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Comparing XRD data for 225C and 300C growth of Si-Heusler.

Comparing XRD data for 225C and 300C growth of Si-Heusler. Some composition assumption for sample grown at 225C. S230 grown at 300C Si Comp = 22.9 at.%. S239 grown at 225C Si Comp = 27 at.%?. Things I noticed:. (022) intensity higher for 225C growth at Heusler Comp

gary-rogers
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Comparing XRD data for 225C and 300C growth of Si-Heusler.

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  1. Comparing XRD data for 225C and 300C growth of Si-Heusler. Some composition assumption for sample grown at 225C.

  2. S230 grown at 300C Si Comp = 22.9 at.% S239 grown at 225C Si Comp = 27 at.%?

  3. Things I noticed: • (022) intensity higher for 225C growth at Heusler Comp • Large area of higher intensity and in-plane lattice matching (65-90)%Co • FWHM shows similar trend • No Significant difference in in-plane peak width for the two growth temperatures • (111) very wide at 225C growth • On the 300C sample, the strain is different for each reflection (the position traces do not collapse on top of each other) wereas they agree in the 225C sample • Comparing Zero Strain w/Si concentration suggests zero strain if Si was 25at% • Zero Strain doesn’t necessarily correspond with highest intensity of narrowest peak

  4. Comparing Chemical Order The idea here is to measure the chemical ordering qualitatively. I’ve divided the integrated intensity of each superlattice peak by the fundamental to remove variations in structural disorder. F=(022)c=(014)h S1=(002)c=(102)h S2=(111)c=(011)h No significant changes in intensity within the “good” region (65-85)% Co No difference in S1/F for the two temperatures Significant difference in intensities for S2/F: the (111) peak is MUCH stronger relative to the fundamental peak for 300C growth

  5. Comparing phi-scan FWHM FWHM vs Comp at Two Growth Temps Example of two components in s239 HeuslerStoichiometry Data Compare • Voigt could not fit well, so I found FWHM via max value and located max/2 in the data after background subraction • S239 had 2 components probably due to 2 distinct populations of grain sizes. I fit the wider as a polynomial background • Clearly, the sample grown at 225C has a narrower width at the Heusler composition

  6. L-scans of (014) on s231 (Si~19at%)Grown at 150C and 1/3 as Thick as Others • A couple bad spots at ~90% Co • Zero strain @ ~84% Co • Position/Strain changes monotonically/linearly • Width strange

  7. Some General Conclusions • Si-concentration is a bigger factor to determine strain than Co/Mn ratio • Higher Co concentration is better ordered than Heuslerstoichiometry regardless of growth temp according to intensities • Large region of composition gives good ordering according to peak widths • These samples are still too different to make a definitive statement on growth temperature • Different Si concentrations • Different layer ordering when grown • Different thicknesses (at least the 150C sample) • Improving the study: • Study Si-dependant samples • Grow all three samples in a immediately after each other rather than venting or composition recalibration to ensure const Si btwn samples

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