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1. ϕ ( ρz ) Distributions in Bulk and Thin-Film Samples for EPMA. Part 2: BadgerFilm: A New Thin-Film Analysis Program

   https://doi.org/10.1017/S1431927620024927  

   Moy, Aurélien; Fournelle, John (April 2021, Microscopy and Microanalysis)

   null (Ed.)

   Since the 1960s, thicknesses and compositions of thin-film specimens have been determined by using the nondestructive technique of electron probe microanalysis. This approach, refined in the 1990s, is based upon models of the ionization depth distribution, the so-called ϕ ( ρz ) distribution, and is capable of analyzing layered specimens. Most of these quantification models have led to commercial programs. However, these programs may have possible limitations: some may not be directly compatible with modern computers, they often are “black boxes” making it difficult to assess the reliability of the results, and they are sometimes expensive enough to restrain many labs from purchasing them. We present a user-friendly, free, open-source program, BadgerFilm, implementing a documented ϕ ( ρz ) model and algorithms allowing the quantification of stratified samples. The program has the ability to calculate absolute X-ray intensities that can be directly compared with Monte Carlo simulations. We give a detailed explanation for the operation of the employed ϕ ( ρz ) model in thin films. A wide range of detailed Monte Carlo simulations and experimental data have been used to evaluate and validate the accuracy of the implemented algorithms. BadgerFilm demonstrated excellent quantification results for the films and in many cases for the substrates. 

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2. Local cation ordering in compositionally complex Ruddlesden–Popper n = 1 oxides

   https://doi.org/10.1063/5.0144766  

   Jiang, Bo; Pitike, Krishna_Chaitanya; Lin, De-Ye; Purdy, Stephen_C; Wang, Xin; Zhao, Yafan; Zhang, Yuanpeng; Metz, Peter; Macias, Antonio; Meyer, III, Harry_M; et al (May 2023, APL Materials)

   The Ruddlesden–Popper (RP) layered perovskite structure is of great interest due to its inherent tunability, and the emergence and growth of the compositionally complex oxide (CCO) concept endows the RP family with further possibilities. Here, a comprehensive assessment of thermodynamic stabilization, local order/disorder, and lattice distortion was performed in the first two reported examples of lanthanum-deficient Lan+1BnO3n+1 (n = 1, B = Mg, Co, Ni, Cu, Zn) obtained via various processing conditions. Chemical short-range order (CSRO) at the B-site and the controllable excess interstitial oxygen (δ) in RP-CCOs are uncovered by neutron pair distribution function analysis. Reverse Monte Carlo analysis of the data, Metropolis Monte Carlo simulations, and extended x-ray absorption fine structure analysis implies a modest degree of magnetic element segregation on the local scale. Further, ab initio molecular dynamics simulations results obtained from special quasirandom structure disagree with experimentally observed CSRO but confirm Jahn–Teller distortion of CuO6 octahedra. These findings highlight potential opportunities to control local order/disorder and excess interstitial oxygen in layered RP-CCOs and demonstrate a high degree of freedom for tailoring application-specific properties. They also suggest a need for expansion of theoretical and data modeling approaches in order to meet the innate challenges of CCO and related high-entropy phases. 

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3. Controllable suppression of the unconventional superconductivity in bulk and thin-film ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ via high-energy electron irradiation

   https://doi.org/10.1103/PhysRevResearch.6.033178  

   Ruf, Jacob P; Noad, Hilary_M L; Grasset, Romain; Miao, Ludi; Zhakina, Elina; McGuinness, Philippa H; Nair, Hari P; Schreiber, Nathaniel J; Kikugawa, Naoki; Sokolov, Dmitry; et al (August 2024, Physical Review Research)

   In bulk ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$, the strong sensitivity of the superconducting transition temperature $T_{\text{c}}$to nonmagnetic impurities provides robust evidence for a superconducting order parameter that changes sign around the Fermi surface. In superconducting epitaxial thin-film ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$, the relationship between $T_{\text{c}}$and the residual resistivity ${\rho }_0$, which in bulk samples is taken to be a proxy for the low-temperature elastic scattering rate, is far less clear. Using high-energy electron irradiation to controllably introduce point disorder into bulk single-crystal and thin-film ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$, we show that $T_{\text{c}}$is suppressed in both systems at nearly identical rates. This suggests that part of ${\rho }_0$in films comes from defects that do not contribute to superconducting pairbreaking and establishes a quantitative link between the superconductivity of bulk and thin-film samples. Published by the American Physical Society2024 

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4. The dynamics of freestanding films: predictions for poly(2-chlorostyrene) based on bulk pressure dependence and thoughtful sample averaging

   https://doi.org/10.1039/d1sm01175h  

   White, Ronald P.; Lipson, Jane E. (November 2021, Soft Matter)

   In this paper we model the segmental relaxation in poly(2-chlorostyrene) 18 nm freestanding films, using only data on bulk samples to characterize the system, and predict film relaxation times ( τ ) as a function of temperature that are in semi-quantitative agreement with film data. The ability to translate bulk characterization into film predictions is a direct result of our previous work connecting the effects of free surfaces in films with those of changing pressure in the bulk. Our approach combines the Locally Correlated Lattice (LCL) equation of state for prediction of free volume values ( V free ) at any given density ( ρ ), which are then used in the Cooperative Free Volume (CFV) rate model to predict τ ( T , V free ). A key feature of this work is that we calculate the locally averaged density profile as a function of distance from the surface, ρ av ( z ), using the CFV-predicted lengthscale, L coop ( z ), over which rearranging molecular segments cooperate. As we have shown in the past, ρ av ( z ) is significantly broader than the localized profile, ρ ( z ), which translates into a relaxation profile, τ ( z ), exhibiting a breadth that mirrors experimental and simulated results. In addition, we discuss the importance of averaging the log of position dependent relaxation times across a film sample (〈log  τ ( z )〉), as opposed to averaging the relaxation times, themselves, in order to best approximate a whole sample-averaged value that can be directly compared to experiment. 

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5. Full-band Monte Carlo simulation of two-dimensional electron gas in (Al x Ga1− x )2O3/Ga2O3 heterostructures

   https://doi.org/10.1063/5.0109577  

   Kumar, Avinash; Singisetti, Uttam (November 2022, Journal of Applied Physics)

   β -Gallium oxide (Ga2O3) is an extensively investigated ultrawide-bandgap semiconductor for potential applications in power electronics and radio frequency switching. The room temperature bulk electron mobility (∼200cm2V−1s−1) is comparatively low and is limited by the 30 phonon modes originating from its 10-atom primitive cell. The theoretically calculated saturation velocity in bulk is 1–2×107cms−1 (comparable to GaN) and is limited by the low field mobility. This work explores the high field electron transport (and hence the velocity saturation) in the 2DEG based on the first principles calculated parameters. A self-consistent calculation on a given heterostructure design gives the confined eigenfunctions and eigenenergies. The intrasubband and the intersubband scattering rates are calculated based on the Fermi’s golden rule considering longitudinal optical (LO) phonon–plasmon screening. The high field characteristics are extracted from the full-band Monte Carlo simulation of heterostructures at 300 K. The overall system is divided into a 2D and a 3D region mimicking the electrons in the 2DEG and the bulk, respectively. The electron transport is treated through an integrated Monte Carlo program which outputs the steady state zone population, transient dynamics, and the velocity–field curves for a few heterostructure designs. The critical field for saturation does not change significantly from bulk values, however, an improved peak velocity is calculated at a higher 2DEG density. The velocity at low 2DEG densities is impacted by the antiscreening of LO phonons which plays an important role in shaping the zone population. A comparison with the experimental measurements is also carried out and possible origins of the discrepancies with experiments is discussed. 

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