Energy loss and straggling of heavy ions in silicon nitride in the low MeV energy range

Energy loss and energy loss straggling in a thin silicon nitride foil was measured for Li, B, C, O, S and Fe ions with energies between 0.4 and 4.0 MeV. The energy distribution of ions after passage of a 34 nm thick foil was measured by an electrostatic deflector with 0.2% energy resolution. Energy loss values are in good agreement with SRIM calculations. Measured energy loss straggling however, is considerably lower than velocity-independent Bohr straggling and also lower than the values predicted by SRIM. This behavior is relatively well explained by a modified Bohr model recently developed by Sigmund.The results give important information for the use of silicon nitride membranes as entrance windows to gas ionization detectors and as exit windows for ‘beam in air’ experiments.