The influence of potential and pH on the thickness and composition of the anodic films formed on n-Si(111) in dilute ammonium fluoride solutions is investigated by photoelectron spectroscopy. A combined electrochemistry/surface analysis system with very low contamination levels is used for the investigation of the oxidic layers. XPS data show that the film thicknesses increase with decreasing pH reaching 25 Angstrom at pH 3. A potential dependence measured at lower coverage at a pH of 4.9 reveals changes in thickness and composition by increasing the potential from flatband to +5 V. Fluorine is incorporated into these films in substantial amounts which otherwise consist predominantly of silicon oxide. Silicon fluoride and silicon oxyfluoride are found. We define a current transmissivity, T-c, of the layers which shows strong variations with potential and pH. For a pH of 3, T-c is about 5 x 10(2) larger than for pH 4.9. The potential dependence shows a variation of T-c by a factor of three and an increase for thicknesses exceeding 5 Angstrom. These observations are explained by a structural transition from a high density pseudomorphic interfacial layer to a more open structure at larger thicknesses (up to 25 Angstrom). The analysis of the UP-spectra shows only little changes of the electron affinity chi with coverage. We obtain chi congruent to 4.15 +/- 0.1 eV. A distinct band bending is not detected. From HeII spectra, we determine the valence band offset DeltaE(v) between Si and the oxidic layer to be 5.2 eV.