We have studied the secondary electron emission from chemical-vapor-deposited diamond films after etching the surface with an oxygen plasma. The etching not only removed hydrogen from the surface but also formed nano-sized diamond whiskers on the surface. As a result, the secondary electron ernission yield was halved. The trap of the secondary electrons by the porous medium was the reason for the decreased emission yield. The morphological effect to the secondary electron emission is discussed. (C) 2003 Elsevier Science B.V. All rights reserved.