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Searching for One of Nature’s Missing Crystal Structures

Searching for One of Nature’s Missing Crystal Structures. Thomas McConkie, David Allred, Gus Hart, Brian Hicks. Overview. What missing crystal structures? Setup and Preparation Experimental Methods Results Continuing the Search. What missing crystal structures?.

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Searching for One of Nature’s Missing Crystal Structures

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  1. Searching for One of Nature’s Missing Crystal Structures Thomas McConkie, David Allred, Gus Hart, Brian Hicks

  2. Overview • What missing crystal structures? • Setup and Preparation • Experimental Methods • Results • Continuing the Search

  3. What missing crystal structures? • “Where are natures missing structures?” • Gus Hart, Nov. 11, 2007 L13Structure

  4. Setup and Preparation • Vacuum system • Roughing, Turbo and Cryo Pumps. • Leaked checked system to minimize unwanted interference by outside air. • Base pressure of (~10-6 torr). • Sputtering Gun

  5. Process • Sputtering • Even coating on all surfaces • Sputtering plasma: Ar+ • Pt • Cd • Magnetron Sputtering • Lower pressure (~10-3 torr). • Better quality

  6. Substrate Analysis Energy dispersive X-ray spectroscopy EDAX Composition Crystal Structure STEM Scanning Transmission electron microscopy

  7. Control • Pure platinum • TEM grid substrate • Composition: • Pt • Crystal Structure: • Face Center Cubic (FCC)

  8. Pt Image

  9. Bragg Diffraction • Patterns of high and low intensities due to constructive and destructive interference of the incident beam (gives spacing in the crystal structure) Constructive Interference Destructive Interference

  10. Branton Campbell's work FCC Peaks Super lattice peaks

  11. Super lattice peaks

  12. Co-Sputtering • Platinum and Cadmium • Very little Cadmium • Substrate: • TEM Grids • Composition ratio: • ~1 Cd : 3Pt on Cd rich side. More Cadmium More Platinum

  13. Results • ~3 Pt : 1 Cd ratio was achieved. • Were not able to detect any of the super lattice peaks.

  14. L13 • Where are you?

  15. Continuing the Search • Grow thicker sample and subject to bulk x-ray analysis • ~8 μm thick • Look for super lattice peaks. • Check for Composition using EDAX and crystal structure using STEM.

  16. Special thanks to : NSF Richard Vanfleet Jeff Farrer Liz Strein Branton Campbell Pictures borrowed from: • Dr. Hart • Wikipedia • commons.wikimedia.org/wiki/Image:Magnetrongun.jpg • www.nanocenter.umd.edu/new_facilities/NispLab.php • www.gfe.rwth-aachen.de/seiteninhalte_english/geraete.htm • www.gildergrids.co.uk/g100-moly-150.gif • www.tulving.com/bullion/CanadianMapleLeaf9995.jpg • www.moosecreekforge.com/index2.html • www.microscopy.ethz.ch/bragg.htm • www.microscopy.ethz.ch/images/ED_Pt.jpg

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