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Epitaxy is the cornerstone of semiconductor technology, enabling the fabrication of single-crystal film. Recent advancements in van der Waals (vdW) epitaxy have opened new avenues for producing wafer-scale single-crystal 2D atomic crystals. However, when it comes to molecular crystals, the overall weak vdW force means that it is a significant challenge for small molecules to form a well-ordered structure during epitaxy. Here we demonstrate that the vdW epitaxy of Sb2O3molecular crystal, where the whole growth process is governed by vdW interactions, can be precisely controlled. The nucleation is deterministically modulated by epilayer–substrate interactions and unidirectional nuclei are realized through designing the lattice and symmetry matching between epilayer and substrate. Moreover, the growth and coalescence of nuclei as well as the layer-by-layer growth mode are kinetically realized via tackling the Schwoebel-Ehrlich barrier. Such precise control of vdW epitaxy enables the growth of single-crystal Sb2O3molecular film with desirable thickness. Using the ultrathin highly oriented Sb2O3film as a gate dielectric, we fabricated MoS2-based field-effect transistors that exhibit superior device performance. The results substantiate the viability of precisely managing molecule alignment in vdW epitaxy, paving the way for large-scale synthesis of single-crystal 2D molecular crystals.This paper reports the van der Waals epitaxial growth of single-crystal Sb2O3, paving the way for precisely managing molecule alignment over nucleation and growth kinetics.

Similar to surfaces of three-dimensional (3D) bulk materials, edges are inevitable in 2D materials and have been studied a lot (e.g., for MoS2). In the current work, taking the ambient-stable MoSi2N4as an example, nonpolar and polar edges as well as polar-edge reconstructions are studied based on first-principles calculations. We demonstrate that a combination of the “local” electron counting model (ECM) at edges and “nonlocal” charge polarity analysis (CPA) across the ribbon is essential for a unified understanding of the “local” edge properties and edge reconstructions in the following aspects. For pristine edges, the semiconducting (metallic) property of nonpolar armchair (polar zigzag) edges is related to CPA, and the spin-paired (spin-polarized) electronic structure of nonpolar (polar) edges is related to the ECM. For polar-edge reconstructions: (1) the polar edges become semiconducting when the reversed dipole from edge-reconstruction partially cancels the accumulated electric dipole within the ribbon; (2) the polar edges can further be spin-paired when edge-reconstruction fulfills the ECM for both the double cation (Mo, Si)-edge and the anion N-edge; and (3) ECM and CPA give the same conclusion for edge-reconstruction. Our analysis of combining ECM and CPA not only gives the general guidance for obtaining spin-paired and semiconducting polar edges but also potentially helps deepen the understanding of edges of other 2D layered materials.

An interesting in-plane anisotropic layered dimetal chalcogenide Ta2NiS5is introduced, and the optical and electrical properties with respect to its in-plane anisotropy are systematically studied. The Raman vibration modes have been identified by Raman spectra measurements combined with calculations of phonon-related properties. Importantly, the Ta2NiS5flakes exhibit strong anisotropic Raman response under the angle-resolved polarized Raman spectroscopy measurements. We found that Raman intensities of the Agmode not only depend on rotation angle but are also related to the sample thickness. In contrast, the infrared absorption with light polarized along the aaxis direction is always larger than that in the caxis direction regardless of thickness under the polarization-resolved infrared spectroscopy measurements. Remarkably, the first-principles calculations combined with angle-resolved conductance measurements indicate strong anisotropic conductivity of Ta2NiS5. Our results not only prove Ta2NiS5is a promising in-plane anisotropic 2D material but also provide an interesting platform for future functionalized electronic devices.

Hydrogenation and electric field are used to tailor the electronic structures of hybrid graphene/hexagonal boron nitride (Gr/BN) and bilayer graphene (Gr/Gr). Without hydrogen adsorption, the electronic structure of Gr/BN is only slightly affected by the electric field, but energy gaps are induced in Gr/Gr because of the breaking of inversion symmetry. Under partial hydrogenation conditions, more interlayer bonds tend to form in Gr/BN than that in Gr/Gr because of the inherent Coulomb attraction, and a band gap is created in Gr/BN even at low hydrogen coverage. The electronic structures of partially hydrogenated Gr/BN and Gr/Gr are both rather insensitive to the electric fields. Under full hydrogenation conditions, Gr/BN and Gr/Gr evolve into diamond-like nanofilms: Gr/BN-BC (interlayer B–C bonding) and Gr/Gr-CC (C–C bonding). Because of the interface-dipole-induced electric field, the band gap of Gr/BN-BC is rather small compared to that of the Gr/Gr-CC. Depending on the direction of the external electric field, the band gap of Gr/BN-BC is linearly increased or decreased, whereas that of Gr/Gr-CC is only decreased. These electric-field-induced band gap modulations in Gr/BN and Gr/Gr as well as their hydrogenation derivatives are results of the Stark effect; they are dependent on the hydrogen coverage and can be understood in terms of the charge distribution of the valence-band maximum and conduction-band minimum.

2D material (2DM) based photodetectors with broadband photoresponse are of great value for a vast number of applications such as multiwavelength photodetection, imaging, and night vision. However, compared with traditional photodetectors based on bulk material, the relatively slow speed performance of 2DM based photodetectors hinders their practical applications. Herein, a submicrosecond-response photodetector based on ternary telluride InSiTe3with trigonal symmetry and layered structure was demonstrated in this study. The InSiTe3based photodetectors exhibit an ultrafast photoresponse (545–576 ns) and broadband detection capabilities from the ultraviolet (UV) to the near-infrared (NIR) optical communication region (365–1310 nm). Besides, the photodetector presents an outstanding reversible and stable photoresponse in which the response performance remains consistent within 200 000 cycles of switch operation. These significant findings suggest that InSiTe3can be a promising candidate for constructing fast response broadband 2DM based optoelectronic devices.