Electrical d.c. conduction mechanism in some newly synthesized mono- and dipyridine quaternary salts in thin films

The study of temperature dependence of the electrical conductivity and thermoelectric power, for some recently synthesized quaternary salts of bipyridine and indolisine pyridine, is reported. Thin film samples (d = 0.10–0.60 μm) deposited from dimethylformamide solutions onto glass substrates were used. Organic films with reproducible electronic transport properties can be obtained if, after deposition, they are submitted to a heat treatment within temperature range 290–500 K.The studied organic salts behave as typical p-type semiconductors. The activation energy of electrical conduction laid in the range 1.40–1.75 eV, while the ratio of charge carrier mobilities ranged between 0.77 and 0.93.The correlations between determined semiconducting parameters and specific molecular structure of the compounds have been discussed.In the higher temperature range (360–500 K), the electronic transport in examined compounds can be interpreted in terms of band gap representation model, while for lower temperatures, Mott's variable-range hopping conduction model may be conveniently used.     

Investigation of electrical conductivity in Schottky-barrier devices based on nickel phthalocyanine thin films

Evaporated multilayer sandwich structure of Au/NiPc/Al was fabricated by thermal evaporation technique. The electrical conductivity of Au/NiPc/Al device has been measured both as prepared and after annealing at 623 K for 2 h. Under forward bias conditions, ohmic and SCLC conductions were identified at low and higher voltages respectively. After annealing, a strong rectifying effect was observed. The potential barrier height and the depletion region width for annealed sample were calculated as 0.96 eV and 70 nm, respectively. Hole and trap parameters for as prepared and after annealing devices, also, were evaluated.     

High deposition rates of uniform films in tetramethylsilane-based plasmas generated by elementary microwave sources in matrix configuration

Plasma scaling up can be achieved by distributing elementary microwave plasma sources on planar rectangular networks. These so-called matrix plasmas can generate uniform sheets of plasma over a wide argon pressure range, from 7.5 to 750 Pa, with densities between 10¹² and 10¹³ cm^− 3. In order to estimate the capabilities of matrix plasmas for PACVD processing in terms of deposition rate and uniformity, SiOCH and SiNCH films were deposited using TMS (tetramethylsilane), as the organic gas precursor of silicon, mixed with oxygen or nitrogen flows. Plasmas of O₂ / TMS and N₂ / TMS gas mixtures can be sustained between 5 and 25 Pa. Variations in the deposition rate as a function of microwave power and nitrogen partial pressure are reported. Thickness uniformity of SiOCH and SiNCH films was measured across a silicon wafer. The obtained deposition rates exceed 1.3 μm/min and the films present a uniformity better than 5% on 75 mm diameter silicon wafers. Composition of the films has also been analyzed by XPS as a function of process parameters: microwave input power, composition of gas mixture, and N₂ partial pressure. In particular, these analyses have shown a very low yield of nitrogen incorporation when using N₂ gas as nitrogen precursor and high Si and Si-Si bonding contents in the films, probably due to a strong fragmentation of the TMS precursor in the high density plasma.     

Solute segregation in an Al2O3f／Al-4.5Cu alloy composite during solidification at different cooling rates

An Al2O3f/Al-4.5Cu composite was made by squeeze casting. The solute segregation in the composite at different cooling rates was studied. The results indicate that the primary crystal of AI-4.5Cu alloy nucleates and grows in the interstice between fibers. The fiber surface cannot serve as site for the heterogeneous nucleation of a primary dendrite. There exists an increasing Cu concentration gradient from the center of the interstice between fibers to the interface or the grain boundaries. There are the eutectic phases around the fibers. The solute segregation in the matrix increases with the cooling rate rising. The amount of eutectic phases followed by imbalance crystalline can be numerically calculated with Clyne-Kurz formula.     

Transient and steady state crack growth kinetics for stress corrosion cracking of a cold worked 316L stainless steel in oxygenated pure water at different temperatures

The stress corrosion cracking (SCC) growth kinetics for a cold worked 316L stainless steel was continuously monitored in high purity water at different temperatures and dissolved oxygen (DO) levels under a K (or K_max) of 30 MPa m^0.5. The total SCC test time was more than 8000 h to make sure the steady state crack growth rate under each test condition could be reached. Crack growth rate (CGR) increases with increasing temperature in the range 110-288 °C. A typical intergranular-cracking mode is identified. Depending on the previous test condition, especially the temperature, three kinds of crack growth kinetics, i.e., increasing with testing time then becoming steady, being constant during the whole period, or decreasing with test time then becoming steady, are identified and discussed. Time-dependent and testing history-dependent crack growth modes were confirmed in two series of tests in 2 ppm DO and 7.5 ppm DO pure water. The apparent activation energies are calculated and compared with other data in different environments under different applied loading levels for understanding the cracking mechanism.