Near and on-substrate plasma characterization in pulsed laser deposition processes.

Although pulsed laser deposition (PLD) of thin films is a mature technique, the actual plasma processes and plasma properties close to the substrate have not been characterized in detail. We present a spectroscopic characterization of the near and on-substrate plasma using a Nd:YAG laser, 340 mJ, 3.5 ns, at 1.06 mm, focused on a rotating calcium doped graphite target, at ~2×10⁹ W/cm², in Argon background. Plasma temperature is inferred from Boltzmann plots of ArII lines and spectra fitting of C₂ swan bands emission. CII and CaII Stark broadening of emission lines is used to infer the plasma electron density. A comparison is made between a free streaming and on substrate plasma. Characteristic temperatures of the free streaming plasma are in the range ~2.5±0.3 eV at early times, ~100 ns after laser plasma formation, which decreases to ~1.2±0.2 eV, at later times, ~560 ns, with electron density ~10¹⁶ cm^-3. Characteristic plasma parameters for the on-substrate plasma are found to be ~0.8 eV and ~10¹⁸ cm^-3, being the higher electron density attributed to on-substrate plasma stagnation. These observations contribute to a better understanding of the plasma processes in PLD.