Optical properties of MgH2 measured in situ in a novel gas cell for ellipsometry/spectrophotometry

TL;DR

This study measures the optical properties of alpha-MgH2 in situ using a novel gas cell setup, revealing it as a transparent insulator with a band gap of 5.6 eV and confirming recent theoretical calculations.

Contribution

It introduces a new experimental setup for in situ optical measurements of MgH2 and provides empirical dielectric data supporting recent band structure theories.

Findings

Alpha-MgH2 is a transparent insulator with 80% transparency in visible spectrum.

The measured band gap of MgH2 is 5.6 eV.

Optical properties of PdHx thin films are also reported.

Abstract

The dielectric properties of alpha-MgH2 are investigated in the photon energy range between 1 and 6.5 eV. For this purpose, a novel sample configuration and experimental setup are developed that allow both optical transmission and ellipsometric measurements of a transparent thin film in equilibrium with hydrogen. We show that alpha-MgH2 is a transparent, colour neutral insulator with a band gap of 5.6 +/- 0.1 eV. It has an intrinsic transparency of about 80% over the whole visible spectrum. The dielectric function found in this work confirms very recent band structure calculations using the GW approximation by Alford and Chou [J.A. Alford and M.Y. Chou (unpublished)]. As Pd is used as a cap layer we report also the optical properties of PdHx thin films.