Effect of moderate heating on the negative electron affinity and photoyield of air-exposed hydrogen-terminated chemical vapor deposited diamond

The effect of moderate heating (200-300 degreesC) in vacuum on the photoemi ssion from air-exposed hydrogen-terminated chemical vapor deposited diamond films was studied in the photon spectral range of 140-210 nm (8.9-5.9 eV). A three- to fivefold enhancement was observed, stable in high vacuum and i n some high purity gases, but unstable in air. The surfaces were also exami ned by x-ray induced photoelectron spectroscopy and ultraviolet induced pho toelectron spectroscopy before and after the heating process and upon expos ure to air and to oxygen. The results provide good evidence that the strong dipole originating from H2O molecules absorbed on the diamond surface is r esponsible for the observed effect. A simple model is presented for quantit ative estimation of the effect. (C) 2001 American Institute of Physics.