Films that can change their optical properties upon exposure to hydrogen offer a wide range of interesting applications. Frequently, the change of optical properties is related to a volume change, which can lead to considerable mechanical stresses causing property deterioration. In an effort to compare the behavior of different material classes that enable hydrogen induced switching, we have studied Mg, Gd, and WOx films. The measurements were carried out using a wafer curvature setup, which allows simultaneous measurements of the mechanical stress and the optical transmission and reflection of the coatings. The magnitude of the stress changes involved in the switching of these materials is found to vary significantly. Stress changes of several GPa are observed in the switching of Gd, while the switching of Mg involves stress changes of several hundreds of MPa. In the case of WOx stress changes of only the order of 100 MPa are found. Reversible switching has been found in the case of WOx. While Gd shows irreversible stress changes upon first switching, it shows reversible behavior upon subsequent switching processes. The Mg films show irreversible switching, and additionally, their durability is found to be hampered by oxidation, which is accelerated by stress induced defect formation in the films. (C) 2003 American Institute of Physics. References: 16
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