Synthesis of new sulphides of transition metal ions in presence of sun light

New sulphides of transition metal ions [M⁺ⁿ = Cu⁺¹, Cu⁺² and Zn⁺²] have been synthesised in sunlight. XRD patterns show that these compounds are not MxSy but are mercaptyl, hydroxyl metal sulphides [M(SH)(OH)(H₂O)₂] which is further ascertained by I.R. spectra showing bands due to T _d-symmetry. ESCA of compound of copper in solid state shows presence of Cu¹⁺ and Cu²⁺ ion. The presence of hydroxyl, mercaptyl, aqua and S^–2 groups has finally been confirmed with TGA, DTA and ESCA. Conductivity and Seebeck coefficient measurements show that compound of copper is p-type semiconductor and compound of zinc is n-type semiconductor. The production of these low cost materials opens an interesting area of research and development for their use in solar cell devices.     

An in situ TEM study of phase formation in gold-aluminum couples

In the gold wire bonding of aluminum in microelectronic devices the presence of aluminum oxide on the metallization surface may be expected. Electron transparent couples containing an oxide layer at the interface were heated in a TEM to determine the effects of a passivation layer on intermetallic formation. Intermetallic phases were evidenced by changes in sample appearance and their structure was determined by electron diffraction. The presence of an oxide at the interface hindered second phase formation at temperatures at which they were usually expected to form. In aluminum rich couples, the formation of the AuAl₂ intermetallic was not observed to form until about 350°C with the oxide present. In a reverse configuration involving a gold rich couple, an amorphous oxide phase was observed between the Al and the advancing Au₂Al front. The movement of the reaction front appeared to be controlled by surface diffusion across this phase.     

Characterization of optically active and photocurable ORMOSIL thin films deposited using the Aerosol process

Aerosol-gel process is a deposition method based on the sol-gel polymerization of a liquid film produced from an ultrasonically sprayed aerosol. This process offers an attractive alternative for the deposition of photocurable SiO₂—TiO₂ ORMOSIL films. 3-(trimethoxysilyl) propylmethacrylate and tetraisopropyl-orthotitanate complexed with methacrylic acid were used as sol-gel precursors. Doping with a terbium:sulphosalicylic acid complex was also studied to test the deposition of spectroscopically active photocurable films. FTIR spectroscopy has been used to study the precursor solutions and ORMOSIL films. It is shown that titanium precursor incorporation enhances the solution reactivity, which yields optical quality thin films. Photopolymerization and photoluminescence properties of the films are reported and discussed with respect to the experimental parameters. The results allow envisaging the UV-imprinting fabrication of Aerosol-gel-derived active waveguides.     

Negative thermal expansion of laminates

Measurements have been carried out on the in-plane and through the thickness thermal expansion coefficients of glass polypropylene fibre composites of 50% volume fraction between room temperature and 120°C. Only in the temperature range 20° to 75°C are reproducible results obtained. It is confirmed that in-plane negative values may be obtained in specific directions. The physical reason for this and its connection with the necessary appearance of a large Poisson ratio is pointed out. The expansivity of the matrix material depends strongly on temperature. Very good agreement between the experimental values and those predicted from the properties of the two constituents is found provided that the value for the expansivity of the polyoropylene is that within the temperature range considered. It is shown that the polypropylene matrix does not provide a matrix which is stable enough in its properties to enable the system to yield consistent negative values of expansivity. An alternative system is proposed and a single experiment confirms that a negative value of the thermal expansivity of as large as –50 × 10^–6 K^–1 may be obtained.