Very thin TiN and ZrN films (<500 nm) were grown on (100) Si substrates at temperatures up to 500 degrees C by the pulsed laser deposition (PLD) technique using a KrF excimer laser under residual vacuum or various mixtures of CH4 or N-2. Auger electron spectroscopy investigations found that films contained a relatively low oxygen concentration, usually below 3.0 at%. Films deposited under residual vacuum or very low N-2 pressures (<3 x 10(-3) Pa) contained 3-6 at% C atoms in the bulk. This fraction grew to 8-10 at% when the deposition was performed under an atmosphere of 2 x 10(-3) Pa CH4. To avoid C atoms incorporation into the bulk a deposition pressure of 10 Pa N-2 was required. X-ray photoelectron spectroscopy investigations found that oxygen was mostly bonded in an oxynitride type of compound, while carbon was bonded into a metallic carbide. The presence of C atoms in the chemical composition of the TiN or ZrN improved the measured hardness of the films. (C) 2013 Elsevier B.V. All rights reserved.