Substrate materials used for growing diamond films were observed to modify thin films’ electron field emission properties significantly. Using heavily doped silicon (LR-Si) as a substrate lowered the turn-on field from(E0)Si=14.4 V/&mgr;mto(E0)LR-Si=9.7 V/&mgr;mand increased the emission current density from(Je)Si=4 &mgr;A/cm2to(Je)LR-Si=40 &mgr;A/cm2(at 16 V/&mgr;m). However, electron field emission properties can be further improved only by using Au precoatings to modify the characteristics of interfacial layer. The turn-on field was lowered further to(E0)Au–Si=8.7 V/&mgr;mand emission current density was increased further to(Je)Au–Si=400 &mgr;A/cm2(at 16 V/&mgr;m). Secondary ion mass spectroscopic examination indicated that the main interaction is the outward diffusion of Au species into amorphous carbon layer, lowering the resistivity of this interfacial layer. The electrons can therefore be transported easily from Si substrate across the interfacial layer to the diamonds and subsequently field emitted. ©1997 American Institute of Physics.