Amorphous Si/C/N nanopowders have been synthesised by laser spray pyrolysis of hexamethyldisilazane-(CH3)(3)SiNHSi(CH3)(3) or HMDS-using a high power tuneable continuous wave CO2 laser and the ultrasonic injection into the laser beam of fine liquid droplets which form an aerosol. Effects of laser power density (expanded or non expanded laser beam) and addition of aluminium (and yttrium) alcoxide to liquid HMDS have been studied using chemical analysis, nitrogen adsorption-desorption, infrared spectroscopy and transmission electronic microscopy (TEM) as characterisation methods. Chemical and structural changes occur with heat treatment under nitrogen at temperatures up to 1600 degrees C. In most cases the powders containing Al (and Y) additives remain in the nanometric range, and their crystallisation is less pronounced than powders made from HMDS without Al (and Y) addition.