TEM sample preparation involved the immersion of a
piece of each film in a mixture of a resin and a hardener
(EpoFix, Struers, volume ratio 15:2) during 24 h at 60 C.
Before observation 60 nm-thick pieces of the embedded films
were cut at room temperature with an Ultramicrotome (Leica
EM UC7) equipped with a diamond knife.