Evidence for acoustic waves induced by focused ion beams

Acoustic waves induced by an intensity modulated focused ion beam have been measured. The experiments were performed with Ga+ ions of 35 keV at a current of 3 nA and variable chopping frequency up to 10 MHz in a common focused ion beam system. The acoustic signals were detected by means of a piezoelectric sensor with integrated pre-amplifier. Frequency and position sensitivity of the sensor has been measured by laser excitation. Ion acoustic measurements have been carried out at the resonance frequencies of the sensor. A dependence on the sample material was found. The results show that the ion acoustic effect can be utilized for imaging and material analysis in focused ion beam systems .