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Photoinduced halide segregation in mixed halide hybrid perovskites [i.e., APb(I1–xBrx)3] represents an intrinsic instability that impedes their commercialization. Resolving this issue requires deve...

Using time-resolved in situ X-ray photoelectron spectroscopy, we identify and suppress rapid degradation mechanisms for cesium-stabilized formamidinium lead iodide perovskite materials used in stat...

Ion migration represents an intrinsic instability of metal halide perovskite solar cells. Here we show that triple-cation FAxMAyCs1–x–yPbI3 [FA+ = (NH2)2CH+, MA+ = CH3NH3+] active layers with mixed...

Herein, we subject formamidinium lead iodide films to oxygen-containing gases (flowing O

Rapid loss in flora diversity, changing patterns of vegetation and land use patterns in the University of Lagos Akoka campus has necessitated investigation on the herb and grass species so as to determine their compositions, structures and diversity within the area. Twenty sampling plots of 10m x 10m each were studied in five selected locations using random sampling. The samples were counted and identified using Flora of West Tropical Africa. A total of 75 taxa (herbs = 53 spp and grasses = 22 spp) belonging to 26 families and 64 genera were recorded in the area. Of all the families, Asteraceae and Euphorbiaceae had the highest number of species with seven species of herbaceous plants each. The Simpson index value was highest in locations A and D (0.98), Shannon index value was highest in location A (3.96); while evenness value was highest in location E (0.92). Among the herbs, Asystasia gangetica had the highest importance index value (40.22%), while Panicum maximum had the highest importance value (34.87%) among the grasses. The results revealed restricted distribution of the species in specific areas probably due to development of infrastructural facilities in the study area. It is recommended that the species with low importance values should be given priorities in terms of conservation policies for future purposes by planting them and protecting their habitats. Keywords: Conservation; Species composition; UNILAG flora; Urbanization

Solution-processed mixed halide perovskites are excellent materials for multijunction solar cells. Unfortunately, light-induced halide phase segregation has prevented their effective integration into working devices. In this study, we rationalize and quantify anion photosegregation in stoichiometric and halide-deficient MAPb(I1–xBrx)3 thin films through kinetic Monte Carlo simulations and complementary optical measurements. Our study reveals that segregation rates are dictated by halide vacancy hopping barriers and are modulated by vacancy concentrations. The simulations further suggest that near-ubiquitous emission energies, which converge on that for MAPb(I0.8Br0.2)3 (i.e., x ≈ 0.2) following photosegregation, arise from the existence of kinetically trapped Br– within nucleated I-rich domains. An established photosegregation excitation intensity threshold is independent of the number of vacancies and instead depends critically on parameters such as carrier diffusion length, lifetime, and bandgap tunabil...

We study the electronic structure and thermoelectric properties of recently synthesized CoAsSb. The calculated bandgap becomes more accurate for increasingly-complex electronic structure methods: generalized gradient approximation, hybrid functionals, self-consistent linearized quasiparticle GW method (LQSGW), and LQSGW with simplified vertex corrections. By equating the bandgaps of each method from a rigid shift of the bands, we evaluate the contributions made to thermoelectric properties beyond the bandgap. In doing so, we evaluate the efficacy of a common-practice: a rigid shift applied to less-costly electronic structure methods in order to gain some accuracy of the more-costly methods. We find that while the shift made the Seebeck coefficients much closer to one another than from the original electronic structures, there remain differences in the Goldsmid-Sharp (thermoelectric) bandgap between the methods and from the intended electronic bandgap. Additionally, some lasting differences in temperature dependence remain between the methods., Comment: 7 pages, 5 figures

Fluorescence intermittency or blinking is observed in nearly all nanoscale fluorophores. It is characterized by universal power-law distributions in on- and off-times as well as 1/f behaviour in corresponding emission power spectral densities. Blinking, previously seen in confined zero- and one-dimensional systems has recently been documented in two-dimensional reduced graphene oxide. Here we show that unexpected blinking during graphene oxide-to-reduced graphene oxide photoreduction is attributed, in large part, to the redistribution of carbon sp2 domains. This reclustering generates fluctuations in the number/size of emissive graphenic nanoclusters wherein multiscale modelling captures essential experimental aspects of reduced graphene oxide's absorption/emission trajectories, while simultaneously connecting them to the underlying photochemistry responsible for graphene oxide's reduction. These simulations thus establish causality between currently unexplained, long timescale emission intermittency in a quantum mechanical fluorophore and identifiable chemical reactions that ultimately lead to switching between on and off states., 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 of sp2 carbon domains.

Graphene, the first discovered and most studied two-dimensional material, has gained increasing interest in the research community due to a combination of unique optical, electronic transport, and structural properties. Single layer graphene is transparent, conductive, strong and flexible. In this work the mechanical flexibility, conductivity, and solution processing of the material are coupled resulting in direct printing of reduced graphene oxide (RGO) strain sensors using 3D printer platforms. Monolayer flakes of commercially available graphene oxide dispersed in water are ink-jet printed and then reduced to form the sensors. The chemical reduction process using ascorbic acid is performed at temperatures compatible with additively manufactured thermoplastics, enabling direct sensor printing during part fabrication. The temperature dependence and piezo-resistance of the sensors are characterized and presented in terms of the variable range hopping model. Experimental results including coupon testing and full-scale flight tests are discussed.Graphene, the first discovered and most studied two-dimensional material, has gained increasing interest in the research community due to a combination of unique optical, electronic transport, and structural properties. Single layer graphene is transparent, conductive, strong and flexible. In this work the mechanical flexibility, conductivity, and solution processing of the material are coupled resulting in direct printing of reduced graphene oxide (RGO) strain sensors using 3D printer platforms. Monolayer flakes of commercially available graphene oxide dispersed in water are ink-jet printed and then reduced to form the sensors. The chemical reduction process using ascorbic acid is performed at temperatures compatible with additively manufactured thermoplastics, enabling direct sensor printing during part fabrication. The temperature dependence and piezo-resistance of the sensors are characterized and presented in terms of the variable range hopping model. Experimental results including coupon testing and...

We report for the first time the synthesis of large, free-standing, Mo2O2(μ-S)2(Et2dtc)2 (MoDTC) nanosheets (NSs), which exhibit an electron-beam induced crystalline-to-amorphous phase transition. Both electron beam ionization and femtosecond (fs) optical excitation induce the phase transition, which is size-, morphology-, and composition-preserving. Resulting NSs are the largest, free-standing regularly shaped two-dimensional amorphous nanostructures made to date. More importantly, amorphization is accompanied by dramatic changes to the NS electrical and optical response wherein resulting amorphous species exhibit room-temperature conductivities 5 orders of magnitude larger than those of their crystalline counterparts. This enhancement likely stems from the amorphization-induced formation of sulfur vacancy-related defects and is supported by temperature-dependent transport measurements, which reveal efficient variable range hopping. MoDTC NSs represent one instance of a broader class of transition metal ...

We have computationally explored workfunction values of Cs2Te5, an existing crystalline phase of the Cs-Te system and a small bandgap semiconductor, in order to search for reduced workfunction alternatives of Cs2Te that preserve the exceptionally high quantum efficiency of the Cs2Te seasoned photoemissive material. We have found that the Cs2Te5(010) surface exhibits a workfunction value of ~ 1.9 eV when it is covered by Cs atoms. Cs2Te5 is analogous to our recently proposed low-workfunction materials, Cs2TeC2 and other ternary acetylides [J. Z. Terdik, et al., Phys. Rev. B 86, 035142 (2012)], in as much as it also contains quasi one-dimensional substructures embedded in a Cs-matrix, forming the foundation for anomalous workfunction anisotropy, and low workfunction values. The one-dimensional substructures in Cs2Te5 are polytelluride ions in a tetragonal rod packing. Cs2Te5 has the advantage of simpler composition and availability as compared to Cs2TeC2, however its low workfunction surface is less energetically favored to the other surfaces than in Cs2TeC2., submitted for publication