Abstract
The study of changes in the atomic structure of a catalyst under chemical reaction conditions is extremely important for understanding the mechanism of their operation. For in situ environmental transmission electron microscopy (ETEM) studies, this requires preparation of electron transparent ultrathin TEM lamella without surface damage. Here, thin films of Pr1-xCaxMnO3 (PCMO, x = 0.1, 0.33) and La1-xSrxMnO3 (LSMO, x = 0.4) perovskites are used to demonstrate a cross-section specimen preparation method, comprised of two steps. The first step is based on optimized focused ion beam cutting procedures using a photoresist protection layer, finally being removed by plasma-etching. The second step is applicable for materials susceptible to surface amorphization, where in situ recrystallization back to perovskite structure is achieved by using electron beam driven chemistry in gases. This requires reduction of residual water vapor in a TEM column. Depending on the gas environment, long crystalline facets having different atomic terminations and Mn-valence state, can be prepared.
Highlights
Rational design of heterogeneous catalysts for high selectivity and turnover of chemical reactions requires detailed knowledge about the activity- and selectivity-determining structural properties, including catalytically active sites
Image of an edge collected from the thin window area; (c) high-resolution scanning TEM (HRSTEM)
Spectral features marked with A, B, C, L2 and L3 are discussed in text
Summary
Rational design of heterogeneous catalysts for high selectivity and turnover of chemical reactions requires detailed knowledge about the activity- and selectivity-determining structural properties, including catalytically active sites. Analysis of atomic and electronic structure of catalyst surfaces and subsurfaces under chemical reaction conditions is essential, since catalysts often undergo significant changes in surface and defect structure in their active state [1,2,3]. Environmental transmission electron microscopy (ETEM) offers unique opportunities in gaining atomic resolution images of surfaces and subsurfaces, formation of surface disorder, as well as spatially resolved spectroscopic information about the electronic structure and oxidation states of catalyst surfaces. The E-cell allows performing tomography [7], collecting high resolution images [8]
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