Nanowires or porous films grown on a substrate normally lack mechanical strength, and may be subject to damage during specimen preparation. When we made cross-sectional TEM specimen for this type of sample, we modified the traditional method by covering the sample with epoxy to improve the film strength, and applying single-section ion milling to protect the film from over-milling.
The sample surface is first covered with G1 epoxy. We choose G1 for this application because it is relatively thick and cures at low temperature. For samples with a dense-growth of nanowires or a thick porous film, a brief moment in vacuum helps to get rid of the air bubbles in the epoxy. The glue is cured at 100 degree C for 10 minutes, until its color turns to a reddish brown. To remove the excess glue and flatten the surface, the sample is then ground and polished until the glue is less than 0.1 mm thick.