We report valence and conduction band densities of states measured via ultraviolet and inverse photoemission spectroscopies on three metal halide perovskites, specifically methylammonium lead iodide ...and bromide and cesium lead bromide (MAPbI3, MAPbBr3, CsPbBr3), grown at two different institutions on different substrates. These are compared with theoretical densities of states (DOS) calculated via density functional theory. The qualitative agreement achieved between experiment and theory leads to the identification of valence and conduction band spectral features, and allows a precise determination of the position of the band edges, ionization energy and electron affinity of the materials. The comparison reveals an unusually low DOS at the valence band maximum (VBM) of these compounds, which confirms and generalizes previous predictions of strong band dispersion and low DOS at the MAPbI3 VBM. This low DOS calls for special attention when using electron spectroscopy to determine the frontier electronic states of lead halide perovskites.
Extremely low energy consumption neuromorphic computing is required to achieve massively parallel information processing on par with the human brain. To achieve this goal, resistive memories based on ...materials with ionic transport and extremely low operating current are required. Extremely low operating current allows for low power operation by minimizing the program, erase, and read currents. However, materials currently used in resistive memories, such as defective HfO x , AlO x , TaO x , etc., cannot suppress electronic transport (i.e., leakage current) while allowing good ionic transport. Here, we show that 2D Ruddlesden–Popper phase hybrid lead bromide perovskite single crystals are promising materials for low operating current nanodevice applications because of their mixed electronic and ionic transport and ease of fabrication. Ionic transport in the exfoliated 2D perovskite layer is evident via the migration of bromide ions. Filaments with a diameter of approximately 20 nm are visualized, and resistive memories with extremely low program current down to 10 pA are achieved, a value at least 1 order of magnitude lower than conventional materials. The ionic migration and diffusion as an artificial synapse is realized in the 2D layered perovskites at the pA level, which can enable extremely low energy neuromorphic computing.
Arsenic is methylated by arsenite (As(III)) S-adenosylmethionine (SAM) methyltransferases (ArsMs). ArsM crystal structures show three domains (an N-terminal SAM binding domain (A domain), a central ...arsenic binding domain (B domain), and a C-terminal domain of unknown function (C domain)). In this study, we performed a comparative analysis of ArsMs and found a broad diversity in structural domains. The differences in the ArsM structure enable ArsMs to have a range of methylation efficiencies and substrate selectivities. Many small ArsMs with 240–300 amino acid residues have only A and B domains, represented by RpArsM from Rhodopseudomonas palustris. These small ArsMs have higher methylation activity than larger ArsMs with 320–400 residues such as Chlamydomonas reinhardtii CrArsM, which has A, B, and C domains. To examine the role of the C domain, the last 102 residues in CrArsM were deleted. This CrArsM truncation exhibited higher As(III) methylation activity than the wild-type enzyme, suggesting that the C-terminal domain has a role in modulating the rate of catalysis. In addition, the relationship of arsenite efflux systems and methylation was examined. Lower rates of efflux led to higher rates of methylation. Thus, the rate of methylation can be modulated in multiple ways.
Hybrid perovskite semiconductors represent a promising platform for color-tunable light emitting diodes (LEDs) and lasers; however, the behavior of these materials under the intense electrical ...excitation required for electrically-pumped lasing remains unexplored. Here, we investigate methylammonium lead iodide-based perovskite LEDs under short pulsed drive at current densities up to 620 A cm
. At low current density (J < 10 A cm
), we find that the external quantum efficiency (EQE) depends strongly on the time-averaged history of the pulse train and show that this curiosity is associated with slow ion movement that changes the internal field distribution and trap density in the device. The impact of ions is less pronounced in the high current density regime (J > 10 A cm
), where EQE roll-off is dominated by a combination of Joule heating and charge imbalance yet shows no evidence of Auger loss, suggesting that operation at kA cm
current densities relevant for a laser diode should be within reach.
Encapsulation of the platinum(IV) prodrug mitaplatin in block copolymer nanoparticles increases drug circulation time in the blood and reduces accumulation in the kidneys, as reported by Lippard and ...colleagues in this issue of ACS Nano. Importantly, controlled drug release from the nanoparticles produces long-term anticancer efficacy, with the prospect of reduced side effects. We highlight the potential that such a strategy holds for the future development of metallodrugs. Metal coordination complexes offer the prospect of novel mechanisms of activity on account of their unique architectures, as well as potential activation mechanisms, including ligand substitution and metal- and ligand-centered redox properties. Nanoparticles offer exciting prospects for improving delivery, cell uptake, and targeting of metallodrugs, especially anticancer drugs, to make them more effective and safer.
Organic-inorganic hybrid perovskite materials are emerging as highly attractive semiconductors for use in optoelectronics. In addition to their use in photovoltaics, perovskites are promising for ...realizing light-emitting diodes (LEDs) due to their high colour purity, low non-radiative recombination rates and tunable bandgap. Here, we report highly efficient perovskite LEDs enabled through the formation of self-assembled, nanometre-sized crystallites. Large-group ammonium halides added to the perovskite precursor solution act as a surfactant that dramatically constrains the growth of 3D perovskite grains during film forming, producing crystallites with dimensions as small as 10nm and film roughness of less than 1nm. Coating these nanometre-sized perovskite grains with longer-chain organic cations yields highly efficient emitters, resulting in LEDs that operate with external quantum efficiencies of 10.4% for the methylammonium lead iodide system and 9.3% for the methylammonium lead bromide system, with significantly improved shelf and operational stability.
Anterior cruciate ligament (ACL) ruptures significantly impact athletes in terms of return to play and loss of long‐term quality of life. Before the onset of this study, understanding the mechanism ...of ACL injury was limited. Thus, the primary focus of this manuscript is to describe our multi‐faceted approach to uncovering the mechanism of noncontact ACL injury (NC‐ACLI) with the goal of developing preventive strategies. The initial qualitative analysis of ACL injury events revealed most (70%) injuries involve minimal to no contact and occurr during landing or deceleration maneuvers in team sports with a minor perturbation before the injury that may disrupt the neuromuscular system leading to poor body dynamics. A series of quantitative videotape studies demonstrated differences in leg and trunk positions at the time of NC‐ACLI in comparison to control subjects. Analysis of the faulty dynamics provoking NC‐ACLI, especially the flat‐footed landing component, supports the theory that an axial compressive force is the critical factor responsible for NC‐ACLI. Our magnetic resonance imaging study demonstrated the NC‐ACLI position was associated with a higher tibial slope, and joint contact occurring on the flat, anterior portion of the lateral femoral condyle versus the round, posterior aspect. Both anatomic conditions favor sliding (pivot shift) over rolling in the presence of an axial compressive force. Subsequent cadaveric studies supported axial compressive forces as the primary component of NC‐ACLI. Both a strong eccentric quadriceps contraction and knee abduction moments may increase the compressive force at the joint thereby lowering the axial threshold to injury. This manuscript summarizes the NC‐ACLI mechanism portion of the 2021 OREF Clinical Research Award.
ExoMol molecular line lists – XXVII. Spectra of C2H4 Mant, Barry P; Yachmenev, Andrey; Tennyson, Jonathan ...
Monthly Notices of the Royal Astronomical Society,
08/2018, Letnik:
478, Številka:
3
Journal Article
We report on a sol–gel-based technique to fabricate MoO3 thin films as a hole-injection layer for solution-processed or thermally evaporated organic solar cells. The solution-processed MoO3 (sMoO3) ...films are demonstrated to have equal performance to hole-injection layers composed of either PEDOT:PSS or thermally evaporated MoO3 (eMoO3), and the annealing temperature at which the sol–gel layer begins to work is consistent with the thermodynamic analysis of the process. Finally, the shelf lifetime of devices made with the sMoO3 is similar to equivalent devices prepared with a eMoO3 hole-injection layer.
Near‐infrared (NIR) light‐emitting diodes (LEDs), with emission wavelengths between 800 and 950 nm, are useful for various applications, e.g., night‐vision devices, optical communication, and medical ...treatments. Yet, devices using thin film materials like organic semiconductors and lead based colloidal quantum dots face certain fundamental challenges that limit the improvement of external quantum efficiency (EQE), making the search of alternative NIR emitters important for the community. In this work, efficient NIR LEDs with tunable emission from 850 to 950 nm, using lead–tin (Pb‐Sn) halide perovskite as emitters are demonstrated. The best performing device exhibits an EQE of 5.0% with a peak emission wavelength of 917 nm, a turn‐on voltage of 1.65 V, and a radiance of 2.7 W Sr−1 m−2 when driven at 4.5 V. The emission spectra of mixed Pb‐Sn perovskites are tuned either by changing the Pb:Sn ratio or by incorporating bromide, and notably exhibit no phase separation during device operation. The work demonstrates that mixed Pb‐Sn perovskites are promising next generation NIR emitters.
Mixed lead–tin perovskites are shown to be efficient near‐infrared light emitters with tunable emission wavelengths from 850 to 950 nm. Devices based on MAPb0.6Sn0.4I3 films with 4‐fluorobenzylammonium iodide additives reach external quantum efficiency of 5%. It is revealed that there is no phase separation during the operation of devices with various Pb:Sn ratios and different mixed iodide and bromide compositions.
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