NanoScope FIB technology article.

Just posted here is the full article discussing the relative merits of both methods of FIBxTEM section extraction and the factors to consider when choosing which is better for your sample types.

You may think the answer is a foregone conclusion, with in-situ foil extraction being clearly more advanced and more effective as an extraction method than ex-situ, but hold on to that thought, as there may be some less obvious issues that are worth your consideration.

Included here is a detailed analysis of each of these rival techniques across the following areas of applicability –

1^st      Speed – with the hands down winner being ex-situ

2^nd     Yield – more controversial with advocates on both sides

3^rd     Quality issues (of the section produced)

4^th     Cost – a clear winner here

5^th     Versatility – not such a common topic but vital for TEM users

6^th     Ease of use – this must be a slam dunk or?

7^th     Special circumstances

Lets just check our terms and the common perception of what’s what for this technique.

FIBxTEM section or foil = The site specific FIB milled sample biopsy that is FIB polished to become electron transparent and extracted to a TEM grid before being transferred to a TEM microscope for more detailed studies.

‘in-situ’ foil extraction – where a ‘thick’ biopsied section is transferred to a TEM grid inside the FIB-SEM instrument using a nano-manipulator and attached there before being FIB polished to the required ‘thinness’ and then transferred to a TEM.

‘ex-situ’ foil extraction – where a site specific feature is thinned to electron transparency BEFORE extraction, then cut free and unloaded from the FIB-SEM and where the section transfer to TEM grid occurs under an optical microscope on the lab bench, before being loaded into the TEM.

In-situ foil extraction (or lift-out) is the recommended approach promoted by both microscope vendors and extraction system suppliers alike. They claim that it is faster, safer, easier, requires less operator training, and produces a sample that is both of higher quality and also able to be ‘reworked’, if not perfect in all respects after the first iteration.

Ex-situ foil extraction however continues to have it’s advocates. They claim that it is significantly cheaper, significantly faster, offers very high yields and is more versatile in the range of materials it may be applied to. It also removes any additional risks to the main instrument, reduces the time needed to prepare samples, and removes additional support costs for the extra hardware.

Advocates of in-situ claim that ex-situ extraction is difficult and suffers from low yield, whereas ex-situ advocates point to the materials limitations of in-situ and scoff at the excessive cost. We have to look at the merits but also the disadvantages of each technique if we are to form a balanced picture.

Download the article here.

In addition – For those readers looking to improve their extraction skillset, we’ll soon be posting our ’10 Tricks and Tips for high yield ex-situ Lift-out’ on Youtube, but if you would like an early preview we’d be happy to chat with you, just click here to let us know.

Also in this article we discuss some of the common challenges of preparing TEM sections from advanced materials systems which can exhibit mechanical distortions during FIB polishing. Conventional wisdom for ex-situ foils would be partial release  to relieve internal stress and allow the section to relax back into a flat form for further polishing. However this approach only works if stress is the cause of the distortion, and this process effectively excludes final polishing for sections that do not return to a fully flat form (actually most of them). For in-situ foils there is no easy remedy to distortion other than cutting away any overlapping piece and trying to be happy with what is left.

NanoScope has developed some new techniques to manage wayward foil behaviour (stress induced or not) while maintaining predictable foil position and form. Join the discussion by posting your comments below, or contact us directly here. Examples of distortions we have seen and found ways to control would include:

Bowing (caused by uneven polishing or internal stress while clamped)

Curling (either symmetrically or asymmetrically)

Bending (can also happen during polishing, SEM inspection or FIB low kV treatment)

Rolling – even like a roller blind – seen with some polymers

Flapping (when a potion of the section to one side of a thinned sub-region folds over

Or my personal favourite ‘flapping about a specific horizontal layer’ like a lowK dielectric (or ‘cat flapping’ as it has been called).

More information on these effects in the article here.

If you have questions or comments about anything you have read here – please don’t hesitate to post a reply or contact us directly:  Lloyd Peto  or Alan Miller.

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