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
L13 Structure

4. Setup and Preparation Vacuum system Sputtering Gun
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 Magnetron Sputtering Even coating on all surfaces
Sputtering plasma: Ar+ Pt Cd
Magnetron Sputtering
Lower pressure (~10-3 torr).
Better quality

6. EDAX Composition Crystal Structure STEM Substrate Analysis
Energy dispersive X-ray spectroscopy
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 Constructive Interference Destructive Interference
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:
More Cadmium
More Platinum
Co-Sputtering
Platinum and Cadmium
Very little Cadmium
Substrate:
TEM Grids
Composition ratio:
~1 Cd : 3Pt on Cd rich side.

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