A
bstract
We systematically analyze the fibration structure of toric hypersurface Calabi-Yau threefolds with large and small Hodge numbers. We show that there are only four such Calabi-Yau threefolds ...with
h
1,1
≥ 140 or
h
2,1
≥ 140 that do not have manifest elliptic or genus one fibers arising from a fibration of the associated 4D polytope. There is a genus one fibration whenever either Hodge number is 150 or greater, and an elliptic fibration when either Hodge number is 228 or greater. We find that for small
h
1,1
the fraction of polytopes in the KS database that do not have a genus one or elliptic fibration drops exponentially as
h
1,1
increases. We also consider the different toric fiber types that arise in the polytopes of elliptic Calabi-Yau threefolds.
Contact engineering is a prerequisite for achieving desirable functionality and performance of semiconductor electronics, which is particularly critical for organic–inorganic hybrid halide ...perovskites due to their ionic nature and highly reactive interfaces. Although the interfaces between perovskites and charge‐transporting layers have attracted lots of attention due to the photovoltaic and light‐emitting diode applications, achieving reliable perovskite/electrode contacts for electronic devices, such as transistors and memories, remains as a bottleneck. Herein, a critical review on the elusive nature of perovskite/electrode interfaces with a focus on the interfacial electrochemistry effects is presented. The basic guidelines of electrode selection are given for establishing non‐polarized interfaces and optimal energy level alignment for perovskite materials. Furthermore, state‐of‐the‐art strategies on interface‐related electrode engineering are reviewed and discussed, which aim at achieving ohmic transport and eliminating hysteresis in perovskite devices. The role and multiple functionalities of self‐assembled monolayers that offer a unique approach toward improving perovskite/electrode contacts are also discussed. The insights on electrode engineering pave the way to advancing stable and reliable perovskite devices in diverse electronic applications.
Rational selection of electrodes plays a critical role in perovskite‐based electronics due to the high reactivity of halide perovskite materials. A comprehensive review of perovskite/electrode interfaces, as well as, state‐of‐the‐art contact engineering, which assists the development of perovskite‐based devices with inhibited interfacial reactions, ohmic carrier transport, and non‐hysteric electronic characteristics, is presented.
A
bstract
We compare the sets of Calabi-Yau threefolds with large Hodge numbers that are constructed using toric hypersurface methods with those can be constructed as elliptic fibrations using ...Weierstrass model techniques motivated by F-theory. There is a close correspondence between the structure of “tops” in the toric polytope construction and Tate form tunings of Weierstrass models for elliptic fibrations. We find that all of the Hodge number pairs (
h
1,1
,
h
2,1
) with
h
1,1
or
h
2,1
≥ 240 that are associated with threefolds in the Kreuzer-Skarke database can be realized explicitly by generic or tuned Weierstrass/Tate models for elliptic fibrations over complex base surfaces. This includes a relatively small number of somewhat exotic constructions, including elliptic fibrations over non-toric bases, models with new Tate tunings that can give rise to exotic matter in the 6D F-theory picture, tunings of gauge groups over non-toric curves, tunings with very large Hodge number shifts and associated nonabelian gauge groups, and tuned Mordell-Weil sections associated with U(1) factors in the corresponding 6D theory.
Organic–inorganic mixed halide perovskites have emerged as an excellent class of materials with a unique combination of optoelectronic properties, suitable for a plethora of applications ranging from ...solar cells to light‐emitting diodes and photoelectrochemical devices. Recent works have showcased hybrid perovskites for electronic applications through improvements in materials design, processing, and device stability. Herein, a comprehensive up‐to‐date review is presented on hybrid perovskite electronics with a focus on transistors and memories. These applications are supported by the fundamental material properties of hybrid perovskite semiconductors such as tunable bandgap, ambipolar charge transport, reasonable mobility, defect characteristics, and solution processability, which are highlighted first. Then, recent progresses on perovskite‐based transistors are reviewed, covering aspects of fabrication process, patterning techniques, contact engineering, 2D versus 3D material selection, and device performance. Furthermore, applications of perovskites in nonvolatile memories and artificial synaptic devices are presented. The ambient instability of hybrid perovskites and the strategies to tackle this bottleneck are also discussed. Finally, an outlook and opportunities to develop perovskite‐based electronics as a competitive and feasible technology are highlighted.
Organic–inorganic halide perovskites show high promise for electronic devices owing to exceptional electrical, optical, and structural properties. The latest breakthroughs in structural, interface, defect engineering, and pattering techniques as applied to halide perovskite transistors, memories and to improve stability issues in perovskites are reviewed. Lastly, the existing challenges and outline for future research directions are provided.
Exceptional electronic, optoelectronic, and sensing properties of inorganic Cs‐based perovskites are significantly influenced by the defect chemistry of the material. Although organic halide ...perovskites that have a polycrystalline structure are heavily studied, understanding of the defect properties at the grain boundaries (GB) of inorganic Cs‐based perovskite quantum dots (QDs) is still limited. Here, morphology‐dependent charge carrier dynamics of CsPbBr3 quantum dots at the nanoscale by performing scanning probe microscopy of thermally treated samples are investigated. The grain boundaries of defect‐engineered samples show higher surface potential than the grain interiors under light illumination, suggesting an effective role of GBs as charge collection and transport channels. The lower density of crystallographic defects and lower trap density at GBs specifically of heat‐treated samples cause insignificant dark current, lower local current hysteresis, and higher photocurrent, than the control samples. It is also shown that the decay rate of surface photovoltage of the heated sample is quicker than the control sample, which implies a considerable impact of ion migration on the relaxation dynamic of photogenerated charge carriers. These findings reveal that the annealing process is an effective strategy to control not only the morphology but also the optoelectrical properties of GB defects, and the dynamic of ion migration. Understanding the origin of photoelectric activity in this material allows for designing and engineering optoelectronic QD devices with enhanced functionality.
The present study investigates morphology‐dependent charge carrier dynamics of CsPbBr3 quantum dots at the nanoscale by performing scanning probe microscopy of thermally treated samples. The annealing process is an effective strategy to control not only the morphology but also the optoelectrical properties of grain boundary defects, and the dynamic of ion migration.
Metal‐halide perovskites have drawn profuse attention during the past decade, owing to their excellent electrical and optical properties, facile synthesis, efficient energy conversion, and so on. ...Meanwhile, the development of information storage technologies and digital communications has fueled the demand for novel semiconductor materials. Low‐dimensional perovskites have offered a new force to propel the developments of the memory field due to the excellent physical and electrical properties associated with the reduced dimensionality. In this review, the mechanisms, properties, as well as stability and performance of low‐dimensional perovskite memories, involving both molecular‐level perovskites and structure‐level nanostructures, are comprehensively reviewed. The property–performance correlation is discussed in‐depth, aiming to present effective strategies for designing memory devices based on this new class of high‐performance materials. Finally, the existing challenges and future opportunities are presented.
Low‐dimensional halide perovskites are among the most rapidly emerging building blocks for optoelectronic applications. This review elucidates the advantages and the crucial role of molecular‐/structure‐level low‐dimensional halide perovskites in achieving high performance and enhanced stability in memory applications.
A
bstract
We find through a systematic analysis that all but 29,223 of the 473.8 million 4D reflexive polytopes found by Kreuzer and Skarke have a 2D reflexive subpolytope. Such a subpolytope is ...generally associated with the presence of an elliptic or genus one fibration in the corresponding birational equivalence class of Calabi-Yau threefolds. This extends the growing body of evidence that most Calabi-Yau threefolds have an elliptically fibered phase.
Integrating multiple semiconductors with distinct physical properties is a practical design strategy for realizing novel optoelectronic devices with unprecedented functionalities. In this work, a ...photonic resistive switching (RS) memory is demonstrated based on solution‐processed bilayers of strontium titanate (SrTiO3 or STO) quantum dots (QDs) and all‐inorganic halide perovskite CsPbBr3 (CPB) with an Ag/STO/CPB/Au architecture. Compared with the single‐layer STO or CPB RS device, the double‐layer device shows considerably improved RS performance with a high switching ratio over 105, an endurance of 3000 cycles, and a retention time longer than 2 × 104 s. The formation of heterojunction between STO and CPB significantly enhances the high resistance state, and the separation of the active silver electrode and the CPB layer contributes to the long‐term stability. More importantly, the photonic RS device exhibits UV–visible dual‐band response due to the photogating effect and the light‐induced modification of the heterojunction barrier. Last, tri‐mode operation, i.e., photodetector, memory, and photomemory, is demonstrated via tailoring the light and electric stimuli. This bilayer device architecture provides a unique approach toward enhancing the performance of photoresponsive data‐storage devices.
A solution‐processed photonic memory is fabricated using all‐perovskite SrTiO3/CsPbBr3 bilayers as the switching media. The resistive switching performance of the device is considerably improved compared to the single‐layer counterparts, exhibiting response to dual UV–visible bands, as well as tri‐mode operation of photodetector, memory, and photomemory.
A
bstract
We find that for many Calabi-Yau threefolds with elliptic or genus one fibrations mirror symmetry factorizes between the fiber and the base of the fibration. In the simplest examples, the ...generic CY elliptic fibration over any toric base surface
B
that supports an elliptic Calabi-Yau threefold has a mirror that is an elliptic fibration over a dual toric base surface
B
˜
that is related through toric geometry to the line bundle −6
K
B
. The Kreuzer-Skarke database includes all these examples and gives a wide range of other more complicated constructions where mirror symmetry also factorizes. Since recent evidence suggests that most Calabi-Yau threefolds are elliptic or genus one fibered, this points to a new way of understanding mirror symmetry that may apply to a large fraction of smooth Calabi-Yau threefolds. The factorization structure identified here can also apply for CalabiYau manifolds of higher dimension.
Plants use extracellular vesicles (EVs) to transport small RNAs (sRNAs) into their fungal pathogens and silence fungal virulence-related genes through a phenomenon called 'cross-kingdom RNAi'. It ...remains unknown, however, how sRNAs are selectively loaded into EVs. Here, we identified several RNA-binding proteins in Arabidopsis, including Argonaute 1 (AGO1), RNA helicases (RHs) and annexins (ANNs), which are secreted by exosome-like EVs. AGO1, RH11 and RH37 selectively bind to EV-enriched sRNAs but not to non-EV-associated sRNAs, suggesting that they contribute to the selective loading of sRNAs into EVs. Conversely, ANN1 and ANN2 bind to sRNAs non-specifically. The ago1, rh11 rh37 and ann1 ann2 mutants showed reduced secretion of sRNAs in EVs, demonstrating that these RNA-binding proteins play an important role in sRNA loading and/or stabilization in EVs. Furthermore, rh11 rh37 and ann1 ann2 showed increased susceptibility to Botrytis cinerea, suggesting that RH11, RH37, ANN1 and ANN2 positively regulate plant immunity against B. cinerea.