ASU SIMS EXPERTS PARTICIPATE IN WORKSHOP

The students, young postdoctoral researchers and professors who recently attended the 4th annual ASU workshop on secondary ion mass spectrometry (SIMS) asked a lot of questions. In their own words, “How can I determine the hosts of hazardous elements in coal? How can I measure germanium in novel synthetic materials? Which trace elements are dissolved in my zircon crystals? What can I learn from analyses of minerals in my meteorite samples?”

The visitors spanned a wide range of interests: from biochemists eager to determine the chemistry of a single cell to tectonicists struggling to understand how continental collision events are recorded in the chemistry of the resulting rocks. They came to ASU to learn how SIMS might help them in their geochemical quests.

SIMS is a surface analysis technique that is sensitive to most of the elements contained i n the periodic table. In SIMS, a high-energy ion beam is focused to a spot and directed at a chosen location on a sample. Secondary ions ejected from the surface as a result of the energetic collisions are accelerated into a mass spectrometer where they are detected as a function of their mass. SIMS is known for its high sensitivity and high spatial resolution in a lateral sense, but is particularly important to the semiconductor industry because of its ability to determine how the chemistry of a sample changes with depth (on the scale of tens of nanometers). Currently ASU has one of the most extensive arrays of SIMS instrumentation, and SIMS expertise, in the world. These attributes result in geochemists from around the world traveling to the NSF-funded National SIMS Facility on ASU’s main campus.

The organizers worked to show the connections between the collection of data during a visit and the events occurring in the vacuum chamber that produce these data. Their philosophy is not to simply help visitors obtain quality analyses, but to act synergistically to help them interpret their results and show them the potential of this instrument to go far beyond their initial goals.

The workshop is unique in that the participants obtained hands-on experience, were taught about mass spectrometry, examined the parts that make up a mass spectrometer (electrostatic lenses, magnets, apertures, slits etc.), learned how to prepare samples appropriate for this technique, and heard about the theories behind the ion-solid interactions that produce the secondary ion signal.

ASU possesses an outstanding combination of equipment and personnel in the mass spectrometry field. Three magnetic sector SIMS (delivered in 1984, 1999, and 2010) form the core of the facility, and two time-of-flight SIMS (TOF-SIMS) are also available. Professor Peter Williams, from the department of chemistry and biochemistry, pioneered many of the theories describing secondary ion formation and practical applications of SIMS to materials science. Professor Richard Hervig, from the School of Earth and Space Exploration, has developed many SIMS techniques for geochemistry and applied them to natural samples from this and other planets as well as a variety of synthetic materials. Professor Lynda Williams, in the School of Earth and Space Exploration, has used this technique on a range of materials at the organic/inorganic interface. Williams, Hervig and Williams are the principal investigators on the ASU SIMS facility grant. Also assisting the workshop were post-doctoral researchers Maitrayee Bose (demonstrating the application of ASU’s new, $3.5M NanoSIMS and Klaus Franzreb (describing semiconductor analyses and applications of Time-of-flight SIMS to research) and graduate student Steve Guggino (sample preparation and post-analysis microscopic characterization).

Source: Richard Hervig, richard.hervig@asu.edu