Pyrite thin films have been obtained by sulphuration of Fe thin films. The influence of temperature and time of sulphuration on crystallite size (determined from XRD patterns) and on grain size (determined by AFM images) of the films have been investigated. It has been found that grain size is always much larger than crystallite size. Grains of higher crystallographic homogeneity are produced when the films are sulphurated at 675-700 K. They are formed by only three or four crystallites. Possible relationships between grain and crystallite growth mechanisms are briefly considered. (c) 2004 Published by Elsevier B.V.