"Seeing is believing".
When a single-walled carbon nanotube is lying on a supporting film, usually made of amorphous carbon with a typical thickness 5 - 15 nm, what do we expect to see?
Aided with extensive image simulations, we concluded that the above situation should be avoided. The contrast due to the nanotube will be overwhelmed by the noise-like image produced the the overlapped carbon film.
L.-C. Qin, X. Zhao, K. Hirahara, Y. Ando and S. Iijima: Electron microscopic imaging and contrast of smallest carbon nanotubes, Chemical Physics Letters 349, 389 (2001).(PDF)