Ion Acoustic Microscope based on IMSA-100 Focused Ion Beam system

An intensity modulated focused ion beam (FIB) which is hitting the surface of a solid, leads to a small temperature variation in the near subsurface region which is sufficient for thermal elastic wave generation. The measurement of these waves can be used for analysis and imaging of surface as well as near subsurface structures in the material. The modified FIB equipment IMSA-100 working with 35 keV Ga+ and Au+ ions and a current of about 3 nA was employed to obtain acoustic images from structures on silicon, aluminum and glass targets. The acoustic signals were detected using a PZT transducer delivering an output voltage of 50 - 100 nV at modulation frequency of 100kHz. The frequency was varied in the range of 60kHz - 2MHz. The obtained lateral resolution of the ion acoustic images at 80 kHz was about 16 µm on silicon and about 7µm on glass and at 2 MHz it decreases to 5 µm and 3 µm, respectively.