Analysis of microstructures using the ion acoustic effect

The interaction of a pulsed ion beam with a solid leads to a small temperature variation in the near subsurface region. Due to the local heating of the target thermal elastic waves were generated. The measurement of these waves gives information about the internal structure and properties of the sample. Experiments were carried out using an intensity modulated beam of high energy ions from a TANDETRON accelerator for the investigation of elastic waves in aluminum, steel, copper and silicon samples as well as for a pulsed low energy focused ion beam (FIB) for acoustic imaging from structures on different targets. The detection of the acoustic signal was provided by piezoelectric transducers based on lead zirconium titanium (PZT) ceramic or on polyvinylidene fluoride (PVDF) films which can be applied in the scanning ion acoustic microscopy. In this case the modulation frequency was varied in the range from 60 kHz to 2 MHz. A lateral resolution of the ion acoustic images near the samples surface of a few micrometers could be obtained.