XPD (X-ray photoelectron diffraction) was used to probe the crystallin
e structure of 3 ML and 6 ML of Ge epitaxially grown on Si(001) surfac
e at room and 400 degrees C temperatures in order to check the tetrago
nal distortion associated with the pseudomorphic growth, Strong eviden
ces for an interfacial intermixing and crystalline growth even at the
room temperature of the substrate has been found by means of the obser
vation of the angular behavior of the Ge 3d photoelectron peak.