Secondary Ion TESCAN Detector

The secondary ion TESCAN detector (SITD) extends the imaging capabilities of a FIB-SEM system by collecting the signal of secondary ions (SI) which provides high surface sensitivity and allows simultaneous acquisition of FIB-generated positive SI and secondary electrons (iSE).
The interaction volume generated by an ion beam is of the order of a few nanometres which is much smaller than the one generated by an electron beam – typically of the order of a few microns. SI and iSE signals are very sensitive and provide information of the uppermost surface layers of the sample with high lateral and depth resolution.

 
One common application of this sensitive surface technique is to detect the presence of oxides and carbides on the surface of metallic samples. Oxides and carbides significantly increase SI yield. Thus when imaging with SI, oxides become very bright. This feature makes SI imaging the ideal technique for identifying corrosion or grain boundary segregation.

The SITD attracts FIB-generated positive secondary ions emitted from the sample surface. The ions hit the conversion electrode of the SITD to be subsequently converted into secondary electrons that are detected in the usual way by an Everhart-Thornley detector. The secondary ion signal is usually much weaker than the FIB generated secondary electron signal, thus longer dwell times and higher probe currents are appropriate for SITD.

 
Secondary Ion TESCAN Detector
Study of high temperature corrosion of an Al-Si protection layer on a nickel-based super alloy. Image acquired using FIB-induced SI (top) and SE (bottom) signals simultaneously. The bright regions show the presence of corrosion.