Ashim Kumar Chakraborty

Galvanostatic deposition and electrical characterization of cuprous oxide thin films

Abstract Semiconducting cuprous oxide (Cu 2 O) thin films, important for low cost solar cell and oxygen or humidity sensor applications, were galvanostatically deposited at 40–60 °C on copper substrates. The deposition kinetics, studied up to a film thickness of about 20 μm, was found to be linear and independent of deposition temperature. The observed film growth rate was in excellent agreement with the growth rates predicted from Faradays law of electrolysis. The deposited films exhibited a preferred (200) orientation. The current-voltage characteristics of the electrodeposited Cu 2 O/Cu diodes exhibited a metal-insulator-semiconductor type of behaviour, suggesting the presence of a thin interfacial insulating layer between Cu 2 O and copper. The electrical conductivity of Cu 2 O films was found to vary exponentially with temperature in the 145–300°C range with an associated activation energy of 0.79 eV.

The synthesis, characterization and sintering of sol-gel derived cordierite ceramics for electronic applications

Cordierite ceramics were synthesized by sol-gel processing using alkoxides and acetate with an aim to use the material as substrate and packaging material. Preparation conditions were optimized by varying the amount and pH of water added and the amount of acetic acid as chelating agent. The powders were characterized by different analytical techniques such as thermogravimetric analysis, differential thermal analysis, surface area by BET, X-ray diffraction, transmission and scanning electron microscopies and infrared spectroscopy. The best product was obtained using 19.6 mol water and 0.34 mol acetic acid with respect to silicon ethoxide. The pH of the water added did not make any significant difference. Sintered materials were characterized by measuring different physical properties such as density, electrical and dielectric properties, thermal expansion, microstructure and composition. Well-sintered bodies could be achieved at 1000 °C in air with a soaking time of 2 h having a density of ∼ 99% theoretical, electrical resistivity of ∼1014 Ωcm, dielectric constant of 5, dielectric loss ∼0.008 and thermal expansion coefficient of 28.5 × 10−7 °C−1, 25–200 °C. X-ray diffraction studies show the phase evolution in these materials is predominantly μ-cordierite (hexagonal high cordierite) and some β-quartz. SEM reveals a uniformly dense microstructure with crystals of granular habit. X-ray photoelectron spectroscopy indicates that the surface composition of the sintered material is slightly enriched with aluminium and deficient in silicon.

X-ray photoelectron spectroscopic studies of conducting polyaniline, poly bisphenol A carbonate and electrochemically synthesized composite of the two

Abstract X-ray photoelectron studies of electrochemically prepared conducting polyaniline (PAN), polycarbonate (PC) and PAN/PC composite films have been studied. The core level spectra of carbon, oxygen, nitrogen and chlorine have been synthesized using Gaussian distribution functions. The analysis of the first two elements indicates the presence of carbonyl group on the surface of PAN samples. The detailed analysis of nitrogen and chlorine spectra show the presence of NCI bonding apart from usual covalent peaks. No major structural modification in the composite film could be detected. Only the presence of covalent chlorine derived from chloroform used to prepare these films have been observed. From the measurement of electrical conductivity of these films it seems that it is the proportion of ionic chlorine, rather than covalent chlorine to nitrogen that is important in determining the conductivities.