Novel geometry for simultaneous resistive, Hall and optical measurement of MgH$_{x}$ thin films

We describe a novel specimen geometry we have used to simultaneously probe optical transmission, sheet resistance and sheet Hall resistance in 100nm Mg films during hydrogen absorption. A Mg-film cloverleaf overlaps four rectangular Pd pads at the corners of a glass slide, a variation on a two-pad geometry used by Ingason and Olafsson for resistive studies of Pd-capped MgH$_{x}$ films [J. Alloys and Compounds \textbf{404- 406} (2005), 469-72.]. Hydrogen diffuses laterally through the Pd pads before entering the magnesium layer from below. The sample holder also includes an LED-photodiode pair for measuring [monochromatic] optical transmission. We show that the simultaneous measurement of these three quantities during the metal-to-insulator transition in a hydriding MgH$_{x}$ film allows for a more complete understanding of the hydriding process in these films.