Effect of annealing and hydrogenation on optical and electrical properties of DC sputtered Mg-Ni bilayer thin films

Abstract

Mg-Ni (150 nm) bilayer thin films were effectively prepared using the magnetron co-sputtering techniqueonto the glass and ITOcoated glass substrates. In order to get homogeneity in the prepared thin film, annealing of the samples was made at 573 K for an one hour in the vacuum. Afterwards films were hydrogenated at 30 psi H2for one hour. The optical, electrical and structural properties of Mg-Ni thin film were studiedusingUV–visspectroscopy, Keithleyelectrometer, Hall Effect measurement and Field emission scanning electron microscopy(FESEM)along with energy dispersive Spectroscopy (EDS).The optical bandgap of as-deposited thin film was found 3.85 eV and after annealing it was decreased to 3.79 eV.Furthermore, bandgap increment has been observed for annealed hydrogenated thin films and it was 3.91 eV.The Hall Effect measurements and I-V characteristics of samples showthe semiconducting nature(n-type) of the filmsand the conductivity increases after annealing and decreases after hydrogenation of the annealed sample.Further, the Hall Effect measurements indicate increment in the Hall mobility of annealed thin films where as it is found to be decreased after hydrogenation of the annealed samples. FE-SEMimagesrepresent uniform deposition of thin film. The composition of elements was recorded through energy dispersive X-ray spectroscopy (EDAX).Accumulation of hydrogen, particularly at the thin film’s interface, blocks the flow of electrons that results in decreased conductivity of thin film after hydrogenation. Therefore, it may be concluded that Mg-NI thin films are suitable for solid state hydrogen storage.