Searching for One of Nature’s Missing Crystal Structures

Thomas McConkie, David Allred, Gus Hart, Brian Hicks

What missing crystal structures?Setup and PreparationExperimental MethodsResultsContinuing the Search

“Where are natures missing structures?”Gus Hart, Nov. 11, 2007

L13 Structure

Vacuum systemRoughing, Turbo and Cryo Pumps.Leaked checked system to minimize

unwanted interference by outside air. Base pressure of (~10-6 torr).

Sputtering Gun

SputteringEven coating on all

surfacesSputtering plasma: Ar+PtCd

Magnetron SputteringLower pressure

(~10-3 torr).Better quality

Composition

Crystal Structur

e

EDAXEnergy dispersive X-ray spectroscopy

STE

M

Scanning Transmission electron microscopy

Pure platinumTEM grid substrateComposition:

PtCrystal Structure:

Face Center Cubic (FCC)

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)

FCC Peaks

Super lattice peaks

Super lattice peaks

Platinum and CadmiumVery little Cadmium Substrate:

TEM GridsComposition ratio:

~1 Cd : 3Pt on Cd rich side.

More Cadmium

More Platinum

~3 Pt : 1 Cd ratio was achieved.

Were not able to detect any of the super lattice peaks.

Where are you?

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.

Special thanks to :NSF

Richard VanfleetJeff FarrerLiz Strein

Branton Campbell