Optical and Electronic Properties of Femtosecond Laser Treated Diamond

Polycrystalline diamond surfaces have been treated in a high vacuum chamber (10-7 mbar) by a femtosecond Ti:Sapphire pulsed laser source (?=800 nm, P=3 mJ, 100 fs), having selectable repetition rate in the range 1 Hz - 1 kHz. Laser beam has been focused perpendicularly to the diamond surface by a 30 cm plano-convex focal length lens and diamond target was moved by an automated X-Y translational stage along the two directions orthogonal to the optical axis. SEM micrographs of samples reveal a surface texturing consisting of ripples with a period of about 250 nm, shorter than the laser wavelength. Raman spectra of processed samples do not point out any evident presence of sp2 and diamond peak does not present any shift or FWHM widening. Surface treated diamond plates have been optically characterized in 190-2000 nm range with a spectrophotometer, showing a significant increase of visible and IR absorption (more than 80%) if compared to untreated specimens (less than 40%). I-V measurements have been performed between -100 V and 100 V, showing a current increase of 6 order of magnitude, from pA to µA range. Spectral photoconductivity measurements in the 190-1200 nm range denote an increase of the photocurrent as well as an enhancement of over-bandgap recombination sudden appear. Optical and electronic properties of femtosecond laser treated diamond will be further investigated and results will be presented: such properties, studied for the first time, will open the path for new application of CVD diamond in solar energy conversion and/or detection.