Preparation of microwave dielectric,Sn<Subscript>0.2</Subscript>Zr<Subscript>0.8</Subscript>TiO<Subscript>4</Subscript>

A simple coprecipitation technique is described for the preparation of tin substituted zirconium titanate ceramic powders.     

ZrO2 as a high-K dielectric for strained SiGe MOS devices

The potential of ZrO₂ thin film as a high-K gate dielectric for scaled MOSFET devices has been studied. ZrO₂ has been deposited directly on a Si_0.8Ge_0.2 substrate by reactive RF magnetron sputtering. An equivalent oxide thickness of < 20 Å with a leakage current of the order of 10^-4 A/cm² at 1 V has been obtained. Well-behaved capacitance-voltage characteristics with an interface state density of 2 × 10¹¹ cm^-2eV^-1 have been achieved. The deposited dielectric exhibits low charge trapping under constant current stressing.     

Ethanol gas sensing properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped ZnO thick film resistors

The characterization and ethanol gas sensing properties of pure and doped ZnO thick films were investigated. Thick films of pure zinc oxide were prepared by the screen printing technique. Pure zinc oxide was almost insensitive to ethanol. Thick films of Al₂O₃ (1 wt%) doped ZnO were observed to be highly sensitive to ethanol vapours at 300°C. Aluminium oxide grains dispersed around ZnO grains would result into the barrier height among the grains. Upon exposure of ethanol vapours, the barrier height would decrease greatly leading to drastic increase in conductance. It is reported that the surface misfits, calcination temperature and operating temperature can affect the microstructure and gas sensing performance of the sensor. The efforts are, therefore, made to create surface misfits by doping Al₂O₃ into zinc oxide and to study the sensing performance. The quick response and fast recovery are the main features of this sensor. The effects of microstructure and additive concentration on the gas response, selectivity, response time and recovery time of the sensor in the presence of ethanol vapours were studied and discussed.     

Enhanced Superconducting Properties of Air-Processed GdBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7-δ</Subscript> Single Domains with BaCO<Subscript>3</Subscript>/BaCuO<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript> Addition

Single domain GdBa₂Cu_7-δ (Gd123) bulk superconductors were fabricated in air by top-seeding melt-texture growth. Performance of the air-processed Gd123 was successfully enhanced by addition of both BaCO₃ and BaCuO_2−x , which suppress the formation of Gd_1+x Ba_2−x Cu₃O_7-δ solid solutions. The optimum doping amount ranges from 0.05 to 0.15, M BaCO₃ and 0.05 to 0.1, M BaCuO_2−x per molar Gd123. The distribution of the second phase particles was observed by scanning electron microscopy. A narrow band formed by Gd₂BaCuO₅ particle concentration appeared around the seeding zone in both a–b plane and c-growth sector in Gd123 single grain. Trapped magnetic field density reached 0.67, T for sample with 24 mm in diameter and 8, mm in thickness and a high critical current density J _c up to 91,200, A/cm² was achieved at 77, K under self-field.     

Microstructure and electrical properties of Al2O3-ZrO2 composite films for gate dielectric applications

Al₂O₃-ZrO₂ composite films were fabricated on Si by ultrahigh vacuum electron-beam coevaporation. The crystallization temperature, surface morphology, structural characteristics and electrical properties of the annealed films are investigated. Our results indicate that the amorphous and mixed structure is maintained up to an annealing temperature of 900 °C, which is much higher than that of pure ZrO₂ film, and the interfacial oxide layer thickness does not increase after annealing at 900 °C. However, a portion of the Al₂O₃-ZrO₂ film becomes polycrystalline after 1000 °C annealing and interfacial broadening is observed. Possible explanations are given to explain our observations. A dielectric constant of 20.1 is calculated from the 900 °C-annealed ZrO₂-Al₂O₃ film based on high-frequency capacitance-voltage measurements. This dielectric characteristic shows an equivalent oxide thickness (EOT) as low as 1.94 nm. An extremely low leakage current density of ∼2×10⁻⁷ A/cm² at a gate voltage of 1 V and low interface state density are also observed in the dielectric film.     

Thermodynamic and Magnetic Properties of Superconductors with Anisotropic Energy Spectrum,MgB<Subscript>2</Subscript>

The behavior of the superconducting transition temperature T _c and that of the jump of electron heat capacity (C _S −C _N )/C _N of the compound MgB₂ at T=T _c with substitution of boron and magnesium atoms by other atoms from the periodic table of the elements, corresponding to introduction of additional electrons or holes in this compound are researched. The microscopic superconductivity theory in MgB₂ systems in the magnetic field parallel to the crystallographic axis (H ‖ c) is built. The magnitude of the upper critical field H _c2 is determined and its temperature dependence in two-band systems with different and identical topologies of Fermi surface cavities of the corresponding bands is studied. The obtained results and their comparisons with the experimental data demonstrate that all kinds of anomalies of the physical properties of the compound MgB₂ are effectively described by the two-band model.     

Compatibility of RuO<Subscript>2</Subscript> electrodes with PZT ceramics

Because of its high electrical conductivity and good diffusion barrier properties ruthenium dioxide (RuO₂) is a good electrode material for use with ferroelectric lead zirconate-titanate (PZT) solid solutions. Under certain conditions, RuO₂ can react with PZT to form lead ruthenate (Pb₂Ru₂O_6·5) during processing at elevated temperatures resulting in lead depletion from PZT. The standard Gibbs energies of formation of RuO₂ and Pb₂Ru₂O_6·5 and activities of components of the PZT solid solution have been determined recently. Using this data along with older thermodynamic information on PbZrO₃ and PbTiO₃, the stability domain of Pb₂Ru₂O_6·5 is computed as a function of PZT composition, temperature and oxygen partial pressure in the gas phase. The results show PbZrO₃-rich compositions are more prone to react with RuO₂ at all temperatures. Increasing temperature and decreasing oxygen partial pressure suppress the reaction. Graphically displayed are the reaction zones as a function of oxygen partial pressure and PZT composition at temperatures 973,1173 and 1373 K.     

Synthesis,characterization and application of semiconducting oxide (Cu<Subscript>2</Subscript>O and ZnO) nanostructures

In the present study, we report the synthesis, characterization and application of nanostructured oxide materials. The oxide materials (Cu₂O and ZnO) have been synthesized by electrolysis based oxidation and thermal oxidation methods. Cuprous oxide (Cu₂O) nanostructures have been synthesized by anodic oxidation of copper through a simple electrolysis process employing plain water (with ionic conductivity, ～6 μS/m) as electrolyte. In this method no special electrolytes, chemicals and surfactants are needed. The method is based on anodization pursuant to the simple electrolysis of water at different voltages. Two different types of Cu₂O nanostructures have been found. One type got delaminated from copper anode and was collected from the bottom of the electrochemical cell and the other was located on the copper anode itself. The nanostructures collected from the bottom of the cell are either nanothreads embodying beads of different diameters, ～ 10–40 nm or nanowires (length, ～ 600–1000 nm and diameter, ～ 10–25 nm). Those present on the copper anode were nanoblocks with preponderance of nanocubes (nanocube edge, ～ 400 nm). The copper electrode served as a sacrificial anode for the synthesis of different nanostructures. Aligned ZnO nanorod array has been successfully synthesized by simple thermal evaporation catalyst free method. Detailed structural characterizations revealed that the as synthesized aligned ZnO nanorods are single crystalline, with a hexagonal phase, and with growth along the [0001] direction. The room-temperature photoluminescence spectra showed a weak ultraviolet emission at 380 nm, a broad blue band at 435 nm and a strong orange-red emission at 630 nm. Structural/microstructural characterization of these nanomaterials have been carried out employing scanning (XL-20) and transmission electron microscopic (Philips EM, CM-12 and Technai 20G²) techniques and X-ray diffraction techniques having graphite monochromater with CuKα radiation (λ =1.54439 Å) (X’Pert PRO PAN analytical). The UV-visible absorption spectra were recorded on Model-VARIAN, Cary 100, and Bio UV-visible spectrophotometer. The photoluminescence (PL) measurement was carried out at room temperature with a He-Cd, a laser excited at 325 nm.     

Li-storage and cycling properties of spinel,CdFe<Subscript>2</Subscript>O<Subscript>4</Subscript>, as an anode for lithium ion batteries

Cadmium ferrite, CdFe₂O₄, is synthesized by urea combustion method followed by calcination at 900°C and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) techniques. The Li-storage and cycling behaviour are examined by galvanostatic cycling, cyclic voltammetry (CV) and impedance spectroscopy in the voltage range, 0·005–3·0 V vs Li at room temperature. CdFe₂O₄ shows a first cycle reversible capacity of 870 (± 10) mAhg⁻¹ at 0·07C-rate, but the capacity degrades at 4 mAhg⁻¹ per cycle and retains only 680 (± 10) mAhg⁻¹ after 50 cycles. Heat-treated electrode of CdFe₂O₄ (300°C; 12 h, Ar) shows a significantly improved cycling performance under the above cycling conditions and a stable capacity of 810 (± 10) mAhg⁻¹ corresponding to 8·7 moles of Li per mole of CdFe₂O₄ (vs theoretical, 9·0 moles of Li) is maintained up to 60 cycles, with a coulombic efficiency, 96–98%. Rate capability of heat-treated CdFe₂O₄ is also good: reversible capacities of 650 (± 10) and 450 (± 10) mAhg⁻¹ at 0·5 C and 1·4 C (1 C = 840 mAg⁻¹) are observed, respectively. The reasons for the improved cycling performance are discussed. From the CV data in 2–15 cycles, the average discharge potential is measured to be ∼0·9 V, whereas the charge potential is ∼2·1 V. Based on the galvanostatic and CV data, ex situ-XRD, -TEM and -SAED studies, a reaction mechanism is proposed. The impedance parameters as a function of voltage during the 1st cycle have been evaluated and interpreted. Dedicated to Prof. C N R Rao on his 75th birthday, and his contributions to science for the past 56 years     

Nano Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Induced Fluxoid Jumps and Low Field Enhanced Critical Current Density in MgB<Subscript>2</Subscript> Superconductor

Nano particle of Fe₃O₄ (nFe₃O₄) up to 6 at% were doped in the superconducting MgB₂ samples. Despite the strong ferromagnetic nature of Fe₃O₄, both the ac susceptibility and the resistivity measurements show that up to 4 at% of Fe₃O₄, T _c =38 K is not changed, whereas for 6% T _c decreases by 6 K. This indicates that a low concentration of Fe does not substitute either the Mg or B sites and probably occupies the intergrain spaces. For 0.5% doped Fe₃O₄, an increase in J _c with respect to the pure MgB₂ samples is observed in the lower field and temperature regions (H<2 T and 20 K) indicating an enhanced flux pinning and the magnetic activation, i.e., the interaction between the magnetic dipole of Fe ion and the vortices is weak in comparison to the effective pinning potential. Whereas, at H>2 T, J _c of the doped samples is always less than that of MgB₂, and the activation is dominant in comparison with the effective pinning potential provided by the doping. Flux jumps are observed in lower T and H regions for the samples doped up to 1% nFe₃O₄ only. Magnetization plots of higher Fe content samples exhibited clear paramagnetic background. Mossbauer measurements for the higher (4, 6 at%) nFe₃O₄ doped MgB₂ samples show that at RT, the hyperfine field for both samples is ∼100 kOe and ∼120 kOe at 90 K. This means that the nFe₃O₄ particles decompose and form possibly an intermetallic Fe-B phase in the matrix.     

Synthesis of SrCrO<Subscript>4</Subscript> nanostructures by onion inner-coat template and their optical properties

This paper describes a bio-template method of the squama inner coat of onion for preparing the SrCrO₄ nanostructures including nanospheres, nanorods and dumbbell-shaped superstructure. The method is able to make SrCrO₄ nanoparticles with average diameters in the range of 90–170 nm, SrCrO₄ nanorods with length in the range 0·70–2 μm, width in the range of 80–180 nm, and SrCrO₄ dumbbell-shaped superstructure with length in the range 10–14 μm. The dumbbell-shaped superstructures are assembled by many SrCrO₄ nanowires with length in the range 10–14 μm and width in the range 30–50 nm. The products were characterized by transmission electron microscope, powder X-ray diffraction, UV-Vis spectroscopy and luminescence spectrophotometer. A possible formation mechanism was also proposed. In the preparation, the SrCrO₄ nanostructures were synthesized at room temperature without any surfactants. This new bio-template method will have potential applications in preparation of the nanoscale materials with different morphologies.     

Synthesis and characterization of monoclinic rare earth titanates,RE<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> (RE = La,Pr, Nd), by a modified SHS method using inorganic activator

The nano particles of phase pure rare earth titanates, synthesized by the SHS technique, get well sintered at lower temperatures compared to the compounds formed by the solid-state method. These dielectrics are highly stable and can be used in the microwave frequency range. We report here a modified SHS method to synthesize phase pure monoclinic RE₂Ti₂O₇ at 350°C through the oxide/nitrate precursors using an inorganic compound, ammonium acetate, in place of the general type of organic activators such as urea, alanine etc. The nanopowders of La₂Ti₂O₇, Pr₂Ti₂O₇ and Nd₂Ti₂O₇ on heating exhibit an exothermic behaviour with a broad maxima in the range 267–284°C and become endothermic with maxima in the range 1043–1220°C; interestingly, the phase pure crystalline material is formed at the temperature of exothermic maxima, as confirmed by XRD.     

On the synthesis,characterization and photocatalytic applications of nanostructured TiO<Subscript>2</Subscript>

Nanocrystalline semiconducting materials are attracting much attention due to their potential applications in solar energy conversion, nonlinear optics, and heterogeneous photocatalysis. In the present investigation, we have synthesized nanostructured TiO₂ photocatalysts, which have been used in the photocatalytic degradation of phenol (one of the most common water pollutants). These catalysts have been prepared through sol-gel technique using titanium tetra-isopropoxide as a raw material for synthesis. Characterization techniques such as XRD, SEM and TEM have been employed for structural/microstructural investigations. XRD results show that the as synthesized TiO₂ nanopowder exhibit anatase phase, TiO₂. The average sizes of the TiO₂ nanopowders are ∼ 5–10 nm. The optical properties of the samples were investigated through UV-visible and fluorescence techniques. It has been observed that absorption edge corresponds to ∼ 410 nm (bandgap, ∼ 3.02 eV). The emission peak in the fluorescence spectrum at ∼ 418 nm corresponds to the bandgap energy of ∼ 2.97 eV. Concentration of phenol (initial concentration, ∼ 100 ppm) with illumination time was monitored by measuring the absorbance of pure and illuminated phenol through UV-visible spectrophotometer. Salient feature of this study relates to the fact that the present sol-gel synthesized TiO₂ nanopowders have been found to be better photocatalysts for phenol degradation than the presently employed commercial TiO₂ (P-25, Degussa) photocatalyst. Thus, whereas phenol concentration, with the presently synthesized TiO₂ nanopowders, the concentration of phenol decreases up to ∼ 32% but for commercial TiO₂ nanopowder (P-25, Degussa), it decreased only up to ∼ 25%. The improved surface area is considered as an important factor for the aforesaid decrease in phenol concentration.     

Interplay of Superconductivity and Ferromagnetism in UGe<Subscript>2</Subscript>

The emergence of pressure induced superconductivity (SC) under the background of ferromagnetic state in 5f-electron based itinerant ferromagnetic superconductor UGe₂ is studied in the single band model by using a mean-field approximation. The solutions to the coupled equations of superconducting gap (Δ) and magnetization (m) are obtained using Green’s function technique and equation of motion method. It is shown that there generally exists a coexistent (Δ≠0, m≠0) solution to the coupled equations of the order parameters in the temperature range 0<T<min (T _C,T _FM), where T _C and T _FM are respectively the superconducting and ferromagnetic transition temperatures. The study of electronic specific heat (C/T), density of states, free energy, etc. are also presented. The specific heat capacity at low temperature shows linear temperature dependence as opposed to the activated behavior. Density of states increases as opposed to the case of a standard ferromagnetic metal. Free energy study reveals that the superconducting ferromagnetic state has lower energy than the normal ferromagnetic state and, therefore, realized at low enough temperature. The agreement between theory and experimental results for UGe₂ is quite satisfactory.      

Characterization and photocatalytic activity of boron-doped TiO<Subscript>2</Subscript> thin films prepared by liquid phase deposition technique

Boron doped TiO₂ thin films have been successfully deposited on glass substrate and silicon wafer at 30°C from an aqueous solution of ammonium hexa-fluoro titanate and boron trifluoride by liquid phase deposition technique. The boric acid was used as an F ⁻ scavenger. The resultant films were characterized by XRD, EDAX, UV and microstructures by SEM. The result shows the deposited film to be amorphous which becomes crystalline between 400 and 500°C. The EDAX and XRD data confirm the existence of boron atom in TiO₂ matrix and a small peak corresponding to rutile phase was also found. Boron doped TiO₂ thin films can be used as photocatalyst for the photodegradation of chlorobenzene which is a great environmental hazard. It was found that chlorobenzene undergoes degradation efficiently in presence of boron doped TiO₂ thin films by exposing its aqueous solution to visible light. The photocatalytic activity increases with increase in the concentration of boron.     

Growth characteristics and electrical properties of La2O3 gate oxides grown by thermal and plasma-enhanced atomic layer deposition

We comparatively investigated thermal and plasma-enhanced atomic layer deposition (T-ALD and PE-ALD, respectively) of lanthanium oxide (La₂O₃) films using tris(isopropyl-cyclopentadienyl)lanthanum [La(iPrCp)₃] as a La precursor. H₂O and O₂ plasma were used as reactants for T-ALD and PE-ALD La₂O₃, respectively. Both of the processes exhibited ALD mode growth with good self-saturation behavior and produced pure La₂O₃ films. However, PE-ALD La₂O₃ showed higher growth rate and dielectric constant value than those of T-ALD La₂O₃. In addition, lower leakage current density and interface state density were observed for PE-ALD La₂O₃, compared to those of the T-ALD La₂O₃. These experimental results indicate that the PE-ALD La₂O₃ process using La(iPrCp)₃ precursor can be one of the viable options applicable into future microelectronic industry.     

Scrubbing of particulate-laden-SO<Subscript>2</Subscript> in a hybrid column

In this article, the performance of a two-stage hybrid (spray-cum-bubble) column on the scrubbing of particulate-laden-SO₂ using water and dilute NaOH is reported. The present system deals with a tapered section in order to achieve the bubble regime. On the other hand, a two-phase critical flow atomizer is used for generating finer drops with high degree of spray uniformity. Detailed experimentation revealed that SO₂ removal was enhanced due to presence of particles (fly ash). Almost 100% SO₂ removal was achieved in water scrubbing. The increase in the enhancement factor of SO₂ absorption in alkaline scrubbing did not follow theoretical linear relationship with the concentration ratio after reaching a value that corresponded to the ∼100% SO₂ removal efficiency. The presence of fly ash particles improved the removal efficiency of hybrid scrubber to about 11% within the range of variables studied. Unique empirical and semi-empirical correlations were developed for predicting the scrubbing performances of the stage-wise hybrid column in water and dilute NaOH respectively. Predicted data were in excellent agreement with the experimental values. The performance of the hybrid column was also compared with the existing systems and very encouraging results were observed.     

Effect of oxygen intercalation on properties of sputtered CuYO<Subscript>2</Subscript> for potential use as <Emphasis Type="Italic">p</Emphasis>-type transparent conducting films

Transparent films of copper yttrium oxide doped with 2% calcium have been prepared by rf magnetron sputtering. The films show a conductivity of 8 Scm⁻¹ on intercalation of oxygen at high pressure, which reduced the transparency in the visible region. The Ca-doped CuYO₂ films before oxygen intercalation show an average transmission of about 60% which reduces to about 45% upon oxygen intercalation. The temperature dependence of the conductivity indicates semiconductor behaviour with low activation energy of 0·59 eV at room temperature. The positive sign of Seebeck coefficient (+274 μVK⁻¹) confirms the p-type conductivity of the films. The optical bandgap of CuYO₂ was found to be 3·15 eV.     

Structural and plasmonic characteristics of sputtered SnO<Subscript>2</Subscript>:Sb and ZnO:Al thin films as a function of their thickness

Heavily doped metal oxide semiconductors are being developed as thin film transparent electrodes for many applications and their deposition at low substrate temperature can extend the use on heat sensitive devices. The structural and electro-optical characteristics of such metal oxide coatings are tightly related and depend on the specific deposition parameters apart from the material composition. In this work, SnO₂:Sb (ATO) and ZnO:Al (AZO) thin films have been prepared by sputtering at room temperature on glass substrates, changing the deposition time to obtain various layer thicknesses from 0.2 to 0.9 μm; and they have been analyzed by X-ray diffraction, spectrophotometry, and Hall-effect measurements. ATO samples crystallize in the tetragonal structure with mean crystallite size increasing from 8 to 20 nm when the film thickness grows. The comparison of Hall mobility and optical mobility values indicates a significant contribution of grain boundary scattering for these ATO layers. Otherwise, AZO films show larger crystallites (21–27 nm) and a strong preferential orientation for analogous thickness increment, resulting in a lower contribution of the grain boundary scattering to the overall Hall mobility. The in-grain mobility for each sample is also related to the respective crystallite size and carrier concentration values.     

CrO<Subscript>2</Subscript>/Ag/YBCO Interface Study with a Flip-Chip Configuration

Transport across a CrC₂/Ag/YBCO interface was studied using a flip-chip configuration. The results were interpreted in the Andreev reflection scenario. It is shown that the surface spinpolarization of CrO₂ film, even after exposing to air, remained close to 100% to theT _c of YBa₂Cu₃O_7−x , a temperature limited by this method.