performing-situ-closed-cell-gas-reactions-transmission-electron

Performing <em>In Situ</em> Closed-Cell Gas Reactions in the Transmission Electron Microscope

Gas reactions studied by in situ electron microscopy can be used to capture the real-time morphological and microchemical transformations of materials at ...

University of Michigan

The effect of gibberellic acid on the content and distribution of silicon in the stem, leaf sheath, and leaf lamina of sugarcane was analyzed in relation to the effect of gibberellic acid on stem growth. Silicon content was measured by neutron activation analysis, and its distribution was followed by scanning electron microscopy and X-ray analysis.Foliarly applied gibberellic acid increased stem length and fresh weight and decreased silicon content. Gibberellic acid treatments had little or no effect on growth or silicon content of leaf laminae or sheaths. The close correlation between increase in growth of an internode in response to gibberellic acid and the decrease in silicon content of that internode indicated a dilution effect of growth on the amount of silicon rather than a direct effect of gibberellic acid on silicon deposition. This conclusion was supported by scanning electrom microscopy, X-ray map photos, and counts of silica cells per unit of epidermis area.

Effect of gibberellic Acid on silica content and distribution in sugarcane.

By coupling techniques of simultaneous secondary (SE) and transmitted electron (TE) imaging at high resolution in a modern scanning transmission electron microscope (STEM), with the ability to heat specimens using a highly stable MEMS-based heating platform, we obtained synergistic information to clarify the behavior of catalysts during in situ thermal treatments. Au/iron oxide catalyst 'leached' to remove surface Au was heated to temperatures as high as 700°C. The Fe2O3 support particle structure tended to reduce to Fe3O4 and formed surface terraces; the formation, coalescence, and mobility of 1- to 2-nm particles on the terraces were characterized in SE, STEM-ADF, and TEM-BF modes. If combined with simultaneous nanoprobe spectroscopy, this approach will open the door to a new way of studying the kinetics of nano-scaled phenomena. 

Understanding catalyst behavior during in situ heating through simultaneous secondary and transmitted electron imaging.

Protocols for conducting in situ transmission electron microscopy (TEM) reactions using an environmental TEM with dry gases have been well established. However, many important reactions that are relevant to catalysis or high-temperature oxidation occur at atmospheric pressure and are influenced by the presence of water vapor. These experiments necessitate using a closed-cell gas reaction TEM holder. We have developed protocols for introducing and controlling water vapor concentrations in experimental gases from 2% at a full atmosphere to 100% at ~17 Torr, while measuring the gas composition using a residual gas analyzer (RGA) on the return side of the in situ gas reactor holder. Initially, as a model system, cube-shaped MgO crystals were used to help develop the protocols for handling the water vapor injection process and confirming that we could successfully inject water vapor into the gas cell. The interaction of water vapor with MgO triggered surface morphological and chemical changes as a result of the formation of Mg(OH)2, later validated with mass spectra obtained with our RGA system with and without water vapor. Integrating an RGA with an in situ scanning/TEM closed-cell gas reaction system can thus provide critical measurements correlating gas composition with dynamic surface restructuring of materials during reactions.

Article	Year
Effect of gibberellic Acid on silica content and distribution in sugarcane. Plant physiology\| PubMed ID: 16661908	1981
Understanding catalyst behavior during in situ heating through simultaneous secondary and transmitted electron imaging. Nanoscale research letters\| PubMed ID: 25419195	2014
Introducing and Controlling Water Vapor in Closed-Cell Electron Microscopy Gas Reactions. Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada\| PubMed ID: 32157982	2020

Wilbur C. Bigelow

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