Absolute quantum photoyield of diamond thin films: Dependence on surface preparation and stability under ambient conditions

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Abstract
Absolute quantum photoyield (QPY) measurements (140–210 nm) of chemical vapor deposited (CVD) diamond films are reported. The dependence of the QPY on hydrogenation by exposure to a hydrogen microwave (MW) plasma and oxidation by a mixture of acids or on exposure to air under ambient conditions have been studied. Films deposited by MWCVD display a higher QPY than those grown by hot filament (HF) CVD. The QPY values are found to depend on the state of the surface. Hydrogen-terminated films 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, has no apparent effect on the photoemission properties. Exposure of the hydrogenated films to ambient conditions results in oxygen adsorption, leading to degradation of the photoemission properties. Analysis of the data within the three-step model of photoemission clearly shows that the state of the surface is a dominant factor determining the QPY.
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