Pd distribution of switchable mirrors based on Mg–Y alloy thin films

• Mg–Y switchable mirror with Pd corresponding to a 3 nm thickness was covered with oxides of Mg and Y.
• The Pd and Mg–Y layers interdiffused and alloyed, and Pd-rich layer appeared between the surface oxide and the Mg–Y layers.
• With increasing deposition time of Pd, Pd was formed on the oxide layer and the Pd layer thickness increased.
• The mirror with switching durability of over 10,000 cycles had a sufficiently thick Pd top layer.

Pd-capped magnesium–yttrium alloy switchable mirrors were found to have high switching durability of over 10,000 cycles between reflective and transparent states. However, the durability decreased with the decreasing Pd thickness. Switchable mirrors with various Pd thicknesses were then prepared by a direct-current magnetron sputtering method, and the degradation in durability was studied by observing the distribution of each element of the switchable mirrors from the film surface to the substrate. X-ray photoemission spectroscopy and transmission electron microscopy showed that Pd with a short sputtering time (corresponding to layer thickness of 3 nm) resulted in surface oxidation of Mg and Y, and no Pd was present at the surface. The deposited Pd was alloyed with the Mg–Y layer and after taking the sample out from the vacuum chamber a Pd-rich layer appeared between the surface oxides and the Mg–Y layers. With increasing deposition time, a Pd layer was formed on the oxide layer and the Pd layer thickness increased. The mirror with switching durability of over 10,000 cycles had a sufficiently thick Pd top layer of ~7 nm and a very thin oxide layer. This thick Pd layer is believed to be the reason for the high switching durability.