S.K. Sen

The kinetics of formation of intermetallics in Ag/In thin film couples

Abstract Silver and indium bimetallic thin film couples have been studied by monitoring the contact and composite electrical resistance behaviour with time for both as-deposited and annealed specimens. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies have also been performed on the samples. Silver reacts with indium at room temperature with the formation of e-AgIn 2 phase, which is diffusion controlled, the activation energy being about 0.43 eV in the temperature range 318–401 K. The activation energy of grain boundary diffusion as determined from contact electrical resistance measurements is about 0.34 eV. Both XRD and TEM indicate the growth of e phase, which gradually transforms to δ-Ag 2 In phase for silver-rich films. Indium diffusion through silver grain boundaries has been observed by SEM. A tentative explanation of the first phase formation is proposed.

The formation of intermetallics in Cu/In thin films

The kinetics of the formation of intermetallics in the Cu–In bimetallic thin film couple have been studied from room temperature to 432 K by measuring the evolution of composite and contact electrical resistance with time and temperature. The resistivity measurements have been supplemented by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Copper reacts with indium even at room temperature to form CuIn intermetallic and assuming a model of defect assisted diffusion into the grains, the activation energy averaged over five different samples is found to be 0.40 eV. The grain boundary diffusion is found to occur with an average activation energy of 0.55 eV. XRD confirms the growth of CuIn intermetallic and on annealing at higher temperature, for copper-rich films copper further reacts with CuIn to form Cu 9 In 4 . Further evidences of solid state reactions and grain boundary diffusion through Cu grain boundaries have been obtained from SEM study. TEM indicates the growth of the grain size on annealing and confirms the presence of the CuIn phase.

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.

Interfacial reactions in bimetallic Ag-Sn thin film couples

Abstract Interfacial reactions in bimetallic Ag-Sn thin film couples have been investigated by measurement of electrical resistance and contact resistance as a function of time and temperature in order to understand kinetic behaviour in the above system where the intermetallic phase γ-Ag3Sn is formed. Since the reaction is found to start at room temperature, the conventional vacuum coating unit has been modified for preparing such films and conducting subsequent measurements without breaking the vacuum. The results from the above different methods of resistance measurement indicate that interfacial reactions are characterized by a mean diffusion coefficient of 10-13 cm2 s-1 at room temperature. X-ray diffraction indicates growth of the γ-Ag3Sn phase immediately after deposition. Scanning electron microscopy confirms the diffusion of tin into silver by grain boundary diffusion rather than by bulk diffusion. The results from transmission electron microscopy confirm the presence of a γ-Ag3Sn phase.

An X-Ray Line Broadening Analysis in the Vacuum-Evaporated Silver Films

An X-ray integral breadth analysis has been made for the 111, 200, 220, 311 and 222 diffraction profiles recorded on a Geiger counter X-ray diffractometer from the vacuum-evaporated thin films of silver in the range of thickness 580 to 2125 A. The analysis based on the methods of single and multiple order of reflection has yielded values for the effective particle sizes and non-uniform micro-strains in the films from a consideration of Gaussian, Cauchy and intermediate parabolic form of distribution, the Gaussian distribution being more favourable. The effective particle size values are found to be small and the strains quite appreciable and these effects which are the manifestations of lattice imperfections present in the films decrease very slowly with increasing film thickness. The dislocation density ρ calculated for the [111] direction from the particle size and strain values for the films above 1000 A thick is of the order of 10 11 cm/cm 3 comparable to that observed for the heavily deformed bulk ma...

An X-ray line profile analysis in vacuum-evaporated silver films

An X-ray Fourier line profile analysis from multiple-order and single-order reflections has been performed considering 111, 200, 220, 311 and 222 reflections recorded in a counter X-ray diffractometer from eight vapour-deposited thin films in the range of thickness 58-212 nm. Detailed analysis of line shift, line asymmetry and Fourier line shapes measurements have been found to yield large concentrations of growth twin stacking faults only in the thin film range with a total absence of intrinsic and extrinsic ones for the entire range. Measurements of the domain size, dislocation density, RMS strains and orientation factors were made, and their dependence on the film thickness investigated.

Particle fracture and plastic deformation in vanadium pentoxide powders induced by high energy vibrational ball-mill

An X-ray powder profile analysis in vanadium pentoxide powder milled in a high energy vibrational ball-mill for different lengths of time (0–250 h), is presented. The strain and size induced broadening of the Bragg reflection for two different crystallographic directions ([001] and [100]) was determined by Warren-Averbach analysis using a pattern-decomposition method assuming a Pseudo-Voigt function. The deformation process caused a decrease in the crystallite size and a saturation of crystallite size of ∼ 10 nm was reached after severe milling. The initial stages of milling indicated a propensity of size-broadening due to fracture of the powder particles caused by repeated ball-to-powder impact whereas with increasing milling time microstrain broadening was predominant. WA analysis indicated significant plastic strain along with spatial confinement of the internal strain fields in the crystallite interfaces. Significant strain anisotropy was noticed in the different crystallographic directions. A near-isotropy in the crystallite size value was noticed for materials milled for 200 h and beyond. The column-length distribution function obtained from the size Fourier coefficients progressively narrowed down with the milling time.

Electrical, dielectric and optical properties of M/Y2O3/M devices

Abstract Thin film capacitors of metal/yttrium oxide/metal sandwich structure have been prepared by the e-beam flash evaporation technique. The surface morphology of the films has been studied using scanning electron microscopy. The current-voltage characteristics at various temperatures showed that the conduction mechanism is of Schottky type. This has been further confirmed by comparing the values of field-lowering coefficient β obtained from I–V characteristics and capacitance measurements and changing the counterelectrode material. It has also been shown that the capacitance and dielectric constant are almost independent of frequency in the range 20–120 kHz. The height of the Schottky barrier is evaluated as 0.46 eV. The optical absorption coefficient α and refractive index n1 of Y2O3 film are evaluated in the wavelength region of 300–800 nm from analyses of the reflectance and transmittance spectra by an approach which eliminates the interference effect. The refractive index has been found to be 1.53 at a wavelength of 700 nm. Two indirect transitions with band gaps of 2.19 and 2.80 eV respectively have been identified from an analysis of the absorption spectra.

Calorimetric and other studies of intermetallic phase formation in Ag/Al bilayer thin films

Silver and aluminium bimetallic thin film couples have been studied using constant heating rate differential scanning calorimetry both on cleaned glass substrates and freshly cleaved NaCl crystals. The most striking feature was the occurrence of two maxima in the reaction rate during the formation of a single product phase, Ag2Al, suggesting a two-step growth process. The activation energy for this reaction was 0.98 eV in the first step and 0.93 eV in the second step. These values are in good agreement with values obtained by a different technique, i.e. Rutherford back-scattering. Transmission electron microscopy, thin film X-ray diffraction, the change in resistance of bilayer films with temperature and thermodynamic and kinetic analyses have been used to investigate the intermetallic phase formation. It was observed that substrate plays an important role in the kinetics of thin-film reaction.

Electrically conducting polyaniline and polyaniline/polycarbonate composite films: Preparation, characterization and electrical conductivity measurements

Polyanilinc (PAN) films and composites of polyaniline with poly bisphenol A carbonate (PC) have been prepared electrochemically. The electrical conductivity measured from room temperature down to 77 K is larger in air than in vacuum and obeys a ID variable range hopping (VRH) mechanism. From DTA analysis of the composite film, an extra peak at 210 °C apart from the usual peaks of PC and PAN has been identified. It is believed to be the result of a chemical interaction between PAN and PC, that is further confirmed from the shift in the carbonyl peak in the FTIR spectra of the composite films. From XPS studies and electrical conductivity measurements of different films it seems that it is the proportion of ionic chlorine rather than covalent chlorine to nitrogen that is more important in determining the conductivity. SEM pictures clearly indicate the formation of a fibrilar network in the composite film, especially inside the craters seen on the surface.