ABSOLUTE QUANTUM PHOTOYIELD OF DIAMOND THIN-FILMS - DEPENDENCE ON SURFACE PREPARATION AND STABILITY UNDER AMBIENT CONDITIONS

Absolute quantum photoyield (QPY) measurements (140-210 nm) of chemica l vapor deposited (CVD) diamond films are reported. The dependence of the QPY on hydrogenation by exposure to a hydrogen microwave (MW) plas ma and oxidation by a mixture of acids or on exposure to air under amb ient conditions have been studied. Films deposited by MWCVD display a higher QPY than those grown by hot filament (HF) CVD. The QPY values a re found to depend on the state of the surface. Hydrogen-terminated fi lms exhibit values above 12% at 140 nm, whereas even small amounts of oxygen strongly degrade the QPY. B-doping, at the level of 1500 ppm, h as no apparent effect oil the photoemission properties. Exposure of th e hydrogenated films to ambient conditions results in oxygen adsorptio n, leading to degradation of the photoemission properties. Analysis of the data within the three-step model of photoemission clearly shows t hat the state of the surface is a dominant factor determining the QPY. (C) 1998 American Institute of Physics. [S0003-6951(98)00536-1].