The effects of boron doping on the electron field emission properties of diamond films were examined using current image tunneling spectroscopy in atomic force microscopy (AFM). Tunneling current-voltage (I-t-V) characteristics measured by AFM indicate that incorporation of boron species induces the presence of the impurity state. The films doped with 3 sccm boron (B3) possess the smallest emission barrier (E-b = 1.65 eV) and the largest emission ratio (eta=38%) among the boron-doped diamond samples. Therefore, B3 diamond films can be turned on at the smallest electric field (E-0 = 8.8 V/mum), exhibiting largest field emission capacity (J(e) = 250 muA/cm(2)). Restated, the electron field emission behavior of diamond films is closely related to the formation of impurity states due to boron doping. (C) 2003 American Vacuum Society.