Wüest M. 51 Wykes M. 82 Yamaguchi M. 17 Ybarra G. 129 Yubero F ...

JUNE 26 MONDAY MORNING
ETCHC-MoM-OR.3 STUDY OF HYDROGEN AND OXYGEN UPTAKE IN SMART
OPTICAL WINDOWS BASED ON YPd AND MgNiPd THIN FILMS BY GDOES. E. Matveeva,
E.Rayon. Centro MTM, Universidad Politécnica de Valencia, Cami de Vera s/n, E-46022
Valencia Spain. R. Escobar Galindo, J.M. Albella. Departamento Física en Ingeniería de Superficies,
Instituto Ciencia de Materiales, Cantoblanco, E-28049 Madrid, Spain.
The use of smart optical windows based on YPd and MgNiPd thin coatings on transparent glass, has
been extensively studied in the last 15 years due to the possibilities of switching the optical and electrical
properties in a reversible and controlled way. The key of the switching process is based on the
absorption of hydrogen by the reflective metal, converting it to a transparent and semiconductor
metal hydride. In our case, the control of the hydration is carried out by an electrochemical process
in which the hydrogen ions are absorbed onto the metallic cathode. During the anodic discharge, the
hydrogen is released from the metal hydride towards the alkali electrolyte where other reactions may
take place (i.e. metal oxidation). These complex processes are localised in-depth the film thickness
(approximately 200 nm) and at the interfaces. Incontrollable oxidation of the active films during anodic
discharge depending on the position in the film of the oxide formed can block the hydrogen diffusion
process and reduce hydrogenation limiting the lifetime of the devices. Therefore, it is crucial
to have a detailed knowledge of the mechanisms of hydrogen and oxygen uptake and release in the
films. Most of the previous studies has been done by X-ray and infrared characterisation techniques,
but they do not provide depth profile information.
As an alternative, in this work, we have made use of the high elemental sensitivity and nanometre
depth resolution of radiofrequency Glow Discharge Optical Emission Spectroscopy (rf-GDOES) to
study the depth profiles of the elements present in the films. In particular, the hydrogen and oxygen
uptake and release was followed in samples subjected to different charge and discharge processes.
GDOES measurements were performed after each electrochemical experiment (charging and discharging),
whose kinetics was recorded,. The most representative observations of the GDOES results
were: i) The resolution of the layer structure of the film (5 nm Pd/metal layer/glass), ii) the detection
and monitoring of hydrogen migration in and out of the film during loading and release cycles and
iii) the revelation of the enhanced oxidation of the film after an anodic discharge. The relation of
these observations with the performance of the devices will be further discussed in this paper.
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