Magnetic,optical and electrical properties of Mn-doped CuCrO<Subscript>2</Subscript> thin films prepared by chemical solution deposition method

CuCrO₂ and CuCrO₂:Mn thin films were prepared on sapphire substrates by chemical solution deposition method. The effects of the annealing temperatures and Mn concentration on the structural, electrical and optical properties were investigated. The X-ray diffraction measurement was used to confirm the c-axis orientation of CuCrO₂ and CuCrO₂:Mn thin films. The maximum transmittances of the films in the visible region are about 65% with direct band gaps of 3.25 eV. All films showed the p-type conduction and semiconductor behavior. The electrical conductivity decreases rapidly with the increase of Mn content, the maximum of the electrical conductivity of 1.35 × 10⁻² S cm⁻¹ is CuCrO₂ film deposited at 600 °C temperature in 10⁻³ Torr vacuum, which is about four orders of magnitude higher than that of the Mn-doped CuCrO₂ thin film. The energy band of the samples is constructed based on the grain-boundary scattering in order to investigate the conduction mechanism. Moreover, the samples exhibit a clear ferromagnetism, which was likely ascribed to originating from the double-exchange interaction between the Mn³⁺ and Cr³⁺ ions.     

Synthesis of polysilisiquioxane used as core layer material of optical waveguide

Colorless and transparent polysilisiquioxane was synthesized using non-hydrolytic sol–gel process. A high degree of poly-condensation and a lower remnant ratio of Si–OCH₃ were calculated by ²⁹Si NMR and ¹H NMR, respectively. After spin-coating, subsequently UV and thermal curing, free-cracked thin films were obtained. The properties of the free-cracked thin films were measured by a prism coupler and thermal analysis system. The refractive index increased to 1.5495 (1,310 nm TE) and 1.5468 (1,550 nm TE), respectively, with the increasing of phenyltrimethoxysilane content to 20 mol%. Birefringence was below 0.0005. The thermo-optic coefficient was about −2.8 × 10⁻⁴ °C⁻¹. The optical loss was 0.20 dB cm⁻¹ at 1,310 nm and 0.75 dB cm⁻¹ at 1,550 nm, which was very important for core layer material of optical waveguide. The results of Thermo-Gravimetric Analysis indicated an excellent thermal stability. All of these properties imply that it will be a promising core layer material of optical waveguide.     

Micro-Raman and photoluminescence study of urchin-like ZnO structure assembled with nanorods synthesized by hydrothermal method

Urchin-like ZnO structures assembled with nanorods have been synthesized by cetyltrimethylammonium bromide-assisted hydrothermal method. The as-obtained products were characterized by powder X-ray diffraction, field-emission scanning electron microscopy for the study of crystal structure and morphology. The ZnO urchin is constructed of well-assembled nanorods of length ~3 μm range and diameter ~20 nm. Micro-Raman study shows characteristic Raman-active mode of hexagonal ZnO at 439 cm⁻¹ and also mode related to defects at ~581 cm⁻¹. The ZnO urchin assembled with nanorods possessed band edge emission at 3.085 eV and defect related visible emission at 2.97, 2.57, and 2.36 eV.     

Dielectric,ferroelectric and optical properties of BaZr<Subscript>0.2</Subscript>Ti<Subscript>0.8</Subscript>O<Subscript>3</Subscript> thin films prepared by sol–gel-hydrothermal process

BaZr_0.2Ti_0.8O₃ thin films on Pt/Ti/SiO₂/Si substrates have been fabricated under low temperature conditions by a sol–gel-hydrothermal technique. The dielectric constant is 247–83 in the frequency range of 1 kHz–1 MHz. The corresponding dielectric loss is ~10⁻². The capacitance–voltage curve shows strong non-linear dielectric behavior leading to a high tunability, up to ~30% at 1 kHz. The remanent polarization and coercive field at room temperature are measured to be ~1.5 μC/cm² and ~90 kV/cm. The infrared optical properties of the thin films are investigated using an infrared spectroscopic ellipsometry in the wave number range of 800–4,000 cm⁻¹. Optical constants of the thin films are simultaneously obtained.     

Carbon modified (CM)-n-TiO2 thin films for efficient water splitting to H2 and O2 under xenon lamp light and natural sunlight illuminations

Visible light-active carbon modified n-type titanium oxide (CM-n-TiO₂) thin films were synthesized by both flame oxidation and a combination of spray pyrolysis and flame oxidation. An undoped reference sample was also synthesized in an electric oven for comparison. Photoresponse of CM-n-TiO₂ and n-TiO₂ was evaluated by measuring the rates of water splitting to hydrogen and oxygen, in terms of observed photocurrent densities. Under monochromatic illumination from a xenon lamp, the integrated photocurrent densities from 300 nm to wavelengths corresponding to band gaps were found to be 1.12, 7.7, and 12.7 mA cm⁻² for optimized oven-made n-TiO₂ (sample 1), flame-made (sample 2), and spray pyrolysis flame-made CM-n-TiO₂ (sample 3) thin films at 0.48, 0.24, and 0.215 V biases, respectively. The corresponding maximum photoconversion efficiencies for these thin films were 0.84%, 7.62%, and 12.89%, respectively. Under actual natural global AM 1.5 sunlight illumination of 1 sun, the photocurrent densities for water splitting were 0.85, 5.89, and 12.27 mA cm⁻² for samples 1, 2, and 3, respectively. These photocurrent densities generated the maximum photoconversion efficiencies of 0.67%, 5.63%, and 12.26% for samples 1, 2, and 3, respectively, under global sunlight illuminations. These values compared well with those found under monochromatic light illumination from the xenon lamp. The increasing efficiencies were found to be consistent with lowering of main band gap from 3.0 eV to 2.65 eV and the generation of mid-gap bands at 1.6 eV and 1.4 eV above the valence band for samples 2 and 3, respectively. Carbon contents were found to be 0.0, 17.60, and 23.23 atom% for samples 1, 2, and 3, respectively. Dedicated to the 85th birthday of John O’ M. Bockris.     

Fabrication and properties of xBiFeO3-(1 − x)Bi4Ti3O12 system by sol–gel process

The thin films of mixture of xBiFeO₃-(1 − x)Bi₄Ti₃O₁₂ (x = 0.4, 0.5, and 0.6) system were prepared by a sol–gel process. The thicknesses of the thin films were 540, 500, and 570 nm, respectively. The crystal structure of all thin films annealed at 650 °C was analyzed by X-ray diffraction. It was found that the thin films at x = 0.4 and 0.5 mainly consisted of a Bi₄Ti₃O₁₂ phase while Bi₅Ti₃FeO₁₅ was the major phase of the thin film at x = 0.6. The thin film (x = 0.6) showed better ferroelectric properties in remnant polarization and polarization fatigue than those observed in the thin films (x = 0.4 and 0.5). The values of remnant polarization 2P _r and coercive field 2E c of the thin film at x = 0.6 were 36 μC/cm² and 192 kV/cm at an applied electric field of 260 kV/cm, respectively. There was almost no polarization fatigue up to 10¹⁰ switching cycles. Also weak ferromagnetism was observed in the thin film at x = 0.6.     

Influences of synthesizing temperatures on the properties of Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> prepared by sol–gel spin-coated deposition

In this work Cu₂ZnSnS₄ (CZTS) suitable for the absorption layer in solar cells was successfully prepared by sol–gel spin-coated deposition. CZTS precursors were prepared by using solutions of copper (II) chloride, zinc (II) chloride, tin (IV) chloride, and thiourea. Texture structures with kesterite crystallinity reflected from the X-ray diffraction of (112), (200), and (312) planes of the CZTS were obtained as synthesized at a temperature of over 240 °C. The absorption coefficients of the CZTS films are higher than 10⁴ cm⁻¹, and the optical-energy gap is about 1.5 eV. Without sulfurization treatment, a near stoichiometry composition of the CZTS is obtained at a synthesizing temperature of 280 °C.     

Electrochemical intercalation of O2− in CuAlO2 single crystal and photoelectrochemical properties

The delafossite CuAlO₂ single crystal, prepared by the flux method, is a low mobility p-type semiconductor with a hole mobility of 1.2 × 10⁻⁵ cm⁻² V⁻¹ s⁻¹. The chronoamperometry showed an electrochemical O²⁻ insertion with a diffusion coefficient D _303K of 3.3 × 10⁻¹⁸ cm² s⁻¹. The thermal variation of D in the range 293–353 K gave an enthalpy of diffusion (ΔH) of 44.7 kJ mol⁻¹. CuAlO₂ is photoactive, and the Mott–Schottky plot indicates a flat band potential of +0.42 V vs saturated calomel electrode and a holes density (N _A) of 10¹⁶ cm⁻³. The photocurrent spectra have been analyzed by using the Gartner model from which the absorption coefficients and diffusion lengths were determined. An optical transition at 1.66 eV, indirectly allowed, has been obtained. The spectral photoresponse provides a high absorption at 480 nm. The low quantum yield (η) is attributed to a small depletion length (440 nm) and a hole diffusion width (271 nm) compared to a very large penetration depth (12 μm).     

Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript>,Tb<Superscript>3+</Superscript> thin films prepared by sol–gel method: structural and optical studies

Y₂O₃: Eu³⁺,Tb³⁺ transparent, high density and optical quality thin films were prepared by the sol–gel dip-coating technique. Yttrium (III) 2,4-pentadionate was used as a precursor by its hydrolysis in ethanol. The doping agents were incorporated in the form of europium and terbium nitrate. Structural, morphological and optical properties of prepared films were investigated for different annealing temperatures in order to establish the ideal processing route that enhances the luminescent properties. X-ray diffraction (XRD) analysis shows the cubic phase for 10-layer films and annealing temperatures higher than 500°C. At 700°C, highly densified (4.52 g cm⁻³) and very smooth films (1.4 nm at 700°C) are produced, composed of crystallites with a grain size of 11 nm. The film thickness, refractive index and porosity, as well as the luminescent properties, were found to vary with treatment temperature.     

CuInSe2 thin-film deposition on flexible plastic substrate: electrolyte recirculation rate and deposition potential effects

Copper indium diselenide (CuInSe₂; CIS) layer was electrolytically plated from an aqueous medium at room temperature onto electroless nickel deposited on flexible plastic (Kapton). The CIS depositions were carried out under constant deposition potentials (−0.5 to −1.1 V vs. Ag/AgCl) and at various electrolyte flow rates (0.3 to 1.5 ml/s) under constant applied current. The resulting thin films were characterized using atomic force microscopy, energy-dispersive X-ray spectroscopy, environmental scanning electron microscopy, and X-ray diffraction. The surface morphology and the atomic composition of the deposited CIS film were found to be influenced by the deposition potential under potential control and the electrolyte recirculation rate under current control. Low electrolyte flow rates under constant current control and high cathodic deposition potential under voltage control favor the deposition of indium. CIS films of uniform deposit, smoother surfaces, and with better adhesion properties are favored by moderate electrolyte recirculation rate. At a current density of 0.6 mA/cm², the electrolyte recirculation rate required to achieve ideal CIS atomic composition was found to be 1.0 ml/s in such a setting. The crystallinity of the film improved after annealing for 2 h at 390 °C under argon atmosphere.     

Structure and dielectric properties of 80%Pb(Zn1/3Nb2/3)O3–20%PbTiO3 thin films prepared by modified sol–gel process

80%Pb(Zn_1/3Nb_2/3)O₃–20%PbTiO₃ (PZN–PT) thin films have been prepared on Pt/Ti/SiO₂/Si substrates using a modified sol–gel method. In our method, niobium pentaoxide is used as a substitution instead of niobium ethoxide which is moisture-sensitivity and much more expensive. Microstructure and electrical properties of PZN–PT thin films have been investigated. X-ray diffraction analysis shows that proper annealing temperature of PZN–PT thin films is 600 °C. The PZN–PT thin films annealed at 600 °C are polycrystalline with (111)-preferential orientations. Field-emissiom scanning electron microscope analysis revealed PZN–PT thin films possess well-defined and crack-free microstructure. The thickness of thin films is 290 nm. The Pt/PZN–PT/Pt capacitors have been fabricated and it presents ferroelectric nature. The remanent polarization (Pr), spontaneous polarization (Ps), and the coercive electric field (Ec) are 8.71 μC/cm², 43.06 μC/cm², and 109 kV/cm at 1 MHz, respectively. The dielectric constant (ε_r) and the dissipation factor (tan δ) are about 500.3 and 0.1 at 1 kHz, respectively.     

The parathiocyanogen electrode

Stable, yellow anodic films of parathiocyanogen (SCN) _x were formed on a platinum electrode from 2.8 M KSCN in methanol at 45 °C at a constant current of 20–40 mA cm⁻² for 15–30 min. Loosely bound orange crystals of a more amorphous character were removed by rinsing to leave an adherent yellow film with sharp Raman bands under 647.1 nm laser excitation at 627 cm⁻¹ (vCS), 1152 cm⁻¹ and 1236–1261 cm⁻¹ (vNN and vCN). The lack of electroactivity and short-lived photocurrents pointed to an insulating film at potentials up to 1.0 V (SHE). At more positive potentials, longer-lasting photocurrents were obtained, consistent with breakdown of the insulating film. XPS scans confirmed N:C:S ratios close to 1:1:1, with a deficiency of S of some 10% due to S lost as sulfate at the film surface. Oxidation of SeCN⁻ in neutral aqueous solution led to the formation of a less-stable orange paraselenocyanogen film with a Raman band at 1256–1267 cm⁻¹, which decomposed within a day to grey selenium. Received: 12 December 1997 / Accepted: 23 March 1998     

Photostimulated changes in WO3 nanosized films

During the irradiation of WO₃ films d = 7–160 nm thick by light at λ = 320 nm (I = (1.5–7) × 10¹⁵ quantum cm⁻² s⁻¹), absorption band at λ = 850 nm appeared along with absorption band edge shift to shorter waves. The subsequent irradiation of samples at λ = 850 nm caused the disappearance of the longwave absorption band. The intrinsic absorption edge of WO₃ films was determined (λ = 320 nm). The degree of transformations of WO₃ films increased under atmospheric conditions as the intensity of incident light and the time of irradiation (1–140 min) grew and as film thickness decreased. A mechanism of photochemical transformations of WO₃ films was suggested. This mechanism included the generation of electron-hole pairs, the recombination of part of nonequilibrium charge carriers, the formation of [eV_a²⁺e] centers, and the isolation of photolysis products.     

Investigation of non-diamond carbon phases and optical centers in thermochemically polished polycrystalline CVD diamond films

Polycrystalline chemical vapor deposition (CVD) diamonds films grown on silicon substrates using the microwave-enhanced CVD technique were polished using the thermochemical polishing method. The surface morphology of the samples was determined by optical and scanning electron microscopes before and after polishing. The average surface roughness of the as-grown films determined by the stylus profilometer yielded 25 μm on the growth side and about 7 μm on the substrate side. These figures were almost uniform for all the samples investigated. Atom force microscopic measurements performed on the surface to determine the average surface roughness showed that thermochemical polishing at temperatures between 700 °C and 900 °C reduced the roughness to about 2.2 nm on both the substrate and growth sides of the films. Measurements done at intermittent stages of polishing using confocal micro-Raman spectroscopy showed that thermochemical polishing is accompanied by the establishment of non-diamond carbon phases at 1353 cm⁻¹ and 1453 cm⁻¹ at the initial stage of polishing and 1580 cm⁻¹ at the intermediate stage of polishing. The non-diamond phases vanish after final fine polishing at moderate temperatures and pressures. Photoluminescence of defect centers determined by an Ar⁺ laser (λl_exct= 514.532 nm) showed that nitrogen-related centers with two zero-phonon lines at 2.156 eV and 1.945 eV and a silicon-related center with a zero-phonon line at 1.681 eV are the only detectable defects in the samples. Received: 26 July 1999 / Accepted: 15 November 1999     

Effect of Al doping on the conductivity type inversion and electro-optical properties of SnO2 thin films synthesized by sol-gel technique

Al doped SnO₂ thin films have been synthesized by a sol-gel dip coating technique with different percentages of Al on glass and silicon substrates. X-ray diffraction studies confirmed the proper phase formation in the films and atomic percentage of aluminium doping in the films was obtained by energy dispersive X-ray studies. SEM studies showed the particle sizes lying in the range 100–150 nm for the undoped films and it decreased with increase of Al doping. Optical transmittance spectra of the films showed high transparency (∼80%) in the visible region and the transparency increases with the increase of Al doping in the films. The direct allowed bandgap of the films have been measured for different Al concentration and they lie within the range of 3.87–4.21 eV. FTIR studies depicted the presence of Sn–O, Al–O, bonding within the films. The room temperature electrical conductivities of the films are obtained in the range of 0.21 S cm⁻¹ to 1.36 S cm⁻¹ for variation of Al doping in the films 2.31–18.56%. Room temperature Seebeck coefficients, S_RT of the films were found in the range +56.0 μVK⁻¹ to −23.3 μVK⁻¹ for variation of Al doping in the films 18.56–8.16%. It is observed that the Seebeck coefficient changes its sign at 12.05% of Al in the films indicating that below 12.05% of Al doping, SnO₂:Al behaves as an n-type material and above this percentage it is a p-type material.     

Effect of sol temperature on the structure,morphology, optical and photoluminescence properties of nanocrystalline zirconia thin films

Transparent nanocrystalline zirconia thin films were prepared by sol–gel dip coating technique using Zirconium oxychloride octahydrate as source material on quartz substrates, keeping the sol at room temperature (SET I) and 60 °C (SET II). X-ray diffraction (XRD) pattern shows the formation of mixed phase [tetragonal (T) + monoclinic (M)] in SET I and a pure tetragonal phase in SET II ZrO₂ thin films annealed at 400 °C. Phase transformation from tetragonal to monoclinic was achieved in SET II film annealed at 500 °C. Atomic force microscopy analysis reveals lower rms roughness and skewness in SET II film annealed at 500 °C indicating better optical quality. The transmittance spectra gives a higher average transmittance >85% (UV–VIS region) in SET II films. Optical spectra indicate that the ZrO₂ films contain direct—band transitions. The sub- band in the monoclinic ZrO₂ films introduced interstitial O⁻defect states above the top of the valance band. The energy bandgap increased (5.57–5.74 eV) in SET I films and decreased (5.74–5.62 eV) in SET II films, with annealing temperature. This is associated with the variations in grain sizes. Photoluminescence (PL) spectra give intense band at 384 and 396 nm in SET I and SET II films, respectively. A twofold increase in the PL intensity is observed in SET II film. The “Red” shift of SET I films and “Blue” shift of SET II films with annealing temperature, originates from the change of stress of the film due to lattice distortions.     

Electrochemical and Structural Characterisation of Dip-Coated Fe/Ti Oxide Films Prepared by the Sol-Gel Route

Thin solid films of mixed Fe/Ti oxide composition (Fe/Ti molar ratios: 0.5∶1, 1∶1, 1.5∶1) have been made from Fe(NO₃)₃ alcoholic solution to which Ti(OiPr)₄ was added. Films have been deposited by the dip-coating technique and heat-treated at 300°C and 500°C. Powders of Fe/Ti oxide heat-treated at 300°C are amorphous, while powders annealed at 500°C for 40 hours transformed to mixed rutile, pseudobrookite and hematite phases. The structure of the XRD amorphous films was identified with the help of near-normal reflection absorption (6°) (IRRA) and near-grazing incidence angle (NGIA) spectroscopy. NGIA FT-IR spectra of films are characterised with a single phonon mode appearing in the spectral range 600–950 cm⁻¹ which shifts with increasing Ti concentration from 675 cm⁻¹ (Fe₂O₃) to 904 cm⁻¹ (TiO₂) thus exhibiting one-mode behavior. Electrochemical investigations made with the help of cyclic voltammetry (CV) and chronocoulometry (CPC) performed in 0.01M LiOH and in 1M LiClO₄/propylene carbonate electrolytes revealed that films are able to uptake reversibly Li⁺ ions with a charge capacity (Q) per film thickness (d) in the range 0.1–0.26 mC/cm²nm and 0.06 mC/cm²nm, respectively. The temperature at which the films were prepared alters the rate of Li⁺ insertion which is faster for less compact films obtained at 300°C. In situ UV-VIS spectroelectrochemical measurements revealed that Fe/Ti oxide films bleached in the UV spectral region (300 nm<λ<450 nm) and colored in the VIS spectral region (450 nm<λ<800 nm), thus exhibiting mixed anodic and cathodic electrochromism.     

Structure and multiferroic properties of Bi<Subscript>5</Subscript>FeTi<Subscript>3</Subscript>O<Subscript>15</Subscript> thin films prepared by the sol–gel method

The Bi₅FeTi₃O₁₅ (BFTO) films of layered structure have been fabricated on Pt/Ti/SiO₂/Si substrates by the sol–gel method. The thermal decomposition behaviors of precursor powder were examined using thermo-gravimetric and differential scanning calorimeters analysis. The optimal heat treatment process for BFTO films were determined to be low-temperature drying at 200 °C for 4 min and high-temperature drying at 350 °C for 5 min followed by annealing at 740 °C for 60 min, which led to the formation of compact films with uniform grains of ~300 nm. The structural, surface topography, ferroelectric and magnetic properties of the films were investigated. The remnant polarization (2P _r) of BFTO thin films under an applied electric field of ~550 kV/cm are determined to be 67.5 μC/cm² . Meanwhile, the weak ferromagnetic properties of the BFTO films were observed at room temperature.     

Optical absorption in solution processed thin films of calcia–alumina binary compounds

UV–visible optical spectra were obtained at room temperature in air for solution-processed thin films of 12CaO·7Al₂O₃(C12A7) on the MgO <100> single crystal substrates after the post-deposition heat treatment at 1,100 °C. Two absorption peaks were observed at 5.3 and 6.1 eV and their presence was attributed to the complex electronic structure of C12A7 and its different energy levels due to the extra-framework species and the framework itself. The peak at 5.3 eV is believed to be associated with O²⁻-Cage Conduction Band type transition whereas the Framework Valence Band to Framework Conduction Band transition is responsible for the peak at 6.1 eV. The nature of electronic transition was found to be direct from the analysis due to Tauc’s law.     

Anode-supported solid oxide fuel cell with electrophoretic deposition-derived electrolyte operated under single-chamber conditions and a methane–air mixture

In this study, samaria-doped ceria (Sm_0.2Ce_0.8O_1.9, SDC) thin film is deposited on the Ni-SDC support by employing the electrophoretic deposition technique. Various factors are considered for the deposition of SDC films. The corresponding microstructure of the deposited SDC film is examined and correlated to the electrochemical performance as a single-chamber solid oxide fuel cell (sc-SOFC). It is found that the microstructure of the SDC film mainly relates to the particle size of SDC. After heat treatment, highly dense SDC film is obtained with the deposition condition of 5 g L⁻¹ of the SDC suspension (average grain size of SDC, 248 nm), 60 V as the applied potential, and the deposition time of 1 min (18 μm in thickness). For the Ni-SDC/SDC/SSC cell, an open circuit potential of 0.92 V and peak power density of 155 mW cm⁻² can be obtained at the furnace temperature of 500 °C.