Sorption properties of NO_2 gas and its strong influence on hole concentration of H-terminated diamond surfaces

摘要

The hole concentration of hydrogen-terminated diamond surfaces was studied during exposure to different concentrations of NO_2 gas. The hole concentration increased during adsorption of NO_2 molecules on the diamond surface, and decreased when the exposure stopped and NO_2 molecules desorbed from the surface. The increase in hole concentration can be directly linked to the NO_2 concentration. The low NO_2 concentration in air (～20 ppb) is responsible the hole concentration normally measured in air, and with increasing NO_2 concentration the maximum hole concentration increases even more. The time evolution of hole concentration was analyzed using the Elovich sorption model. Further analysis based on the Ritchie model indicated that an adsorbed NO_2 molecule occupies two different surface sites. Temperature-dependent measurements indicate low activation energy between 0.1 and 0.2 eV.