Continuous down-scaling of silicon based transistors results in device lengths of less than 100nm. This requires a reduction of the gate dielectric thickness to less than 15Å which is not possible for SiO2 due to an increasing leakage current. One of the most promising candidates for a replacement material for the gate dielectric is HfO2 [Wilk GD, Wallace RM, Anthony JM. J Appl Phys 2001; 89:5243].In this work we applied X-ray photoelectron spectroscopy (XPS) and photoelectron diffraction measurements in order to study the interface of hafnium oxide to Si(100). The high resolution measurements were performed with synchrotron radiation at beamlines 5 and 11 at DELTA (Dortmund). For the first time, photoelectron diffraction patterns for this system were recorded. The spectral resolution allowed to separate different spectral components.The preparation of hafnium oxide films on Si(100) was performed by evaporation of hafnium at a partial oxygen background pressure of 1×10-8mbar. Three different spectral components were observed in the hafnium 4f photoemission signal by high resolution XPS. The photoelectron signals with binding energies shift of 3.1 and 1.2eV with respect to signal of hafnium silicide were assigned to hafnium dioxide and hafnium silicate, respectively. The corresponding high-resolution diffraction patterns result from different local environments for each component. The experimental patterns are compared with simulations for a model structure of hafnium silicide.