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From the Editor Nanoanalysis of Presolar Grains


When I see a polished section of an iron meteorite in a museum, I think how amazing it is that this piece of solar system debris survived its descent through the Earth’s atmosphere to provide us with physical evidence of solar system formation. T ese meteorites, from the metallic core of a planet or asteroid that broke into fragments, contain phases originally analyzed for elemental composition decades ago using X-ray spectrometry in the electron probe microanalyzer (EPMA). As traditionally operated, the EPMA has a spatial resolution of analysis about 1 µm. However, recent research on certain types of meteorites requires much better spatial resolution. T ere are three main types of meteorites: iron meteorites, stony meteorites, and stony-iron meteorites. Some stony meteorites, known as chondrites, are aggregates of early solar system components and occasionally contain small inclusions believed to have originated in debris that predates our solar system. T ese sub-µm-sized presolar grains have unusual isotope signatures in various elements, and some may contain nanometer-sized diamonds. T ese meteorites require “nanoanalysis,” elemental analysis with a spatial resolution on the order of a few nanometers, about a hundred times better than that possible with the EPMA. One method of achieving nanoanalysis is to produce an electron-transparent thin specimen of the meteorite and analyze it using X-ray spectrometry in a scanning transmission electron microscope (STEM-EDX); in this case the analytical spatial resolution can be 1–5 nm. Another method is to analyze a polished bulk specimen with Auger electron spectrometry (AES), where the primary electron beam can be focused to 5–10 nm and Auger electrons escape from within 3 nm of the surface, yielding an analytical resolution of about 10 nm. A third method known as atom probe tomography (APT) uses position-sensitive time-of-fl ight mass spectrometry to locate atoms in three dimensions with near-atomic resolution (<1 nm).


Finding presolar grains in a chondrite requires mass spectrometry: nano-scale secondary ion mass spectrometry (NanoSIMS) can identify grains with presolar isotope ratios for later AES analysis (see article in this issue by Floss), and APT can fi nd grains with presolar isotope ratios as well as determine the compositions of phases within these grains (article by Lewis et al.). Finally, many site-specifi c analyses require specimen preparation to be done with a focused ion beam (FIB) milling instrument. A new mounting method simplifi es specimen preparation for APT. T is method has been applied to atomic-level analysis of an iron-nickel meteorite (article by Rout et al.).


Charles Lyman Editor-in-Chief


Publication Objective: to provide information of interest to microscopists.


Microscopy Today is a controlled-circulation trade magazine owned by the Microscopy Society of America that is published six times a year in the odd months. Editorial coverage spans all microscopy techniques including light microscopy, scanning probe microscopy, electron microscopy, ion-beam techniques, and the wide range of microanalytical methods. Readers and authors come from both the life sciences and the physical sciences. The typical length of an article is about 2,000 words plus fi gures and tables; feature articles are longer. Interested authors should consult “Instructions for Contributors” on the Microscopy Today website: www.microscopy-today.com.


ISSN 1551-9295


Disclaimer The Microscopy Society of America and the editors cannot be held responsible for opinions, errors, or for any consequences arising from the use of information contained in Microscopy Today. The appearance of advertising in Microscopy Today does not constitute an endorsement or approval by the Microscopy Society of America of any claims or information found in the advertisements. By submitting a manuscript to Microscopy Today, the author warrants that the article is original or that the author has written permission to use copyrighted material published elsewhere. While the contents of this magazine are believed to be accurate at press time, neither the Microscopy Society of America, the editors, nor the authors can accept legal responsibility for errors or omissions.


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Editorial Staff


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Editorial Board Nasim Alem, Penn State University Arlan Benscoter, Lehigh University John Bozzola, Southern Illinois University Peter Crozier, Arizona State University Vinayak Dravid, Northwestern University David Grubb, Cornell University Bryan Huey, University of Connecticut Heather Lowers, U.S. Geological Survey John Mackenzie, North Carolina State Univ. Paul Maddox, U. of North Carolina–Chapel Hill Ania Majewska, U. Rochester Med School Joseph Michael, Sandia National Labs Caroline Miller, Indiana University Brian M. Patterson, Los Alamos National Lab John Reffner, John Jay College, SUNY Ian Robertson, University of Wisconsin Phillip Russell, Appalachian State University Glenn Shipley, Citizen Microscopist Robert Simmons, Georgia State University Bradley Thiel, SUNY Polytechnic Institute Simon Watkins, University of Pittsburgh Cynthia Zeissler, Nat. Inst. of Stds. and Tech. (NIST)


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