Field of Expertise: Advanced Material Science

Chemical degradation and morphological instabilities during focused ion beam prototyping of polymers: a problem and a solution
Angelina Orthacker
Center for Electron Microscopy
15:20 - 17:30 Thursday 24 October 2013 Foyer Alte Technik

During the last decade focused ion beam (FIB) processing has become a unique tool for the site specific fabrication of ultrathin lamellas suitable for transmission electron microscopy. Due to its versatile functionalities, this method has also attracted increasing attention as a rapid prototyping tool for surface modification and 3D surface structuring with spatial resolutions down to the nanometer range. However, focused ion beam processing of soft matter, such as polymers or biological samples, often leads to chemical and morphological instabilities. In this study the behaviour of various polymers under ion beam exposure is investigated using different patterning parameters and strategies with the goal of finding a way of processing soft matter and causing only an acceptable minimum amount of damage. Methods treating not only physical but also chemical behaviour, including scanning electron microscopy, atomic force microscopy, Raman spectroscopy and simultaneous thermal analysis were used. During processing of polymers three temperature regimes can be observed. At low temperatures all polymers investigated show stable chemical and morphological behaviour, very high temperatures lead to instable processing conditions in all cases and in the intermediate temperature regime the behaviour is dependent on the type of polymer processed. It is shown, that polymers which rather cross-link in the proximity of the beam show stable morphologies in this regime, while polymers that rather undergo chain scission are morphologically very instable and even show tendencies to develop a creeping phase, where material follows the beam. Finally alternative patterning strategies are suggested, which allow stable processing conditions even for the most challenging polymers (such as PMMA), which mainly undergo chain scission.