Chemically Amplified Dehydration of Thin Oxide Films
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Abstract
The hydrous material Al(PO<sub>4</sub>)<sub>0.6</sub>O<sub>0.6</sub>·<i>z</i>H<sub>2</sub>O (AlPO) is studied in thin-film
form to determine whether bulk diffusion or near-surface densification
controls thermal dehydration. From X-ray reflectivity measurements,
a dense surface crust is found to form on heating AlPO films. Capacitance–voltage
measurements reveal the presence of mobile protons associated with
trapped −OH and H<sub>2</sub>O in the films. Deposition of
a thin solution-processed HfO<sub>2</sub> top coat on the AlPO film
lowers the dehydration temperature by 250 °C. Characterization
of the AlPO/HfO<sub>2</sub> interface by medium energy ion scattering
and transmission electron microscopy reveals little interdiffusion
between the layers. The top coat affects densification of the near-surface
region of the AlPO film, thereby amplifying water loss at low temperatures
