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1. X-ray emission spectroscopy: an effective route to extract site occupation of cations

   https://doi.org/10.1039/c8cp04628j  

   Bhargava, Anuj; Chen, Cindy Y.; Finkelstein, Kenneth D.; Ward, Matthew J.; Robinson, Richard D. (November 2018, Physical Chemistry Chemical Physics)

   Cation site occupation is an important determinant of materials properties, especially in a complex system with multiple cations such as in ternary spinels. Many methods for extracting the cation site information have been explored in the past, including analysis of spectra obtained through K-edge X-ray absorption spectroscopy (XAS). In this work, we measure the effectiveness of X-ray emission spectroscopy (XES) for determining the cation site occupation. As a test system we use spinel phase Co x Mn 3−x O 4 nanoparticles contaminated with CoO phases because Co and Mn can occupy all cation sites and the impurity simulates typical products of oxide syntheses. We take advantage of the spin and oxidation state sensitive Kβ 1,3 peak obtained using XES and demonstrate that XES is a powerful and reliable technique for determining site occupation in ternary spinel systems. Comparison between the extended X-ray absorption fine structure (EXAFS) and XES techniques reveals that XES provides not only the site occupation information as EXAFS, but also additional information on the oxidation states of the cations at each site. We show that the error for EXAFS can be as high as 35% which makes the results obtained ambiguous for certain stoichiometries, whereas for XES, the error determined is consistently smaller than 10%. Thus, we conclude that XES is a superior and a far more accurate method than XAS in extracting cation site occupation in spinel crystal structures. 

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2. In-cycle evolution of thickness and roughness parameters during oxygen plasma enhanced ZnO atomic layer deposition using in situ spectroscopic ellipsometry

   https://doi.org/10.1116/6.0003830  

   Traouli, Yousra; Kilic, Ufuk; G_Kilic, Sema; Hilfiker, Matthew; Schmidt, Daniel; Schoeche, Stefan; Schubert, Eva; Schubert, Mathias (September 2024, Journal of Vacuum Science & Technology A)

   We investigate the time evolution of ZnO thin film growth in oxygen plasma-enhanced atomic layer deposition using in situ spectroscopic ellipsometry. The recently proposed dynamic-dual-box-model approach [Kilic et al., Sci. Rep. 10, 10392 (2020)] is used to analyze the spectroscopic data post-growth. With the help of this model, we explore the in-cycle surface modifications and reveal the repetitive layer-by-layer growth and surface roughness modification mechanisms during the ZnO ultrathin film deposition. The in situ complex-valued dielectric function of the amorphous ZnO thin film is also determined from the model analysis for photon energies of 1.7–4 eV. The dielectric function is analyzed using a critical point model approach providing parameters for bandgap energy, amplitude, and broadening in addition to the index of refraction and extinction coefficient. The dynamic-dual-box-model analysis reveals the initial nucleation phase where the surface roughness changes due to nucleation and island growth prior to film coalescence, which then lead to the surface conformal layer-by-layer growth with constant surface roughness. The thickness evolution is resolved with Angstrom-scale resolution vs time. We propose this method for fast development of growth recipes from real-time in situ data analysis. We also present and discuss results from x-ray diffraction, x-ray photoelectron spectroscopy, and atomic force microscopy to examine crystallographic, chemical, and morphological characteristics of the ZnO film. 

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3. Study of microstructure of iron species in plants using X ray absorption spectroscopy

   https://doi.org/10.18260/1-2-530.540.660.1139-54978  

   Lee, David; Rahman, Mashtura; Sharma, Shivansh; Ventourat, Michael; Torreno, Julianne; Guha, Nealesh; Cheung, Tak_Choi David; An, Guozheng; Dehipawala, Sunil; Robinson, Lexi; et al (March 2025, ASEE Conferences)

   The X-ray absorption spectroscopy including Extended X ray Absorption Fine Structure (EXAFS) , X ray Absorption Near Edge Structure (XANES) and X-ray absorption near edge and pre edge feature is used to analyze the nature and concentration of iron in plants, spinach and parsley. Primary data was collected at Cornell High Energy Synchrotron Source. Data analyses were done by community college students. EXAFS data analysis process include edge normalization, background subtraction, transformation to k space from energy, Fourier transformation, back transform of selected peaks, and curve fitting to identify type and number of near neighbor atoms. X-ray absorption pre=edge feature, which appears as very small absorption peak before the main peak, is used to study ironoxygen bonding and asymmetry of iron compounds. Pre edge data analysis include extraction of the pre-edge from main absorption spectrum, normalization to main edge height, and Lorentzian fit to back ground subtracted data. X-ray absorption data from spinach and parsley, as well as several iron supplements and the soil of which plants were grown was analyzed. The preliminary data analysis pre edge feature yields two forms of iron in both plants. One form has oxygen as near neighbor atoms and the other without oxygen. 

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4. Discussion to: Bayesian graphical models for modern biological applications by Y. Ni, V. Baladandayuthapani, M. Vannucci and F.C. Stingo

   https://doi.org/10.1007/s10260-021-00600-7  

   Schweinberger, Michael (January 2021, Statistical Methods & Applications)

   It is a pleasure to congratulate Ni et al. (Stat Methods Appl 490:1–32, 2021) on the recent advances in Bayesian graphical models reviewed in Ni et al. (Stat Methods Appl 490:1–32, 2021). The authors have given considerable thought to the construction and estimation of Bayesian graphical models that capture salient features of biological networks. My discussion focuses on computational challenges and opportunities along with priors, pointing out limitations of the Markov random field priors reviewed in Ni et al. (Stat Methods Appl 490:1–32, 2021) and exploring possible generalizations that capture additional features of conditional independence graphs, such as hub structure and clustering. I conclude with a short discussion of the intersection of graphical models and random graph models. 

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5. Pinpointing lattice-matched conditions for wurtzite ScxAl1−xN/GaN heterostructures with x-ray reciprocal space analysis

   https://doi.org/10.1063/5.0221374  

   Kumar, Rajendra; Gopakumar, Govardan; Abdin, Zain Ul; Manfra, Michael J; Malis, Oana (July 2024, Applied Physics Letters)

   Using comprehensive x-ray reciprocal space mapping, we establish the precise lattice-matching composition for wurtzite ScxAl1−xN layers on (0001) GaN to be x = 0.14 ± 0.01. 100 nm thick ScxAl1−xN films (x = 0.09–0.19) were grown in small composition increments on c-plane GaN templates by plasma-assisted molecular beam epitaxy. The alloy composition was estimated from the fit of the (0002) x-ray peak positions, assuming the c-lattice parameter of ScAlN films coherently strained on GaN increases linearly with Sc-content determined independently by Rutherford backscattering spectrometry [Dzuba et al., J. Appl. Phys. 132, 175701 (2022)]. Reciprocal space maps obtained from high-resolution x-ray diffraction measurements of the (101¯5) reflection reveal that ScxAl1−xN films with x = 0.14 ± 0.01 are coherently strained with the GaN substrate, while the other compositions show evidence of relaxation. The in-plane lattice-matching with GaN is further confirmed for a 300 nm thick Sc0.14Al0.86N layer. The full-width-at-half-maximum of the (0002) reflection rocking curve for this Sc0.14Al0.86N film is 106 arc sec and corresponds to the lowest value reported in the literature for wurtzite ScAlN films. 

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