Iron thin films of less than 100 nm have been grown on Si(100) wafers by DC magnetron sputtering at well-controlled substrate temperatures. Three different sets of samples have been prepared in order to study the influence of the preparation conditions on their magnetic properties: i) natural oxidized samples, ii) "in-situ" partially oxidized and iii) non-oxidized iron thin films. For the last two sets, a gold film prior to expose the air capped the samples. XRD and EXAFS experiments have been performed to obtain the size and the shape of the grains. They provide a columnar growth for samples prepared at room temperature and a diminution of the grain size along the normal to the surface when the preparation temperature decreases.