The H-terminated surface of diamond when activated with NO2 produces a surface conduction layer that has been used to make field effect transistors (FETs). Previous reports have suggested that during NO2 exposure (NO2-activation), NO2 − forms on the diamond surface and generates positive carriers (holes) in the diamond, making the diamond surface conductive. We report here on X-ray-photoelectron-spectroscopy (XPS) surface characterization of single crystal diamonds and on infrared absorption of diamond powder. After activation, XPS showed the presence of N atoms on the diamond surface, but infrared absorption found no evidence of NO2 −, but instead NO3 − is present on the diamond surface. Two wet chemistry techniques determined the concentration of NO3 − per milligram of diamond powder. With the powder's surface area measured by the BET technique, the surface NO3 − concentration was measured to be between 6.2 × 1013 and 8.2 × 1013 cm−2. This is in the same range as the carrier densities, 3 × 1013 to 9 × 1013 cm−2, determined by Hall mobility and surface conductivity measurements of single crystal diamonds. Using similar techniques, the concentration of NO2 − was determined to be <1012 cm−2. Both the surface conductance and the surface H atoms are stable in dry nitrogen, with or without NO2-activation, but the surface conductance, the concentrations of H atoms both with and without activation and NO3 − decrease when exposed to laboratory air over a period of hours to days. Infrared absorption measurements showed the reduction of surface NO3 − and H atoms during laboratory air exposure, but gave no indication of what reactions are responsible for their loss in laboratory air.
- Molecular adsorption
- Nitrogen dioxide
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Mechanical Engineering
- Materials Chemistry
- Electrical and Electronic Engineering