Optical and electrical properties of SnO2 films prepared by chemical vapour deposition

Transparent and conducting SnO₂ films are prepared at 500°C on quartz substrates by chemical vapour deposition technique, involving oxidation of SnCl₂. The effect of oxygen gas flow rate on the properties of SnO₂ films is reported. Oxygen with a flow rate from 0·8–1·35 lmin⁻¹ was used as both carrier and oxidizing gas. Electrical and optical properties are studied for 150 nm thick films. The films obtained have a resistivity between 1·72 × 10⁻³ and 4·95 × 10⁻³ ohm cm and the average transmission in the visible region ranges 86–90%. The performance of these films was checked and the maximum figure of merit value of 2·03 × 10⁻³ ohm⁻¹ was obtained with the films deposited at the flow rate of 1·16 lmin⁻¹.     

Growth and characterization of laser-deposited Ag-doped YBa2Cu3O7−x thin films on bare sapphire

Microstructural and superconducting properties of YBa₂Cu₃O_7−x thin films grownin situ on bare sapphire by pulsed laser deposition using YBa₂Cu₃O_7−x targets doped with 7 and 10 wt% Ag have been studied. Ag-doped films grown at 730°C on sapphire have shown very significant improvement over the undoped YBa₂Cu₃O_7−x films grown under identical condition. A zero resistance temperature of 90 K and a critical current density of 1·2×10⁶ A/cm² at 77 K have been achieved on bare sapphire for the first time. Improved connectivity among grains and reduced reaction rate between the substrate and the film caused due to Ag in the film are suggested to be responsible for this greatly improved transport properties.     

Electrochemical synthesis of Tl-based highT c single-phase superconductor thin films

Co-deposition of the Tl-based superconductors using electrodeposition technique was successfully carried out. Different processing parameters such as deposition potential, current density, deposition period etc were studied. The Tl-based alloyed thin films were deposited at a constant potential of −1·25V with respect to SCE electrode onto silver substrates and oxidized at 850°C in oxygen atmosphere. The samples thus prepared showed superconducting behaviour below 122·5 K and the critical current density was 1·5×10³A/cm². Electrochemical synthesis of Tl-based highT _c single-phase superconductor thin films is also reported.     

Preparation and characterization of indium oxide (In2O3) films by activated reactive evaporation

The electrical and optical properties of In₂O₃ films prepared at room temperature by activated reactive evaporation have been studied. Hall effect measurements at room temperature show that the films have a relatively high mobility 15 cm²v⁻¹s⁻¹, high carrier concentration 2·97 × 10²⁰/cm³, with a low resistivityρ = 1·35 × 10⁻³ ohm cm. As-prepared film is polycrystalline. It shows both direct and indirect allowed transitions with band gaps of 3·52eV and 2·94eV respectively.     

Studies on thick films of photoconducting cadmium sulphide

Highly photosensitive films of CdS have been prepared using the thick film technique. The films obtained from the composition containing CdS-100, CdCl₂−10 and CuCl₂−0·05 parts by weight (reacted at 500° C) are found to give the best photosensitivity on firing at 600° C. The ratio of light to dark current ∼10⁸–10⁹ which is considerably higher than what is reported for thin films, single crystals and sintered layers. A strong chemisorption of oxygen is found to be responsible for high photosensitivity. The spectral response for doped CdS film is similar to that obtained for thin films, single crystals and sintered layers and also shows a red shift with increasing Cu concentration. However, the undoped CdS has a broad spectral response at room temperature ranging fromλ=550 to 690 nm; unlike the thin films and single crystals which give a sharp peak atλ=510 to 520 nm. A probable explanation has been suggested for this type of behaviour. NCL Communication No. 2502.     

Physical Properties of AZ91D Measured Using the Draining Crucible Method: Effect of SF<Subscript>6</Subscript>

The draining crucible (DC) technique was used for measurements on AZ91D under Ar and SF₆. The DC technique is a new method developed to simultaneously measure the physical properties of fluids, the density, surface tension, and viscosity. Based on the relationship between the height of a metal in a crucible and the outgoing flow rate, a multi-variable regression is used to calculate the values of these fluid properties. Experiments performed with AZ91D at temperatures from 923 K to 1173 K indicate that under argon, the surface tension (N · m⁻¹) and density (kg · m⁻³) are [0.63 − 2.13 × 10⁻⁴ (T − T _L)] and [1656 − 0.158 (T − T _L)], respectively. The viscosity (Pa · s) has been determined to be [1.455 × 10⁻³ − 1.209 × 10⁻⁵ (T − T _L)] over the temperature range from 921 K to 967 K superheat. Above 967 K, the viscosity of the alloy under argon seems to be constant at (2.66 × 10⁻⁴ ± 8.67 × 10⁻⁵) Pa · s. SF₆ reduces the surface tension of AZ91D.     

Measurement of Gibbs energies of formation of CoF2 and MnF2 using a new composite dispersed solid electrolyte

Gibbs energies of formation of CoF₂ and MnF₂ have been measured in the temperature range from 700 to 1100 K using Al₂O₃-dispersed CaF₂ solid electrolyte and Ni+NiF₂ as the reference electrode. The dispersed solid electrolyte has higher conductivity than pure CaF₂ thus permitting accurate measurements at lower temperatures. However, to prevent reaction between Al₂O₃ in the solid electrolyte and NiF₂ (or CoF₂) at the electrode, the dispersed solid electrolyte was coated with pure CaF₂, thus creating a composite structure. The free energies of formation of CoF₂ and MnF₂ are (± 1700) J mol⁻¹; {fx37-1} The third law analysis gives the enthalpy of formation of solid CoF₂ as ΔH° (298·15 K) = −672·69 (± 0·1) kJ mol⁻¹, which compares with a value of −671·5 (± 4) kJ mol⁻¹ given in Janaf tables. For solid MnF₂, ΔH°(298·15 K) = − 854·97 (± 0·13) kJ mol⁻¹, which is significantly different from a value of −803·3 kJ mol⁻¹ given in the compilation by Barinet al.     

Thickness dependent electrical properties of CdO thin films prepared by spray pyrolysis method

A large number of thin films of cadmium oxide have been prepared on glass substrates by spray pyrolysis method. The prepared films have uniform thickness varying from 200–600 nm and good adherence to the glass substrate. A systematic study has been made on the influence of thickness on resistivity, sheet resistance, carrier concentration and mobility of the films. The resistivity, sheet resistance, carrier concentration and mobility values varied from 1·56–5·72×10⁻³ Ω-cm, 128–189 Ω/□, 1·6–3·9×10²¹ cm⁻³ and 0·3–3 cm²/Vs, respectively for varying film thicknesses. A systematic increase in mobility with grain size clearly indicates the reduction of overall scattering of charge carriers at the grain boundaries. The large concentration of charge carriers and low mobility values have been attributed to the presence of Cd as an impurity in CdO microcrystallites. Using the optical transmission data, the band gap was estimated and found to vary from 2·20–2·42 eV. These films have transmittance around 77% and average reflectance is below 2·6% in the spectral range 350–850 nm. The films aren-type and polycrystalline in nature. SEM micrographs of the CdO films were taken and the films exhibit clear grains and grain boundary formation at a substrate temperature as low as 523 K.     

Preparation, characterization and conductivity studies of Li3?2xAl2?xSbx(PO4)3

New NASICON type materials of composition, Li_3−2x Al_2−x Sb _x (PO₄)₃ (x = 0·6 to 1·4), have been prepared and characterized by powder XRD and IR. D.C. conductivities were measured in the temperature range 300–573 K by a two-probe method. Impedance studies were carried out in the frequency region 10²−10⁶ Hz as a function of temperature (300–573 K). An Arrhenius behaviour is observed for all compositions by d.c. conductivity and the Cole-Cole plots obtained from impedance data do not show any spikes on the lower frequency side indicating negligible electrode effects. A maximum conductivity of 4·5 × 10⁻⁶ S cm⁻¹ at 573 K was obtained for x = 0·8 of the Li_3−2x Al_2−x Sb _x (PO₄)₃ system.     

The orthobaric liquid and vapor densities of tetramethylsilane and of 2,2-dimethylpropane

The orthobaric densities of tetramethylsilane and 2,2-dimethylpropane have been measured by means of a hydrostatic density balance. For tetramethylsilane the liquid density has been determined from 289.73 K to the critical point 448.60 K and the vapor density from 353.55 K to the critical point, while for 2,2-dimethylpropane the liquid density has been measured from 290.88 K to the critical point 433.71 K and the vapor density from 349.01 K to the critical point. The results are represented well by the extended-scaling equation of Wegner with three correction terms and the critical indices α,β, andΔ ₁, obtained from renormalization-group theory. The fit is not improved by a term expressing an anomaly in the diameter using either of the exponents (1−α) or 2β. The critical density for tetramethylsilane is estimated as (0.2436±0.0001) g·cm⁻³ and that for 2,2-dimethylpropane as (0.2318±0.0001) g·cm⁻³.     

Sol–gel synthesis and electrical characterization of (Pb, Ca)TiO3 thin films

Calcium modified lead titanate films have been prepared on Pt/Ti/SiO₂/Si substrates using a sol–gel route. The sols were prepared from propanediol solutions of Pb(CH₃COO)₂·xH₂O, Ti(OC₃H₇)₂(CH₃COCHCOCH₃)₂ and Ca(NO₃)₂·xH₂O. Tetragonal phase (Pb, Ca)TiO3 films could be produced by firing the coatings at 650°C for 30 min. The limiting thickness of crack-free single layers was ∼0.4 μm, but 3 μm thick films could be made by a multiple deposition technique. Dielectric and ferroelectric parameters were determined for single layer 0.5 μm films for compositions up to 30 mol% Ca. The average values of remanent polarization, P_r and coercive field, E_c decreased with increasing Ca content from ∼11 μC cm⁻² and ∼125 Kv cm⁻¹ for a 10 mol% Ca composition to ∼8 μC cm⁻² and 80 kV cm⁻¹ for 30 mol% Ca films. It was noted that the statistical variation in electrical values across each film was greater than in PZT films made by a similar sol–gel route. Reasons for this are discussed in terms of the incidence of physical defects in the films. This revised version was published online in November 2006 with corrections to the Cover Date.     

Preparation of high dispersed nickel pastes for thick film electrodes

Ultra-thinning of Ni paste films for BME-MLCC (Base Metal Electrode Multilayered Ceramic Capacitor) internal electrode was investigated. Adding various dispersants, ball-milling powder, and using the pre-dispersion process to improve Ni paste dispersion and properties of the paste electrodes/thick films, were employed. The paste containing 200 nm sized Ni powders, ethyl cellulose vehicle (η = 2.98 × 10⁴ mPa-s at 0.1 s⁻¹), and Emphos PS-21A as a dispersant proved to be the most desirable candidate. This paste thick film showed the smallest surface roughness (R _a = 0.10 μm and R _max = 0.97 μm) at a viscosity (η = 2.80 × 10⁵ mPa-s at 0.1 s⁻¹) adaptable to screen-printing. In addition, the Ni paste/thick film had the low sheet resistivity (ρ = 1.11 × 10⁻⁴ Ωcm) and an excellent microstructure after sintering at 1,290 °C for 3 h in a 97% N₂/3% H₂ atmosphere.     

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.     

Thermophysical Property Measurements of Liquid Gadolinium by Containerless Methods

Thermophysical properties of liquid gadolinium were measured using non-contact diagnostic techniques with an electrostatic levitator. Over the 1585 K to 1920 K temperature range, the density can be expressed as ρ(T) = 7.41 × 10³ − 0.46 (T − T _m) (kg · m⁻³) where T _m = 1585 K, yielding a volume expansion coefficient of 6.2 × 10⁻⁵ K⁻¹. In addition, the surface tension data can be fitted as γ(T) = 8.22 × 10² − 0.097(T − T _m)(10⁻³ N · m⁻¹) over the 1613 K to 1803 K span and the viscosity as η(T) = 1.7exp[1.4 × 10⁴/(RT)](10⁻³ Pa · s) over the same temperature range.     

Curie temperatures and 0°K magnetic moments of zinc-substituted lithium ferrites

Because of their several attractive features including relatively high Curie temperatures, substituted lithium ferrites have become important for applications at microwave frequencies. Néel collinear arrangement of spins onA andB sublattices is unable to satisfactorily explain the 0°K saturation moments and the observed Curie temperatures of the zinc-substituted lithium ferrites, especially at concentrations of zincz>0·3 in the formula Li_0·5−z/2Zn_zFe_2·5−z/2O₄. Rosencaig’s localized canting model has been extended and used to compute 0°K magnetic moments and Curie temperatures of these ferrites with substitution levels up toz=0·7. Reasonably good agreement between the calculated and experimental values, both for the 0°K magnetic moments and the Curie temperatures, has been obtained using exchange parameters ratios based on the valuesJ _aa=−20°K,J _bb=−8°K andJ _ab=J _ba=−29°K.     

Superheating of YBa2Cu3O7−x thin-film microbridges

It is found that the hysteresis that develops with decreasing temperature in the current-voltage characteristics of thin-film YBa₂Cu₃O_7−x microbridges is due to superheating of the bridges by the transport current. The heat transport coefficient is determined to be α=5500–7500 V/(cm²·K) and the thermal resistance of the YBa₂Cu₃O_7−x /MgO film-substrate interface is R _if=(1.3–1.8)×10₋₄ (cm²·K)/W. Pis’ma Zh. Tekh. Fiz. 23, 56–62 (June 26, 1997)     

Thick-film nitrogen-monoxide sensors for analysis of the combustion products of organic fuels at heat-and-power plants

The method of metal-screen printing is used to obtain thick films of WO₃ that are highly selective to NO. The films are then used to make nitrogen monoxide sensors that can detect concentrations of (5–1000)·10⁻⁶ while operating at temperatures within the range 175–300°C. A prototype of a system for continuously monitoring NO in power-plant emissions has been designed and built. Translated from Izmeritel'naya Tekhnika, No. 1, pp. 34–36, January, 1997.     

Investigation on Phase Transitions and Thermodynamic Properties of 1-Dodecylamine Hydrochloride (C<Subscript>12</Subscript>H<Subscript>25</Subscript>NH<Subscript>3</Subscript>Cl)(s) by an Improved Adiabatic Calorimeter

1-Dodecylamine hydrochloride was synthesized by the solvent-thermal method. The structure and composition of the compound were characterized by chemical and elemental analyses, the X-ray powder diffraction technique, and X-ray crystallography. The main structure and performance of an improved automated adiabatic calorimeter are described. Low-temperature heat capacities of the title compound are measured by the new adiabatic calorimeter over the temperature range from 78 K to 397 K. Two solid-to-solid phase transitions have been observed at the peak temperatures of (330.78 ± 0.43) K and (345.09 ± 0.16) K. The molar enthalpies of the two phase transitions of the substance were determined to be (25.718 ± 0.082) kJ · mol⁻¹ and (5.049 ± 0.055) kJ · mol⁻¹, and their corresponding molar entropies were calculated as (77.752 ± 0.250) J · mol⁻¹ · K⁻¹ and (14.632 ± 0.159) J · mol⁻¹ · K⁻¹, respectively, based on the analysis of heat–capacity curves. Experimental values of heat capacities for the title compound have been fitted to two polynomial equations. In addition, two solid-to-solid phase transitions and a melting process of C₁₂H₂₅NH₃Cl(s) have been verified by differential scanning calorimetry.     

InGaAsp-i-n photodiodes for fibre-optic communication

High purity layers of In_{1 −x} Ga _x As have been grown by liquid phase epitaxy using a novel impurity gettering technique with rare earth atoms. The electron concentration could thus be decreased from 3 × 10¹⁸ cm⁻³ to 2·4 × 10¹⁵ cm⁻³ and the mobility increased from 7 110 cm²/Vs to 18,981 cm²/Vs (100 K). The excellent quality of the layers has been evidenced by X-ray diffraction and photoluminescence measurements. The fabrication ofp-i-n photodiodes using this technique is described and reliability aspects addressed.     

Effect of Melt Processing Programme on Microstructure and Properties of YBCO Thick Films

The screen printing technique was used in the fabrication of YBa₂Cu₃O_7−σ (YBCO) superconducting thick films on yttria stabilised zirconia (YSZ) substrates. Different slow cooling rates were used in the preparation of YBCO thick films after fast cooling from the melt processing temperature. The effects of the melt processing programme on texturing, microstructure and superconducting properties of the melt processed YBCO films were studied. Slow cooling rates between 1005 and 990 °C were effective in increasing the interaction of viscous molten with reduced film/substrate, and hence a relatively large grain size has been obtained. Moreover, different c-axis texturing ratios and grain morphologies were observed.