1. ISU Updates
Rupa Dumpala, Scott Broderick, Joaquin Peralta and Krishna Rajan

2. Summary of Previous Results
Atom probe experimentation
Atomic scale measurement of gas-solid reactions of Al and Oxygen
Compound formation
Study of Interfacial chemistry
Environmental chamber for in-situ gas reactions – Unique features and capabilities
Collaborations:
Maryland – Sample prepared by Maryland by reacting Si microtips; analysis of samples by ISU
Van Duin group – Use of atom probe results for experimental inputs into ReaxFF simulations

3. Progress Atom probe experimentation
-3D interface analysis of gas solid reactions - Iso surface concentrations
-Interfacial chemistry, morphology, etc.
Atomic scale measurement of gas-solid reactions of Si and oxygen
Refinements in Environmental chamber set up for in-situ gas reactions
Future Steps
Gas solid reactions of near space environment condition
Surface reactions / orientation dependence of reactions

4. Chemistry of Gas-Solid Reactions
We have analyzed gas-solid reactions of materials and the resulting bonds
The Al-O compounds shown are from an Al2O3 phase. By measuring the compounds, we get a more local chemical measurement – Al2O3 phase comprised of Al2O, Al2O2, AlO and AlO2 clusters.
Oxidation of Aluminum at 450 C, 2.5 x 10-3 Torr for 10 min.

5. Interface from Gas-Solid Reactions
Measurement of two dimensional interfaces.
Bulk Al2O3 phase
Bulk Al phase
Interface
Interface shown from reaction of O and Al. Identify Al2O3 as bulk phase of gas-solid reaction, and perovskite phase at the interface.
We have further developed this approach to imaging of 3D interfaces. - Interface shape - Interface uniformity

6. 3D Interface from Gas-Solid Reactions
The shape of the sample --- all collected atoms are imaged
Diffusion Profile

7. 3D Interface from Gas-Solid Reactions
Iso surface-Al (41%)
Instead of imaging each atom, we are showing the surface corresponding to the concentrations measured in the diffusion profiles.
Diffusion Profile

8. 3D Interface from Gas-Solid Reactions
Iso surface-Al (80%)
Diffusion Profile

9. 3D Interface from Gas-Solid Reactions
Iso surface- O (1.93%)
Diffusion Profile

10. 3D Interface from Gas-Solid Reactions
Iso surface-Al (97%)
Diffusion Profile

11. O (1.93%)
Al (80%)
Al (41%)
Al (97%)
Image of changing interfacial isosurfaces with changing interfacial chemistry.
Interface is uniform, and the shape of interface does not change significantly with chemistry.

12. Future Result: Surface Reactions from Gas-Solid Reactions
Results shown for O and Si reaction. Reaction sites identified and resulting compounds / bonds identified.
We will expand this approach to consider orientational dependence of reactions and measure compound formations as a function of orientation – expand work beyond chemical reactions to incorporate crystallography.

13. APT Environmental Chamber Update
Improvements made to environmental chamber:
Vacuum in chamber improved two orders of magnitude to 10-8 torr
Control of gas pressure enhanced for finer measurement and representation of space conditions
Increased possible gas systems that can be introduced into chamber to CO.