Measurement of the thickness of the surface layer on amorphous Ge films using spectroscopic ellipsometry: validity of effective medium modeling

Amorphous Ge films prepared using rf-diode sputtering were exposed to air for periods from 15 min to several days. These samples were placed in a windowless cell in which an Ar gas flow was maintained and spectroscopic ellipsometry measurements were performed. The surface of each sample was then rinsed with deionized water and in situ measurements obtained. Differences were interpreted as resulting from partial or complete removal of the layer that formed from air exposure. Changes in the thickness of this layer were determined using (i) effective medium modeling and (ii) the exact equations of ellipsometry. Within the limits for each method, the thickness values are identical.