A 13.56 MHz inductively coupled plasma system has been used to deposit diamond from CH4/O2 in H2, CO in H2' and CH4/CO2 in H2 plasmas. Depositions were made on substrates of silicon and quartz with surfaces modified by scratching, or coated with Diamond-Like Carbon (DLC), or left unmodified. The C atom to 0 atom ratio was systematically varied as well as the total concentration. Polycrystalline films, faceted particles and spherical particles were deposited. We found that a C:0 ratio of 1:1 with a total concentration between 2% and 3% in hydrogen resulted in large area polycrystalline films for the deposition parameters investigated.