ISU Updates

• Rupa Dumpala, Scott Broderick, Joaquin Peralta and Krishna Rajan

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

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

Chemistry of Gas-Solid Reactions

We have analyzed gas-solid reactions of materials and the resulting bonds

• Oxidation of Aluminum at 450 C, 2.5 x 10-3 Torr for 10 min.

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.

Interface from Gas-Solid Reactions

Measurement of two dimensional interfaces.

Bulk Al2O3 phase Bulk Al phase

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

Interface

Diffusion Profile

3D Interface from Gas-Solid Reactions

The shape of the sample --- all collected atoms are imaged

Diffusion Profile

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

3D Interface from Gas-Solid Reactions

Iso surface-Al (80%)

Diffusion Profile

3D Interface from Gas-Solid Reactions

Iso surface- O (1.93%)

Diffusion Profile

3D Interface from Gas-Solid Reactions

Iso surface-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.

Al (41%)

Al (80%)

Al (97%)

O (1.93%)

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.

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.