The Local Bonding Environment of Amorphous In-Zn-O Films Studied by X-ray Absorption Fine Structure and Total X-ray Scattering Using Synchrotron Radiation

The structure of amorphous In-Zn-O (a-IZO) thin films was investigated using X-ray absorption fine structure (XAFS) and total X-ray scattering techniques. In spite of the lack of long-range periodicity, a-IZO thin films were found to exhibit significant ordering on short length scales. It was found that indium and zinc are 6- and 4- fold coordinated with oxygen, respectively, as they are in their native crystalline structures. The InO6 and ZnO4 polyhedra were also found to exhibit edge-sharing connectivity. Although the edge-shared polyhedra had a significant distribution of bond lengths, the next-nearest neighbor metal atoms occurred at approximately the same composition found using bulk composition measurements. The wide temperature and composition range where IZO films remain amorphous is likely due to the structural frustration induced by Zn-centered tetrahedrons and In-centered octahedrons

Coronal Heating as Determined by the Solar Flare Frequency Distribution Obtained by Aggregating Case Studies

Flare frequency distributions represent a key approach to addressing one of the largest problems in solar and stellar physics: determining the mechanism that counter-intuitively heats coronae to temperatures that are orders of magnitude hotter than the corresponding photospheres. It is widely accepted that the magnetic field is responsible for the heating, but there are two competing mechanisms that could explain it: nanoflares or Alfv\'en waves. To date, neither can be directly observed. Nanoflares are, by definition, extremely small, but their aggregate energy release could represent a substantial heating mechanism, presuming they are sufficiently abundant. One way to test this presumption is via the flare frequency distribution, which describes how often flares of various energies occur. If the slope of the power law fitting the flare frequency distribution is above a critical threshold, $\alpha=2$ as established in prior literature, then there should be a sufficient abundance of nanoflares to explain coronal heating. We performed $>$600 case studies of solar flares, made possible by an unprecedented number of data analysts via three semesters of an undergraduate physics laboratory course. This allowed us to include two crucial, but nontrivial, analysis methods: pre-flare baseline subtraction and computation of the flare energy, which requires determining flare start and stop times. We aggregated the results of these analyses into a statistical study to determine that $\alpha = 1.63 \pm 0.03$. This is below the critical threshold, suggesting that Alfv\'en waves are an important driver of coronal heating.Comment: 1,002 authors, 14 pages, 4 figures, 3 tables, published by The Astrophysical Journal on 2023-05-09, volume 948, page 7