<title>Comparative study of deposition of thin films by laser-induced PVD with femtosecond and nanosecond laser pulses</title>

Abstract

The influence of temporal pulse length on laser induced PVD of diamond-like carbon (DLC) as well as Si and Cu films is investigated, using 30 ns and 500 fs UV laser pulses of 248 nm. For the case of the DLC films the laser generated plasma is analyzed by time of flight (TOF) and also by optical emission spectroscopy. The TOF measurements of ablated carbon particles exhibit striking differences between nanosecond and femtosecond laser irradiation. In the case of 30 ns ablation, cluster formation is quite evident in the TOF mass spectra, which coincides with the observation of micron-sized particulates on the deposited DLC films. No evidence for cluster formation is found in the TOF spectra obtained from the femtosecond plasma. The corresponding optical emission spectra indicate a high contribution of C<SUP>+</SUP>, rather than C<SUB>2</SUB>, and larger molecules in the nanosecond case. In addition, much higher kinetic particle energies (in the keV range) have been measured, which are known to be favorable with respect to DLC film formation. Consequently, high optical quality DLC films without particulates can be grown by femtosecond laser induced PVD. The differences of the two pulse durations are also discussed with respect to ablation characteristics, plume formation, and deposition rates.