Focused Ion-Beam Milling and Lifting of Sample for Transmission Electron Microscopy

H. K. D. H. Bhadeshia

Focused ion-beam (FIB) systems can be used to cut out specimens from specific regions of a sample for further studies. The process involves milling the sample using the focused ion beam, whilst it is under observation so that identified areas of the sample can be removed. In some cases, the ion beam itself can be used to image the region of interest before the machining begins. A better method involves using a dual beam instrument in which a scanning electron microsope is used for continuous observations whilst the machining is accomplished with the ion beam. In the FIB lift-out technique, thin membranes are extracted from bulk samples for studies using transmission microscopy.

The following movies show the thinning of the foil sample for lifting out. You can see a platinum layer on surface of cross sectioned, corroded steel inside a grain of metal (the two lines at the start, right and left, are grain boundaries). The platinum layer serves to protect the milled surface from scratches during milling. The final rectangular features are steps remaining after the cutting TEM-foil off the sample.

The technique has the major advantage over conventional methods of TEM sample presentation, in that samples can be extracted from specific locations. Furthermore, the range of materials from which samples can be extracted is enormous - even corrosion products such as chlorides and sulphides are ameanable to FIB machining, and can be investigated in a transmission electron microscope after lift out.

The videos below have generously been provided by Dr Vratko Vokal, MSSI, University of Limerick, Eire.

The image on the right shows the final thin foil from the FIB milling operation, with dimensions 10 μm by 7 μm by 0.2 μm. The process of extraction can be seen in the adjacent movies.


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