Filament-assisted chemical vapor deposition (CVD) diamond film growth on Si(100) was studied using x-ray photoelectron spectroscopy (XPS) in a system that couples a growth chamber to an ultrahigh vacuum analytical chamber. Diamond nucleates and grows on a SiC layer formed on the Si(100) substrate [D. N. Belton and S. J. Schmieg, Appl. Phys. Lett.54, 416 (1989)]. After about 17 h growth XPS showed no Si signal from the substrate, no detectable contaminants, and only carbon present in survey scans. Electron energy loss spectroscopy (EELS) spectra obtained by x-ray excitation of the C 1slevel can be used as a fingerprint for distinguishing diamond from graphite or carbides [D. N. Belton and S. J. Schmieg, J. Vac. Sci. Technol. A8, 2353 (1990)]. The identification of a continuous diamond film was confirmed with Raman spectroscopy and scanning electron microscopy (SEM).