Abstract
The use of focused ion beams, whilst permitting the targetted preparation of thin specimens for Transmission Electron Microscopy, also results in modification of the material to be investigated as a result of energy being transferred into the material. This undesirable effect is normally limited to the surface of the material, which is particularly unfavourably orientated towards the impinging ion beam. If the crystal structure and composition of areas close to the surface of such specimens need to be characterised, protective layers may be used. However, those layers, depending on the applied deposition technique, may interact with the sample surface as well thus affecting the results of the analysis. In the work presented here, the possible interactions which might occur between the various protective coatings of ion-beam deposited Platinum, electron beam deposited Platinum, Silicon Oxide or adhesively bonded Gold foil and the subsequent FIB-preparation of the oxide layers on Ni-Ti alloys are investigated, with respect to and how these might affect the TEM-images obtained of areas close to the surface of such specimens. It is shown that the use of adhesively bonded Gold foil as a protective coating, in particular, permits comprehensive characterisation of the surface, including the use of high-resolution TEM, to be carried out, up to the surface of the Oxide layer itself.
Kurzfassung
Der Einsatz fokussierter Ionenstrahlen erlaubt die Zielpräparation von dünnen Proben für die Transmissionselektronenmikroskopie, führt aber gleichzeitig aufgrund der eingebrachten Energie zu Modifikation des zu untersuchenden Materials. In der Regel beschränken sich ungewollte Wechselwirkungen auf die Materialoberfläche, da diese besonders ungünstig zum Ionenstrahl ausgerichtet ist. Sollen Kristallstruktur und Zusammensetzung oberflächennaher Probenbereiche charakterisiert werden, kommen Schutzschichten zum Einsatz, die je nach Beschichtungsverfahren aber ebenfalls mit der Probenoberfläche Wechselwirken und Untersuchungsergebnisse beeinflussen können. In der vorliegenden Arbeit wurde untersucht, welche Wechselwirkungen durch die Schutzschichten Ionenstrahlplatin, Elektronenstrahlplatin, Siliziumoxid oder adhäsiv haftender Goldfolie und anschließender FIB-Präparation bei Oxidschichten auf Ni-Ti-Legierungen auftreten, und wie diese sich auf die Darstellungsmöglichkeiten der oberflächennahen Bereiche auswirken. Es hat sich gezeigt, dass insbesondere bei Verwendung von adhäsiv haftender Goldfolie als Schutzschicht eine umfassende Charakterisierung inklusive hochauflösender TEM bis an die Oberfläche des Oxids ohne Einschränkung durchführbar ist.
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