Abstract2D crystals can serve as templates for the realization of new van der Waals (vdW) heterostructures via controlled assembly of low‐dimensional functional components. Among available 2D crystals, black phosphorus (BP) is unique due to its puckered atomic surface topography, which may lead to strong epitaxial phenomena through guided vdW assembly. Here, it is demonstrated that a BP template can induce highly oriented assembly of C60 molecular crystals. Transmission electron microscopy and theoretical analysis of the C60/BP vdW heterostructure clearly confirm that the BP template results in oriented C60 assembly with higher‐order commensurism. Lateral and vertical devices with C60/BP junctions are fabricated via a lithography‐free clean process, which allows one to investigate the ideal electrical properties of pristine C60/BP junctions. Effective tuning of the C60/BP junction barrier from 0.2 to 0.5 eV and maximum on‐current density higher than 104 mA cm−2 are achieved with graphite/C60/BP vertical vdW transistors. Due to the formation of high‐quality C60 film and the semitransparent graphite top‐electrode, the vertical transistors show high photoresponsivities up to ≈100 A W−1 as well as a fast response time under visible light illumination.
Low-dimensional nanostructures of halide perovskites have been receivingextensive research interest for their superior optical, electrical, and stability characteristics over their conventional bulk counterparts. In particular, the unique surficial characteristics of well-defined 1D nanowires have shown high feasibility for high performance optoelectronic applications. The key aspect of endorsing this nanoscale form factor in practical applications lies in securing dimensional uniformity and controllability in large scales, which generally requires complicated lithographic procedures. In this work, a simple, rapid, and widely applicable strategy for the direct synthesis and printing of wellaligned nanowire arrays on a large scale is demonstrated. By employing blade coating methods with sophisticatedly controlled stick-slip motions, periodically resolved transverse 3D meniscus enables uniform directional growth of highly crystalline CsPbI 3 nanowires without the need for templates. A systematic investigation of morphological evolutions with respect to kinetic processing variables is conducted, along with a comprehensive suite of structural and optical analyses for the synthesized nanowire arrays. A single nanowire photodetector is employed to demonstrate the superiority and applicability of the fabrication strategy. Finally, a 2D image recognition is demonstrated by using an array of photodetectors fabricated via a fast (<2 min) direct printing of nanowire arrays on wafers.
The properties of metal-semiconductor junctions are often unpredictable because of non-ideal interfacial structures, such as interfacial defects or chemical reactions introduced at junctions. Black phosphorus (BP), an elemental two-dimensional (2D) semiconducting crystal, possesses the puckered atomic structure with high chemical reactivity, and the establishment of a realistic atomic-scale picture of BP's interface toward metallic contact has remained elusive. Here we examine the interfacial structures and properties of physically-deposited metals of various kinds on BP. We find that Au, Ag, and Bi form single-crystalline films with (110) orientation through guided van der Waals epitaxy. Transmission electron microscopy and X-ray photoelectron spectroscopy confirm that atomically sharp van der Waals metal-BP interfaces forms with exceptional rotational alignment. Under a weak metal-BP interaction regime, the BP's puckered structure play an essential role in the adatom assembly process and can lead to the formation of a single crystal, which is supported by our theoretical analysis and calculations. The experimental survey also demonstrates that the BP-metal junctions can exhibit various types of interfacial structures depending on metals, such as the formation of polycrystalline microstructure or metal phosphides. This study provides a guideline for obtaining a realistic view on metal-2D semiconductor interfacial structures, especially for atomically puckered 2D crystals.
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