Electronic excitation effects on Fe 2 O 3 films by high-energy ions

For better understanding of electronic excitation effects on materials with small bandgap, we have extended measurements to Fe2O3 (hematite) films. Applying carbon-foil (100 nm)-collector method, we have measured amounts of Fe in the C-collector as a function of fluence of 198 MeV Xe, 99 MeV Xe and 89 MeV Ni ions with the equilibrium charge. From the slope of Fe amount vs ion fluence with the efficiency fc of C-collector (0.3), sputtering yields Y are obtained to be 81.7, 57.9 and 38.3 by these ions, assuming stoichiometric sputtering. It appears that the sputtering yields are much larger than the calculated sputtering yields based on the elastic collisions. We have obtained Y = BSen with n = 1.25 and B = 1.2, Se being the electronic stopping powers (keV/nm). Optical direct bandgap is obtained to be 2.6 eV. The present Fe2O3 results are found to be within the bandgap scheme. Also, we have studied modifications of atomic structure using X-ray diffraction and optical absorption. Electronic excitation effects on modifications of these properties are described and compared with low-energy ion, 100 keV Ne ion impact. A mechanism is discussed for electron-lattice coupling.