X-RAY PHOTOELECTRON DIFFRACTION INVESTIGATION OF CE SEGREGATION AND FILM MORPHOLOGY DURING FIRST STAGE HETEROEPITAXY OF SI ON GE(001)

X-ray photoelectron diffraction (XPD) and its chemical selectivity hav e been used in conjunction with surface atom titration by ultra-violet photoelectron spectroscopy and conventional X-ray photoelectron spect roscopy to investigate the interplay between Ge segregation acid growt h morphology in the earliest stages (0-12 monolayers) of Si solid-sour ce-epitaxy on Ge(001)-2 x 1 surfaces held at room temperature (RT) aci d at 400 degrees C. A detailed examination, as a function of the Si co verage, of the forward scattering peak contrasts in the [111] and [001 ] directions of the Si 2p and Ge 3d polar angle distributions provides a diagnostic of whether or not a particular atom is in the top layer (segregation) and yields information about the stacking sequences (mor phology). These investigations allowed us to conclude in favour of an initial Si bilayer patch-growth-mode exempt of segregation at RT and o f a floating Ge surface at 400 degrees C, the Si agglomeration staying rather mild in the first monolayers. Accessorily, the XPD-specific pr oblems of electron defocusing effects through long atomic chains and s train-induced lattice expansion or contraction have also been addresse d.