Oak Ridge National Laboratory

About: Oak Ridge National Laboratory is a facility organization based out in Oak Ridge, Tennessee, United States. It is known for research contribution in the topics: Neutron & Ion. The organization has 31868 authors who have published 73724 publications receiving 2633689 citations. The organization is also known as: ORNL.

Perovskite–fullerene hybrid materials suppress hysteresis in planar diodes

Abstract: Solution-processed planar perovskite devices are highly desirable in a wide variety of optoelectronic applications; however, they are prone to hysteresis and current instabilities. Here we report the first perovskite-PCBM hybrid solid with significantly reduced hysteresis and recombination loss achieved in a single step. This new material displays an efficient electrically coupled microstructure: PCBM is homogeneously distributed throughout the film at perovskite grain boundaries. The PCBM passivates the key PbI3(-) antisite defects during the perovskite self-assembly, as revealed by theory and experiment. Photoluminescence transient spectroscopy proves that the PCBM phase promotes electron extraction. We showcase this mixed material in planar solar cells that feature low hysteresis and enhanced photovoltage. Using conductive AFM studies, we reveal the memristive properties of perovskite films. We close by positing that PCBM, by tying up both halide-rich antisites and unincorporated halides, reduces electric field-induced anion migration that may give rise to hysteresis and unstable diode behaviour.

Parameter-free calculations of X-ray spectra with FEFF9

Abstract: We briefly review our implementation of the real-space Green's function (RSGF) approach for calculations of X-ray spectra, focusing on recently developed parameter free models for dominant many-body effects. Although the RSGF approach has been widely used both for near edge (XANES) and extended (EXAFS) ranges, previous implementations relied on semi-phenomenological methods, e.g., the plasmon-pole model for the self-energy, the final-state rule for screened core hole effects, and the correlated Debye model for vibrational damping. Here we describe how these approximations can be replaced by efficient ab initio models including a many-pole model of the self-energy, inelastic losses and multiple-electron excitations; a linear response approach for the core hole; and a Lanczos approach for Debye–Waller effects. We also discuss the implementation of these models and software improvements within the FEFF9 code, together with a number of examples.

The genome of Laccaria bicolor provides insights into mycorrhizal symbiosis

Abstract: Mycorrhizal symbioses—the union of roots and soil fungi—are universal in terrestrial ecosystems and may have been fundamental to land colonization by plants1,2. Boreal, temperate and montane forests all depend on ectomycorrhizae1. Identification of the primary factors that regulate symbiotic development and metabolic activity will therefore open the door to understanding the role of ectomycorrhizae in plant development and physiology, allowing the full ecological significance of this symbiosis to be explored. Here we report the genome sequence of the ectomycorrhizal basidiomycete Laccaria bicolor (Fig. 1) and highlight gene sets involved in rhizosphere colonization and symbiosis. This 65-megabase genome assembly contains 20,000 predicted protein-encoding genes and a very large number of transposons and repeated sequences. We detected unexpected genomic features, most notably a battery of effector-type small secreted proteins (SSPs) with unknown function, several of which are only expressed in symbiotic tissues. The most highly expressed SSP accumulates in the proliferating hyphae colonizing the host root. The ectomycorrhizae-specific SSPs probably have a decisive role in the establishment of the symbiosis. The unexpected observation that the genome of L. bicolor lacks carbohydrate-active enzymes involved in degradation of plant cell walls, but maintains the ability to degrade non-plant cell wall polysaccharides, reveals the dual saprotrophic and biotrophic lifestyle of the mycorrhizal fungus that enables it to grow within both soil and living plant roots. The predicted gene inventory of the L. bicolor genome, therefore, points to previously unknown mechanisms of symbiosis operating in biotrophic mycorrhizal fungi. The availability of this genome provides an unparalleled opportunity to develop a deeper understanding of the processes by which symbionts interact with plants within their ecosystem to perform vital functions in the carbon and nitrogen cycles that are fundamental to sustainable plant productivity.

Biochemical Limitations to Carbon Assimilation in C3 Plants—A Retrospective Analysis of the A/Ci Curves from 109 Species

Abstract: differences in the assimilation of atmospheric CO2 depends upon differences in the capacities for the biochemical reactions that regulate the gas-exchange process. Quantifying these differences for more than a few species, however, has proven difficult. Therefore, to understand better how species differ in their capacity for CO2 assimilation, a widely used model, capable of partitioning limitations to the activity of ribulose-l,5-W.sphosphate carboxylase-oxygenase, to the rate of ribulose 1,5-tophosphate regeneration via electron transport, and to the rate of triose phosphate utilization was used to analyse 164 previously published A/C, curves for 109 C3 plant species. Based on this analysis, the maximum rate of carboxylation, Vcmax, ranged from 6/umol m~2 s"1 for the coniferous species Picea abies to 194jj,mol m" 2 s"1 for the agricultural species Beta vulgaris, and averaged 64^mol m" 2 s"1 across all species. The maximum rate of electron transport, Jmx, ranged from 17/^mol m~2 s"1 again for Picea abies to 372/j.mol m~2 s"1 for the desert annual Mahastrum rotundifolium, and averaged 134fxmol m~2 s"1 across all species. A strong positive correlation between Vc^x and Jmax indicated that the assimilation of CO2 was regulated in a co-ordinated manner by these two component processes. Of the AjC{ curves analysed, 23 showed either an insensitivity or reversed-sensitivity to increasing CO2 concentration, indicating that CO2 assimilation was limited by the utilization of triose phosphates. The rate of triose phosphate utilization ranged from 4-9/xtnol m" 2 s"1 for the tropical perennial Tabebuia rosea to 20-1 /xmol m~2 s"1 for the weedy annual Xanthium strumarium, and averaged 101 ftmol m" 2 s"1 across all species. Despite what at first glance would appear to be a wide range of estimates for the biochemical capacities that regulate CO2 assimilation, separating these species-specific results into those of broad plant categories revealed that Vcmax and Jmax were in general higher for herbaceous annuals than they were for woody perennials. For annuals, Vc^^ and Jmax averaged 75 and 154ftmol m~2 s"1, while for perennials these same two parameters averaged only 44 and 97/xmol m~2 s"1, respectively. Although these differences between groups may be coincidental, such an observation points to differences between annuals and perennials in either the availability or allocation of resources to the gas-exchange process.