The effect of electron fluence on the decomposition of sapphire (Al2O3) was studied in situ by Auger electron spectroscopy (AES). The decomposition was primarily detected by monitoring the evolution of the low kinetic energy Auger transitions of aluminum in Al2O3 (54 eV) and in metallic aluminum (68 eV). The decomposition of sputter-cleaned sapphire started at a fluence of similar to 4.9 x 10(19) electrons/cm(2) (7.8 C/cm(2)). This fluence was independent of the electron fluxes used in this work, except the lowest, which indicates that heating due to electron bombardment does not significantly affect the decomposition behavior. Electron-induced decomposition takes place in a minimum of the first five atomic layers of the substrate, as revealed by the evolution during irradiation of the high energy Al peaks associated with Al2O3 (1388 eV) and metallic aluminum (1396 eV). Comparison of the evolution of low and high kinetic energy Auger transitions demonstrates that the decomposition kinetics are much faster for the first monolayer than for the subjacent atomic layers. The surface condition strongly influences the decomposition kinetics. Thus, a carbon layer adsorbed at the alumina surface significantly increases the threshold dose for decomposition. The carbon layer most probably acts as a diffusion barrier for the oxygen produced during decomposition. An equation for the decomposition rate of the first monolayer of alumina is established. The integral of this equation gives a good fitting to the experimental data. It is found that the Auger signal of aluminum from sapphire does not disappear even if the entire region has been decomposed. This effect is due to backscattered electrons that promote Auger electron excitations outside the irradiated region.