In Situ Preparation of Pr1-xCaxMnO3 and La1-xSrxMnO3 Catalysts Surface for High-Resolution Environmental Transmission Electron Microscopy

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.

Dynamic observation of manganese adatom mobility at perovskite oxide catalyst interfaces with water

“…Surface termination of the manganite films in H 2 O. The study of surface termination of epitaxial perovskite films using environmental high-resolution transmission electron microscopy (ETEM) was demonstrated by Roddatis et al 42 and requires careful TEM lamella preparation, as documented in the Supplementary Figs. 8-11 and the associated text.…”

“…Although this value might vary between different oxides, ΔH ad,ox < ΔH ad = −44 kJ/mol for H 2 O on bulk water reflects exothermic water adsorption on oxide surface at much reduced pressures. In the HV of the ETEM (p ≥ 10 −5 Pa), the effect of H 2 O condensation on manganite surfaces can be only avoided by using a cold trap that is reducing the partial pressure of H 2 O in HV by one order of magnitude 42 . The thickness of the adsorbed water layer in the ETEM experiments as a function of p H 2 O is calculated by using the energy balance between surface energy γ s of the oxide in HV, the surface energy γ H 2 O of liquid H 2 O to vapor and ΔH ad (see Supplementary Fig.…”

“…In situ environmental transmission electron microscopy (ETEM) in combination with aberration correction and image simulation has developed to a level where it can provide atomic resolution real space information about the equilibrium surface reconstruction in various ambient conditions [38][39][40] including strategies for controlling the impact of electron beam 41,42 . The recent development of atomic scale dynamic studies show surface mobility of Ce atoms on CeO 2 facets in high vacuum 43 and a transition of a TiO 2 surface reconstruction in H 2 O from static to dynamic after adding CO 44 .…”

Trends of epitaxial perovskite oxide films catalyzing the oxygen evolution reaction in alkaline media

“…Interestingly, the amorphization sometimes observed for on the surface of perovskite oxides can be reversible, e.g. preparation-induced amorphous regions on the surface recrystallized in the presence of water on Pr0.64Ca0.36MnO3 [67,142,143]. In contrast, Pr0.9Ca0.1MnO3 remained crystalline in water vapor but showed cation dynamics on the surface [143].…”

“…The symbol shape indicates the substrate and the color the B-site metal. The data was taken from refs [28,53,[62][63][64][65][66][67][68][69][70][54][55][56][57][58][59][60][61]…”