isu updates rupa dumpala, scott broderick, joaquin peralta and krishna rajan
TRANSCRIPT
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ISU Updates
• Rupa Dumpala, Scott Broderick, Joaquin Peralta and Krishna Rajan
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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
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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
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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.
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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
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Diffusion Profile
3D Interface from Gas-Solid Reactions
The shape of the sample --- all collected atoms are imaged
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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.
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Diffusion Profile
3D Interface from Gas-Solid Reactions
Iso surface-Al (80%)
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Diffusion Profile
3D Interface from Gas-Solid Reactions
Iso surface- O (1.93%)
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Diffusion Profile
3D Interface from Gas-Solid Reactions
Iso surface-Al (97%)
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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%)
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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.
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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.