Suchergebnisse

Despite the advances in the methods for fabricating nanoscale materials, critical issues remain, such as the difficulties encountered in anchoring, and the deterioration in their stability after integration with other components. These issues need to be addressed to further increase the scope of their applicability. In this study, using epitaxial mesoscopic host matrices, materials are spatially confined at the nanoscale, and are supported, anchored, and stabilized. They also exhibit properties distinct from the bulk counterparts proving their high quality nanoscale nature. ZnFe₂O₄ and SrTiO3 are used as the model confined material and host matrix, respectively. The ZnFe₂O₄ phases are spatially confined by the SrTiO₃ mesoscopic matrix and have strongly enhanced ferrimagnetic properties as compared to bulk and plain thin films of ZnFe₂O₄ , with a Curie temperature of ≈500 K. The results of a series of control experiments and characterization measurements indicate that cationic inversion, which originates from the high interface-to-volume ratio of the ZnFe₂O₄ phase in the ZnFe2O4–SrTiO₃ nanocomposite film, is responsible for the magnetization enhancement. An exchange bias is observed, owing to the coexistence of ferrimagnetic and antiferromagnetic regions in the confined ZnFe₂O₄ phase. The magnetic properties are dependent on the ZnFe₂O₄ crystallite size, which can be controlled by the growth conditions. ; Chaewoon Park and Rui Wu contributed equally to this work. We acknowledge the 2017 Research Fund (1.170080.01) of UNIST (Ulsan National Institute of Science & Technology). This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP; Ministry of Science, ICT & Future Planning) (No. 2017R1C1B5075626). The work in Cambridge was funded by the Leverhulme Trust grant # RPG-2015-017, and EPSRC grants EP/N004272/1 and EP/M000524/1. Sandia National Laboratories is a multi-program laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. We also acknowledge the support from the U.S. National Science Foundation (DMR-1643911) for the TEM work at Purdue University.

Hybrid perovskite-based optoelectronic devices are demonstrating unprecedented growth in performance, and defect passivation approaches are highly promising routes to further improve properties. Here, the effect of the molecular ion BF4-, introduced via methylammonium tetrafluoroborate (MABF4) in a surface treatment for MAPbI3 perovskite is reported. The optical spectroscopic characterisations shows that the introduction of tetrafluoroborate leads to reduced non-radiative charge carrier recombination with a reduction in first order recombination rate from 6.5 × 106 to 2.5 × 105 s-1 in BF4--treated samples, and a consequent increase in photoluminescence quantum yield by an order of magnitude (from 0.5% to 10.4%). 19F, 11B and 14N solid-state NMR is used to elucidate the atomic-level mechanism of the BF4- additive-induced improvements, revealing that the BF4- acts as a scavenger of excess MAI by forming MAI–MABF4 cocrystals. This shifts the equilibrium of iodide concentration in the perovskite phase is presumably due to the formation of MAI-MABF4 cocrystal, thereby reducing the concentration of interstitial iodide defects that act as deep traps and non-radiative recombination centers. These collective results allow us, for the first time, to elucidate the microscopic mechanism of action of BF4-. ; S.N. would like to acknowledge Royal Society-SERB Newton International Fellowship for funding. S.D.S. acknowledges the Royal Society and Tata Group (UF150033) and the EPSRC (EP/R023980/1). This work has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 841136. M.A.H. acknowledges support from the Royal Society (RP/R1/180147). S.M. thanks the EPRSC for funding. J.L.M-D. and W.-W. L. thank the UK Royal Academy of Engineering, grant CiET1819_24, EPSRC grants EP/N004272/1, EP/P007767/1, the Winton Programme for the Physics of Sustainability, and Bill Welland.