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Metal halide perovskites (MHPs) are low‐temperature processable hybrid semiconductor materials with exceptional performances that are revolutionizing the field of optoelectronic devices. Despite their great potential, commercial deployment is hindered by MHPs lack of stability and durability, mainly attributed to ion migration and chemical interactions with the electrodes. To address these issues, 2D layered MHPs are investigated as possible device interlayers or active material substitutes. Here, the 2D perovskite (PEA)2PbBr4 is considered that is recently discussed as promising candidate for X‐ray direct detection. While the increased resilience of (PEA)2PbBr4 radiation detectors has already been reported, the physical mechanisms responsible for such improvement compared to 3D perovskites are not still fully understood. To unravel the charge transport process in (PEA)2PbBr4 crystals thought to underly the device better performance, an investigation technique is adapted previously used on highly resistive inorganic semiconductors, called photo induced current transient spectroscopy (PICTS). It is demonstrated that PICTS can reliably detect three trap states (T1, T2, and T3), and that their evolution upon X‐ray exposure can explain (PEA)2PbBr4 superior radiation tolerance and reduced aging effects. Overall, the results provide essential insights into the electrical characteristics of 2D perovskites and their potential application as reliable direct X‐ray detectors. [ABSTRACT FROM AUTHOR]

X-ray detection for personal dosimetry requires sensitive, stable and non-toxic materials. At the same time, scalability onto large-area and flexible substrates is emerging as a desirable property. To satisfy these requirements, novel materials to be employed as the active layer of direct X-ray detectors are needed. In this search for easy-processability, large area, efficient and non-toxic materials for direct X-ray detection, we assess the performance of a layered metal-organic chalcogenide [AgSePh]M, recently proposed as representative of a novel excitonic semiconductors platform. Here we demonstrate that [AgSePh]M can be successfully applied as direct ionizing radiation detecting layer, reaching sensitivities up to (180 ± 10) ^C Gy-1 cm-2 and competitive limit of detection down to (100 ± 30) nGy s-1. Moreover, it offers good stability and reproducibility of detection after 100 Gy of irradiation and upon bending to a curvature radius of 5 mm. [ABSTRACT FROM AUTHOR]

In contrast to inorganic quantum wells, hybrid quantum wells (HQWs) based on metal‐organic semiconductors are characterized by relatively soft lattices, in which excitonic states can strongly couple to lattice phonons. Therefore, understanding the lattice's impact on exciton dynamics is essential for harnessing the optoelectronic potential of HQWs. Beyond 2D metal halide perovskites, layered metal‐organic chalcogenides (MOCs), which are an air‐stable, underexplored material class hosting room‐temperature excitons, can be exploited as photodetectors, light emitting devices, and ultrafast photoswitches. Here, the role of phonons in the optical transitions of the prototypical MOC [AgSePh]∞ is elucidated. Impulsive stimulated Raman scattering (ISRS) allows the detection of coherent exciton oscillations driven by Fröhlich interaction with low‐energy optical phonons. Steady state absorption and Raman spectroscopies reveal a strong exciton‐phonon coupling (Huang‐Rhys parameter ≈1.7) and its anharmonicity, manifested as a nontrivial temperature‐dependent Stokes shift. The ab initio calculations support these observations, hinting at an anharmonic behavior of the low‐energy phonons <200 cm−1. These results untangle complex exciton‐phonon interactions in MOCs, establishing an ideal testbed for room‐temperature many‐body phenomena. [ABSTRACT FROM AUTHOR]

Numerous efforts have been undertaken to develop rectifying antennas operating at high frequencies, especially dedicated to light harvesting and photodetection applications. However, the development of efficient high frequency rectifying antennas has been a major technological challenge both due to a lack of comprehension of the underlying physics and limitations in the fabrication techniques. Various rectification strategies have been implemented, including metal‐insulator‐metal traveling‐wave diodes, plasmonic nanogap optical antennas, and whisker diodes, although all show limited high‐frequency operation and modest conversion efficiencies. Here a new type of rectifying antenna based on plasmonic carrier generation is demonstrated. The proposed structure consists of a resonant metallic conical nano‐antenna tip in contact with the oxide surface of an oxide/metal bilayer. The conical shape allows for an improved current generation based on plasmon‐mediated electromagnetic‐to‐electron conversion, an effect exploiting the nanoscale‐tip contact of the rectifying antenna, and proportional to the antenna resonance and to the surface‐electron scattering. Importantly, this solution provides rectification operation at 280 THz (1064 nm) with a 100‐fold increase in efficiency compared to previously reported results. Finally, the conical rectifying antenna is also demonstrated to operate at 384 THz (780 nm), hence paving a way toward efficient rectennas toward the visible range. [ABSTRACT FROM AUTHOR]

Despite the availability of chemistries to tailor the pore architectures of microporous polymer membranes for chemical separations, trade-offs in permeability and selectivity with functional group manipulations nevertheless persist, which ultimately places an upper bound on membrane performance. Here we introduce a new design strategy to uncouple these attributes of the membrane. Key to our success is the incorporation of phase-change metal-organic frameworks (MOFs) into the polymer matrix, which can be used to increase the solubility of a specific gas in the membrane, and thereby its permeability. We further show that it is necessary to scale the size of the phase-change MOF to nanoscopic dimensions, in order to take advantage of this effect in a gas separation. Our observation of an increase in solubility and permeability of only one of the gases during steady-state permeability measurements suggests fast exchange between free and chemisorbed gas molecules within the MOF pores. While the kinetics of this exchange in phase-change MOFs are not yet fully understood, their role in enhancing the efficacy and efficiency of the separation is clearly a compelling new direction for membrane technology. [ABSTRACT FROM AUTHOR]

The material demands for metal-organic frameworks (MOFs) for next-generation energy-efficient CO2 capture technologies necessitate advances in their expedient and scalable synthesis. Toward that end, the recently discovered expanded MOF-74, or M2(dobpdc), where M = divalent metal cation and dobpdc = 4,4'-dioxido-3,3'-biphenyldicarboxylate, can now be prepared in minutes via a controlled dissolution-crystallization route from divalent metal oxides as precursors. We show that the available surface area of the metal oxide plays a critical role in the precursor dissolution, which was found to be rate-limiting. Based on this understanding of the reaction trajectory, we pushed the chemical transformation to its fringe kinetic limit by configuring the metal oxide precursors as ligand-free colloidal metal oxide nanocrystals, which allowed MOF formation in less than 1 min. MOFs prepared by this strategy were highly crystalline, with BET surface areas on par with conventional multihour syntheses from metal halide salts. This method was also applied successfully in the synthesis of M2(dobdc) MOFs, highlighting its generality. Our work challenges the conventional wisdom that plurality of steps in MOF formation is inherently time-intensive. [ABSTRACT FROM AUTHOR]

Graphene impurities provide both a source of mobility-limiting disorder and a means to desirably alter graphene electronic structure. Adsorbates on graphene can, for example, induce Coulomb scattering, alter electron-phonon interactions, shift the chemical potential, change the effective dielectric constant and-in cases such as 'graphane'-form whole new two-dimensional materials. While these effects have thus far been primarily studied with spatially averaged techniques, understanding the microscopic physics of such behaviour requires local-probe exploration of the subnanometre-scale electronic and structural properties of impurities on graphene. Here we describe scanning tunnelling microscopy and spectroscopy measurements made on individual Co atoms deposited onto back-gated graphene devices. We find that the electronic structure of Co adatoms can be tuned by application of the device gate voltage, and that the Co atoms can be reversibly ionized. Large screening clouds are observed to form around Co adatoms ionized in this way, and we observe that some intrinsic graphene defects also show charging behaviour. Our results provide new insight into charged-impurity scattering in graphene, as well as the possibility of using graphene devices as chemical sensors. [ABSTRACT FROM AUTHOR]

A facile method is reported for the direct (polymer-free) transfer of layer-area graphene from metal growth substrates to selected target substrates. The direct route, by avoiding several wet chemical steps and accompanying mechanical stresses and contamination common to all presently reported layer-area graphene transfer methods, enables fabrication of layer-area graphene devices with unprecedented quality. To demonstrate, we directly transfer layer-area graphene from Cu growth substrates to holey amorphous carbon transmission electron microscopy (TEM) grids, resulting in robust, clean, full-coverage graphene grids ideal for high resolution TEM. [ABSTRACT FROM AUTHOR]