The hole channel of hydrogen (H)-terminated diamond surface can be linked to adsorption of a specific gas species on the surface. O
3, NO
2, NO, and SO
2 were identified as adsorbates, which induce holes on the H-terminated diamond surface. During NO
2 adsorption, hole sheet concentration, p
s, saturated at a certain value, however, in the NO
2 gas concentration range of>300 ppm, the values were the same. Therefore we determined that the high limit of p
s is∼9×10
13 cm
−2, which is 5.7% of the surface C-H bonds for (001) orientation. X-ray photoelectron spectroscopy investigation showed upward band bending and partial oxidation but no C-N bonds of the H-terminated surface after exposure to air and NO
2. We propose a NO
2 adsorption/desorption and hole-doping model to explain these experimental results.
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