The importance of gas scattering processes on the stoichiometry deviations of laser deposited films

Laser ablation of a BiSrCaCuO (2212) target is performed in vacuum, both in reactive (O2) and inert (Ar) atmospheres (0.1 mbar). Two substrates are properly located in the chamber in order to collect material from the scattering of the ablated species by the foreign atmosphere and from the re-emission and/or re-sputtering processes occurring in the growing films. The results show that the latter processes are very weak and may affect to 3% of the deposited material at the most. Whereas films deposited in vacuum are nearly stoichiometric, significant deviations are observed in the composition of films grown in the presence of a foreign gas, that are qualitatively similar in Ar and in O2 environments. The results show clearly that these deviations are related to scattering processes prior to deposition and not to chemical reactions in the gas phase or re-emission processes from the growing film. These scattering processes are more important for the lighter species, thus explaining the Bi enrichment of the films in the presence of a foreign gas.