We report persistent photocurrent measurements of carbon nanotube networks with various pressures of hydrogen, ammonia and oxygen gases. The maximum build-up photocurrent drops substantially as the gas pressure is increased. However, the decay time is very sensitive to the gas species. While the decay time increases significantly under oxygen, only a modest increase is observed under H2 and NH3. The ab initio electronic structure calculations show that a physical adsorption of O2 molecules induces a shallow trap level within the band gap of the carbon nanotube, which is associated with an increase in the decay time.
- Carbon nanotubes