M. Vashistha

Hydrogen in obliquely deposited LaNi5 thin films

Abstract During the last decade, thin film metal hydride has become an emerging field of research. The effect of hydrogen charging/discharging on the electrical resistance of obliquely deposited (θ=0°,30°,45°,60°,75°) LaNi _5 thin films of thickness 130±0.5 nm was investigated. It was found that the activation of LaNi_5 thin films for hydrogen absorption is fairly simple. The change in resistance due to hydrogen absorption increases with the angle of deposition and decreases with desorption of hydrogen. Thin films deposited at large angle absorb more hydrogen than low angle deposited LaNi_5 films. This is due to the structure variation in these thin films as a result of “self-shadowing effect”. Hydrogen absorption/desorption is also fast for films deposited at higher angles.

Electrical conductivity of ion irradiated Ge20Se80-xBix thin films

Abstract Amorphous chalcogenide semiconductor Ge20Se80−xBix thin films have been bombarded with 75 MeV Ni ions at room temperature. The ion irradiation induced effects on the electronic properties have been monitored by DC conductivity measurements over a temperature range of 77– 476 K . The electrical conductivity and conduction activation energy changes on irradiation.

Kinetics of hydrogen absorption in obliquely deposited MmNi4.5Al0.5 thin films

Abstract MmNi4.5Al0.5 thin films of thickness about 1050 A were obliquely deposited at 3×10−5 torr pressure by thermal evaporation on to a glass substrate at room temperature. The resistance of the films deposited at different angles increases with the absorption of hydrogen and decreases with desorption. The resistance of the samples also increases with the angle of deposition. The change in resistance value is taken as a measure of the amount of hydrogen absorbed in the samples. It is observed that the amount of hydrogen absorbed increases with the deposition angle which is due to an increase in the porosity of thin films.

Kinetics and the thermal decomposition of Sodium Alanate in the presence of MmNi4.5Al0.5 nanoparticles

Sodium Alanate (NaAlH4) is a promising hydrogen storage material due to its high hydrogen content (7.6 wt% of H2), and relatively moderate dehydrogenation and rehydrogenation temperatures. The addition of an appropriate catalyst to NaAlH4 results in a reversible release of 5.5 wt% H2 in a low temperature range of about 90 to 150 °C. Catalyst nano particles of MmNi4.5Al0.5 (henceforth referred to as Mm) to NaAlH4 were added by mechanical ball milling (BM) in mass ratios of 100:5, 100:10, and 100:20, respectively. Thermal decomposition studies were performed at various temperatures (90–150 °C) and a significant improvement in the dehydrogenation was observed after the addition of Mm to the NaAlH4. Un-doped ball milled NaAlH4 released 1.55 wt% of H2 at 150 °C in 60 min, and Mm added NaAlH4 released 3.10–3.25 wt% of H2 were released, respectively. Kinetics analysis was done by using model fit, model free fitting and the obtained activation energy values for both have shown good agreement and the possible decomposition mechanism in all samples by nucleation-growth-saturation mechanism. The improved thermodynamics and kinetics can be attributed to the uniform dispersion and catalytic effect of the Mm nanoparticles, and also to the effect of ball milling.

Effect of a sulphur layer on obliquely deposited titanium thin films for a hydrogen absorption mechanism

Abstract Titanium thin films of about 1050 A thickness were obliquely deposited at a pressure of 5 × 10 −5 torr by thermal evaporation on to a glass substrate at room temperature. The resistance of the films deposited at different angles ( θ = 0°, 30°, 45°, 60°, 75°) and absorption of hydrogen increases with the angle of deposition. The change in resistance value is taken as a measure of the amount of hydrogen absorbed in the samples. It is observed that the amount of hydrogen absorbed increases with deposition angle which is due to an increase in the porosity of thin films. The sulphur layer (thickness 160 A) deposited on the titanium thin film was found to produce a marked improvement in the properties of thin film for hydrogen storage and charging rate becomes faster in comparison to titanium thin films.