Its good you can see few scattered CDs because CDs are too small and tedious to view under TEM.

It needs lot of patience to search in each part of the grid. Tips to take care in sample preparation is to dispersed CDs well – for dispersion use sonication or vortexing and using very small amount of CDs. (Thin sample). If still having a problem, try image using AFM.

Anithadevi Sekar thanks for your answer, I always use the ultra sound in dispersing my sample and I obtain the same images. However, most of the published work regarding this point post images with high number of carbon dots in every photo.