Enhancement of electron emission from near-coalescent nanometer thick continuous diamond films

In this study we report on the dependence of electron emission properties of undoped diamond films on film thickness. It was found that regardless of primary excitation, the electron emission exhibits maximum values for near-coalescent nanometer thick continuous diamond films. The electron emission induced by photons, ions, electrons and electric fields was consistently investigated and compared for diamond film thicknesses from 70 nm up to 4.7 μm.The absolute quantum photoyield (QPY) value at photon energy of 8.85 eV increases with film deposition time from 2.5% (carbonized silicon substrate) to 14% for a continuous 70 nm thick diamond film, followed by a decrease to 12% and stabilization for films of thicknesses above ∼150–200 nm. The initial coefficient of ion induced electron emission (IIEE), by 140 keV Ar+ ions, also reaches its maximum value of 116 at ∼100 nm diamond film thickness and decreases to 90–100 for thicker films. The secondary electron emission (SEE) shows maximum yield (δmax) at primary electron energy of ∼1000 eV. The dependence of δmax on film thickness displays similar behavior as QPY value: it obtains its maximum value of δmax ∼10 at film thickness of ∼100 nm and drops to somewhat constant value of δmax ∼6.6 for thicker films. The threshold field, required for field electron emission (FEE) current of 0.3 μA/cm2, reaches its minimum of ∼8.5 V/μm for ∼100 nm thick diamond film and monotonically increases for thicker diamond films.Possible reasons for the phenomenon of enhanced electron emission from the 70–100 nm thick diamond films have been discussed.