Pioneering Development of Atomic Resolution In Situ Environmental Transmission Electron Microscopy for Probing Gas-Solid
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Pioneering Development of Atomic Resolution In Situ Environmental Transmission Electron Microscopy for Probing Gas-Solid Reactions and In Situ Nanosynthesis Pratibha L. Gai 1,2,* and Edward D. Boyes 1 1 2
DuPont, Central Research and Development, Wilmington, DE 19880-0356, U.S.A. University of Delaware, Department of Materials Science, Newark, DE, U.S.A.
ABSTRACT Highlights of our pioneering development of atomic resolution in situ environmental transmission electron microscope (ETEM) for direct probing of gas-solid reactions and in situ nanosynthesis are described. Dynamic studies on supported nanoparticle catalysts and carbon nanotubes under different reaction environments have been carried out. The results provide deep insights into the dynamic nanostructure of the materials and their mode of operation.
INTRODUCTION Many dynamic processes do not occur in nature, science or industry in a typical TEM high vacuum environment. Dynamic in situ data related to the real world need to be obtained under controlled conditions of gas/vapor/liquid environment and temperature. Direct observations of microstructural evolution under dynamic reaction conditions is a powerful structural tool in the chemical and materials sciences. In situ ETEM under controlled reaction conditions provides dynamic information on processes which can not be obtained directly and readily by other techniques [1]. In ETEM (also referred to as environmental-HRTEM, EHRTEM), a gas reaction cell (or environmental cell (ECELL) or microreactor) is fitted inside an electron microscope column, which is differentially pumped. In situ direct examination of chemical and material reactions is important since insights into reaction mechanisms can be obtained and transient phases formed under reaction conditions can be observed [1]. Reviews of the important scientific impact of ETEM in solid state chemical and materials sciences, including catalysis research, are provided by references [1-10]. ETEM is especially important since post reaction examinations of a static material at room temperature (RT) do not accurately represent its dynamic state and there may be atmospheric contamination which can cause serious errors in interpretation. EXPERIMENTAL DETAILS Recently an atomic resolution in situ ETEM has been pioneered by Gai and Boyes [7-9] which enables probing of gas-solid reaction processes directly at the atomic level. The whole EM column in a high resolution 300 kV CM30T HR (S)TEM has been extensively modified with the introduction of a fully integrated and permanently mounted environmental (ECELL) system for atomic resolution studies of dynamic gas-solid reactions in controlled atmospheres and for in situ nanosynthesis. Highlights of this development [8] include a unique ETEM design with objective lens polepieces incorporating radial holes for the first stage of differential pumping.
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In addition, the controlled environment ECELL volume is the regular sample chamber of the ETEM. It is separated from the rest of the column by th
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