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 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.

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

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%) Diffusion Profile

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.

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.