VSe2 is a typical two-dimensional (2D) transition-metal dichalcogenide material with various physical properties, such as ultrahigh electrical conductivity, controversial magnetism, and active catalytic properties. However, controllable preparation of VSe2 2D structures poses many challenges, and their application has not yet been developed. Here, we controllably synthesize VSe2 2D flakes on highly oriented pyrolytic graphite (HOPG) using molecular beam epitaxy. By controlling the growth temperature and the evaporation rate of the source, we obtained various morphologies of VSe2 flakes, including single- and multilayers with triangular and belt shapes. Compared with the triangular structures of the flakes, the one-dimensional nanobelt structures have a larger edge density and can provide more catalytic active sites. Hydrogen evolution reaction results indicate that the belt-shaped VSe2 flakes exhibit superior catalytic performance. Due to the presence of plenty of edges, the overpotential of the belt-shaped VSe2 is 543 mV at a current density of 1 mA/cm2, which is much lower than that in the triangular flakes. The VSe2 flakes with a larger edge density are more conductive than the regular triangular flakes after loading metal atoms due to the efficient dispersion of the metal atoms. As a result, the multistructure of Co particle-decorated VSe2 flakes achieves a high catalytic performance with 352 mV overpotential at a current density of 10 mA/cm2, demonstrating their potential applications in the catalyst field.

The combination of a topological insulator and an antiferromagnet is expected to exhibit the quantum anomalous Hall effect due to the breaking of the time-reversal symmetry. As a layered antiferromagnet, CoNb 3 S 6 was recently found to exhibit an anomalous Hall effect below the Neél temperature (T N = 29 K). Here, we report the controllable growth of Bi nanowires and Bi 2 Se 3 thin films on CoNb 3 S 6 substrates using molecular beam epitaxy. The composition and morphology of the as-prepared Bi nanowires and Bi 2 Se 3 thin films were studied by atomic force microscopy, X-ray photoelectron spectroscopy, and scanning tunneling microscopy. We found that the as-grown Bi nanowires with abundant sizes are oriented along high-symmetry directions of the substrate, forming firework-like structures. Such firework-like structures of Bi nanowires exhibit a high edge-to-surface ratio as well as a strong anisotropy, highly desirable for photoelectric devices and industrial catalysts. The absence of oxidation peaks verifies that the asprepared samples are of high quality and air stability, very promising for applications.

In this work, we investigated how the electrical and photoelectrical properties of InSe based devices depend on the interfaces made with standard materials such as SiO2, BN, and PMMA. The use of a BN layer is found to not only change the carrier type but also weaken the out-of-plane vibration of InSe. Field-effect transistor devices show a p-type behavior for InSe on SiO2, while for InSe on BN, the majority carriers are electrons. Moreover, due to the weakened electron–phonon interaction the electron mobility of InSe on BN is more than two magnitudes greater than its hole mobility on SiO2. A p–n junction diode is also demonstrated with InSe/SiO2 and InSe/BN with a rectification ratio as high as 102 and a photoresponsivity of 52 A/W, which can be enhanced to 103 and 1.6 × 104 A/W with a PMMA coverlayer. Our results may be useful for the design of high-performance van der Waals heterojunction photodetectors.

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Graphene analogs composed of Bi, Sb, and Sn, respectively, are predicted to be great candidates to realize the quantum spin Hall effect at high temperatures and have attracted intensive research interest in recent years. However, their structural and electronic properties are greatly affected by substrates. Here, we epitaxially grow Bi, Sb, and Sn overlayers on various substrates. We observed the formation of Au–Bi alloy on Au(111) substrates, while α-Bi was formed on the TaIrTe4, TiSe2and Cr2Ge2Te6 substrates. Large-scale thin films of α-Bi, α-Sb and β-Sn can be prepared on the TiSe2 substrates due to the high quality of the substrates with very few defects. The lattice of the Sb films is slightly compressed on the TiSe2 substrates, due to the interfacial interaction. α-Sn transitions to β-Sn on the TiSe2 substrates with increasing Sn coverages. Our work is very helpful for tuning the structural and electronic properties of epitaxial Bi, Sb, and Sn films via proper substrates.

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