Austin Shearin pg. 1

MAT 760 Homework 4 Topas and EDX measurements

Using the EDX measurements from the SEM, we can see a list of the possible elements in the sample we have. The data from the EDX is as follows:

EDX ResultsPre-annealed sample Post-annealed sampleCopper substrate Silicon substrate Copper substrate Silicon substrateElement Atomic % Element Atomic % Element Atomic % Element Atomic %C 5.21 C 1.22 C 3.13 C 1.28O 66.95 O 70.68 O 68.65 O 67.00Na 0.31 Na 0.32 Na 0.34 Na 0.32Mg 0.43 Mg 0.44 Mg 0.43 Mg 0.44Al 6.81 Al 7.02 Al 7.09 Al 7.74Si 17.45 Si 17.90 Si 17.80 Si 20.34S 0.17 S 0.15 K 0.77 K 0.98K 0.78 K 0.79 Ca 0.13 Ca 0.18Ca 0.14 Ca 0.14 Ti 0.09 Ti 0.13Ti 0.10 Ti 0.10 Fe 1.25 Fe 1.59Fe 1.19 Fe 1.23 Cu 0.30Cu 0.46

Looking at the results, with the very minute percentages of certain elements, I regarded them as mostly noise. Carbon is hard to justify being in the samples as there is a carbon buildup from exposure to the SEM. Copper can be eliminated as its only present on the copper substreate. The largest percentages of elements that I believed were not noise were silicon, oxygen, aluminum, and iron. It’s also safe to assume that with the large amount of oxygen, and since these were found in nature, that these elements are in the form of oxides. I looked for the (.cif) files for the molecules of Fe2O3, Al2O3, and SiO2 on the international crystallography database. From the multiple space groups of each of the molecules, I first looked up which appeared most commonly in nature and used Mercury software to identify the most intense peaks that corresponded with the XRD data we have. I used (.cif) files for these space groups of molecules:

Molecule Space groupSiO2 P 32 2 1Al2O3 R -3cFe2O3 R -3c

Finally, I fitted the XRD data in the Topas Software with the results as follows:

The pre-annealed sample had much more amorphous structure in it so I had to use a much high order background to get a decent fit. I also excluded the regions before 15° as it was an amorphous peak and wasn’t good for the fitting results. My goodness of fit was 1.43.

Austin Shearin pg. 2

Austin Shearin pg. 3

The annealed sample had much less background and had sharper peaks. I was able to get a much better fit. My goodness of fit got down to 1.16.

Austin Shearin pg. 4

My phase percentages from the Topas fitting is as follows:

Topas Phase PercentagesPre-annealed Post-annealedMolecule Phase Percentage (%) Molecule Phase Percentage (%)SiO2 58.973 SiO2 50.209Al2O3 39.687 Al2O3 36.631Fe2O3 1.339 Fe2O3 13.160

It can be seen that the EDX atomic percentages correlate to the Topas phase percentages. The pre-annealed sample had a weaker fit, but the Topas phase percentage for iron oxide matches up better with the EDX atomic percentage results.

I’ve attempted to insert the files I have into my paper below: