substitution of Si atoms reduced the remanent polarization in BLT films but improved insulating properties. It was also demonstrated that fatigue endurance could be controlled by the concentration of dopant atoms, which was thought to be due to the decrease in oxygen vacancy concentration.