Search

This is the first of a series of papers that will introduce a user-friendly, detailed, and modular Galactic Chemical Evolution Model , GalCEM , that tracks isotope masses as a function of time in a given galaxy. The list of tracked isotopes automatically adapts to the complete set provided by the input yields. The present iteration of GalCEM tracks 86 elements broken down into 451 isotopes. The prescription includes massive stars, low-to-intermediate-mass stars, and Type Ia supernovae as enrichment channels. We have developed a preprocessing tool that extracts multidimensional interpolation curves from the input yield tables. These interpolation curves improve the computation speeds of the full convolution integrals, which are computed for each isotope and for each enrichment channel. We map the integrand quantities onto consistent array grids in order to perform the numerical integration at each time step. The differential equation is solved with a fourth-order Runge–Kutta method. We constrain our analysis to the evolution of all light and intermediate elements from carbon to zinc, and lithium. Our results are consistent up to the extremely metal-poor regime with Galactic abundances. We provide tools to track the mass rate change of individual isotopes on a typical spiral galaxy with a final baryonic mass of 5 × 10 ^10 M _⊙ . Future iterations of the work will extend to the full periodic table by including the enrichment from neutron-capture channels as well as spatially dependent treatments of galaxy properties. GalCEM is publicly available at https://github.com/egjergo/GalCEM .

Metal halide perovskite materials (MHPs) are a family of next-generation semiconductors that are enabling low-cost, high-performance solar cells and optoelectronic devices. The most-used halogen in MHPs, iodine, can supplement its octet by covalent bonding resulting in atomic charges intermediate to I− and I0. Here, we examine theoretically stabilized defects of iodine using density functional theory (DFT); defect formation enthalpies and iodine Bader charges which illustrate how MHPs adapt to stoichiometry changes. Experimentally, X-ray photoelectron spectroscopy (XPS) is used to identify perovskite defects and their relative binding energies, and validate the predicted chemical environments of iodine defects. Examining MHP samples with excess iodine compared with near stoichiometric samples, we discern additional spectral intensity in the I 3d5/2 XPS data arising from defects, and support the presence of iodine trimers. I 3d5/2 defect peak areas reveal a ratio of 2:1, matching the number of atoms at the ends and middle of the trimer, whereas their binding energies agree with calculated Bader charges. Results suggest the iodine trimer is the preferred structural motif for incorporation of excess iodine into the perovskite lattice. Understanding these easily formed photoactive defects and how to identify their presence is essential for stabilizing MHPs against photodecomposition.

Fluorescence blinking has been recently observed in two-dimensional graphene oxide systems, yet its origin has so far remained elusive. Here, the authors unveil the nature of such long timescale emission intermittency and link it to the distribution ofsp2 carbon domains.