Thermal expansion of doped lanthanum gallates

Thermal expansion of several compositions of Sr and Mg-doped LaGaO3 including an A-site deficient composition (La0.9Sr0.1)(0.98)(Ga0.8Mg0.2)O-2.821 were measured in the temperature range from 298 to 1273 K. The effect of doping on thermal expansion was studied by varying the composition at one site of the perovskite structure (either A or B), while keeping the composition at the other site invariant. Thermal expansion varied nonlinearly with temperature and exhibited an inflexion between 550 and 620 K, probably related to the change in crystal structure from orthorhombic to rhombohedral. The dependence of average thermal expansion coefficient (alpha (av)) on the dopant concentration on either A or B site of the perovskite structure was found to be linear, when the composition at the other site was kept constant. Mg doping on the B-site had a greater effect on the average thermal expansion coefficient than Sr doping on the A-site. Cation deficiency at the A-site decreases thermal expansion when compositions at both sites are held constant.

Study of stress Relief Patterns In Diamond-Like Carbon-Films

An optical microscopy study of stress relief patterns in diamondlike carbon films is presented. Interesting stress relief patterns are observed which include the well known sinusoidal type, branching pattern and string of beads pattern. The last one is shown to relieve stresses under marginal conditions. Two new stress relief patterns are noted in the present study. One of them is of a sinusoidal shape with two extra branches at every peak position. The distribution of different stress relief forms from the outer edge of the films towards the interior is markedly dependent on film thickness. Our new patterns support the approach in which the stress relief forms have been analysed earlier using the theory of plate buckling.

Optical properties of activated reactive evaporated TiO2 films

This paper discusses the optical properties of single-layer TiO2 films deposited using an activated reactive evaporation process. The combined effects of substrate temperature (in the range 70–200 °C) and discharge currents (0–400 mA) on refractive index, extinction coefficient and packing density of these films are investigated. Significant changes in refractive index values have been observed with increases in substrate temperature and discharge current. The change in refractive index is correlated with the variation in packing density. The variation in extinction coefficient was reduced using the combined effects of substrate temperature and discharge currents. A comparison with films deposited in neutral oxygen has also been made.

Magnetic properties of pure, Sr- and Ca-Doped La2NiO4+δ ceramics: Onset of high-Tc superconductivity

We present the results for the temperature and field dependence of the magnetic for ceramic materials of the composition La2−xMxNiO4, with M=Sr or Ca and 0≤x≤0.4. The onset of a strong diamagnetism has been observed at temperatures between 8 and 70 K, depending on sample composition, annealing conditions. and thermal cycling procedures. The results are similar to those obtained earlier for monocrystalline samples and are likewise interpreted as due to the onset of superconductivity in a minority phase. A comparison with the results for superconducting La1.8Sr0.2Cu0.9Ni0.1O4 ceramics is also made; this illustrates some unique features of the nickelate systems, such as the high values of the critical fields Hc1 and Hc2. The differences between monocrystalline and ceramic systems are also discussed.

A Photoelectron Spectroscopic Study Of The Interaction Of Oxygen, Nitrogen And Transition-Metals With C-60 Films

Evidence is presented for the strong interaction of oxygen and nitrogen with solid films of buckminsterfullerene based on core-level spectroscopic studies. Cr, Ni and Cu deposited on C60 films interact strongly giving rise to large changes in the C(Is) and C(2p) binding energies as well as the (2p) binding energies of the transition metals.

Formation of Single-Phase Indium Selenide Thin Films by Elemental Evaporation

Formation of crystalline, monophasic indium selenide (InSe) thin solid films by elemental evaporation on hot glass substrates (400 to 530 K) is reported. The compound formation as well as the composition of the formed films are confirmed by X-ray photoelectron spectroscopy (XPS) analysis. The crystallinity of the rhombohedral InSe films can be improved by post-depositional annealing for t < 30 min at 533 K. The InSe thin films become Se-deficient at higher temperatures of deposition or longer duration of annealing. Optical studies reveal the bandgap to be around 1.29 eV. Under optimum conditions of preparations the lowest resistivity of ≈ 12.8 Ω cm is obtained. Durch Verdampfen aus den Elementen auf heiße Glassubstrate (400 bis 530 k) werden dünne, kristalline, einphasige Indiumselenid (InSe)-Festkörperschichten gebildet. Sowohl die Bildung der Verbindung als auch die Zusammensetzung der Schichten werden durch Röntgen-Photoelektronenspektroskopie (XPS) untersucht. Die Kristallinität der rhomboedrischen InSe-Schichten kann durch eine Temperung bei 533 K für t < 30 min nach der Abscheidung verbessert werden. Die dünnen InSe-Schichten zeigen nach Abscheidung bei höheren Temperaturen oder längerer Temperungsdauer einen Se-Unterschuß. Optische Untersuchungen ergeben, daß die Bandlücke bei etwa 1,29 eV liegt. Unter optimalen Präperationsbedingungen wird ein niedrigster Widerstand von ≈ 12.8 Ω cm erreicht.

Electronic states in a disordered metal: Magnetotransport in doped germanium

We observe a sharp feature in the ultra-low-temperature magnetoconductivity of degenerately doped Ge:Sb at H∼25 kOe, which is robust up to at least three times the critical density for the insulator-metal transition. This field corresponds to a low-energy scale characteristic of the special nature of antimony donors in germanium. Its presence and sensitivity to uniaxial stress confirm the notion of metallic impurity bands in doped germanium.

dc reactive magnetron sputtering of titanium‐structural and optical characterization of TiO2 films

This paper deals with the reactive sputtering of titanium in an argon and oxygen mixture. The variation in cathode potential as a function of oxygen partial pressure has been explained in terms of cathode poisoning effects. The titania films deposited during this process have been studied for their structural and optical characteristics. The effect of substrate temperature (from 25 to 400 °C) and annealing (from 250 to 700 °C) on the packing density, refractive index, extinction coefficient, and crystallinity has been investigated. The refractive index varied from 2.24 to 2.46 and extinction coefficient from 2.6 × 10-3 to 10.4× 10-3 at 500 nm as the substrate temperature increased from 25 to 400 °C. The refractive index increased from 2.19 to 2.35 and extinction coefficient changed from 3.2× 10-3 to 11.6 × 10-3 at 500 nm as the annealing temperature was increased from 250 to 700 °C. Anatase and rutile phases have been observed in the films deposited at 400 °C substrate temperature and annealed at 300 °C. The changes in the optical constants at higher substrate temperature have been attributed to an increase in packing density, oxygen content, and crystallinity of the films.

Dynamics of freely suspended films with surface tension

We have studied the hydrodynamics of freely suspended membranes, liquid as well as crystalline, with surface tension. We find that nonlinear coupling to thermally excited undulations gives a singular contribution to the kinetic coefficients of these systems at low frequency and wavenumber. Our results differ in some important respects from those of Katz and Lebedev on this problem, and can be tested in mechanical impedance as well as time-correlation studies.

Effect of substrate temperature on the properties of ZrO2 films prepared by d.c. reactive magnetron sputtering

Studies of ZrO2 films prepared by d.c. reactive magnetron sputtering are described. The effects of substrate temperature on the packing density, refractive index, extinction coefficient and crystallinity phase have been investigated in the temperature range 25–450 °C. The refractive index varied from 1.84 to 1.95 and extinction coefficient from 2 × 10−3 to 9.6 × 10−3. This was explained on the basis of an increase in packing density from 0.686 to 0.813. The change in packing density has been attributed to a decrease in the oxygen condensation at higher temperatures. Annealing results in a decrease in refractive index and increase in extinction coefficient. The films deposited at 150 °C showed a monoclinic phase which transforms to a tetragonal phase at higher substrate temperatures.

AC impedance spectroscopic characterization of 10 mol% MgO doped ZnO varistors

The performance parameters e.g. non-linear coefficient (α) and breakdown electric field (Eb1mA/cm2) of ZnO based ceramic varistors were found to improve after the addition of 10 mol% MgO. The improvement in the varistor properties is examined by ac impedance spectroscopy technique in the frequency range (1 Hz–10 MHz) between temperature 25–250°C and understood in terms of differing contributions from the equivalent electrical circuit elements.

Effect of Substrate and Annealing Temperatures on Mechanical Properties of Ti-rich NiTi Films

The effect of substrate and annealing temperatures on mechanical properties of Ti-rich NiTi films deposited on Si (100) substrates by DC magnetron sputtering was studied by nanoindentation. NiTi films were deposited at two substrate temperatures viz. 300 and 400 degrees C. NiTi films deposited at 300 degrees C were annealed for 4 h at four different temperatures, i.e. 300, 400, 500 and 600 degrees C whereas films deposited at 400 degrees C were annealed for 4 h at three different temperatures, i.e. 400, 500 and 600 degrees C. The elastic modulus and hardness of the films were found to be the same in the as-deposited as well as annealed conditions for both substrate temperatures. For a given substrate temperature, the hardness and elastic modulus were found to remain unchanged as long as the films were amorphous. However, both elastic modulus and hardness showed an increase with increasing annealing temperature as the films become crystalline. The results were explained on the basis of the change in microstructure of the film with change in annealing temperature.

Comparison of the effect of processing parameters and degradation on the DC and microwave properties of thin films and polycrystalline bulk high-Tc superconducting materials

The sharp increase in microwave power loss (the reverse of what has previously been reported) at the transition temperature in high-Tc superconducting systems such as YBaCu oxide (polycrystalline bulk and thin films obtained by the laser ablation technique) and BiPbSrCaCu oxide is reported. The differences between DC resistivity ( rho ) and the microwave power loss (related to microwave surface resistance) are analysed from the data obtained by a simultaneous measurement set-up. The influence of various parameters, such as preparation conditions, thickness and aging of the sample and the probing frequency (6-18 GHz), on the variation of microwave power loss with temperature is outlined.

Effects of thermal annealing on the properties of zirconia films prepared by ion-assisted deposition

The effect of thermal annealing in the range 300–800 °C on the properties of zirconia films prepared by ion assisted deposition was studied. It was found that at low temperature the cubic phase is formed. This phase is stable up to 700 °C. All the films exhibit a monophasic monoclinic structure at 800 °C. The stress, estimated from X-ray patterns, shows a transition from tensile to compressive with increasing ion fluence. The refractive index and extinction coefficient do not seem to change appreciably up to 700 °C, showing a marked degradation thereafter. Single step annealing to the highest temperature was found to result in better stability than multistep annealing.