It has been reported that a sample prepared by ion beam milling has a sandwich structure with amorphous on two sidewalls and crystal in the middle. In this paper, the sandwich structure of such a single crystal TEM sample was studied experimentally. A novel sample and its fabrication process were reported. The sandwich structure can be observed directly in TEM with this sample. When the crystal layer in monocrystal silicon TEM sample is less than 18 nanometers, or when the sample is thinner than 64 nanometers, the sample will be observed as fully amorphous. Removal of the amorphous layer on the sample sidewalls is crucial to get TEM pictures of better quality.