For beta-FeSi2 formation, interdiffusion and silicidation are key processes in order to achieve better crystallinity, orientation and material properties. Transmission electron microscope (TEM) for the structural analysis and synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) for the diffusion process analysis are reviewed for the nanoscopic observation through the beta-FeSi2 formation. The TEM analysis provides nanostructure of interface region ( beta-FeSi2/Si) obtained by ion beam sputter deposition (IBSD) method at 600-800 degreesC. The substrates were prepared by several methods, such as ordinary chemical etching of Si or ion beam sputtering, etc. Cross-sectional TEM images and electron diffraction patterns were obtained for the interface of silicide and Si substrate. The images showed that "damaged" surface produced by ion sputtering and subsequent thermal annealing provides quite smooth interface and epitaxially grown films compared with the chemically etched Si, which has atomically flat surface. The SR-XPS results provide compositional changes in the run region nondestructively. Vapor deposited iron on Si substrate was measured after various annealing temperatures. The gradual changes of the composition from the topmost surface to the deeper region were clearly observed from the obtained results. (C) 2004 Elsevier B.V. All rights reserved.