Light-assisted adsorption processes in nanocrystalline diamond membranes studied by femtosecond laser spectroscopy
Abstract
We report on femtosecond photoluminescence spectroscopy of nanocrystalline diamond membranes(thickness ∼1000 nm) prepared by microwave plasma enhanced chemical vapour deposition (CVD)technique. The decay of photoluminescence excited by the blue femtosecond light pulses (405 nm) reflects the photoexcited charge carrier dynamics in the sub-band gap energy states.
The photoluminescence is strongly influenced by ambient conditions and by the laser irradiation (405 nm, 70 fs pulses). Under lower ambient air pressure (5–300 Pa) the photoluminescence intensity increases and the photoluminescence decay gets faster.
For higher air pressures (N600 Pa) the photoluminescence intensity decreases and the photoluminescence decay rates do not evolve. We interpret the observed different behaviour of the photoluminescence in the two air pressure intervals in terms of a thin water layer condensed on the surface at higher air pressures.