Diamond films and islands grown by chemical vapor deposition were implanted with boron, sodium, and carbon ions at doses of 1014–1015/cm2. This structural modification at the subsurface resulted in a significant reduction of the electric field required for electron emission. The threshold field for producing a current density of 10 mA/cm2can be as low as 42 V/&mgr;m for the as‐implanted diamond compared to 164 V/&mgr;m for the high qualityp‐type diamond. When the ion‐implanted samples were annealed at high temperatures in order to anneal out the implantation‐induced defects, the low‐field electron emission capability of diamond disappeared. These results further confirm our earlier findings about the role of defects in the electron emission from undoped orp‐type doped diamond and indicate that the improved emission characteristics of as‐implanted diamond is due to the defects created by the ion implantation process. ©1995 American Institute of Physics.