Structural, optical and electrical characterizations of Mg/Ti/Ni multilayer thin films deposited by DC magnetron sputtering for hydrogen storage

Abstract

Magnesium (Mg) based alloys are the most promising hydrogen storage and fuel cell alloys due to their high hydrogen content. In the present work, multilayer thin films (Mg/Ti/Ni) were prepared using direct current (DC) magnetron sputtering method. Multilayered Mg/Ti/Ni thin films were investigated by analyzing the data of different characterizations such as surface, structural, optical and electrical. Uniformity of the deposited thin films was analyzed by Field Emission Scanning Electron Microscope (FE-SEM) and Energy Dispersive Spectrometry (EDS) confirmed the presence of elemental composition. X-ray Diffractometer (XRD) was used to analyze structural characteristics of annealed thin films before and after hydrogenation. The variation in optical absorption and band gap has been observed, with the hydrogenation of thin film and having a larger band gap (3.27 eV) as compared to annealed thin films (2.81 eV). The semiconducting behavior of films is revealed by current voltage (I–V) characteristics of the films, and conductivity reduces after annealing and hydrogenation i.e. from 6.36 to 1.41 kΩ−1cm−1. Furthermore, Hall mobility of annealed without hydrogenated and annealed with hydrogenated thin film was improved (in the order of 103) as compared with as-deposited film. Improvement certainly helps the movement of hydrogen particularly after hydrogenation, the accumulation of hydrogen, particularly at the thin film's interface, obstructs the flow of electrons, resulting in a decrease in thin film conductivity. As a result, multilayer Mg/Ti/NI thin films are the good choice in the consideration for solid state hydrogen storage purpose.