ORIGINAL PAPER Cryo ultra-low-angle microtomy for XPS-depth profiling of organic coatings T. Greunz & B. Strauß & S. E. Schausberger & B. Heise & B. Jachs & D. Stifter Received: 31 October 2012 / Revised: 28 February 2013 / Accepted: 4 March 2013 # Springer-Verlag Berlin Heidelberg 2013 Abstract In X-ray photoelectron spectroscopy (XPS) Ar + ion sputtering is usually used for depth profiling. However, for such samples as organic coatings, this is not feasible because of degradation. Also, measurement of a depth pro- file on a conventionally prepared cross-section is not possi- ble if, for example, sample thickness is below the smallest available measurement spot size of the XPS system. In our approach we used a rotary microtome to cut samples under a shallow tilting angle of 0.5° to obtain an extended cross- section suitable for XPS investigations. We also used liquid nitrogen cooling to ensure an exposed area of higher quality: topography measurements with a novel optical 3D micro- scope and by atomic force microscopy revealed the linearity of the inclined sections. With our cryo ultra-low-angle microtomy (cryo-ULAM) preparation technique we were able to determine, by XPS, elemental and chemical gradi- ents within a 25 μm thick polyester-based organic coating deposited on steel. The gradients were related to, for exam- ple, depletion of the crosslinking agent in the sub-surface region. Complementary reflection electron energy-loss spectroscopy measurements performed on the cryo-ULAM sections also support the findings obtained from the XPS depth profiles. Keywords XPS . REELS . Ultra-low-angle microtomy . Compositional depth profiling . Organic coatings . Crosslinking agent Introduction Organic coatings on (zinc-coated) steel substrates are used for numerous applications in the construction and automo- tive industries and for household appliances. The longevity of steel substrates can be extended by coating the surface with an organic layer which helps to prevent corrosion and corrosion-induced damage. Besides their protective and functional aspects, organic coatings are also used for deco- rative purposes. In both cases they are expected to last for long periods. High demands are put on these systems, with, e.g., weathering and durability properties being important for exterior use. Although organic coatings have been de- veloped in industry for decades, the chemical structure and composition of the organic coatings finally applied is, often, not totally defined or known, calling for more accurate analysis to enable further improvement of their formulation. For chemical investigations X-ray photoelectron spec- troscopy (XPS) enables surface characterization of the sys- tem of interest. Moreover, XPS depth profiles are suitable for determination of possible gradients within the specimen. Common depth-profiling techniques, for example sputtering with noble gas ions, e.g. Ar + ions, in combination with surface-sensitive techniques, for example XPS, can be ap- plied to a vast of number of materials. XPS-based depth profiling has been being used to study surface and embed- ded oxide structures in zinc–chromium coated steel sheets Published in the topical collection Applied Surface Analysis with guest editors Karl-Heinz Müller, Hubert Paulus, and Mark Schülke. T. Greunz (*) : S. E. Schausberger : B. Heise : D. Stifter Christian Doppler Laboratory for Microscopic and Spectroscopic Material Characterisation, Center for Surface and Nanoanalytics, Johannes Kepler Universität Linz, Altenbergerstraße 69, 4040 Linz, Austria e-mail: theresia.greunz@jku.at B. Strauß voestalpine Stahl GmbH, voestalpine-Straße 3, 4031 Linz, Austria B. Jachs Institute of Polymer Science, Johannes Kepler Universität Linz, Altenbergerstraße 69, 4040 Linz, Austria Anal Bioanal Chem DOI 10.1007/s00216-013-6894-1