Diamond films with different grain morphologies were prepared in order to compare their field electron emission properties. For the diamond films with well-oriented grains, the field electron emission properties are enhanced when the grain shape changes from flat to flattened pyramid and then to pyramid due to the increase in the field enhancement factors. Compared with the well-oriented diamond films, the diamond film with randomly oriented grains exhibits larger emission current due, to the increase in the effective emission area. For the diamond film with cauliflowerlike grains, the nanotip structures improve the electron emission properties significantly through an increase in both the field enhancement factor and the effective emission area. (c) 2006 American Vacuum Society.