The dielectric functions and optical band gaps of thin films of amorphous and cubic crystalline Mg~2NiH~4

• Published in: Thin solid films 2012-09, Vol.520 (22), p.6786-6792
• Main Authors: Selj, J.H., Mongstad, T., Hauback, B.C., Karazhanov, S.Zh
• Format: Article
• Language: English
• Subjects: Band gap estimation; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Crystallinity; Dielectric thin films; Dielectrics, piezoelectrics, and ferroelectrics and their properties; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Ellipsometry; Exact sciences and technology; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Magnesium nickel hydride; Metal hydride; Optical instruments, equipment and techniques; Optical properties; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of specific thin films; Physics; Polarimeters and ellipsometers; Structural properties; Surface double layers, schottky barriers, and work functions; Thin film
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2012.07.044

Magnesium nickel hydride films have earlier been suggested for several optoelectronic applications, but the optical properties and band gap have not been firmly established. In this work, the dielectric functions and the optical band gaps of thin films of Mg2NiH4 have been determined experimentally from optical modeling using spectroscopic ellipsometry and spectrophotometry in the photon energy range between 0.7 and 4.2eV. Samples were prepared by reactive sputtering, resulting in a single-layer geometry that could easily be studied by ellipsometry. Crystalline samples were prepared by annealing the as-deposited amorphous films ex-situ. The resulting films remained in the high temperature cubic Mg2NiH4 structure even after cooling to room temperature. Tauc analysis of the dielectric functions shows that Mg2NiH4 films exhibit a band gap of 1.6eV for the amorphous structure and 2.1eV for the cubic crystalline structure. ► Ellipsometry and spectrophotometry is applied to study thin films of Mg2NiH4. ► Amorphous and crystalline films have been characterized. ► Band gaps: 1.6eV for amorphous, 2.1eV for cubic crystalline Mg2NiH4.