The discovery of two‐dimensional (2D) materials with unique electronic, superior optoelectronic, or intrinsic magnetic order has triggered worldwide interest in the fields of material science, ...condensed matter physics, and device physics. Vertically stacking 2D materials with distinct electronic and optical as well as magnetic properties enables the creation of a large variety of van der Waals heterostructures. The diverse properties of the vertical heterostructures open unprecedented opportunities for various kinds of device applications, e.g., vertical field‐effect transistors, ultrasensitive infrared photodetectors, spin‐filtering devices, and so on, which are inaccessible in conventional material heterostructures. Here, the current status of vertical heterostructure device applications in vertical transistors, infrared photodetectors, and spintronic memory/transistors is reviewed. The relevant challenges for achieving high‐performance devices are presented. An outlook into the future development of vertical heterostructure devices with integrated electronic and optoelectronic as well as spintronic functionalities is also provided.
The diverse properties of van der Waals heterostructures open unprecedented opportunities for various types of device applications inaccessible in conventional heterostructure materials. Research progress of vertical heterostructure device applications in vertical transistors, infrared photodetectors, and spintronic devices is reviewed, together with a discussion on the challenges and opportunities in the future development of multifunctional devices.
Objective
To assess the accuracy of dynamic computer‐assisted implant surgery.
Materials and methods
An electronic search up to March 2020 was conducted using PubMed, Embase, and the Cochrane Central ...Register of Controlled Trial to identify studies using dynamic navigation in implant surgery, and additional manual search was performed as well. Clinical trials and model studies were selected. The primary outcome was accuracy. A single‐arm meta‐analysis of continuous data was conducted. Meta‐regression was utilized for comparison on study design, guidance method, jaw, and systems.
Results
Ten studies, four randomized controlled trials (RCT) and six prospective studies, met the inclusion criteria. A total of 1,298 drillings and implants were evaluated. The meta‐analysis of the accuracy (five clinical trials and five model studies) revealed average global platform deviation, global apex deviation, and angular deviation were 1.02 mm, 95% CI (0.83, 1.21), 1.33 mm, 95% CI (0.98, 1.67), and 3.59°, 95% CI (2.09, 5.09). Meta‐regression shown no difference between model studies and clinical trials (p = .295, 0.336, 0.185), drilling holes and implant (p = .36, 0.279, 0.695), maxilla and mandible (p = .875, 0.632, 0.281), and five different systems (p = .762, 0.342, 0.336).
Conclusion
Accuracy of dynamic computer‐aided implant surgery reaches a clinically acceptable range and has potential in clinical usage, but more patient‐centered outcomes and socio‐economic benefits should be reported.
By virtue of the layered structure, van der Waals (vdW) magnets are sensitive to the lattice deformation controlled by the external strain, providing an ideal platform to explore the one‐step ...magnetization reversal that is still conceptual in conventional magnets due to the limited strain‐tuning range of the coercive field. In this study, a uniaxial tensile strain is applied to thin flakes of the vdW magnet Fe3GeTe2 (FGT), and a dramatic increase of the coercive field (Hc) by more than 150% with an applied strain of 0.32% is observed. Moreover, the change of the transition temperatures between the different magnetic phases under strain is investigated, and the phase diagram of FGT in the strain–temperature plane is obtained. Comparing the phase diagram with theoretical results, the strain‐tunable magnetism is attributed to the sensitive change of magnetic anisotropy energy. Remarkably, strain allows an ultrasensitive magnetization reversal to be achieved, which may promote the development of novel straintronic device applications.
An ultrasensitive magnetization reversal in the van der Waals magnet Fe3GeTe2 is realized by strain. Remarkably increased coercive field, Curie temperature, and transition temperature between single‐ and labyrinthine‐domain states under tensile strain are also observed. The strain‐tunable magnetism could result from the sensitive change of magnetic anisotropy energy with the theoretical results.
Atomically precise enantiomeric metal clusters are scarce, and copper(I) alkynyl clusters with intense circularly polarized luminescence (CPL) responses have not been reported. A pair of chiral ...alkynyl ligands, (R/S)‐2‐diphenyl‐2‐hydroxylmethylpyrrolidine‐1‐propyne (abbreviated as R/S‐DPM) we successfully prepared and single crystals were characterized of optically pure enantiomeric pair of atomically‐precise copper(I) clusters, Cu14(R/S‐DPM)8(PF6)6 (denoted as R/S‐Cu14), which feature bright red luminescence and CPL with a high luminescence anisotropy factor (glum). A dilute solution containing R/S‐Cu14 was nonluminescent and CPL inactive at room temperature. Crystallization‐ and aggregation‐induced emission (CIE and AIE, respectively) contribute to the triggering of the CPL of R/S‐Cu14 in the crystalline and aggregated states. Their AIE behavior and good biocompatibility indicated applications of these copper(I) clusters in cell imaging in HeLa and NG108‐15 cells.
Atomically precise chiral CuI alkynyl nanoclusters R/S‐Cu14 with inherent chirality were synthesized for the first time. Crystallization‐ and aggregation‐induced emission (CIE and AIE, respectively) trigger circularly polarized luminescence (CPL) with an unprecedented luminescence anisotropy factor (glum).
The high‐bias electrical characteristics of back‐gated field‐effect transistors with chemical vapor deposition synthesized bilayer MoS2 channel and Ti Schottky contacts are discussed. It is found ...that oxidized Ti contacts on MoS2 form rectifying junctions with ≈0.3 to 0.5 eV Schottky barrier height. To explain the rectifying output characteristics of the transistors, a model is proposed based on two slightly asymmetric back‐to‐back Schottky barriers, where the highest current arises from image force barrier lowering at the electrically forced junction, while the reverse current is due to Schottky‐barrier‐limited injection at the grounded junction. The device achieves a photoresponsivity greater than 2.5 A W−1 under 5 mW cm−2 white‐LED light. By comparing two‐ and four‐probe measurements, it is demonstrated that the hysteresis and persistent photoconductivity exhibited by the transistor are peculiarities of the MoS2 channel rather than effects of the Ti/MoS2 interface.
Ti Schottky contacts on molybdenum disulfide (MoS2) result in rectifying current–voltage output characteristics, explained by image‐force barrier lowering at metal/MoS2 interfaces. The two back‐to‐back Schottky junctions can be exploited for efficient photodetection. Hysteresis and persistent photoconductivity are transistor features due to charge trapping in defects, and are properties of the MoS2 channel rather than effects of the contacts.
Divergent synthesis for precise constructions of cyclic unsymmetrical diaryl disulfides or diselenides and polythiophenes from CF3‐containing 1,3‐enynes and S8 was developed when the ortho group is ...F, Cl, Br, and NO2 on aromatic rings. Meanwhile, disulfides (diselenides) were also quickly constructed when the ortho group is H. These transformations undergo cascade thiophene construction/selective C3‐position thiolation process, featuring simple operations, divergent synthesis, broad substrate scope, readily available starting materials, and valuable products. A novel plausible radical annulation process was proposed and validated by DFT calculations for the first time. A series of derivatizations about the thiophene (TBT) and disulfides were also well‐represented.
A divergent synthesis for construction of cyclic unsymmetrical diaryl disulfides, diselenides, and polythiophenes from CF3‐containing 1,3‐enynes (ortho=F, Cl, Br, NO2, S8) was developed. Disulfides (diselenides) were constructed under mild conditions for ortho=H. These transformations undergo a cascade thiophene construction/selective C3‐position thiolation process, with mild conditions, broad substrate scope, and good functional‐group tolerance.
Summary
Drought is a normal and recurring climate feature in most parts of the world and plays a major role in limiting crop productivity. However, plants have their own defence systems to cope with ...adverse climatic conditions. One of these defence mechanisms is the reprogramming of gene expression by microRNAs (miRNAs). miRNAs are small noncoding RNAs of approximately 22 nucleotides length, which have emerged as important regulators of genes at post‐transcriptional levels in a range of organisms. Some miRNAs are functionally conserved across plant species and are regulated by drought stress. These properties suggest that miRNA‐based genetic modifications have the potential to enhance drought tolerance in cereal crops. This review summarizes the current understanding of the regulatory mechanisms of plant miRNAs, involvement of plant miRNAs in drought stress responses in barley (Hordeum vulgare L.), wheat (Triticum spp.) and other plant species, and the involvement of miRNAs in plant‐adaptive mechanisms under drought stress. Potential strategies and directions for future miRNA research and the utilization of miRNAs in the improvement of cereal crops for drought tolerance are also discussed.
Considering the ubiquitous nature and ready synthesis of amides, and the great significance of organofluorine‐containing species, the cross‐coupling of amides and polyfluoroarenes, leading to new ...carbon–carbon bond‐forming methodologies, would find useful applications in synthesis, late‐stage functionalization, and rapid generation of molecular diversity. Herein, we present a novel synthesis of α‐polyfluoroaryl amines via Sm/SmI2‐mediated deoxygenative cross‐coupling of aromatic amides with polyfluoroarenes through direct C−H functionalization. The structural and functional diversity of these readily available precursors provides a versatile and flexible strategy for the streamlined synthesis of α‐polyfluoroaryl amines. Combining experimental and theoretical studies, a novel plausible mechanism of the α‐aminocarbene‐mediated C−H insertion has been revealed, which may stimulate future work for the development of novel methods in amine synthesis.
An attractive deoxygenative cross‐coupling of amides with polyfluoroarenes was successfully achieved. Aromatic amides act as readily available carbene precursors through a Sm/SmI2‐mediated deoxygenation process, and the insertion of the carbene into the C−H bond of polyfluoroarene affords architecturally complex and functionally diverse α‐polyfluoroaryl amines in a single step.
C‐Acyl glycosides are versatile intermediates to natural products and medicinally relevant entities. Conventional cross‐coupling strategies to secure these molecules often relied on two‐component ...manifolds in which a glycosyl precursor is coupled with an acyl donor (pre‐synthesized or generated in situ) under transition metal or dual catalysis to forge a C−C bond. Here, we disclose a three‐component Ni‐catalyzed reductive regime that facilitates the chemoselective union of glycosyl halides, organoiodides and commercially available isobutyl chloroformate as a CO surrogate. The method tolerates multiple functionalities and the resulting products are obtained in high diastereoselectivities. Theoretical calculations provide a mechanistic rationale for the unexpectedly high chemoselectivity of sequential cross‐electrophile couplings. This approach enables the expeditious assembly of difficult‐to‐synthesize C‐acyl glycosides, as well as late‐stage keto‐glycosylation of oligopeptides.
Reductive nickel catalysis was leveraged to orchestrate the multicomponent union of glycosyl halides, organoiodides and isobutyl chloroformate to assemble C‐acyl glycosides in high anomeric selectivities. Computational studies provided insights that rationalize the origin of the high chemoselectivity. The method is applicable to the synthesis of complex C‐linked disaccharides and late‐stage keto‐glycosylation of peptides.
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